CN117817120A - Method and system for controlling the global equiaxed crystal structure of nickel-based alloy laser welded joints - Google Patents
Method and system for controlling the global equiaxed crystal structure of nickel-based alloy laser welded joints Download PDFInfo
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- CN117817120A CN117817120A CN202410183247.5A CN202410183247A CN117817120A CN 117817120 A CN117817120 A CN 117817120A CN 202410183247 A CN202410183247 A CN 202410183247A CN 117817120 A CN117817120 A CN 117817120A
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
- B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
- B23K26/00—Working by laser beam, e.g. welding, cutting or boring
- B23K26/20—Bonding
- B23K26/21—Bonding by welding
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
- B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
- B23K26/00—Working by laser beam, e.g. welding, cutting or boring
- B23K26/12—Working by laser beam, e.g. welding, cutting or boring in a special atmosphere, e.g. in an enclosure
- B23K26/123—Working by laser beam, e.g. welding, cutting or boring in a special atmosphere, e.g. in an enclosure in an atmosphere of particular gases
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
- B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
- B23K26/00—Working by laser beam, e.g. welding, cutting or boring
- B23K26/20—Bonding
- B23K26/32—Bonding taking account of the properties of the material involved
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
- B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
- B23K26/00—Working by laser beam, e.g. welding, cutting or boring
- B23K26/70—Auxiliary operations or equipment
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Abstract
本发明属于镍基合金激光焊接技术领域，公开了镍基合金激光焊接接头全域等轴晶组织调控的方法及系统，通过全域功率调制激光改变了激光焊接过程的高斯热源分布，有效调控了激光焊接过程中的镍基合金焊缝微观组织形态；解决了传统激光焊接技术焊接接头柱状晶粒，成分偏析等缺陷所导致的力学性能以及抗腐蚀性能的不均一性，从而使镍基合金服役部件因其中弱相快速失效等问题。本发明通过对全域功率调制激光扫描模式及相位功率的精准控制，获得全域等轴晶接头，实现镍基高温合金管材的“去焊缝化”成形，开发处以高可靠、低成本、长寿命为特征的光热熔盐换热装备。
The present invention belongs to the technical field of nickel-based alloy laser welding, and discloses a method and system for regulating the global equiaxed crystal structure of nickel-based alloy laser welding joints. The Gaussian heat source distribution of the laser welding process is changed by global power modulation laser, and the microstructure morphology of the nickel-based alloy weld in the laser welding process is effectively regulated; the inhomogeneity of mechanical properties and corrosion resistance caused by defects such as columnar grains and component segregation in welding joints of traditional laser welding technology is solved, so that the nickel-based alloy service parts fail quickly due to weak phases therein. The present invention obtains a global equiaxed crystal joint by accurately controlling the global power modulation laser scanning mode and phase power, realizes the "weld removal" forming of nickel-based high-temperature alloy pipes, and develops photothermal molten salt heat exchange equipment characterized by high reliability, low cost, and long life.
Description
Technical Field
The invention belongs to the technical field of nickel-based alloy welding, and particularly relates to a method and a system for regulating and controlling global equiaxial crystal structure of a nickel-based alloy laser welding joint.
Background
With the rapid development of new energy industry, intermittent power such as wind power, photovoltaic and the like is accessed in a high proportion, and the grid peak shaving contradiction is increasingly aggravated. Therefore, the energy-storage type photo-thermal power station with the main purpose of deep peak regulation is built, continuous, stable and schedulable high-quality power output is realized, the problem of clean energy consumption is solved, and the important means and key support of a novel power system with new energy as a main body are built. Although the photo-thermal power generation industry chain is relatively complete and mature, part of core links still have short technical plates, such as reliable forming of key parts such as heat absorption pipes, molten salt pumps and molten salt valves for restraining and driving molten salt to flow and exchange heat, and the like, which still is a main technical bottleneck for restraining rapid development and deployment of photo-thermal power stations and molten salt energy storage systems. The heat absorption tube of the tower type fused salt photo-thermal power station heat collector is a core component for guaranteeing uninterrupted long-life efficient economical operation of the photo-thermal power station, the length of the heat absorption tube is 40m, the diameter of the heat absorption tube is 21mm, the wall thickness of the heat absorption tube is 1.2mm, and the heat absorption tube is formed by adopting Inconel625 superalloy to be curled and welded. The tower type fused salt photo-thermal power station heat absorption tube screen works for a long time under the working conditions of high heat flow, unsteady state, non-uniform heating in the axial direction and the circumferential direction, and is extremely easy to 'explode tube' from weak positions such as welding seams under the action of multiple loads such as fused salt corrosion and thermal stress. Therefore, the ultra-long thin-wall superalloy welded pipe of the photo-thermal power station collector has quite high manufacturing difficulty and technical threshold, and a key technical system for batch manufacturing and quality control is not formed yet.
