DE1268851B - Use of a nickel-titanium alloy - Google Patents

Description

Use of a nickel-titanium alloy The invention relates to the use of a nickel-titanium alloy of 30 to 50 "1, Ti 'balance nickel, which is characterized by unusual mechanical and physical properties.

Most intermeiallic compounds are very brittle and have no ductility at room temperature. Despite many other exceptionally good properties that such compounds have - for example, they retain their strength at high temperature - their brittleness at room temperature makes them practically unusable for any structural application. The invention now provides a remedy here.

The invention accordingly consists in the use of an alloy of 30 to 50'110 Ti, the remainder being nickel, as a material for objects which are produced by hot deformation and optionally cold deformation and whose structure has a Ti within a temperature range of about 500 to -75 ° C. Ni-phase in connection with a Ti-Ni3-phase, distributed in a Ti-Ni-matrix, possesses, with paramagnetic property, high hardness in the mentioned temperature range, corrosion resistance, high impact Z; ability, good elongation, ductility and high mechanical damping.

Further advantages and features are explained in the following description of the invention: There are three possible phases in the alloy used. The chemical conversion follows the reaction equation TiNi z-- Ti2Ni + TiNi3 The starting materials for the alloy are, for example, granulated nickel of a high degree of purity, as it comes on the market under the trade name "Moon Nickel", and commercially pure titanium in ingot form. The technology of the alloy can be divided into three stages, namely a) melting of the alloy, b) machining of the molten and cast alloy, c) heat treatment of the machined material. a) Melting the alloy Because of its high titanium content, the alloy is melted in the arc melting process, using either self-consuming electrodes or permanent electrodes and a water-cooled crucible melting furnace. Under certain circumstances, induction melting can also be used when using a ceramic crucible (for example made of ZrO2) if the nickel is first melted and then the correct amount of titanium is added. After adding the titanium, the alloy should be poured quickly to prevent undesirable interaction between the titanium and the crucible material. A trial melting in a less refractory MgO crucible was satisfactory in that the oxide content of the melt was increased to the allowable level of about 0.18 percent by weight. b) Machining of the alloys melted in the arc All cast alloys between about 52 and 56 percent by weight nickel and correspondingly about 48 to 44 percent by weight titanium can be hot worked without any prior heat treatment.

In one trial, a stoichiometric Ni-Ti compound of 55.1 weight percent nickel and 44.9 weight percent titanium was hot worked between about 650 and 1100.degree. C., with the preferred hot working range between 700 and 900.degree. Further tests showed that the alloys containing over 56 percent by weight nickel, i.e. H. from 56 to 64 percent by weight nickel, require prior heat treatment in order to be hot workable. This heat treatment consisted of heating the alloy to about 1050 ° C. until it was thoroughly heated and then slowly cooling it to room temperature. In deviation from this, the alloys can be heated to about 1050 ° C. and kept at this temperature until they are completely heated and then slowly cooled to 850 ° C. and kept at this temperature until they have uniformly assumed this temperature inside and outside. They are then slowly cooled to room temperature. The principle in the aforementioned heat treatment prior to processing is to precipitate the excess nickel from the solution and combine it with the compound phase TiNi to form the compound phase TiNi3. This leads to an extensible base metal in which brittle Ti-Ni3 components have been broken into, which have coalesced to form harmless particles. The two-phase Ti-Ni + excess Ti-N'3 alloy described above could be rolled at any temperature between 700 and 900.degree.

It has also been shown that hot extrusion is an effective means of converting the stem-like crystal orientation into the equiaxed orientation and thus for hot workability of the compounds with a higher nickel content (58 to 62 percent by weight Ni) by conventional working processes such as rolling, upsetting, forging, etc. ., leads. Such hot pressing eliminates any difference that would otherwise exist in hot working these higher nickel compounds.

c) Heat treatment of the machined material The hardness of alloys, which contain between 52 to 56 percent by weight nickel and the rest of titanium and were predominantly single-phase TiNi, could only be influenced slightly by any heat treatment, independently of the cooling.

