JP5077943B2 - PtTi high temperature shape memory alloy - Google Patents

Description

  The invention of this application relates to a PtTi high temperature shape memory alloy to which PtTi or Ir is added.

Conventionally, TiNi is mainly known as a shape memory alloy, but it is used at a temperature near room temperature. In order to be used as a high temperature sensor or actuator used in a chemical plant, an engine, etc., a shape memory alloy that operates at a high temperature is required. Therefore, development of high-temperature shape memory alloys such as addition of a refractory metal to TiNi has been performed (see, for example, Patent Document 1). Further, Patent Document 2 related to the proposal of the present applicant also discloses data as shown in a comparative example described later for an Ir-added PtTi high-temperature shape memory alloy.
JP-A-8-60277 JP 2004-162178 A

  However, it is not easy to raise the temperature at which the shape memory effect appears, and it is therefore difficult to develop a superelasticity or pseudoelasticity effect that recovers strain by unloading stress after loading at high temperature.

  An object of this invention is to provide the PtTi type | system | group high temperature shape memory alloy which can express a pseudoelastic effect in view of such a situation.

The PtTi high-temperature shape memory alloy of the present invention 1 is subjected to a homogenization heat treatment at a transformation temperature or higher for 1 hour or longer, and then at a transformation temperature or lower and directly quenched at the stress load-unloading compression test temperature. At a temperature of 200 to 900 ° C. that is equal to or lower than the transformation temperature of the PtTi high-temperature shape memory alloy and is the temperature of the stress load-unloading compression test. It is characterized by exhibiting elasticity .

Invention 2 is characterized in that in the PtTi high temperature shape memory alloy of Invention 1, Ir is added and a part of Pt is substituted with Ir.
Invention 3 is characterized in that in the PtTi high temperature shape memory alloy of Invention 2, Ir is added to the Pt-50 at% Ti alloy in an amount of less than 50 at%, and a part of Pt is substituted with Ir.

According to the PtTi and Ir-added PtTi high-temperature shape memory alloy of the invention of this application, a PtTi and Ir-added PtTi high-temperature shape memory alloy having a high expression temperature of the shape memory effect is realized.
Moreover, it is below the transformation point temperature , and a pseudo-elastic effect that recovers the strain appears by unloading the stress after loading at the temperature of the stress load- unloading compression test .

It is an X-ray diffraction pattern at room temperature of the test material after heat treatment. It is a chart of the result of having performed the differential thermal analysis about the test material. It is the transmission electron microscope image which showed the typical structure | tissue of Ir addition PtTi alloy. It is the chart which gave compression strain to the Pt-12.5at% Ir-50at% Ti alloy, and measured the subsequent thermal expansion and contraction. It is a graph which shows the difference in the behavior by the heat processing (a) in Example 1 , and the heat processing (b). It is a graph which shows the result of the stress load-unloading compression test of Example 2 . It is a graph which shows the result of the stress load-unloading compression test of Example 3 . It is a graph which shows the result of the stress load-unloading compression test of Example 4 . It is a graph which shows the result of the stress load-unloading compression test of Example 5 . It is a graph which shows the result of the stress load-unloading compression test of Example 5 . It is a graph which shows the result of the stress load-unloading compression test of Example 6 .

Hereinafter, the PtTi and Ir-added PtTi high-temperature shape memory alloy of the invention of this application will be described in more detail with reference to examples.
The PtTi alloy in the Ir-added PtTi high-temperature shape memory alloy of the invention of this application takes a B2 structure at a high temperature and a B19 structure at a low temperature, and causes martensitic transformation having a deep relationship with the shape memory effect. Based on this martensitic transformation, the PtTi alloy exhibits a shape memory effect around 1000 ° C. Then, by adding Ir to the PtTi alloy, the temperature at which the shape memory effect is manifested rises, and the shape memory effect is exhibited at around 1200 ° C. From this, it can be said that the PtTi alloy to which Ir is added is a high-temperature shape memory alloy that can be used in a temperature range of 1000 ° C. to 1200 ° C. Application as a material for high temperature sensors and actuators used in chemical plants and engines is promising.