Inconel625 alloy is a solid solution type nickel base alloy with Mo and Nb as main strengthening elements, and is widely used in applications requiring a combination of moderate strength and excellent corrosion resistance at 800 ℃. The weldability, mechanical properties and corrosion resistance of Inconel625 alloys are greatly controlled by the redistribution behavior of the alloying elements and the resulting microstructure during solidification of the weld joint fusion zone. For Mo, nb and other alloy elements with small distribution coefficient, the alloy elements are meltedThe primary columnar subgrain epitaxial growth and the secondary phase are precipitated along the grain boundary. The corrosion resistance of Inconel625 alloy welds is generally lower than that of the solution annealed state, mainly due to segregation of alloy elements in the fusion zone, high-angle grain boundaries formed by columnar subgrain junctions, and localized corrosion induced by intergranular chain secondary phases formed by solute element segregation. For example, inconel625 alloy weld joint precipitate phase formation results in a dendritic inter-crystalline region depleted of alloying elements in a Cl-containing alloy - Is characterized by containing Fe 3+ Is often observed to selectively corrode in both the reducing environment and the high temperature oxidizing environment. Therefore, the formation process of the nickel-based superalloy welded joint multi-stage microstructure is analyzed, and a microstructure multi-stage cooperative control method is provided and is a key point for regulating and controlling a nickel-based superalloy welded forming structure.
The corrosion resistance of nickel-base superalloy welded joints is highly dependent on the structural morphology and space occupation ratio of the precipitated phases. Laves phase, MC phase and gamma' phase formed in Inconel625 alloy welding process and M formed under high-temperature service condition 23 C 6 And delta have adverse effects on intergranular corrosion properties, and the morphology, distribution and content of these precipitated phases are highly dependent on segregation of alloying elements such as Nb and Cr. Therefore, the mass transfer and heat transfer of a welding process molten pool are regulated and controlled, the segregation of alloy elements caused by columnar sub-crystal epitaxial growth is inhibited, and the thermodynamic driving force generated by precipitated phases can be effectively weakened; the structural characteristics of the weld joint crystal grains are textured, the ratio of the large-angle crystal boundary is reduced, and the dynamic conditions of the growth of the precipitated phase can be effectively regulated. The effect of the weld forming process parameters on the microstructure is primarily reflected in the temperature gradient and solidification rate of the molten pool metal during the welding process. The temperature gradient and the time-space variation of the solidification growth rate determine the nucleation and growth of the solidification structure and the columnar-equiaxed transformation process. By selecting proper technological parameters, the thermal process of solidification of weld metal is designed, and the effective regulation and control of the grain structure can be realized. For example, by adjusting the scanning strategy during the nickel-base superalloy additive forming process, tailoring specific thermal processes and solidification patterns, the target texture can be targetedTo implant to a specific site. In addition to the scanning strategy, spatial and temporal modulation of the laser beam intensity may also provide additional degrees of freedom for site-specific grain structure control. Song et al prepared Inconel625 alloy by additive using galvanometer laser as heat source, found that the stirring action of galvanometer laser to the molten pool discontinued the growth of coarse dendrite, and broken grains as the core of equiaxed crystal growth, which could achieve the purpose of refining grains, regulating grain boundary. Meanwhile, the cooling speed of a molten pool formed by the galvanometer laser is high, and solute elements are captured by a gamma matrix before Laves phases are formed, so that the volume fraction of the Laves phases in a deposition layer is reduced by half, and the tensile strength and corrosion performance are respectively increased by 56.95% and 62.3%. The results show that the method for adjusting and controlling the weld joint forming coefficient, the precipitated phase structure morphology, the small-angle grain boundary orientation and the equiaxed grain ratio by designing the cooperative adjusting and controlling method which meets the target tissue structure and the complex heat requirement corresponding to ideal precipitation has great feasibility for improving the reliability of the nickel-based superalloy weld joint metal.
In summary, how to control the structure of the nickel-based alloy laser welding joint; how to control the composition segregation of the nickel-base alloy in the laser welding joint; how to improve the molten salt corrosion resistance of nickel-base alloys is the subject of the present invention.
Aiming at the problem of weld quality regulation in the process of resisting molten salt corrosion Inconel625 alloy pipe manufacture, by analyzing the forming mechanism of a microstructure in the welding process and the damage characteristic in a molten salt environment, the invention tries to design mass and heat transfer in the solidification process of a molten pool, realizes multidimensional regulation of molten salt corrosion resisting structure of a nickel-based superalloy welding joint, realizes a novel method and a novel process for reliable welding of the nickel-based superalloy, and provides powerful theory and technical support for developing the forming manufacture and quality control of key parts of a molten salt energy storage system characterized by high reliability and long service life. Through the above analysis, the problems and defects existing in the prior art are as follows:
(1) The traditional laser welding joint characterized by a Gaussian heat source is formed by the fact that long-size columnar crystals which are grown in an epitaxial mode are intersected at the center of a welding seam, and the long-size columnar crystals grow, so that the nickel-based alloy has directionality in corrosion performance and mechanical performance, and the comprehensive performance of the nickel-based alloy is reduced.
