JP5057320B2 - Pd-added TiNb-based shape memory alloy - Google Patents

Description

  The present invention relates to a TiNb-based shape memory alloy to which Pd is added.

  TiNi is mainly used as the shape memory alloy, and is used near room temperature. However, shape memory alloys that operate at high temperatures are required for use as high-temperature sensors and actuators used in chemical plants and engines.

On the other hand, TiNi is also used as a biomaterial for bone replacement. However, since Ni has strong allergenicity and carcinogenicity to the human body, TiNb was developed as a Ni-free shape memory material for living bodies, and shape memory. In order to improve the effect, addition of a third element has been studied (for example, see Non-Patent Document 1).
Four members of Inabai, TiNbGe alloy structure and shape memory characteristics, Abstracts of Spring Meeting of the Japan Institute of Metals (2004)

  The present invention is to provide a new TiNb-based alloy that is a shape memory alloy that operates at a high temperature that can be used as a high-temperature sensor or an actuator used in a chemical plant or an engine, and that can also be used as a biomaterial. It is said.

  As a result of intensive studies to solve the above problems, it has been found that by adding Pd to a TiNb-based shape memory alloy, the shape memory effect is exhibited at a high temperature and can be used at a temperature of 200 ° C. or higher. It was. It was also found that the Young's modulus was 60 GPa, which is close to 30 GPa, which is the Young's modulus of bone, and can be used as a biomaterial. The present invention has been completed based on the above technical knowledge.

That is, the present invention provides, in a first, niobium titanium (Ti) (Nb) is added 20-50 mass%, further para di um (Pd) is added less than 14 mass% from 0.5 mass%, 60 % Or more of cold rolling .

Present invention, the second is characterized by the thermal treatment of more than 10 minutes at a transformation point temperature or more is applied.

Third , the present invention is characterized in that a plate-like ω phase is formed by a rapid cooling treatment.

  According to the present invention, a shape memory alloy that operates at a high temperature is provided, and is expected to be applied to a high temperature sensor such as a chemical plant or an engine or an actuator. In addition, application as a biomaterial with low toxicity is expected.

Pd added TiNb based shape memory alloy of the present invention, titanium (Ti), niobium (Nb) in was added 20 -50 mass%, further para di um (Pd) is added less than 14 mass% from 0.5 mass% It is a thing. Within this composition range, the TiNb-based alloy becomes a β phase having a bcc structure at a high temperature and an α "phase having an orthorhombic structure at a low temperature, and a martensitic transformation having a deep relationship with a shape memory effect occurs. The martensitic transformation temperature is increased, and the TiNb-based alloy is brittle, but the addition of Pd improves the ductility and facilitates cold working, and the amount of Pd added is less than 0.5 mass % to less than 14 mass %. When the added amount of Pd is 14 mass % or more, martensitic transformation does not occur.

  Such a Pd-added TiNb-based shape memory alloy is preferably subjected to 60% or more cold rolling. Cold rolling at 60% or more tends to cause martensitic transformation. Furthermore, after cold rolling, it is preferable to perform a heat treatment for 10 minutes or more at a temperature not lower than the transformation point temperature. The heat treatment increases the certainty of the martensitic transformation.

A Ti-30Nb-3Pd ( mass %) alloy was cold-rolled to 90% and then heat-treated at 700 ° C. for 10 minutes. The temperature dependence of the electrical resistance of the obtained sample was examined, and the phase transformation temperature was examined. As shown in FIG. 1, when the temperature is increased, the transformation from the α ″ phase to the β phase starts at 415 ° C. (688 K) (As), and the transformation ends (Af) at 489 ° C. (762 K). As the temperature was lowered, reverse transformation from β phase to α ″ phase started at 289 ° C. (562 K) (Ms), and reverse transformation was completed at 247 ° C. (520 K) (Mf).

FIG. 2 shows the results of examining the phase transformation temperature of the Ti-30Nb-3Pd ( mass %) alloy by differential thermal analysis. When the temperature was raised, the transformation from the B19 ′ phase to the B2 phase started at 405 ° C. (678K) (As), and the transformation was finished (Af) at 499 ° C. (772K). The transformation temperature is approximately the same as the temperature measured by electrical resistance. What should be noted in the results of differential thermal analysis is that it was confirmed that the ω phase was formed at 127 ° C. (400 K), although it was not apparent from the measurement of electrical resistance. The ω phase is often observed in Ti alloys and is a phase that suppresses the shape memory effect. In this alloy, once the temperature is raised to the transformation temperature or higher, the peak due to the ω phase is not observed in the second temperature rise, and the once disappeared ω phase does not appear again due to the subsequent temperature change. From this, this alloy is considered to have excellent shape memory performance.

FIG. 3 shows the results of a tensile test at room temperature of the Ti-30Nb-3Pd ( mass %) alloy. A plateau curve observed when valiant rearrangement occurs due to martensitic transformation appears, confirming that the phase transformation shown in FIGS. 1 and 2 is martensitic transformation.

FIG. 4 shows the shape recovery rate when the Ti-30Nb-3Pd ( mass %) alloy is deformed by a tensile test and the deformed sample is heated to a temperature equal to or higher than the transformation point. When a tensile strain of about 3% was applied, shape recovery of 90% occurred. When the tensile strain increases, the recovery rate decreases. However, it can be confirmed that it can sufficiently function as a shape memory alloy when operating at a strain of several percent.

