JPS5896844A - Very rapidly cooled shape memory ni-ti alloy - Google Patents

Abstract

PURPOSE:To obtain a homogeneous shape memory alloy having a very small thickness and superior mechanical characteristics by spouting a molten Ni- Ti alloy in an inert gas toward the surface of a metallic roll rotating at a high speed. CONSTITUTION:A molten alloy consisting of 50 atomic% Ni and 50 atomic% Ti is melted in inert gaseous Ar and pelletized. The pelletized mother alloy is put in a quartz pipe 1-1 and melted by heating with an electric furnace 1-3 to prepare a molten metal 1-2. By rapidly introducing gaseous Ar into the pipe 1-1 from one end 1-7, the molten metal 1-2 is spouted from the slit of the other end of the pipe 1-1 toward the surface of a metallic roll 1-4 rotating at a high speed to obtain a metallic thin strip 1-6 having <=100mum thickness and about 50mum average thickness by very rapid cooling. The thin strip alloy 1-6 has [110] axes oriented in the longitudinal direction and [100] axes oriented in the vertical direction. A circular hole may be used in place of the slit to obtain a linear alloy having <=100mum diameter.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a new Ni-Ti-based shape memory alloy, which has conventionally been difficult to process.

Conventional Ni-Ti-based shape memory alloys are made by melting and casting a base alloy with a predetermined composition in vacuum, inert gas, or normal air, and then heating the alloy at 500°C.
After annealing at a high temperature of ~600°C, it is cold rolled. While repeating this annealing and cold rolling operation, a wire rod is manufactured by plate material or wire drawing processing. This method requires extremely high processing costs for the product. The obtained plate material has rough workability, depending on the composition, and its thickness is 1lII11, and in the case of a wire material, its diameter is 1cm. This number indicates the minimum possible thickness or diameter, and the range of use is limited due to the size of this number.

In the production of a Ni-Ti-based shape memory alloy, the present invention provides the following steps:
By using the ultra-quenching method, we aim to significantly reduce the cost of products and improve mass production, and create homogeneous metal ribbons and linear memory alloys that are as thin and thin as possible and have excellent mechanical properties. The purpose is to According to the ultra-quenching method of the present invention, ribbons with a thickness of 100 μm or less and linear products with a diameter of 100 μm or less can be produced.

According to the present invention, in the ribbon, the crystal grains of the alloy are arranged in the longitudinal direction (
110) It is possible to provide a memory alloy in which the [100] axis is oriented in the direction perpendicular to the plate surface, and in the case of a linear one, the (110) axis is oriented in the longitudinal direction.

Even if shape memory alloys change shape when heated to a predetermined temperature and then rapidly cooled, they return to their original shape as the temperature is increased.

The composition of the shape memory alloy is FePt + In-
Cd+Fe-Nr *Ni-Atl stainless steel, T
i -Ni +Cu-Zn-At, etc., but the one currently commercialized is Ti - which can be used in polycrystalline form.
Only Ni alloy and Cu-Zn-At alloy. Cu-
Zn-At alloys are cheap, but compared to Ni-Ti alloys, their shape recovery performance is very poor, so K is not suitable for locations where the required recovery stress, recovery strain, etc. are large, or where repeated use is required. do not have.

In particular, for applications that require a large number of repetitions, Ti-N
i-alloy is suitable. However, Ti--Ni alloys are easily oxidized at high temperatures and will oxidize in the air at temperatures above 400°C, so when performing heat treatment at 500°C or higher, it is necessary to carry out the heat treatment in vacuum or in an inert gas. In processing such as annealing and cold rolling, care must be taken regarding the atmosphere, temperature, etc.

The present invention can be applied to all shape memory alloys, such as Ti-Ni alloys that are difficult to process and Cu-Zn-At alloys that are relatively easy to process.

The present invention will be described in detail. A master alloy having a predetermined composition of 50 atoms of Ni and 50 atoms of Ti is melted in an inert gas of Ar or in vacuum, and then divided into appropriate amounts. As an example of the ultra-quenching method, as shown in FIG. 1, a quartz tube 1-11C with a slit-shaped hole made at one end 1-7, a pellet of the above-mentioned master alloy is inserted, and the tube is heated in an electric furnace 1-3 or by high-frequency induction heating. The alloy is heated above the melting point of the alloy to melt it. The molten metal 1-2 is suddenly exposed to Ar from one end 1-7 of the quartz tube 1-1.
Metal roller 1 that rotates at high speed while introducing gas
-4 and performs an ultra-quenching operation to obtain a metal ribbon 1-6 with a thickness of 100 μm or less and an average of about 50 μm. These operations are performed in vacuum or in an inert gas because the Ti-Ni alloy is easily oxidized. 1-
5 shows the vacuum container. Since the Cu-Zn-At alloy is chemically relatively stable, it is ultra-quenched in the atmosphere to obtain a metal ribbon. In the case of a linear shape, a circular hole may be used instead of a slit at one end of the quartz tube 1-1. The thickness of the ultra-quenched shape memory alloy of the present invention can be controlled by appropriately selecting the ceramic material, but since the cooling rate is inversely proportional to the thickness of the sample, it is possible to control the thickness of the thin ribbon. It is difficult to create because it has little ultra-quenching effect and is easily oxidized. Therefore, the ribbon-shaped alloy of the present invention has a thickness of 10
A diameter of 0 μm or less, and in the case of a linear alloy, a diameter of 100 μm or less is desirable from the viewpoint of product cost and mass productivity. Furthermore, a major feature of the present invention is that the crystal grains of the sample are oriented, unlike those produced by conventional processing methods such as annealing, rolling, and wire drawing. As shown in Figure 2,
Ultra-quenched shape memory alloy thin strip 2-2 or linear alloy 2-
The [110] axis is oriented in the IH1 longitudinal direction, and the [100] axis is oriented in the direction perpendicular to the ribbon surface in the ribbon. By these, etc.
The alloy of the present invention has superior mechanical properties compared to conventional processed products, and its recovery strength has improved by more than 50%. When using this crystal orientation aXX diagram and irradiating the thin plate surface with X-rays, the reflection intensity from the (hkt) plane of the crystal I (
hkt) etc. In the Ti-Ni system, the higher the cooling rate, the better the degree of orientation, the smaller the crystal grain size, and the higher the mechanical strength.