(2) The center of a joint weld formed by traditional laser welding forms segregation of subgrain scales, and the subgrain boundaries cannot form Cr-rich oxide films resistant to molten salt corrosion due to the fact that the subgrain boundaries are lean in Cr caused by element segregation, so that the joint rapidly fails in a non-uniform corrosion mode in a molten salt environment.
(3) The application reliability of the nickel-based alloy in the photo-thermal molten salt environment is low, the maintenance cost is high and the service life is short due to the non-uniformity of the microstructure component performance of the existing nickel-based alloy laser welding joint.
Disclosure of Invention
Aiming at the problems existing in the prior art, the invention provides a method for regulating and controlling the global equiaxed crystal structure of a nickel-based alloy laser welding joint, so as to realize the 'defluxing and seaming' forming of a nickel-based superalloy pipe, and develop photo-thermal molten salt heat exchange equipment featuring high reliability, low cost and long service life.
The invention discloses a method for regulating and controlling the global equiaxed crystal structure of a nickel-based alloy laser welding joint, which comprises the following steps: selecting Inconel625 in solid solution state for welding test, wherein the size of a welding test plate is 160 multiplied by 70 multiplied by 1mm, and the welding mode is butt joint; and a global power modulation laser welding system with the dual functions of laser galvanometer and power modulation is adopted to accurately control the welding process.
Further, the global power modulated laser welding system can control the power level of up to 36 phase points in a closed motion cycle (360 DEG), and each phase point can be adjusted in a follow-up manner,
further, by setting the welding parameters for each of the 36 phase points of the global power modulated laser, the welding process is precisely controlled.
Further, before welding, the welding shielding gas is argon with the purity of 99.99 percent, and the gas flow rate is 10-15 L.min -1 。
Further, for global power modulated laser control: laser power of 1.4-1.6kW (same as conventional laser welding) and welding speed of 10-15mm/s (same as conventional laser welding); the oscillation frequency of the full-area-rate modulated laser is 100Hz, and the oscillation amplitude is 0.4-0.6mm.
Further, a manner of reducing scan domain edge energy input is employed.
The invention provides a universal power modulation laser welding system which is particularly suitable for welding an Inconel625 nickel-based alloy, and can realize accurate welding of a butt welding test plate, wherein the size of the test plate is 160 multiplied by 70 multiplied by 1mm, and the laser power in the welding process is subjected to universal modulation by the function of laser galvanometer plus power modulation so as to control the equiaxial crystal structure of a welding joint.
The universal power modulation laser welding system has the capability of controlling the power of up to 36 phase points in a closed movement period, and the power of each phase point can be dynamically adjusted according to welding requirements, so that the comprehensive control of the isometric crystal structure of the nickel-based alloy laser welding joint is realized.
The system precisely controls the laser welding process of the Inconel625 nickel-based alloy by setting specific welding parameters such as laser power, welding speed, oscillation frequency, amplitude and the like on 36 phase points, and ensures that the welded joint has excellent equiaxial crystal structure characteristics.
The full-domain power modulation laser welding system adopts argon with the purity of 99.99 percent as protective gas before welding, the gas flow rate is set to be 10-15 L.min < -1 >, and the microstructure of a welding joint can be optimized by reducing the energy input of the edge of a scanning domain, so that the welding quality is improved.
The invention further aims to provide an application of the method for regulating and controlling the global equiaxed crystal structure of the nickel-based alloy laser welding joint in the field of nickel-based alloy laser welding.
In combination with the technical scheme and the technical problems to be solved, the technical scheme to be protected has the following advantages and positive effects:
firstly, the invention controls the heat source distribution in the nickel-based alloy welding process by using the universal power modulation laser, regulates and controls the microstructure form of the nickel-based alloy welding joint, changes columnar grains with directional performance into equiaxed grains with uniform and fine performance, and simultaneously greatly reduces the component segregation in the nickel-based alloy welding process of the prior laser welding technology. And in the service process of the nickel-based alloy part in the molten salt environment, the welding joint is prevented from being corroded by weak phase so as to be corroded rapidly. Various problems of the traditional laser welding nickel-based alloy are solved, and an important foundation is laid for the service of the nickel-based alloy under a molten salt energy storage system.
Secondly, the invention obtains the global equiaxial crystal joint through the accurate control of the global power modulation laser scanning mode and the phase power, realizes the 'defluxing and sewing' forming of the nickel-based superalloy pipe, and develops the photo-thermal molten salt heat exchange equipment with the characteristics of high reliability, low cost and long service life.
The segregation of the alloy element in the universal power modulated laser welded joint is relatively small compared with the traditional laser welding, and is relatively uniform unlike the continuous element segregation formed by the traditional laser welding, and the segregation is mainly the grain boundary and crystal nucleus of equiaxed crystal as the metallographic structure observed before. Wherein the segregation of Nb is obvious, and the segregation of Ni, cr and Mo is relatively weak, and particularly Cr is basically uniformly distributed. The element segregation caused by the traditional laser, particularly the nickel-base alloy intergranular Cr-deficiency phenomenon caused by Cr segregation is basically eliminated, the molten salt corrosion resistance of the nickel-base alloy welding joint is obviously improved, and the corrosion resistance of the welding joint consistent with the base body can be ensured under the molten salt environment. The invention has wider application prospect in the field of photo-thermal salt.