FIG. 5 shows the results of differential thermal analysis of a Ti-30Nb-14Pd ( mass %) alloy that has been similarly cold-rolled and heat-treated. Although appearing slightly peak upon heating is, since no peak appears at the time of cooling was found that does not occur phase transformation in TiNb based alloy obtained by adding Pd 14 mass%, the added amount of Pd be less than 14 mass% It should be pointed out.

  6 and 7 show the results of differential thermal analysis of the Ti-30Nb-3Pd alloy that was not heat-treated after cold rolling, respectively. FIG. 6 shows the result of the first differential thermal analysis, and FIG. 7 shows the result of the second differential thermal analysis. In the first time, a peak due to phase transformation is observed (FIG. 6). However, the peak disappears in the second time (FIG. 7), and it is confirmed that the phase transformation does not occur. The effectiveness of heat treatment after cold rolling is pointed out.

  8 and 9 show the results of differential thermal analysis of the Ti-40Nb alloy, respectively. FIG. 8 shows the result of the first differential thermal analysis, and FIG. 9 shows the result of the second differential thermal analysis. The peak due to the phase transformation appears clearly both in the first and second times, and it can be clearly seen that the phase transformation has occurred.

  FIG. 10 shows the results of differential thermal analysis of the Ti-40Nb-16Pd alloy. A peak due to phase transformation appears during heating, but does not appear during cooling, confirming that no phase transformation occurs in this alloy.

The ω phase formed in the Ti alloy described above is granular, and this granular ω phase is considered to be a cause of the brittleness of the Ti alloy. However, it was confirmed from the quenching material of the TiNb alloy to which Pd was added that some ω phases were plate-like. FIGS. 11A and 11B are TEM bright and dark field images, and a plate-like fine ω-Ti phase appears. FIG. 11C shows an SAED pattern, which shows reflection from two ω-Ti phases and a β-Ti matrix. FIG. 11D is a HREM micrograph showing two ω-Ti phases in the matrix (one is a plate-like ω1 phase and the other is a granular ω2 phase). The quenching material used for the observation is a water cooling material having a composition of Ti-30Nb-3Pb ( mass %) and subjected to heat treatment at 900 ° C. for 1 hour after cold rolling. It is considered that the addition of Pd suppressed the coarsening of the granular ω phase and caused the formation of a plate-like ω phase. The plate-like ω phase is a newly discovered phase.

FIG. 12 (a) is a tensile stress-strain curve measured at room temperature for a quenched material of a Ti-30-Nb-3Pd ( mass %) alloy and a Ti-40Nb ( mass %) alloy. Ti-30Nb-3Pd alloy quench material formed primarily from plate-like ω phase exhibits an elongation of up to 29%, up to 22% of Ti-40Nb alloy quench material formed from a ″ -Ti martensite phase. Also, as shown in the enlarged portion of the tensile stress-strain curve, the Ti-30Nb-3Pd alloy quenching material has a longer plateau than the Ti-40Nb alloy quenching material. This result suggests that the alloy containing plate-like ω phase shows higher shape memory behavior.

  The shape memory behavior of the two alloy quenched materials was evaluated by the shape recovery rate. As shown in FIG. 12B, the shape recovery rate of the Ti-30Nb-3Pd alloy quenching material is 20% larger than the shape recovery rate of the Ti-40Nb alloy quenching material at any strain value.

  From the above, the plate-like ω phase formed by adding Pd and quenching has the same function as the a ″ -Ti martensite phase, which was thought to be the only cause of the shape memory performance of the TiNb alloy. It is concluded that this contributes to the improvement of ductility and shape memory behavior of TiNb-based alloys.

It is the figure which showed the temperature dependence of the electrical resistance of a Ti-30Nb-3Pd alloy. It is the figure which showed the result of the differential thermal analysis of a Ti-30Nb-3Pd alloy. It is a tensile stress-strain curve at room temperature of a Ti-30Nb-3Pd alloy. It is the figure which showed the shape recovery rate after the tension test of Ti-30Nb-3Pd alloy. It is the figure which showed the result of the differential thermal analysis of Ti-30Nd-14Pd alloy. It is the figure which showed the result of the differential thermal analysis of the 1st time of Ti-30Nb-3Pd alloy which does not heat-process after cold rolling. It is the figure which showed the result of the differential thermal analysis of the 2nd time of the Ti-30Nb-3Pd alloy which does not give heat processing after cold rolling. It is the figure which showed the result of the differential thermal analysis of the 1st time of Ti-40Nb alloy. It is the figure which showed the result of the differential thermal analysis of the 2nd time of Ti-40Nb alloy. It is the figure which showed the result of the differential thermal analysis of Ti-40Nb-16Pd alloy. (A) and (b) are TEM bright and dark field images of a TiNb alloy quenched material to which Pd is added, (c) is a SAED pattern, and (d) is a HREM micrograph. (A) is the tensile stress-strain curve measured at room temperature about the quenching material of Ti-30Nb-3Pd alloy and Ti-40Nb alloy. (B) is the figure which showed the shape recovery rate with respect to the distortion of each alloy quenching material.

Claims (3)

Niobium (Nb) is 20-50Mass% added warm to titanium (Ti), a further palladium (Pd) is Pd added TiNb based shape memory alloy which is added less than 0.5 mass% or al 14mass%, 60% or more A Pd-added TiNb-based shape memory alloy characterized by being subjected to cold rolling.
Pd added TiNb based shape memory alloy according to claim 1, wherein the heat treatment of more than 10 minutes at a transformation point temperature or more is applied. Pd added TiNb based shape memory alloy according to claim 1 or 2 by fast cooling, characterized in that the plate-shaped ω phase has formed.