  In the Ir-added PtTi high-temperature shape memory alloy of the invention of this application, the Ti amount is limited to 42 to 63 at%. This is because the PtTi alloy becomes a B2 single phase within the above range, and other phases appear in the other ranges and affect the martensitic transformation.

Ir to be added is partly substituted for Pt of the PtTi alloy and is dissolved. The amount of Ir added is less than 50 at% in the case of a Pt-50 at% Ti alloy. The addition of 50 at% Ir results in an IrTi alloy, causing a phase transition of B2 → monoclinic phase and no martensitic transformation. The alloy is subjected to a homogenization heat treatment at a temperature not lower than the transformation temperature for 1 hour or longer, and then directly quenched to the temperature not higher than the transformation temperature and maintained for 1 hour or longer to exhibit pseudoelasticity.
[Comparative example]

Patent Document 2 is a patent application in which the inventor's group is an inventor, and is re-posted as a comparative example of the present invention. That is, 12.5, 25, 37.5, 42, 46 at% of Ir is added to a Pt-50 at% Ti alloy to prepare an alloy in which Pt is substituted, and Pt-50 at% Ti alloy and Ir-50 at% Ti alloy are produced. Compared with. After heat treatment at 1250 ° C. for 24 hours, it was quenched in ice-salt water.

  The crystal structure of the specimen after heat treatment at room temperature was examined by X-ray diffraction. The result is the X-ray diffraction pattern of FIG. As the amount of Ir added increases, B19 changes to a slightly distorted structure, but it is confirmed that the B2 phase at a high temperature is transformed into another phase based on B19.

  Differential thermal analysis was performed on the specimen. FIG. 2 is a chart showing the results. An endothermic reaction is confirmed for all alloys except the IrTi alloy. It is revealed that a phase transformation is taking place. The transformation temperature is increased by the addition of Ir, and reaches 1250 ° C. for the Pt-46 at% Ir-50 at% Ti alloy. It is confirmed that the shape memory effect can be obtained at a higher temperature by adding Ir.

  A transmission electron microscope image of FIG. 3 shows a typical structure of the above Ir-added PtTi alloy. This transmission electron microscope image is of a Pt-37.5 at% Ir-50 at% Ti alloy, but the transmission electron microscope image shows a martensitic structure often observed in alloys martensitic transformed.

  FIG. 4 is a chart in which compressive strain is applied to a Pt-12.5 at% Ir-50 at% Ti alloy and the subsequent thermal expansion and contraction are measured. The TMS on the vertical axis means the length of elongation / contraction when the temperature rises and falls.

  Martensitic transformation is induced by applying compressive strain. When the sample is heated in this state, reverse transformation occurs at the transformation point and changes to a high temperature phase. The transformation strain introduced by the martensitic transformation is large, and the strain is released at the transformation point, so that the sample is greatly elongated instantaneously (around 1300 K). When cooled after the high temperature phase is reached, martensite transformation occurs again at the transformation point, but only shrinkage is observed, and it does not return to the initial length. Such a phenomenon suggests shape memory recovery by martensitic transformation.

FIG. 5 is a stress strain curve obtained by subjecting a Pt-12.5 at% Ir-50 at% Ti alloy to different heat treatments and then applying a stress load-unloading compression test at 900 ° C.
(A) Treatment: A heat treatment at a transformation temperature or higher for 1 hour, followed by quenching in 0 ° C. ice-salt water to produce a martensite phase.
(B) Treatment: After heat treatment for 1 hour above the transformation temperature, quenching at 900 ° C. below the transformation temperature and heat treatment for 1 hour to produce a martensite phase.
In the treatment (a), martensitic variant rearrangement clearly appeared, and after unloading, 2% strain recovery was shown by raising it above the transformation temperature. (See Fig. 5 (a))
On the other hand, in the process (b), the strain recovered 100% when unloading after applying the strain as 16%. This is a “pseudoelastic effect” in which the rearranged martensite variant returns to its original state upon unloading. (See FIG. 5 (b))

  FIG. 6 shows stress strain curves when (a) Pt-50 at% Ti and (b) Pt-37.5 Ir-50Ti alloy were subjected to the treatment (b) of Example 1 and subjected to a compression test. It can be seen that the pseudoelastic effect appears even when the composition changes.