1) The traditional laser spot diameter is small, and the whole-domain power modulation laser is in a spiral line shape and has a certain amplitude, so that the nickel-based alloy is heated uniformly, and then the heat of a molten pool can be accurately regulated and controlled by controlling the power of 36 phase points, and meanwhile, the laser power of a welding joint area can be dispersed by laser beam oscillation.
2) The element segregation caused by the traditional laser, particularly the nickel-base alloy intergranular Cr-deficiency phenomenon caused by Cr segregation is basically eliminated, the molten salt corrosion resistance of the nickel-base alloy welding joint is obviously improved, and the corrosion resistance of the welding joint consistent with the base body can be ensured under the molten salt environment. The invention has wider application prospect in the field of photo-thermal salt.
3) The heat source distribution in the nickel-based alloy welding process is controlled by the universal power modulation laser, and the microstructure form of the nickel-based alloy welding joint is regulated and controlled, so that columnar grains with directional properties are changed into equiaxial grains with uniform and fine properties, the nickel-based alloy welding seam removing treatment is realized, and the joint which is homogeneous with a matrix is obtained.
4) In the service process of the nickel-based alloy component in the molten salt environment, the welded joint is not subjected to weak phase rapid corrosion, and the development part is photo-thermal molten salt heat exchange equipment with the characteristics of high reliability, low cost and long service life.
Thirdly, the global equiaxed crystal structure regulation and control method for the nickel-based alloy laser welding joint provided by the invention has the following remarkable technical progress:
1. improvement of welding precision and quality
By using a global power modulation laser welding system with the function of laser galvanometer and power modulation, the accurate control of the welding process is realized. The high precision control ensures that the welding joint has more uniform and optimized equiaxed crystal structure, thereby remarkably improving the mechanical property and corrosion resistance of the welding joint and enhancing the welding quality.
2. Innovative application of power modulation
This method of global power modulation is innovative in welding technology by controlling the power level of up to 36 phase points in one closed motion cycle and allowing dynamic adjustment of each phase point. It allows finer tuning of the energy input, providing conditions for achieving a global distribution of equiaxed crystals in the solder joint.
3. Optimization of welding process
By setting the welding parameters of 36 phase points of the global power modulation laser, the method can accurately adjust the power output of the laser according to the actual requirements of the welding process. This ability makes the welding process more stable and controllable, helping to reduce welding defects such as hot cracks and air holes, etc., and thereby improving the overall performance of the welded joint.
4. Optimized use of a shielding gas
By using high-purity argon as welding protective gas, the cleaning and stability of the welding environment are ensured, and the quality and performance of the welding joint are further improved.
5. Fine tuning of welding parameters
By setting specific laser power, welding speed, oscillation frequency and amplitude, and by reducing the scan-domain edge energy input, these fine-tuned welding parameters are critical to achieving global regulation of equiaxed grain structure, helping to achieve a more uniform microstructure in the welded joint.
The method for regulating and controlling the global equiaxed crystal structure of the nickel-based alloy laser welding joint not only realizes the optimization of the microstructure of the welding joint, but also improves the overall performance and welding quality of the welding joint, provides an effective technical means for high-performance nickel-based alloy welding, and has important industrial application value.
Drawings
In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings that are needed in the embodiments of the present invention will be briefly described below, and it is obvious that the drawings described below are only some embodiments of the present invention, and other drawings may be obtained according to these drawings without inventive effort for a person skilled in the art.
FIG. 1 is a schematic diagram of a global power modulated laser welding process according to an embodiment of the present invention; (a) a galvanometer laser system, (b) a gradient power setting, (c) a scan path;
FIG. 2 shows (a) a conventional laser Gaussian heat source distribution, (b) a conventional laser joint macro-morphology, (c) a local amplification of (b), (d) a global power modulated laser welding heat source distribution, (e) a global power modulated laser joint macro-morphology, and (f) a local amplification of (e);
FIG. 3 is an EPMA graph under a conventional laser Gaussian heat source provided by an embodiment of the present invention; (a) Ni, (b) Cr, (c) Mo, (d) Nb, (e) Al, and (f) Ti;
FIG. 4 is a graph of EPMA results of global power modulated laser versus equiaxed crystals in the weld provided by embodiments of the present invention; (a) Ni, (b) Cr, (c) Mo, (d) Nb, (e) Al, and (f) Ti;
FIG. 5 is a graph of (a) the weight loss of a sample in molten salt and (b) a graph of a sample weight loss fit provided by an embodiment of the present invention;
fig. 6 is a graph of the surface corrosion profile of a welded joint in two welding modes according to an embodiment of the present invention, (c) dip corrosion under conventional laser for 1200h, (d) dip corrosion under global power modulated laser for 1200h for local amplification of (c), and (b) dip corrosion under global power modulated laser for (a).
