JPH03274248A - Manufacture of ni-ti series intermetallic compound - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Field of Application) The present invention relates to a method for producing a NiTi-based shape memory alloy by powder metallurgy.

(Prior Art and Problems to be Solved by the Invention) As a method for producing a NiTi-based shape memory alloy by a conventional combustion synthesis method, for example, as disclosed in Japanese Patent Application Laid-Open No. 63-307229, titanium powder and nickel powder are used. A raw material mixed powder is obtained by mixing the raw material mixed powder, and a synthesis reaction is started by externally inputting heat into a part of the raw material mixed powder under a high degree of vacuum, and the synthesis reaction is started by the reaction generated heat generated by this synthesis reaction. NiTi is synthesized by a self-propagating high temperature synthesis method that propagates throughout the raw material mixed powder.
Ni
A method for producing a shape memory alloy has been proposed to produce an ingot of a Ti intermetallic compound. In the above publication (Example 1), the densification treatment refers to hot isostatic pressing (HIP) of an ingot in a molten and solidified state against a vacuum.
or remelted in a vacuum and cast into a mold.

However, although hot isostatic pressing (HIP) is a preferable method for achieving high density, the process itself is expensive and the productivity is poor due to the batch type non-continuous processing process. Furthermore, the method of re-melting the alloy material in a vacuum and casting it into a mold also has the problem that the manufacturing cost inevitably increases because the alloy material is once manufactured and then melted again.

(Problems to be Solved by the Invention) The present invention solves the above-mentioned problems of the conventional method, that is, ingots in a melted and solidified state are subjected to vacuum heat treatment or hot processing without employing HIP treatment. An object of the present invention is to provide a method for manufacturing a NiTi-based shape memory alloy that is highly productive, inexpensive, and has excellent material properties by directly densifying it by a method.

(Means for Solving the Problems) The present inventor found that the relative density of the NiTi-based material as produced by the combustion synthesis method is 50 to 55%, and although high purity NiTi is not necessarily formed, ~120
By performing vacuum heat treatment in the range of 0℃, 100%N
It is possible to form iTi, and the hot workability of this material is extremely good, and it can be used for manufacturing steel materials such as hot forging, hot rolling, and hot extrusion within the range of 900°C to 1200°C. It was discovered that it can be processed using existing hot processing equipment, and there is no need to worry about cracking during processing. The present invention was completed based on this knowledge, and its gist is as follows: (1) Powders containing N1 and Ti as main components are mixed, and the resulting mixed powder is placed in a vacuum and The mixed powder is maintained at a temperature higher than the temperature at which it can self-combust due to reaction generated heat generated in the synthesis reaction of the mixed powder, heat is inputted into a part of the mixed powder from the outside to start the synthesis reaction, and the reaction is performed. In a method for producing NiTi-based intermetallic compounds using a combustion synthesis method in which the generated reaction heat is sequentially propagated to unreacted powders, the product after combustion synthesis has a temperature of 900°C~! 2
A method for producing a NiTi-based intermetallic compound, comprising performing vacuum heat treatment at a fi degree in the range of 00°C for 3 to 50 hours.

(2) Mix powders each containing N1 and Ti as main components, and place the resulting mixed powder in a vacuum, and the mixed powder can self-combust due to reaction generated heat generated in a synthesis reaction of the mixed powder. The NiTi-based intermetallic compound is produced by a combustion synthesis method in which the temperature is maintained above the temperature, heat is input from the outside into a part of the mixed powder to start the synthesis reaction, and the reaction generated heat generated in the reaction is sequentially propagated to the unreacted powder. In the manufacturing method, the product after combustion synthesis is heated to 900°C to 12°C.
1. A method for producing a NiTi-based intermetallic compound, which comprises performing mechanical hot working such as forging and hot rolling at a temperature in the range of 00° C. and a rolling reduction of 50% or more.

(() Powders containing Nl and Ti as main components are mixed, and the resulting mixed powder is heated in a vacuum so that the mixed powder can self-combust due to reaction generated heat generated in the synthesis reaction of the mixed powder. The NiTi-based intermetallic compound is produced by a combustion synthesis method in which the temperature is maintained above the temperature, heat is input from the outside into a part of the mixed powder to start the synthesis reaction, and the reaction generated heat generated in the reaction is sequentially propagated to the unreacted powder. In the manufacturing method, the product after combustion synthesis is heated to 900°C to 12°C.
After vacuum heat treatment at a temperature in the range of 00°C for 3 to 50 hours, the reduction rate was 5 at a temperature in the range of 900°C to 1200°C.
The present invention provides a method for producing a NiTi-based intermetallic compound, characterized by subjecting it to mechanical hot working such as 0% or more microstructure and hot rolling.

