MXPA96002384A - Method for erosion of surface surfaces using a liquor jet - Google Patents

Abstract

A jet of liquid is used to roughen the surface of a substrate, such that it allows a subsequent thermal spray coating material to adhere tightly to the surface. The substrate is preferably a superalloy that is either based on nickel, titanium or cobalt. The method initially provides a high-pressure liquid jet and moves the jet of liquid through the surface of the substrate at a rate, such that it distributes liquid to the surface on a scale of amounts of at least about 0.7 kg. / cmý. The high pressure liquid jet is preferably provided with a reservoir which is maintained at a pressure in the range of about 189.2 MPa to 358 MPa. A preferred embodiment employs an initial discharge of sand to the surface of the substrate to remove a uniform finish from the substrate, prior to application of the liquid jet. The initial discharge of sand, allows substantially decreased pressures and quantities of applied liquid mass, to achieve desired scales of surface regosity

Description

METHOD FOR EROSION OF SURFACE SURFACES USING A LIQUID JET FIELD OF THE INVENTION This invention relates to a method for applying thermal spray coatings to superalloys, and more particularly, to a method for preparing a surface of superalloy to allow the Thermal spray coating adheres rigidly to it. BACKGROUND OF THE INVENTION In general, metallic substrates that are going to be coated by a thermal spray coating process, initially become rough, by discharging sand to achieve a rough surface, which allows good mechanical bonding to be achieved. The discharge of sand, by its nature, leaves a residue of sand inclusions within the substrate. The sand material may include silicon carbide and iron particles, but in most applications, it is composed of angular aluminum particles. Silicon carbide, is no longer used for treatment by discharge of sand from superalloys at high temperatures, due to the concern to form phases of low melting point, which, possibly affects the life of effort / rupture. To date, substantially all treatments are carried out by means of sand discharge, using alumina particles. The term "superalloy" includes alloys based on cobalt, titanium and nickel, which exhibit high levels in both strength and hardness. For some applications, sand inclusions present a concern. Interphase specifications, between a superalloy substrate and the coating, limit the amount of sand included. Turbine blade coatings for use in aircraft engines should meet most of the limitations of including high-strength interfaces. Therefore, the prior art had to conform to the inclusion limits of sand, although it achieved a desired level of surface roughness to ensure a rigid bond for a subsequently applied coating. Although a superalloy must exhibit an appropriate surface roughness to achieve a well-coupled thermal spray coating, the surface must also be clean. Therefore, oils, fats and surface oxides, such as those that can be obtained from a previous pretreatment, should be avoided. The prior art has achieved clean substrates requiring the use of a wet abrasive cleaning process, which also adds fine sand inclusions to the surface of the superalloy. Since the wet abrasive cleaning process was followed by a dry sand discharge process, the combination added significant inclusions, that is, up to 15% of the level of interfaces. It has been found that the presence of alumina sand inclusions, over a somewhat clean interface, allows reactions to occur during a subsequent heating treatment, which results in an undesirable interface decoration. Accordingly, it is an object of this invention to provide an improved method for achieving a surface roughness level of a superalloy, where sand inclusions are avoided. It is a further object of this invention to provide an improved method for roughening a surface of a superalloy by employing a jet of high pressure liquid. SUMMARY OF THE INVENTION A liquid jet is used to roughen the surface of a substrate in such a way as to allow a subsequent thermal spray coating material to adhere strongly to the surface. Preferably, the substrate is a superalloy, which is based either on nickel or cobalt. The method initially provides a jet of liquid at high pressure, and moves the jet of liquid through the surface on a scale of amounts of at least about 0.7 kg / cm2 to about 5.5 kg / cm2. The jet of high pressure liquid, preferably it is provided with a reservoir that is maintained at a pressure in the range of about 193.2 MPa to 358 MPa. A preferred embodiment employs an initial discharge of sand to the surface of the substrate, to remove a smooth finish from the substrate, prior to the application of the liquid jet. The initial sand discharge allows substantially decreased pressures and amounts of applied liquid mass to achieve desired scales of surface roughness. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a graph of metal erosion against mass of water supplied, illustrating the erosion of "IN-718" for deposit pressures of 207 MPa, 276 MPa, and 345 MPa. Figure 2 is a graph of erosion of metal against mass of water supplied, illustrating the erosion of treated "IN-718", for deposition pressures of 207 MPa, 276 MPa, and 345 MPa. Figure 3 is a graph of metal erosion against mass of water supplied, illustrating the erosion "IN-718" treated, for deposit pressures of 207 MPa, 276 MPa, and 354 MPa. Figure 4 is a graph of metal erosion versus water jet pressure for "IN-718", which illustrates a comparison between a surface with sand discharge and a surface to which no sand discharge has been applied. Figure 5 is a graph of erosion weight loss against mass of water supplied, for a variety of superalloys from a reservoir maintained at 354 MPa. Figure 6 is a graph of metal erosion against mass of water supplied for "MAR-M 509 ° from a reservoir maintained at 220.8 MPa, 276 MPa, and 358.8 MPa." Figure 7 is a graph of weight loss by erosion against mass of water supplied, showing erosion of "RENE 80" for a deposit maintained at 276 MPa and 354 MPa.