In contrast, the hardness properties of alloys that contain between 56 to 64 percent by weight nickel and the rest of them titanium. be affected by heat treatment, and in particular by the exhaust cooling. When such alloys are heated to over 900 ° C and quenched in water to room temperature, they take on a high hardness. For example, reached an alloy of 60 weight percent nickel and 40 weight percent titanium when quenched from a temperature which was 900 to 1100-'C, a hardness varied between 58 and 62 Rc, as shown in Table I below. Table 1 Average hardness of a 60-Ni-40-Ti (60 percent by weight Ni, 40 percent by weight Ti) - Alloy when water is cooled from different temperatures Deterrent hardship temperature comments (C) (R ,.) 1110 62 The air was 1000 61 warming and quenching 900 58 ken unhindered access to the rehearsals The same alloy (60 percent by weight nickel, 40 percent by weight titanium) achieved a final hardness of about 35 Rc when furnace-cooled (the average cooling rate was about 50 C per hour). This hardness is roughly equal to the hardness of mixed crystals of the TiNi phase (52 to 56 percent by weight nickel), as can be seen from Table 11 .

The table values clearly show that the non-stoichiometric Ti-Ni alloys. that is, those which contain Ni in excess can be hardened by quenching. It can also be seen that an alloy of 56 percent by weight nickel and the rest of titanium forms the transition between the hardenable and non-hardenable alloys and that a large excess of the hardness-causing components of nickel in the form of TiNi3 (above about 64 percent by weight Ni) is used for this to reduce the hardness of quenching. As a result, the preferred range for greatest hardenability is between 58 and 62 weight percent nickel. Table II Hardness at Nickel water remark (Weight deterrent percent) (R ,.) 50 31 52 21 When the air was 54 20 warming and quenching 55 36 ken unhindered access 56 44 -to the rehearsals 58 60 60 62 Hardness when cooling down in the oven 61 63 35Rc 62 62 64 59 When the air was 66 57 warming and quenching 68 56 ken unhindered access 70 49 to the samples 72 46 The hardness of the hardenable nickel-titanium alloy (56 to 64 percent by weight nickel, otherwise titanium) can be attributed to a lower hardness. if this is necessary for a particular application. Such reduction must be based on the best compromise between mechanical properties for the particular application. The reduction in hardness of quenchable alloys can be achieved by A) slowing the cooling rate of the heat treated alloy to a hardness between 35 Rc (furnace cooling) and 62 Rc (water quenching) and B) tempering. The tempering is carried out by heating the hardened alloy again to temperatures below the transition point of the phase boundary between the Ti-Ni Table III Alloy rolling temperature hardness Composition Type of alloy shaking TiNi arc melting with sample did not warm up - 30 to 31 Rolled permanent electrode TiNi also. 600 38 TiNi as well. 700 38 TiNi like 950 32 to 34 TiNi desgl. ION) 39 TiNi like 1100 39 to 41 Ti, Ni like sample could not be hot rolled 53 Ti, Ni, like 950, cannot be hot-rolled TiN'3 like sample could not be hot rolled 34 TiNi3 similar to 1050 cannot be hot-rolled It can be seen from the above values that the room temperature hardness increases with the rolling temperature, which is undoubtedly due to the higher heating temperature and the rapid cooling. It can also be seen that while the Ti, -Ni alloy is quite hard (53 Rc), the Ti-N'3 component has a hardness (34 Rc) that is closer to that of the Ti-Ni alloy. Despite the much lower hardness of TiNi3, it is similar to the Ti, -Ni component in that it is brittle, even at high coincident temperatures.

With alloys. which contain between 50 and 70 percent by weight nickel and the remainder titanium. it has been observed that these alloys retain their hardness properties regardless of temperature. for example over a temperature range from room temperature to 463 C and down to -75 C. Alloys. those close to the stoichiometric Ti-Ni compound without TiN'3 and Ti, Ni (54.5 to 55.1 percent by weight N #) even showed a tendency towards "secondary hardening". This can be seen from Table VIII.