(Function) Mechanical hot working in the present invention is mechanical working in a so-called hot region that does not include hot isostatic pressing (HIP), and includes hot forging, hot rolling, etc. belongs to

The material after combustion synthesis is not necessarily! It does not constitute a 00% NiTi intermetallic compound, has poor workability when subjected to hot working as it is, and has poor mechanical properties thereafter. However, in the range of 900°C to 1200°C, 3 to 5 on,';
The above-mentioned drawbacks can be overcome by performing a vacuum heat treatment between the two. This is due to the soaking solution treatment effect and is due to diffusion sintering forming a more complete compound. 900℃
If it is less than 1200°C, the effect will be small, and if it exceeds 1200°C, the material will melt, so the temperature range was set to 900°C to 1200°C.

Further, the treatment time is required to be at least 3 hours to cause the reaction, and although a long time is effective, the upper limit was set at 50 hours from a practical standpoint.

In the method of producing NiTi-based materials by combustion synthesis, hot working the material after combustion synthesis at a reduction rate of 50% or more in the range of 900°C to 1200°C is very effective for densification. At temperatures below 900°C, the deformation stress is too high and it is difficult to process this material, and at temperatures above 1200°C the material begins to melt, so the temperature range was limited to the above range. In addition, although the reduction rate was set to 50% or more, the relative density of the NiTi-based material as produced by the combustion synthesis method is 50~
Since the density is 55%, it is necessary to perform hot working of at least 50% in order to increase the density to 100%. As for the upper limit of the rolling reduction rate, the higher it is, the higher it can be <99%, but the common sense upper limit is 95%, and considering high density and refinement of the material structure at the same time, hot working of 85% or more is desirable.

An example of a powder self-combustion synthesis apparatus is shown in Fig. 1.

That is, in FIG. 1, 1 is a high vacuum container, and 2 is a high vacuum container.
is an electric furnace and has a heater 10 on its inner wall. The electric furnace 2 houses a raw material mixed powder 4, and a refractory crucible 3 equipped with an ignition resistance heating wire 5 connected to an electrode 8 for igniting the mixed powder 4 is installed. 6 is the vacuum exhaust system,
7 is a sealing mechanism, and 9 is a temperature control thermoelectric χ/■.

Examples of NiTi will be described below.

(Example 1) The oxygen content h' is 0.08 in NlI amount% and the average particle size is 50.
- with Ti coating and an average particle size of 20 with an oxygen content of 0.05%
um of N1 powder were mechanically mixed in a 1:1 molar ratio.

3 kg of this mixed powder was stored in the refractory melter 3 of the self-combustion synthesis apparatus shown in Fig. 1, and the ignition furnace shown in Fig. A tungsten heater, which is an example of the resistance heating wire 5, was ignited by passing a current of 25 A at a voltage of 30 V for 4 seconds. As a result of examining the compound after the reaction by X-ray diffraction, more than 95% was NiT.
It was confirmed that i. Further, as a result of chemical analysis of the compound after the reaction, the oxygen content was 0.10%, nitrogen 0.015%, carbon 0.06%, and hydrogen o, ooe%.

The density of the compound after the reaction was measured using the Archimedes method, and the relative density was 55%. This compound is 2
1100℃x in a vacuum sintering furnace with a vacuum degree of 1O-7Torr
As a result of soaking the TOH and examining the viscous crystal structure by X-ray diffraction, it was confirmed that 100% NiTi was formed.

(Example 2) T with an oxygen content of 0.08% by weight and an average particle size of 50-
i powder and N with an average particle size of 20- at oxygen 3 right mo, 05%
1 powder were mechanically mixed in a 1:1 molar ratio.

3 kg of this mixed powder was inserted into the self-combustion synthesis apparatus shown in Fig. 1, and the temperature was 300°C and the degree of vacuum was 2 x 10-'To
Under the conditions of rr, a current of 25 A was passed for 4 seconds at a voltage of 30 V through a tungsten heater, which is an example of a resistance heating wire for ignition shown in FIG. 1, to ignite it. As a result of examining the compound after the reaction by X-ray diffraction, it was confirmed that 95% or more was NiTi. Also,
As a result of chemical analysis of the compound after the reaction, the oxygen content was 0.
10%, nitrogen 0.015%, carbon 0.0B%, hydrogen 0.
It was 0.0013%.

The density of the compound after the reaction was measured using the Archimedes method, and the relative density was 55%. This compound is 2
1100℃X in a vacuum sintering furnace with a vacuum level of 10'' Torr
After soaking for 10 hours, the crystalline structure was examined by X-ray diffraction, and it was confirmed that 100% NiTi was formed.

After this heat treatment, a round bar of 40 mmφ x 200 m is cut out, vacuum sealed in a stainless steel tube, annealed for 5 hours in a heating furnace heated to 050°C, and then heated to 10 mmφ using a hot extrusion device. A round bar was manufactured (reduction rate of about 94%). The relative density of this round bar was measured and found to be 100%, and it was confirmed from the optical microscope observation that the micropores that existed during combustion synthesis had been eliminated.

After surface grinding, this round bar material is repeatedly cold rolled and annealed.
．． It was made into a wire rod of 8 mm. When this wire was measured using the Ms wet temperature electrical resistance measurement method, it showed a temperature of 48°C, and the temperature AI' at which shape memory returns was 71°C. This wire was shaped into a coil with shape memory, combined with a bias spring to create a shape memory element, and as a result of a fatigue test in which it was alternately immersed in 80°C hot water and 15°C water, it did not break more than 105 times.