Figure 8 is a graph of surface roughness against erosion weight loss for "RENE 80" under the conditions shown in the graph of Fig. 7. Figure 9 is a plot of erosion weight loss against mass of water supplied for 3 steel samples, by means of a water jet from a tank maintained at 354 MPa. Figure 10 is a graph of threshold pressure versus hardness to achieve initial erosion by a water jet of "I N-718", "MAR-M 509" and "REN E 80". Figure 11 is a plot of water mass delivered against water jet pressure to achieve an erosion of 4.5 mg / cm2 for cobalt-based and nickel-based super alloys. DETAILED DESCRIPTION OF THE PREFERRED MODALITY A high-pressure water jet is used to roughen a surface of a superalloy in preparation for a subsequent thermal spray coating. The objective is to reduce to a minimum, the inclusions of interfaces on the surface of the superalloy from the step to make it rough. In many water jet applications, such as metal cutting or ceramic cutting, abrasive material is added to the high pressure water jet, and dramatically increases its cutting speed. This invention does not employ abrasives in the water jet, only a pure liquid that has been filtered and cleaned by reverse osmosis.

As will be evident from the following data, it has been determined that a pure water jet exhibiting a required pressure can provide sufficient surface erosion of a superalloy (or other metal) with little or no surface inclusion, which it may adversely affect a thermal spray coating applied later. In addition to allowing the erosion of the surface, the water jet spray also provides a cleaning action on the surface of the substrate. The main findings of this invention are the following: 1. A critical minimum of water jet threshold pressure is required for the erosion of superalloys and other metals.