Example-1 89.5g of T1 with a purity of 99.9%, 110.5g of Ni with a purity of 999%, TiO, 498-NiO,
502, melted in Ar gas by high-frequency induction heating, and cast into molds having a volume of 5 to 8 crn to form ultra-quenched inlets.

This pellet is placed in a quartz tube with a rectangular slit of 15 cm in length and 0.45 oaO in width at one end, and placed in a vacuum tube containing a high-speed rotating metal roller inside. Using a pump, 10-6
Vacuum to a pressure of Torr. Next, attach the quartz tube to 135
After heating to 0℃ and the metal pellet completely melts,
He or Ar gas at 0.3 to 0.5 atm was rapidly introduced from the other end of the quartz tube, and the molten metal was heated through the slit of the quartz tube with a diameter of 300 m and a width of 40 crn for 1600 r.
The metal ribbon obtained by ultra-quenching by spraying onto the circumferential surface of a copper roller rotating at pm is a long strip with a width of 15 cm, a thickness of 50 μm, and a length of 20 m, with an average crystalline The particle size was 5-8 μm. As a result of X-ray diffraction, the degree of orientation of the [110] axis in the longitudinal direction was 90% or more, and the degree of orientation of the (100) axis in the direction perpendicular to the thin plate surface was 95% or more. In addition, the degree of orientation Q(110) or Q(10
0) is the (hkz
) surface, then Q(110)-(ΣIhho/ΣIhkt-Σ■hho
””hMV('-Σ■hho/1%)Q(100)
=(ΣIhoo'1Ihkj−Σ工hoo””F )/
”-ΣILo'ri I theory).

Here, Ihkt is the sample of the present invention. (2) chkt is the diffraction intensity from the (hkt) plane of a conventional non-oriented sample.

This ri-Ni ultra-quenched metal ribbon is formed into a desired shape in an inert gas at a temperature of 650° C. or in a vacuum, and then rapidly cooled and plastically deformed at room temperature.

Afterwards, this shape memory alloy was soaked in hot water at a temperature of 90°C to recover its shape, and the amount of recovery was up to 20°C.
The recovery stress was 90-2 at maximum, which exceeded the properties obtained by normal processing methods by more than 50%.

When mass-produced, the product cost was found to be 115 to 1/10 of that of a product produced using a normal processing method.

Example 2 An alloy pellet made in the same manner as Example 1 was made with a diameter of 0.
．． Put it in a quartz tube with 11 circular orifices,
The sample obtained by ultra-quenching in a vacuum container in the same manner as in Example-1 was a memory alloy with a linear diameter and a slightly elliptical cross-sectional shape of 80 μm. X-ray diffraction shows that the orientation of the [110] axis in the longitudinal direction of the linear memory alloy, the degree of orientation Q (110), is 90 degrees or more, and the amount of recovery when shape memorized is 15 to 20%. Maximum stress is 80-90
kg/m.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing an example of the ultra-quenching apparatus of the present invention, and FIG. 2 is a diagram showing a linear or ribbon-shaped shape memory alloy that has been ultra-quenched. 1-1...Quartz tube with slotted and T-shaped holes at the bottom end, 1-
2... Molten metal, 1-3... Electric furnace, 1-4...
Metal roller, 1-5... Vacuum container, 1-6... Ultra-quenched metal ribbon, 1-7... Inert gas inlet of quartz tube, 2-1... Linear Alloy, 2-2... Thin ribbon of memory alloy. Figure 1

Claims (2)

[Claims] (1) An ultra-quenched Ni-Ti-based shape memory alloy, which is in the form of a thin strip with a thickness of 100 μm or less, or in the form of a line with a diameter of 10011 m or less, and is produced by an ultra-quenching method. (2) In the ribbon shape, the crystal grains of the alloy are aligned in the longitudinal direction (110
) axis and the [100] axis is oriented in the direction perpendicular to the thin plate surface, and in the case of a linear type, the [110) axis is oriented in the longitudinal direction. Super rapid cooling N
i-Ti shape memory alloy.