The elongation properties were measured for both alloys with 54.5 and 55.1 percent by weight nickel and the rest with titanium. In each case a standard sample with a diameter of 6.45 mm and a height of 25.4 mm was used. The samples were lapped lengthways. to prevent transverse notches. In order to exclude the oxidation of the sample surfaces and to reduce the penetration of the elements oxygen, nitrogen and hydrogen, a vacuum or controlled atmosphere heat treatment was carried out. The vacuum heat treatment was carried out in an evacuated quartz tube. The tensile strength results, and the Ti-Ni + Ti-Ni, phase (about 900 "C) and slow cooling achieved, the final tempering hardness being determined by the heating temperature, the exposure time to this temperature and the cooling rate The tempering treatments are carried out in a helium or argon atmosphere to prevent temperatures exceeding 600 Q. In many cases, however, the heat treatment in air will suffice.

Further hardness values for TiNi, Ti, Ni and TiNi3 are given in table Ill compiled. which were obtained are summarized in Table IV.

From the above results it can be seen that the elongation can be up to 15.5 ", 1" with an average of 7 to 10 ',' n. For an intermetallic compound, this elongation at room temperature is an unusually and unexpectedly high value. It can also be seen that the 0.2 yield strength varies considerably with composition and heat treatment, while the tensile strength at rupture and the modulus of elasticity remain largely constant regardless of the composition and the heat treatment.

To determine the impact strength of C har py square samples were carefully edited, used. The sample surfaces were hand-lapped in the longitudinal direction in order to largely eliminate cross scratches. The tests were carried out in a standard Riehle machine. The results are shown in Table V.

Here, too, as in the elongation tests, unusual notched impact strength values were achieved compared to most intermetallic compounds. For both Ti-Ni alloys the minimum value was 3.18 mkg, even with undersized samples. The increase in the notched impact strength at temperatures below freezing point is particularly emphasized.

Samples with an alloy with 55.1 percent by weight Ni and the rest of titanium were subjected to a series of the usual corrosion tests and exposed to the attack by oxidation. The results of these tests are recorded in Tables VI and VII. Table IV Tensile test results (Sample dimensions: 6.45mm diameter - 25.4mm) Tensile Strength Yield Strength 0.2 Yield Strength One Elasticity Sample treatment when tearing lacing 1 module Comments (kg, MM2) (kg / mm2) (ll; ",) (1) / o) 1 (kgmm2) Alloy with 54.5 percent by weight Ni, otherwise Ti (room temperature) 800 "C, 1 hour oven- 79 28.1 8.1 - 8.1 - 10 ' broke outside cooled *) of the measuring length 800, - 'C, 1 hour water- 87 28.6 15J 16.0 8.3 - 1 W chilled *) Alloy with 54.5 percent by weight Ni, otherwise Ti (test temperature: 85 to 88.9 C) 800 "C, 1 hour oven - 77.8 32.9 3.6 - 7.9 - lW broke outside cooled *) of the measuring length 800 'C, 1 hour water 81.2 3K7 10.9 13.0 7.9 - 10' chilled *) 1 Alloy with 55.1 percent by weight Ni, otherwise Ti (room temperature) Hot forged at 900'C, 87.9 57.2 8.1 - 7.9 - 10 ' air cooled 1000'C, 30 minutes oven- 82.0 39.5 7.2 - 6.8 - 10 ' hardness 26 R, chilled *) 1000'C, 30 minutes oven- 803 23.6 3.2 - 7.3 - 103 broke outside cooled **) the measuring length, Hardness 24 R 1000'C, 30 minutes oven - 98.9 25.5 9.9 - hardness 24 R, chilled **) 1000'C, 30 minutes 57.8 50.1 3.5 - 72 - 10 ' hardness 33 R, water-cooled ") 1000'C, 30 minutes 59.3 43.8 4.5 - 8.3 - 10 ' hardness 31 Rc water-cooled ") Heat treatment was carried out in an argon atmosphere. The sample was enclosed in an evacuated quartz tube during the heat treatment. Table V Impact bending test results on samples made from Ni-Ti alloys (The samples were free of cracks and had a square cross-section) Alloy composition NiTi specimen dimensions Notched impact strength Cross-section test conditions (C har py) (Weight percent) (mm) (mkg) 54.5 *) 7.48 - 7.48 Test temperature: 24 # C 3.87 54.5 *) 7.48 - 7.48 Test temperature : 51.7'C 4.42 54.5 *) 7.48 - 7.48 Test temperature : 93.3'C 4.08 54.5 *) 7.48 - 7.48 Test temperature : -80'C 5.54 54.5 *) 7.48 - 7.48 cooling to -80'C in water 3.18 warmed by rt and 15 minutes stabilized in air from RT 54.5 *) 7.48 - 7.48 cooling to -80'C in water 3.46 warmed by RT, in air by RT stabilized, then on 71.1'C heated 55.1 7.51 7.51 Test temperature: 24 "C 3.32 55.1 7.51 7.51 Test temperature: 93.3 "C 3.87 55.1 7.51 7.51 Test temperature : -80 C 5.95 The samples were taken from hot forged bars. The samples were taken from hot rolled plates. Table VI Corrosive Agents Effect_ Salt water spray slightly whitish low - 20 "/, solution, 35'C, hit on the back 96 hours of rehearsal, no attack on the exposed surface Sea water - 192 hours none Normal air atmosphere none Normal treatment none Table VII Oxidation behavior Weight gain due to oxidation Trial at different temperatures duration (G) (Hours) 6001 C 800 'C -1 OOW C 2 0.001 0.016 GA67 4 0.001 0.017 0.079 6 0.0013 0.020 0A88 8 0.0013 0.022 0.094 10 0.0014 0.023 0.100 12 0.0015 0.025 0.105 From Table VI it can be seen that in each case the attack was negligible and only with very drastic salt sprays was a noticeable film formed where the sample was held. The passivity of these alloys to corrosion attacks is certainly a highly desirable property, for example for shipbuilding materials.