The threshold pressure of the water jet varies with the hardness of the substrate. 2. A minimum quantity of water (or other liquid) must be supplied, and an amount exceeded, in order to produce a substantial erosion in the substrate. Until that amount of water has been supplied, ponderable erosion does not occur. The period before which erosion begins is called the "incubation period". 3. It has been found that a pretreatment with discharge of light sand to remove the finish from the surface of the substrate substantially accelerates the subsequent erosion action of the water jet. Pretreatment with light sand discharge eliminates the incubation period, allows lower water jet pressures to be used, and redirects the threshold pressure of the water jet to achieve a desired level of erosion. The useful scale of erosion of the water jet of a substrate is when an adequate level of roughness has been obtained, with a minimum of substrate removal. The minimum rugosity required for a thermal spray coating is approximately 2032 μm and one superalloy (ie "IN-718") is achieved at approximately 5 mg / cm2 removal (approximately 6.35 μm substrate thickness). The maximum roughness for a subsequent thermal spray coating is approximately 12700 μm due to the self-coating and shading of a subsequent thermal spray coating, and, therefore, the coverage is incomplete at the interface and resistance to reduced bonding. In order to achieve adequate roughness of the surface, it has been determined that a minimum average thickness removal is approximately 5.08 μm, which corresponds to a removal of approximately 4.5 mg / cm2 from a normal superalloy surface. The maximum thickness removal that can be accepted is approximately 50.8 μm. This limit is based on a concern for the reduction in cross-section of a thin-walled superalloy, used for turbine blade applications. Said thickness removal corresponds to an erosion of approximately 45 mg / cm2 of the surface of the substrate. Furthermore, it has been determined that an adequate and useful roughness for a subsequent thermal spray coating is approximately 4064 μm and is obtained in "I N-718" at erosion of 10 mg / cm2. To achieve a rough superalloy surface suitable for a subsequent thermal spray coating, the preferred scales of roughness, erosion and loss of thickness are as follows: roughness - 1270-12700 μm; erosion - 4.4-45 mg / cm2; and loss of thickness - 6.35-50.8 μm The most preferred scales of roughness, erosion and loss of thickness are the following: roughness - 2032-5080 μm; erosion - 5-20 mg / cm2 thickness loss - 6.35-25.4 μm The above scales can be achieved by applying a water jet that is scrutinized through the surface in a tracking manner. The water jet must exhibit a pressure that is at least above the threshold pressure for the alloy that is becoming rough. In addition, the speed of sweep of the water jet is set in such a way that the mass of water applied per unit area is greater than a critical quantity supplied. It has also been found that a pretreatment by a light discharge of sand to the surface, allows a faster action to roughen the surface, by a subsequent water jet application, with lower pressures of water jet. As will be apparent from the following data, the invention has been tested on both nickel-based superalloys or cobalt-based superalloys, which will be referred to hereinafter by their trade names: "IN-718"; "MAR-M 509" and "RENE 80". The compositions of each of the aforementioned alloys (in% by weight) is as follows: "IN-71 8" carbon 0.05 chromium 19 aluminum 0.5 titanium 1.0 molybdenum 3.0 niobium 5.0 zirconium 0.01 boron 0.005 iron 18 BOX "MAR-M 509" carbon 0.55-0.65 chrome 21 .0-24.0 nickel 9.0- 1 1 .0 tungsten 6.5-7.5 tantalum 3.0-4.0 titanium 0.15-0.25 zirconium 0.40-0-60 manganese 0.10 max silicon 0.40 max boron 0.01 max iron 1.50 max sulfur 0.015 max cobalt rest TABLE 2"RENE 80" cobalt 9.5 chromium 14 molybdenum 4 tungsten 4 titanium 5 aluminum 3 carbon 0.17 zirconium 0.13 boron 0.015 nickel rest C UROPE 3 EXPERIMENTAL The experimental work was achieved using a Pressure Flow Intensifier Model 9X, capable of reaching a maximum water pressure of 358 MegaPascals. The water jet was defined by a sapphire hole with a diameter of 0.4 mm, and the current was tracked through test substrates at various transverse speeds, but all with a common deion of 0.76 mm between the traced traces. The distance of the surface of the substrate to the jet outlet nozzle was 7.6 cm in each part, which was found as the distance for maximum erosion effect. A single erosion trace had a width of approximately 1.5 mm. The substrates of the alloy were weighed before and after exposure to the water jet, as well as their thicknesses were measured. Erosion was calculated as milligrams of mass loss, per square centimeter of surface area. Most of the samples were round buttons, 25.4 mm in diameter and 3.2 mm in thickness, but some had dimensions of a single sample, cuts from the base of a turbine blade or sheet material. The high pressure pump had the following water flow rates through the 0.4 mm hole. At reservoir pressures of 207, 276 and 345 MPa: 3.49, 3.97, and 4.50 liters / minute. From these flow rates and tracking speed, the mass of water supplied to each specimen was calculated in kilograms per square centimeter.

An initial investigation of the effect of the high pressure jet on several alloy samples was carried out at a deposition pressure of 345 MPa and at a transverse speed of 30.5 cm / min. Based on these results, another coupling specimen was operated at both fast and slow transverse speed, depending on whether the first loss of erosion was relatively large or small. These groups of data with multiple points are shown in the Figures. The "IN-718" was an annealed solution for one hour at 954 ° C and had a hardness of "Rockwell B" of 103. The samples of "MAR-M 509" had a casting condition with a hardness of "Rockwell C" "superficial of 31 .0. The samples of "R ENE 80" were cut transversely from a rod directionally, to which an annealed standard solution was provided for four hours at 1200 ° C under vacuum, with a final hardness of 39.4 HRc. The original "MAR - M 509" surfaces were ground and then finished by vibrations with triangular aluminum medium in water, producing an initial finished surface of 0.5 micrometers. The surface of "RENE 80" was ground to a finish of 0.3 micrometers. The corroded surfaces were examined in a scanning electron microscope, and the roughness was measured with a portable "Taylor-Hobsen" rugosimeter at a 0.76 mm cutting setting. Fig. 1 is a graph for "I N-718" of water mass supplied (in kg / cm2) against corroded metal (mg / cm2). Two important aspects of the water jet erosion process were evident from the graph of Fig. 1. One is that there is a minimum mass of water required to impact on the substrate "IN-718" before it becomes a weighted erosion, that is, an incubation period. Therefore, no substantial erosion occurs at 276 MPa, until after 0.8 kg / cm2 of water has been delivered through the substrate. At such time, erosion begins and increases exponentially. At 345 MPa, the incubation period ends at approximately 0.5 kg / cm2. The second aspect is that there is a threshold pressure required for ponderable erosion and that 207 MPa is only slightly above the threshold. It has been determined that a threshold for annealed solution of "IN-718" is approximately 196 MPa. From the Bernoulli equation, the threshold pressure can be converted to jet velocity, and therefore the corresponding threshold velocity for "IN-718" is 650 meters per second.