  FIG. 7 shows the results of repeated tests at 900 ° C. of the alloy treated in (b) of Example 1. As the number of repeated tests increases, the amount of distortion is increased, but it can be seen that even when 16% of strain is applied in five repeated tests, the strain is recovered 100%.

  FIG. 8 shows the results of repeated compression tests at 1000 ° C. of an alloy obtained by performing the treatment (b) of Example 1 on Pt-25Ir-50Ti. Even in this composition, it is apparent that the strain is recovered by the stress load-unloading compression test and also exhibits multiple strain recovery.

  FIG. 9 shows the results of a repeated compression test at 910 ° C. of an alloy obtained by performing the treatment (b) of Example 1 on Pt-50Ti. As the number of repeated tests increases, the amount of strain increases, but it can be seen that even in this composition, strain is recovered 100% even when strain is applied up to 16%.

  FIG. 10 shows the result of the repeated compression test at 910 ° C. of the alloy obtained by applying the treatment (b) of Example 1 to Pt-50Ti. In this figure, the sample unloaded after applying 16% strain is again shown. The result of repeating the test to give 10% distortion and unloading is shown. It is clear that the pseudoelastic effect is repeatedly exhibited without plastic deformation even when repeated five times.

FIG. 11 shows that Pt-50Ti was changed from 900 ° C. in the treatment (b) of Example 1 to 200 ° C., heat-treated for 1 hour above the transformation temperature, and then quenched at 200 ° C. below the transformation temperature for 1 hour. The result of the repeated compression test at the time of producing | generating a martensite phase is shown. It can be seen that even when strain is applied up to 14%, the strain has recovered 100%.
The last curve is 14% strain applied and unloaded, then 8% strain is applied again, but all strain is recovered after unloading. Similarly, since the strain recovery is complete as compared with the third curve from the left to which 8% strain is applied, it is also clear that the pseudoelastic effect appears more clearly by repeatedly applying stress.

  Of course, the invention of this application is not limited by the above embodiments. It goes without saying that various modes are possible for details such as the production conditions of PtTi and Ir-added PtTi alloys.

  As is clear from the above, the shape memory alloy of the present invention exhibits a pseudoelastic effect in a wide temperature range of 200 to 900 ° C.

  As described in detail above, the invention of this application provides a PtTi and Ir-added PtTi high-temperature shape memory alloy that can be applied to high-temperature devices that exhibit a shape memory effect and a pseudoelastic effect at high temperatures.

Claims (3)

A PtTi high temperature shape memory alloy made of a Pt-42 to 63 at% Ti alloy,
Perform homogenization heat treatment for 1 hour or more above the transformation temperature,
After that , it is below the transformation temperature, directly quenched to the temperature of the stress load-unloading compression test, and kept at that temperature for 1 hour or more to produce a martensite phase,
A PtTi high-temperature shape memory alloy characterized by exhibiting pseudoelasticity in the range of 200 to 900 ° C. which is equal to or lower than the transformation temperature of the PtTi high-temperature shape memory alloy and is the temperature of the stress load-unloading compression test . The PtTi high temperature shape memory alloy according to claim 1, wherein Ir is added and a part of Pt is substituted with Ir . 3. The PtTi high temperature shape memory alloy according to claim 2, wherein Ir is added to the Pt-50 at% Ti alloy in an amount of less than 50 at%, and a part of Pt is replaced with Ir.