(″)!, Example 3) The oxygen content is 0.05% by weight and the average particle size is 40ttm.
Ti powder, oxygen content Jln 0.02%, average particle size 3
0 um of N1 powder was mechanically mixed in a molar ratio of l:1.

30 kg of this mixed powder was inserted into the self-combustion synthesizer shown in Fig. 1, and the temperature was 300°C and the degree of vacuum was 2 x 1O-6T.
25 A current was applied for 4 seconds at a voltage of 30 V to the tungsten heater, which is an example of a resistance heating wire for ignition shown in FIG. As a result of examining the compound after the reaction by X-ray diffraction, 95% or more was confirmed to be NiTi. Also,
As a result of chemical analysis of the compound after the reaction, the oxygen content was 0.
09%, nitrogen 0.014%, carbon 0.05%, hydrogen 0.
It was 0.0013%.

The density of the compound after the reaction was measured using the Archimedes method, and the relative density was 56%. This compound is 2
1150℃X in a vacuum sintering furnace with a vacuum degree of to-'Torr
After performing soaking treatment for 10 hours and examining crystal lateral movement by X-ray diffraction, it was confirmed that 100% NiTi was formed.

After this heat treatment, a round bar of 80 mm φ x 000 m + * was cut out and vacuum sealed in a stainless steel tube.
Immediately after firing in a heating furnace heated to 50°C for 5 hours, forging was repeated to a diameter of 40 mm using a hot forging device, and after further annealing in a heating furnace at 930°C for 3 hours, a round bar of 15 lφ was obtained. (total refractive index of approximately 96.5%). The relative density of this round bar was measured and found to be 100%, and it was confirmed from the optical microscope observation that the micropores that existed during combustion synthesis had been eliminated.

After surface grinding, this round bar material is repeatedly cold rolled and annealed.
．． It was made into a wire rod with zero resistance. When this wire was measured using the Ms humid temperature electrical resistance measuring method, it was found to be 49°C, and the Ar temperature, the temperature at which shape memory returns, was 70°C. This line corresponds to women's underwear (
As a result of conducting a washing-equal life test on the product used as the core wire of a brassiere (bra), it was confirmed that the product could withstand 500 washes.

(Effects of the Invention) Since the method for manufacturing the shape memory alloy NiTi of the present invention is constructed and operates as described above, it is possible to mechanically hot-process a compound with superior material properties at an inexpensive cost compared to conventional methods. Effects such as being able to be manufactured in the manufacturing process are H.

[Brief explanation of drawings]

FIG. 1 is a schematic cross-sectional view of a self-propagating combustion synthesis device.

Claims (3)

[Claims] (1) Powders containing Ni and Ti as main components are mixed, and the resulting mixed powder is placed in a vacuum, and the mixed powder can self-combust due to reaction generated heat generated in the synthesis reaction of the mixed powder. The NiTi-based intermetallic compound is produced by a combustion synthesis method in which the temperature is maintained above the temperature, heat is input from the outside into a part of the mixed powder to start the synthesis reaction, and the reaction generated heat generated in the reaction is sequentially propagated to the unreacted powder. In the manufacturing method, the product after combustion synthesis is heated to 900°C to 1200°C.
A method for producing a NiTi-based intermetallic compound, comprising performing vacuum heat treatment for 3 to 50 hours at a temperature in the range of °C. (2) Powders containing Ni and Ti as main components are mixed, and the resulting mixed powder is placed in a vacuum, and the mixed powder can self-combust due to reaction generated heat generated in the synthesis reaction of the mixed powder. The NiTi-based intermetallic compound is produced by a combustion synthesis method in which the temperature is maintained above the temperature, heat is input from the outside into a part of the mixed powder to start the synthesis reaction, and the reaction generated heat generated in the reaction is sequentially propagated to the unreacted powder. In the manufacturing method, the product after combustion synthesis is heated to 900°C to 1200°C.
1. A method for producing a NiTi-based intermetallic compound, which comprises performing mechanical hot working at a temperature in the range of °C and a reduction rate of 50% or more. (3) Powders containing Ni and Ti as main components are mixed, and the resulting mixed powder is placed in a vacuum, and the mixed powder can cause self-combustion due to reaction generated heat generated in the synthesis reaction of the mixed powder. The NiTi-based intermetallic compound is produced by a combustion synthesis method in which the temperature is maintained above the temperature, heat is input from the outside into a part of the mixed powder to start the synthesis reaction, and the reaction generated heat generated in the reaction is sequentially propagated to the unreacted powder. In the manufacturing method, the product after combustion synthesis is heated to 900°C to 1200°C.
After vacuum heat treatment for 3 to 50 hours at a temperature in the range of °C, the reduction rate is 50% at a temperature in the range of 900 to 1200 °C.
NiT characterized by being subjected to the above mechanical hot working
A method for producing an i-based intermetallic compound.