In Figure 2, similar erosion conditions were carried out on an aged "IN-718", which was annealed for one hour at 954.4 ° C and then aged for eight hours at 718 ° C plus an additional ten hours at 621 .1 ° C. The old "N I-718" had a Rockwell B hardness of 1 15. Note that the erosion values of the metal were considerably lower than those shown in Fig. 1, which shows a different dependence on substrate hardness.

The experiments shown in Fig. 1, were repeated, for a sample of "I N-718" that was subjected to a pretreatment with a light sand discharge to remove the original uniform finish of the sample (see Fig. 3). An 240-mesh angular alumina sand was used with a discharge head placed 5.08 cm from the sample at a 90 ° inclination angle. The applied sand pressure was 2.9 kg / cm2. After pretreatment with sand discharge, the sample was subjected to water jet erosions at reservoir pressures of 207 MPa, 276 MPa, and 345 MPa. Note that in each case, a substantial increase in the erosion value is evident at the respective pressures of the water jet. In Figure 4, a direct comparison is shown between the values of erosion of the metal for a sample, to which a sand discharge was applied and then subjected to a water jet procedure to roughen it against a portion of the same sample, which was subjected to the water jet procedure to make it rough, without the initial discharge of sand. In the graph of Fig. 4, the amount of metal erosion is plotted against water jet pressure, and it should be noted that erosion begins at a considerably lower pressure when the sample has been subjected to a sand discharge, compared to the sample that was not sprayed with sand. In Fig. 5, the mass of water supplied to the substrate is plotted against loss of erosion weight for a variety of materials that have been subjected to a water jet roughness procedure at 345 MPa. The data of "IN-718" discussed above (solution annealed 1 hour at 954.4 ° C) are plotted, and the erosion data for a sample of "IN-718" in a condition of excess solution (4 hours at 1079.4 ° C) have been added, as well as, the data for a titanium sample, 6 weight percent aluminum, 4 weight percent vanadium. The titanium alloy behaved in some way, like the "IN-718" (1 hour / 954.4 ° C), but the "IN-718" (4 hours / 1079 ° C) exhibited a much greater corrosion for a similar mass of water supplied. As can be seen from the data plotted in Fig. 5, there was a substantial difference in erosion weight loss achieved in the "IN-718" samples, depending on the state of heat treatment. For the case of water jet erosion at 345 MPa, a weight loss of 40 mg / cm2 was achieved, a roughness of 7.5 micrometers was achieved in "IN-718" annealing 1 hour at 954.4 ° C, but a roughness of 1 1.5 micrometers in the "IN-718" annealed 4 hours at 1079 ° C. At the same jet pressure and mass of water supplied, the material with excess solution had substantially more erosion loss and greater roughness. The erosion tendency of the "MAR-M 509", as a function of water mass supplied to the substrate, is shown in Fig. 6. The erosion data curve at 349 MPa increases exponentially with the increase in water mass inclination. A similar but still exponential curve is observed at 276 MPa, suggesting both curves, a threshold or incubation period occurring at the beginning of the erosion action. In Fig. 7, the erosion of "RENE 80" is shown on a graph of erosion weight loss against mass of water supplied. Note that it is clearly seen that there is a threshold value of about 1 kg / cm2 before the weighted erosion occurs. The surface roughness of corroded "R EN E 80" samples, is shown in Fig 8, as a function of erosion weight loss. The roughness rises rapidly with erosion, and then moves to a limiting value of about 30 micrometers to a high corroded weight loss. It should be remembered that the weight loss at 220 mg / cm2 corresponds to approximately a surface removal of 269.25 μm. This is substantially more than the modest surface removal required for thermal spray preparation. However, at a weight loss of approximately 10 mg / cm 2, it was found that roughness of approximately 5 micrometers occurred, which was very suitable for a subsequent thermal spraying application. In Fig. 9, the results of the water jet erosion tests on steels having hardness of 40, 50 and 60 of Rockwell "C" are shown. Again, it should be noted that erosion weight loss depends substantially on the hardness of the substrate, as well as the applied water jet pressure and mass of water used to demonstrate that a substrate, which has been subjected to to a method for water jet roughness, will provide a good basis for a plasma spray coating, a nickel-based superalloy turbine blade, was cleaned and roughened in one step, using appropriate water jet parameters found previously. The blade originally had a dark surface oxide, but was completely removed by the water jet roughness procedure. The loss of weight due to erosion of the blade was 10.7 mg / cm2, a removal of approximately 0.012 mm in thickness. The blade was then coated with an extra layer of "MCrAIY" (where M is nickel, cobalt or iron) by plasma spraying with argon, vacuum heat treatment, finishing and hammering. An excellent bond was obtained and the interface was absolutely clean on all sides. The above results indicate that each tested substrate material exhibits a threshold pressure below which the erosion of the surface does not begin. In Fig. 10, a graph of threshold pressure versus hardness (Rockwell B) is shown for the three main superalloys that were studied, "IN-718"; "MAR-M 509" and "REN E 80". Note that the hardness was increased, the threshold pressure increased exponentially. In Fig. 1 1, the mass of water supplied is plotted against water jet pressure for both cobalt-based superalloys and nickel-based superalloys. In each case, the mass of water supplied was that required to achieve an erosion of 4.5 mg / cm2 of the substrate. Note that for the cobalt-based superalloys, the mass of water supplied varies from about 0.7 kg / cm2 to 359 MPa at 5.5 kg / cm2, at approximately 302.4 MPa. In contrast, nickel-based superalloys exhibit a lower mass of water required to achieve a similar erosion state and lower water-jet pressures (e.g., approximately 1.5 kg / cm2 at 276 MPa). In summary, previous studies indicate that threshold water jet pressures are present for each substrate material below which erosion will not occur. These pressures are shown in Table 4. THRESHOLD PRESSURE Material MPa "MAR-M 509" 21 1 .14 MPa "RENE - 80" 247.78 MPa "IN-718" 196.65 MPa TABLE 4 Table 5 below shows the critical mass of water required to achieve the established levels of erosion, in the variety of substrates tested. Each of the entries in the Table 5, establishes, at least, a minimum level of erosion of 4.5 mg / cm2, the mass of water required at the indicated pressure. Also, there is an entry (for all but one substrate) which indicates the mass of water required to achieve a maximum level of erosion of I (5 mg / cm2) The entries in Table 5, which have an asterisk, on values interpolated between values obtained experimentally TABLE 5 CRITICAL MASS OF H7O TO ACHIEVE ESTABLISHED EROSION Although the above description has been based on the use of water as the source of jet erosion, those skilled in the art will know that other pure liquids can be appropriately substituted. Said liquids are ethylene glycol, high density alcohols, polywater, etc. It should be understood that the foregoing description is only illustrative of the invention. Those skilled in the art can devise various alternatives and modifications, without departing from the invention. Accordingly, it is intended that the present invention encompass all such alternatives, modifications and variations that fall within the scope of the appended claims.