Detailed Description
The present invention will be described in further detail with reference to the following examples in order to make the objects, technical solutions and advantages of the present invention more apparent. It should be understood that the specific embodiments described herein are for purposes of illustration only and are not intended to limit the scope of the invention.
The technical scheme provided by the invention is as follows:
1) Step one: two nickel-based alloys of the same material are selected as the weldment, for example, two plates of Inconel625 alloy are butted. The size of the processed welding test plate is 160 multiplied by 70 multiplied by 1mm, and the two welding parts are subjected to surface cleaning, degreasing, descaling and the like so as to facilitate the post laser welding operation.
2) Step two: in a closed movement period (360 degrees), setting 36 phase points, adjusting the positions of the phase points, adjusting the power difference of the adjacent phase points to be 5%, forming a circumferential array around the center of laser, setting the oscillation frequency of the galvanometer laser to be 100Hz and the amplitude to be 0.4-0.6mm, and adjusting the position of the galvanometer laser to be aligned with the center of a welding seam.
3) Step three: and the power modulation system is used for setting welding parameters of each of 36 phase points of the global power modulation laser and realizing accurate control of a welding process. The laser power is set to be 1.4-1.6kW, the welding speed is set to be 10-15mm/s, and the vibrating mirror laser system and the power modulation system are overlapped and used for overlapping the two functions, so that the autonomous setting of the laser power waveform and the phase in the scanning period can be realized.
4) Step four: before welding, the welding protecting gas is argon with the purity of 99.99 percent, and the gas flow rate is 14-16 L.min < -1 >.
5) Step five: and the molten salt corrosion simulation system is used for cutting the Inconel625 welding joint into 15.0mm multiplied by 10.0mm multiplied by 1.0mm by using a linear cutting machine, and a welding line is positioned in the middle of a corrosion sample. Samples were sanded sequentially with #240, #400, #800, #1000 and #2000 silicon carbide sandpaper and 0.05 μm Al 2 O 3 The slurry was polished to obtain a mirror finish for corrosion experiments. The size of the corrosion sample was measured using a vernier caliper and weighed using an electronic balance with an accuracy of 0.01 mg. Selection of Al 2 O 3 The crucible was used as a reaction vessel for corrosion test, and Al was washed with ethanol (AR grade) in an ultrasonic cleaner 2 O 3 Crucible for 60 minutes. These crucibles were dried at 600 ℃ for 10 hours to thoroughly clean them. Finally, the sample was weighed by an electronic balance having an accuracy of 0.1 mg. The molten salt composition for corrosion is 40% KNO 3 +60％NaNO 3 To simulate an actual use environment. Molten salt is added into a crucible, a stainless steel shell is sleeved outside, a bottle mouth is sealed by using an adhesive tape, and the whole process is carried out in a glove box filled with argon. Finally, the crucible is placed into a box-type resistance furnace, and the soaking test time is 30 days.
6) Step six: and the mass test module is used for measuring the weight of the sample before and after corrosion by using an electronic balance with the accuracy of 0.1 mg. And (3) putting the sample into deionized water and absolute ethyl alcohol, and cleaning molten salt on the surface of the corroded sample by using an ultrasonic cleaner. The samples were then dried with cold air and weighed using an electronic balance to determine mass changes during corrosion.
In order to realize the regulation and control of the global equiaxed crystal structure of the nickel-based alloy laser welding joint, the following is a specific embodiment:
1) Preparing welding materials:
the Inconel625 nickel-based alloy in a solid solution state is selected as a welding material, so that the material is ensured to have good welding performance and high-temperature strength.
Test panels of dimensions 160 x 70 x 1mm were prepared and used in a butt weld to simulate the joint configuration in an actual welding application.
2) Welding system configuration:
a global power modulated laser welding system is used that integrates the "laser galvanometer + power modulation" function. The laser galvanometer is used for quickly and accurately changing the focal position of the laser beam, and the power modulation is used for controlling the output of laser power, so that the accurate control of heat input in the welding seam forming process is realized.
3) Welding process control:
during welding, the system is able to control the laser power level for up to 36 phase points in one closed cycle of motion. This means that the laser power at each phase point can be adjusted during the welding process according to the specific location of the weld and the welding stage to optimize the cooling rate and temperature profile of the weld, thereby affecting the direction and size of grain growth.
By precisely setting the welding parameters (such as laser power, welding speed, oscillation frequency and amplitude) of each phase point, the overall control of the welding process is realized so as to promote the formation of equiaxed crystals.
4) Welding shielding gas and parameter settings:
argon with a purity of 99.99% was used as a shielding gas before welding to prevent oxidation and contamination during welding. The gas flow rate was set to 10-15L/min to ensure a sufficient protective effect.
The laser power was set in the range of 1.4-1.6kW and the welding speed was 15mm/s to ensure sufficient penetration and good formation of the weld.
The global power modulation laser oscillation frequency is set to be 100Hz, and the oscillation amplitude is between 0.4 and 0.6mm so as to adjust the interaction between the laser and the material and further optimize the distribution of heat input.