From Table VII it can be seen that at 600 ° C. the initial oxidation was very low and the build-up of oxide after the first two hours was negligible. At 800'C the oxidation progressed gradually after the first two hours, and at 1000'C the initial oxidation was very rapid and progressed gradually. The detachment of the oxide surface was easy to difficult at 800 and 1000 ° C.

The ability to connect is extremely important for the processing of building materials. In order to obtain information about the weldability of Ni-Ti material, two beveled, 3.2 mm thick, hot-rolled plates made of TiNi were butt-welded together in an arc using helium. There were few difficulties to overcome to achieve the joint and the weld interface appeared free of cracks and porosity. On the basis of this finding, the weld is to be regarded as very strong and tough. In addition, the investigation of the magnetic properties of the welded part shows that it is just as paramagnetic as the base material.

Among the various exceptional properties of Ni-Ti alloys, paramagnetic behavior is of paramount importance. A paramagnetic material is considered to be a material whose specific permeability is greater than 1 and is practically independent of the magnetizing force. The nickel-titanium alloys in the composition with Ti, Ni, TiNi and TiN'3 are highly paramagnetic despite the high proportion of nickel present in these alloys. Alloys with 54 to 60 percent by weight Ni and the rest of Ti were evaluated magnetically after various thermal treatments at widely varying temperatures. The magnetic investigations related to the measurements of the magnetic susceptibility as well as the permeability. In these tests it was found that the permeability very much approaches the value 1 , regardless of the temperature, the residual mechanical stress or the previous heat treatment. Great care must be taken to avoid any oxide coatings in cases where the Ti-Ni alloys are to be used for non-magnetic applications. This is due to the combination of some Ni of the alloy with 02 to form a ferromagnetic oxide layer and the combination of Ti + Q to form TiO2, creating a thin, high nickel surface layer that is ferromagnetic.

The unusual mechanical damping effect is also of particular importance with these Ni-Ti alloys. The stoichiometric alloy shows a one-time and drastic change in vibration damping even with small changes in temperature and composition, both in the direct arc-cast state and after heat processing. Quantitative and qualitative studies have shown that the damping of an alloy with 54.5 percent by weight Ni and otherwise Ti with a low Fe content (about 0.1 percent by weight) from a highly damping material at room temperature (25'C) to a material with very low damping properties at 54'C and above. Internal friction tests, which were carried out on a round wire 0.9 mm in diameter, showed that the logarithm of the amplitude fell from 2.3 to 1.1 in 35 periods at room temperature (25'C), while the logarithm of the amplitude of the same Wire only dropped from 2.3 to 2.1 in 35 periods when heated to 93'C. This clearly shows the change in the damping properties of machined wire made of an alloy of 54.5 percent by weight Ni, about 0.1 percent by weight Fe and the rest of Ti. In the damping behavior, however, even more noticeable differences have been observed with such an alloy when they are in the arc - is in the as-cast state. This change in damping properties appears to be related to the phase equilibrium of the alloy system. As the temperature is increased, the Ti-Ni phase increases in quantity at the expense of reducing the out-of-phase components (Ti2Ni and TiNi3). As soon as this occurs, the damping capacity is significantly reduced. This depends on the presence or absence of the Ti, -Ni phase together with the Ti-Ni phase.

