JPH0368945B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for processing a Ti-Ni alloy. Ti-Ni intermetallic compounds and alloys in which some of them are replaced with other elements (Cu, Fe) are known to have a remarkable shape memory effect (U.S. Pat. No. 3,174,851, JP-A-53 -28518 etc.) Such Ti-Ni alloys have good hot workability, but cold workability depends on the alloy composition, as there is a correlation between the transformation properties and mechanical properties of the Ti-Ni alloy. and change. On the Ni-excess side, the transformation temperature
As (°C) is below room temperature, and the workability is so poor that cold rolling and wire drawing are almost impossible. Table 1 shows the transformation temperature As (℃) of a test in which Ti-Ni alloy was heated at 700℃ for 2 hours and then water quenched when the Ni concentration was varied, and when a base material with a wire diameter of 7 mm was cold drawn. shows the maximum machining rate.

[Table] As is clear from Table 1, on the Ni-excess side, the As point is lower than room temperature and the processing rate is small. Figure 1 shows the change in yield stress at room temperature 25°C with respect to the Ni concentration of the Ti-Ni alloy.
% or more). Therefore, an object of the present invention is to improve the cold workability of Ti-Ni alloys on the Ni-excessive side (50.3 at or more). For this purpose, the tensile stress and elongation rate of the Ti-Ni alloy in the parent phase state and martensitic phase state were investigated, and the results were as shown in Figure 2. i.e. Ti-Ni alloy with Ni49.5at (As=80°)
The wire was drawn at room temperature and at a temperature of 80℃ or higher, and the stress and elongation rate were investigated. As is clear from FIG. 2, deformation of the material in the matrix state requires high stress from the start of processing, and it has been found that processing in the martensitic phase is easier. Based on this new fact, the inventor has determined that As
As of the Ti-Ni alloy on the Ni-excessive side where the point is below room temperature
After investigating various methods of raising the As point to form a martensitic phase at room temperature, we discovered that by heat-treating the alloy at a temperature below 550°C, it is possible to raise the As point above room temperature. The present invention was made based on such new findings, and is a method for processing a Ti-Ni alloy in which Ni is 50.3 at% or more and the As point is below room temperature. In order to achieve the above,
This is a method for processing a Ti-Ni alloy, which is characterized in that the alloy is heat treated at 550°C or lower and then cold worked at room temperature. The heat treatment atmosphere is air, nitrogen gas,
Any gas such as argon gas may be used. According to the present invention, on the Ni-excess side (50.3 at% or more)
Ti-Ni alloy also has an As point above room temperature and is in a martensitic phase at room temperature, so cold working is easy. Conventionally, when cold working Ti--Ni alloys on the Ni-excess side, cold working and a heat treatment step of heating to 700° C. and water quenching have been alternately repeated. The purpose of the heat treatment in this case is to remove mechanical strain, and the cold working rate is usually about 5%, and as shown in Table 1 above, the maximum cold working rate is about 10%.
It was hot. However, if processed using dry ice or liquid nitrogen to maintain the temperature below the As point, it is usually 30%
Although a certain processing rate can be obtained, since the processing equipment is also equipped with a cooling device, it becomes complicated and the work efficiency of the operator is poor, making it impractical. However, according to the present invention, cold working can be performed at room temperature with a high working rate. FIG. 3 shows the results of measuring the relationship between the heat treatment temperature of the alloy and the As point for various Ni concentrations. In the same figure, curves a, b, c, and d have Ni concentrations of 51.11 at%, 50.77 at%, 50.56 at%, and 50.30 at%, respectively.
This is the case. As is clear from the figure, for all alloys, the As point is 25°C or higher when the heat treatment temperature is 550°C or lower. Examples of the present invention will be described below. For Ti-Ni alloys containing 51 at% Ni, the elongation and tensile stress when stretched at room temperature were measured for those annealed at 700°C and those heat treated at 500°C. The results are shown in FIG. Curve a is the material annealed at 700°C, and curve b is the material heat-treated at 500°C. As is clear from the figure, the tensile stress of the present invention shown by curve b is particularly small from the start of processing, and it shows the same tendency as the martensitic phase curve in Fig. 2, making it easier to process. I understand that there is something. Next, for Ti-Ni alloys with various Ni concentrations shown in Table 2, after heating to 500 °C as heat treatment, water quenching, and cold wire drawing of wire diameter 7 mm, the maximum processing rate was measured. . The results are shown in Table 2 along with the As points. Note that the maximum machining rate is the machining rate on the verge of fracture.

[Table] It can be seen that all of them show a processing rate of 30% or more. In particular, for alloys with excessive Ni, not only the cold working rate was significantly higher than before, but also the working time was shortened. In addition, when each sample after processing was subjected to heat treatment to impart a shape memory effect as in the conventional method, the shape memory effect was the same as that obtained by the conventional method and no deterioration was observed. As described above, in the present invention, Ti-Ni on the Ni-excess side
The alloy is heat treated at 550℃ or less and then cold worked, but in order to obtain the required dimensions and shape, both the heat treatment and cold working steps are not only carried out once, but also It may be repeated several times alternately.

[Brief explanation of drawings]

Figure 1 is a diagram showing the relationship between Ni concentration and yield stress, Figure 2 is a diagram showing the relationship between elongation rate and tensile stress in the martensitic phase and matrix state of Ti-Ni alloy, The figure shows the relationship between heat treatment temperature and reverse transformation temperature As for Ti-Ni alloys with various Ni concentrations. Figure 4 shows the relationship between 700℃ annealed material and 500℃ heat-treated material for 51 at% Ni-Ti alloy. It is a figure showing the relationship between elongation rate and tensile stress about.

Claims (1)

[Claims] 1. In a method for processing a Ti-Ni alloy in which Ni is 50.3 at% or more and the reverse transformation start temperature As is below room temperature, the alloy is heat treated at 550 ° C. or below in order to make the reverse transformation start temperature of the alloy above room temperature, A method for processing a Ti-Ni alloy, which is characterized by cold working at room temperature.