5) Energy input optimization:
by reducing the energy input at the edges of the scan field, the size of the heat affected zone can be reduced, reducing the probability of formation of a hot zone, which helps to reduce the undesirable grain growth direction and promote the formation of equiaxed crystals.
Through the scheme, the universal regulation and control of the equiaxed crystal structure in the Inconel625 nickel-based alloy laser welding joint can be realized, so that the microstructure and performance of the welding joint are improved.
According to the material disclosed by the invention, a solid solution state Inconel625 is selected for a welding test, the size of a welding test plate is 160 multiplied by 70 multiplied by 1mm, and the welding mode is butt joint.
The welding equipment adopts a universal power modulation laser welding system with the dual functions of laser galvanometer and power modulation, and the structural composition of the system is shown in figure 1 a. The full-domain power modulation laser welding system is characterized in that a power control function is added through research and development on the basis of an original laser scanning galvanometer welding system, the power of up to 36 phase points can be controlled within a closed movement period (360 degrees), each phase point can be adjusted in a follow-up mode, and the welding process is accurately controlled by setting welding parameters of each of 36 phase points of the full-domain power modulation laser.
The superposition of the two functions can realize the autonomous setting of the laser power waveform and the phase in the scanning period. Compared with the traditional laser scanning galvanometer welding system, the universal power modulation laser welding system has larger regulation and control space and more accurate regulation and control capability on the molten pool heat-mass transmission process. In contrast, the welding test used a conventional laser featuring a gaussian heat source and a globally power-modulated laser for welding, with the welding parameters shown in table 1. Fig. 1b is a schematic diagram of setting phase point power in a single scan domain when the global power modulated laser realizes gradient power input, the red dot size corresponds to the power size, and the power difference between adjacent phase points is 5%. Fig. 1c shows the scan path during global power modulated laser welding. Welding experiments as a comparison, a conventional laser welding featuring a gaussian heat source and a global power modulated laser welding comparison experiment were employed. Each test plate is polished by sand paper to remove an oxide film on the surface, and the surface oil stains are cleaned by acetone, so that experimental differences caused by different welding test plates are reduced.
Table 1 welding parameters for two welding modes
Before the welding experiment is carried out, the welding protecting gas is argon with the purity of 99.99 percent, and the gas flow rate is 10-15 L.min -1 。
For conventional laser welding: the laser power is 1.4-1.6kW, the welding speed is 15mm/s, no controllable phase point exists, and the oscillation frequency and the oscillation amplitude are avoided, so that the traditional Gaussian heat source distribution is formed.
For global power modulated laser control: the laser power was 1.5kW (same as conventional laser welding) and the welding speed was 15mm/s (same as conventional laser welding). The oscillation frequency of the full-area-rate modulated laser is 100Hz, and the oscillation amplitude is 0.4-0.6mm. In order to avoid overheat of a heat affected zone caused by accumulation of heat at the edge of a molten pool due to superposition of scanning paths, a mode of reducing energy input at the edge of a scanning domain is adopted.
Molten salt corrosion test:
the Inconel625 weld joint was cut with a wire cutting machine to 15.0mm x 10.0mm x 1.0mm with the weld in the middle of the corrosion sample. Samples were sanded sequentially with #240, #400, #800, #1000 and #2000 silicon carbide sandpaper and 0.05 μm Al 2 O 3 The slurry was polished to obtain a mirror finish for corrosion experiments. The size of the corrosion sample was measured using a vernier caliper and weighed using an electronic balance with an accuracy of 0.01 mg. Selection of Al 2 O 3 The crucible was used as a reaction vessel for corrosion test, and Al was washed with ethanol (AR grade) in an ultrasonic cleaner 2 O 3 Crucible for 60 minutes. These crucibles were dried at 600 ℃ for 10 hours to thoroughly clean them. Finally, the sample was weighed by an electronic balance having an accuracy of 0.1 mg. The molten salt composition for corrosion is 40% KNO 3 +60％NaNO 3 To simulate an actual use environment. Molten salt is added into a crucible, a stainless steel shell is sleeved outside, a bottle mouth is sealed by using an adhesive tape, and the whole process is carried out in a glove box filled with argon. Finally, the crucible is placed into a box-type resistance furnace, and the soaking test time is 30 days.