The phase equilibrium theory is confirmed by the fact that the alloys which have Ni or Ti in excess over the stoichiometric composition have significantly different damping properties at room temperature. For example, the Ti-rich alloys (less than 54.5 percent by weight Ni) show high damping properties at room temperature, while Ni-rich alloys (with more than 54.5 percent by weight Ni) have poor damping properties at room temperature. It is thus shown that the Ti2-Ni phase, coupled with TiNi, develops the high damping ability. Any reduction in the Ti.-Ni phase, for example increasing the Ni content, increasing the temperature, impurities Mechanical properties of hot-extruded 60% Ni-Ti alloy (Standard specimens with a 10 mm square cross section were used.) Heat treatment Average hardness Impact strength Tensile strength Elongation Young's modulus ( Charpy) (RI.) (Rnkg) (kg / MM2) (0, g » (kgmm2) Extruded 50 8.4 126 1 9.5 1 Water quenched 61 5.25 112 1 11.6 10 ' Oven cooling 41 7.2 98 8 8.6 - 10 ' Quenched and 58 105 1 8.95 - 10 ' tempered at 640'C The properties of the new Ni-Ti alloys are summarized in Table VIII.

In summary, it can be seen that Ni-Ti alloys containing between 50 and 70 percent by weight Ni and the remainder Ti have been developed which have an unusual combination of properties, such as great hardness over a wide temperature range and in particular at temperatures which lie below freezing point. The alloys also have unusually good elongation and impact strength at the same temperatures. The alloys, which are in a range of 50 to 70 percent by weight Ni, can be divided into those alloys which contain between 52 and 56 percent by weight Ni and otherwise Ti, and those which contain between 56 and 64 percent by weight Ni and otherwise Ti exhibit. The first-mentioned alloys are largely single-phase Ti-Ni compounds, whereby they can be worked both slightly warm and at room temperature and show an unusual elongation at room temperature. The last-mentioned alloys are characterized by the fact that they are multiphase materials (in particular TiNi + TiNi3) which can be hardened to a high degree of hardness. The combination of the hardenability of these alloys with the characteristic paramagnetic behavior (the magnetic permeability is below 1.02) is of great importance and leads to their use in high-quality, non-magnetic tools and building materials that remain non-magnetic, withstand the attack of corsion and withstand wear and tear. Table VIII Compilation of properties of Ni-Ti alloys 55.1 weight a) Physical properties percent Ni-Ti alloy Specific weight (25'C), g / cri0 ........ 6.45 Melting point, `C ........... 1240 to 1310 Crystal structure ............. cscl Changes caused by Fe, etc., cause slight changes in the Ti-Ni / Ti2-Ni phase equilibrium and thus cause drastic changes in the vibration-damping behavior. This unusual damping phenomenon makes these alloys suitable for use in temperature sensing devices or where it is desired to dampen mechanical vibrations (noises). 55.1 Weight a) Physical properties percent Ni-Ti alloy Space lattice, Parometer, 3.015 Electrical resistance (25 - C), Microohm em ............ 80 Electrical resistance (900- C), Microohm em ............ 132 Linear expansion coefficient cient (24 to 900'C), pro - C 10.4 - W ' Recrystallization temperature, 'C 550 to 650 Magnetic permeability .... 1.002 Magnetic susceptibility K 196 to 550 # C) ......... 5 to 9 - 10 ' b) Mechanical 54.5 weight 55 1 weight Properties percent percent Ni Ni Tensile strenght, kg7mnr '77.4 to 87.3 57.6 to 98.5 0.2 stretch border, kgmnr '28 .1 to 38.7 32.2 to 57.2 Young's module, kg mrrr '7.88 to 103 bis 8.3-10' up to 8.3 - 103 Elongation, "to 15.5 to IU 0 Constriction, 0 0 ..... ... to 16 Hardness, Rockwell-A. 42 to 52 65 to 68 Notched bar toughness, mkg 24-- C (room temperature). 3.87 3.32 -80- C .... 5.54 5.95 Flexural strength, kg min- ' . . . . 152.0 Continuation b) Mechanical 54.5 weight 55.1 weight properties percent percent Ni Ni modulus of elasticity, kg / mnr ' 7.95 103 hot hardness *), - HV 25-C (room temperature). 230 330 260-'C ..... 215 230 463'C ..... 230 295 593 'C ..... 65 95 649 # C ..... 45 50 The samples were quenched before the test was carried out.