Claims (7)

1. CLAIMS 1. A method for roughening a surface of a substrate, said method comprising the steps of: a. provide a prior roughness by means of a sand discharge through the surface of the substrate; b. provide a jet of liquid, at least at a pressure of 189.2 MPa; and c. moving said jet of liquid through such surface of said substrate, at a rate such that it supplies the liquid to said surface on a scale in amounts between 0.7 kg / cm2 and 5.5 kg / cm2.
2. 2. The method of claim 1, wherein the following step is added: a. deposit a layer of metallic, ceramic or "cer et" material on said surface using a thermal spray coating device.
3. 3. The method of claim 1, wherein the jet pressure and the amount of liquid supplied to said surface is adjusted to roughen said surface within a range of 1270-12700 microns.
4. The method of claim 1, wherein the jet pressure and the amount of liquid supplied to said surface are adjusted to corrode said surface at a loss of thickness not to exceed 50.8 μm.
5. 5. The method of claim 1, wherein said substrate is a superalloy selected from the group consisting of alloys based on nickel, cobalt-based alloys, iron-based alloys, and titanium-based alloys. The method of claim 1, wherein said liquid jet comprises a liquid flow selected from the group consisting of water, ethylene glycol, alcohols or polywater. The method of claim 2, wherein the thermal spray device of the coating is selected from the group consisting of plasma spray, detonation gun, high-speed oxy-fuel, and high-speed impact melting.