After the end of the experiment, the weight of the sample before and after corrosion was measured using an electronic balance with an accuracy of 0.1 mg. And (3) putting the sample into deionized water and absolute ethyl alcohol, and cleaning molten salt on the surface of the corroded sample by using an ultrasonic cleaner. The samples were then dried with cold air and weighed using an electronic balance to determine mass changes during corrosion. The corrosion weight loss is calculated as the change in mass of the sample divided by the surface area of the sample (ΔW/S). The average corrosion rate is shown in formula (1):
Corrosion rate＝(W×K)/(A×T×D)(1)
wherein K is a constant (g.m) -2 h -1 ) K is generally set to 1.00×10 for nickel-base alloys 4 The method comprises the steps of carrying out a first treatment on the surface of the T is exposure time (h); a is the area of the sample (cm 2 ) The method comprises the steps of carrying out a first treatment on the surface of the D is the density of the sample (g.cm -3 )。
Treatment results:
the energy input of the Inconel625 alloy molten pool range under the two modes of the traditional laser and the global power modulation laser is shown in figure 2, which is different from a Gaussian distribution mode (figure 2 a) that the traditional laser welding heat is concentrated at the center of the molten pool, and the global power modulation laser is used for providing conditions for the formation of equiaxed crystals because scanning tracks overlap in the edge area of the molten pool and the similar isothermal area of a wide range is formed in the molten pool range due to the arrangement of the low energy input of the phase point of the edge of the molten pool in the invention, and the temperature gradient which is suddenly reduced under the Gaussian heat source mode is not formed as shown in figure 2 d.
Fig. 2b and 2c show the metallographic structure of a conventional laser welded joint, and it can be seen that the welded joint is mainly composed of epitaxially grown long-sized columnar crystals and finally meets at the center of the weld, and an obvious weld center line exists. Fig. 2e and 2f show the metallographic structure of the universal power modulation laser joint, which mainly consists of equiaxed crystals with tiny weld centers, only small tiny columnar crystals appear at the edges of the weld, and obvious circular laser beam stirring traces are arranged at the weld joint. From the grain size perspective, the global power modulated laser weld has a small grain size, mainly because the stirring of the laser beam to the molten pool prevents dendrite growth and refines grains, the columnar grain size of the traditional laser is about 100 μm, and the fine equiaxed grains formed by the global power modulated laser are about 10 μm. The traditional laser spot diameter is small, and the global power modulation laser is in a spiral line shape and has a certain amplitude, so that the nickel-based alloy is heated uniformly, the heat of a molten pool can be accurately regulated and controlled by controlling the power of 36 phase points, meanwhile, laser power of a welding joint area can be dispersed by laser beam oscillation, the cooling rate of weld metal is increased, liquid metal flows and concentrates at the front part of the molten pool, the solidification speed of the molten pool is increased, and crystal grains at the edge of a fusion area do not have enough time to grow up, so that the influence range of a heat affected zone is obviously reduced by the global power modulation laser welding joint, and the welding quality is improved.
EPMA is used to observe the distribution of joint elements under different welding methods of the Inconel625 alloy as shown in FIGS. 3 and 4. In a welded joint formed by a traditional laser Gaussian heat source, the main alloy elements are significantly segregated. Wherein Ni and Cr segregate into dendrites, and Nb and Mo segregate into dendrites. During the growth of columnar crystals, dendrite nuclei preferentially grow, so that Ni and Cr in liquid metal are gathered to dendrite nuclei, and Nb and Mo are discharged into inter-dendrite areas during the process of dendrite nucleation, so that Nb and Mo are continuously accumulated, sites with extremely high Nb and Mo contents are formed at certain positions of the inter-dendrite areas, and particularly the content of Nb at certain positions is even more than 3 times that of a matrix. The segregation phenomenon generated in the columnar crystal growth process can generate larger component supercooling at the front edge of the columnar crystal, so that the epitaxial growth of the columnar crystal is accelerated.
The segregation of the alloy element in the universal power modulated laser welded joint is relatively small compared with the traditional laser welding, and is relatively uniform unlike the continuous element segregation formed by the traditional laser welding, and the segregation is mainly the grain boundary and crystal nucleus of equiaxed crystal as the metallographic structure observed before. Wherein the segregation of Nb is obvious, and the segregation of Ni, cr and Mo is relatively weak, and particularly Cr is basically uniformly distributed. The element segregation caused by the traditional laser, particularly the nickel-base alloy intergranular Cr-deficiency phenomenon caused by Cr segregation is basically eliminated, the molten salt corrosion resistance of the nickel-base alloy welding joint is obviously improved, and the corrosion resistance of the welding joint consistent with the base body can be ensured under the molten salt environment. The invention has wider application prospect in the field of photo-thermal salt.
The mass of the samples before and after corrosion was measured using an electronic balance, the data for each point being the average of three samples tested in parallel, the error bars representing the standard deviation. As can be seen from the corrosion weight loss curve graph 5, the corrosion weight loss of the corrosion samples in the two different welding modes is obviously higher than that of the base metal, the weight loss of the base metal is basically 0 along with the corrosion process, and the corrosion rate is basically unchanged. The corrosion weight loss of the two welding corrosion samples gradually increases with the time, but the corrosion rate gradually decreases. Compared with the traditional laser welding, the sample welded by the universal power modulation laser welding has the advantages that the corrosion weightlessness and the corrosion rate are obviously smaller under the same corrosion time, and the corrosion weightlessness of the traditional laser welding sample even reaches three times of that of the universal power modulation laser welding sample at 1200 h. Moreover, the error bars of conventional laser welded samples are significantly longer than the global power modulated laser welds, and one explanation of this outcome of the present invention is: there is significant element segregation in the dendrite nuclei and inter-dendrite regions of the conventional laser welded joint, such that corrosion of the conventional laser welded sample is unstable, whereas equiaxed grain tissue element segregation formed by the global power modulated laser sample welded joint is relatively weak, and corrosion is relatively uniform, such that the mass difference of each parallel sample of the conventional laser welded corrosion sample is large, while the mass difference between the global power modulated laser corrosion samples is small, which significantly distinguishes the corrosion resistance therebetween.