Claims (2)

Claims: 1. Use of an alloy consisting of 30 to 50 '2 o titanium. The rest of nickel, as a material for objects. which are produced by hot deformation and optionally cold deformation and whose structure has a Ti-Ni phase in conjunction with a Ti-Ni3 phase within a temperature range of about 500 to -75 C. distributed in a Ti-Ni matrix, has, with paramagnetic properties, high hardness in the specified temperature range, corrosion resistance, high notched impact strength, good elongation, ductility and high mechanical damping. 2. Use of an alloy according to Claim 1 with 44 to 48 ' , Ti. The balance is nickel, deformed according to Claim 1, as a material for objects with particularly high ductility. whose structure mainly consists of a Ti-Ni phase within the temperature range from about 500 to -75 C. 3. Use of an alloy according to claim 2, which is subjected to hot working in a temperature range from 650 to 1,100 C, preferably from 700 to 900 C after melting, for the purposes of claim 2. 4. Use of an alloy according to claim 1 with more as 45.5 to 50 "" Ti, remainder nickel, deformed according to claim 1. as a material for objects with particularly high mechanical damping at room temperature. whose rumors essentially have a Ti-Ni phase within the temperature range from about 500 to -75 C. 5. Use of an alloy according to claim 1 with 36 to 44 "" Ti. The remainder is nickel, deformed according to claim 1 and also annealed and quenched, as a material for objects with particularly great hardness. whose tears within the temperature range from about 500 to -75 C essentially have a Ti-Ni3 phase, distributed in a Ti-Ni matrix. 6. Use of an alloy according to claim 5, which is preheated after melting to about 1050-'C until it is completely heated and is then subjected to a heat treatment at 700 to 900 ° C, for the purposes of claim 5. 7, use of an alloy according to claim 5, which is subjected to Melting heated to about 1050 C until completely heated and then slowly cooled to a temperature of about 850 C and kept at this temperature until a uniform temperature is assumed and then slowly cooled to room temperature and then hot worked, for the purposes of claim 5. 8. Use of an alloy according to claim 5, which, after hot working according to claim 6 or 7, is heated to over 900 ° C and then preferably quenched at a temperature between 900 and 1100 ° C by water cooling or by furnace cooling at an average cooling rate of about 50 C is cooled per hour, for the purposes of claim 5. 9. Use of an alloy according to Claim 5 which, after hot working according to claim 6 or 7 and after heat treatment according to claim 8, is brought to a temperature below the transition point of the phase boundary between the Ti-Ni and the Ti-Ni + Ti-Ni3 phase to 900 C and is then slowly cooled, for the purposes of claim 5. 10. Use of an alloy according to claim 1 with 36 to 44 " 0 Ti, remainder nickel, deformed according to claim 1, as a material for paramagnetic objects whose structure is within the temperature range of about 500 to -75 C essentially has a Ti-Ni phase. 11. Use of an alloy according to claim 1 with 44.9 to 45.5% Ti, balance nickel, deformed according to claim 1, as a material for objects with particularly high impact strength, the structure of which is within the temperature range of about 500 to -75 C im essentially has a Ti-Ni phase. 12. Use of an alloy according to claim 1 with 45 () / () Ti. The remainder nickel, deformed according to claim 1, as a material for objects with particularly high corrosion resistance, the structure of which within the temperature range from about 500 to -75 ° C essentially a Ti-Ni phase possesses. Publications considered> M. Hart sen and K. An derko, Constitution of Binary Alloys, 1958, pp. 1049-1053; M c Q ui 11 a n. Titanium, 1956, p. 127.