The corrosion of the welded joint surface was observed using SEM, and fig. 6 shows the surface corrosion morphology of Inconel625 alloy welded joint immersed in a nitrate salt environment in two welding modes. As can be seen from fig. 6c, the surface of the welded joint under the conventional laser can see clear grain boundaries and columnar subgrain boundaries after molten salt corrosion, and the ridge corrosion products adhere to the center of the weld and the grain boundaries, and corrosion cracks are formed at the columnar subgrain boundaries. After the sample is etched for 1200h, a large number of etch pits and hollowed-out structures appear from the sample surface of fig. 6d, and edge-warped etch products adhere to the etch pits.
Fig. 6a shows the surface corrosion profile of an Inconel625 alloy joint formed by global power modulated laser welding after immersion in a molten nitrate salt environment. It can be seen that after 1200 hours of soaking, the equiaxed grain profile can be seen on the sample surface of fig. 6b, which is consistent with the elemental segregation morphology of the globally power-modulated laser joint of fig. 4, which also illustrates the relationship between the two. The corrosion products on the surface of the sample are even and smooth. Under the corrosive environment of nitrate, the nickel-based alloy welded joint is corroded in an equiaxed crystal form, the crystal grains of the corroded surface are uniformly corroded, the cavitation and the shedding are avoided, and the inconsistent corrosion resistance of the nickel-based alloy joint caused by overlarge element component difference is avoided. The weld joint components of the nickel-base alloy are ensured to be uniform, and the corrosion resistance is stable, and the component characterization diagram of the EPMA nickel-base alloy weld joint elements in fig. 4 is consistent. Greatly improves the service life of the nickel-base alloy in molten salt corrosion environment and reduces the use cost.
Example 1: isometric crystal control welding of nickel-based alloy Inconel625
1) And (3) material selection: a solid solution state Inconel625 nickel-based alloy was used as a welding material, and a plate having a size of 160X 70X 1mm was used for a butt welding test.
2) Welding system configuration: and a global power modulation laser welding system with the functions of laser galvanometer and power modulation is used for welding test, so that the accurate control of the welding process is ensured.
3) Welding parameter setting: the laser power was set at 1.5kW and the welding speed was 15m/s. The oscillation frequency of the global-rate modulated laser was set to 100Hz and the oscillation amplitude was set to 0.5mm.
4) The protective gas is used: during the welding process, argon gas with a purity of 99.99% was used as a shielding gas, and the flow rate was set to 15L/min to keep the weld area clean and prevent oxidation.
5) Power modulation application: in the welding process, the power of 36 phase points is precisely adjusted through a global power modulation laser welding system so as to realize the global distribution of equiaxed crystals in the welding seam area.
6) And (3) welding quality inspection: after the welding is completed, macroscopic and microscopic inspection is carried out on the welding seam, and the formation condition of the equiaxed crystal structure and the overall quality of the welding joint are evaluated.
Example 2: optimizing welding parameters to improve Inconel625 weld joint performance
1) Test panel preparation: and selecting an Inconel625 nickel-based alloy plate with the size of 160 multiplied by 70 multiplied by 1mm, and preparing for butt welding.
2) Welding system settings: and performing welding operation by using an advanced global power modulation laser welding system with a laser galvanometer and power modulation function.
3) And (3) adjusting welding parameters: to further optimize the weld quality, the laser power was adjusted to 1.5kW, the welding speed was adjusted to 15m/s, the global power modulated laser oscillation frequency was adjusted to 100Hz, and the oscillation amplitude was adjusted to 0.5mm to accommodate the physical characteristics of Inconel 625.
4) And (3) shielding gas adjustment: 99.99% purity argon gas was used at a flow rate of 15L/min during welding to optimize the welding environment and prevent oxidation of the weld.
5) Welding is performed: in the welding process, the global power modulation laser welding system adjusts according to the preset phase point power, precisely controls the welding energy and ensures the uniform distribution of the isometric crystals in the welding seam area.
6) Welded joint analysis: after the welding is completed, the quality of the welded joint, in particular the distribution of equiaxed crystals and the mechanical strength of the welded joint are evaluated by metallographic analysis and mechanical property testing.
The above two examples demonstrate how global tuning of equiaxed grain structure in Inconel625 nickel-based alloy welded joints can be achieved by precise control of welding parameters and by advanced laser welding techniques, thereby improving weld quality and joint performance.
The foregoing is merely illustrative of specific embodiments of the present invention, and the scope of the invention is not limited thereto, but any modifications, equivalents, improvements and alternatives falling within the spirit and principles of the present invention will be apparent to those skilled in the art within the scope of the present invention.
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