Rising martensitic transformation temperature is required to develop HTSMAs. Then, we have focused on the alloys consisting of Ti and precious metals such as TiPt, TiPd and TiAu due to their high martensitic transformation temperatures. To strengthen these compounds and control phase transformation temperature, third elements were partially substituted to the alloys. Some of the TiPd–base compounds indicated 100% shape recovery at temperature range between 400-450 °C. The effect of third elements on phase transformation and shape memory effects was investigated.

Equiatomic TiPt exhibits very high transformation temperatures (~1300 K) from B2 to B19 orthorhombic martensitic phase. However TiPt exhibits negligible (~0–11%) shape memory effect and low strength (~450 MPa) in martensite and very low strength (~20 MPa) in B2 phase region. Then in this study, we compared the high temperature strength and shape memory properties of Ti–50Pt by partial substitution of Platinum (Pt) belonging to group 10 of periodic table with Cobalt (Co) belonging to group 9 and Ruthenium (Ru) belonging to group 8 of periodic table respectively. Partial substitution of Pt with Co and Ru was found effective in improving the high temperature strength and shape memory properties of Ti–50Pt alloy. However partial substitution of Pt with Ru was found more effective than Co due to more effective solid solution strengthening effect. Ti–45Pt–5Co and Ti–45Pt–5Ru alloys have potential for high temperature shape memory materials applications.

•Compressive strength was systematically measured for Ir-1at%X alloys at 2223 K.•The solid solution hardening effect for each element was identified.•The weight of Ir alloys decreased linearly during isothermal oxidation at 1373 K.Compressive strengths of twelve Ir-1at%X binary alloys were evaluated at 2223 K to understand the strengthening effects of alloying elements. The alloying elements were selected from group 4 to group 10 in the periodic table. The maximum strength of about 65 MPa was obtained in Ir–Hf and Ir–Zr alloys. The effect of adding multiple alloying elements on strength was also investigated. Isothermal oxidation behavior was investigated at 1373 K for Ir alloys including Nb and/or Hf. The weight of all the tested alloys decreased linearly during the oxidation test, indicating that Ir oxide evaporated during oxidation.

The phase transformation and high-temperature shape memory effect of Ti(Pt, Ir) were investigated. First, the Ti-rich phase boundary of Ti(Pt, Ir) was investigated by phase composition analysis by secondary electron microscopy (SEM) using an electron probe X-ray micro analyzer (EPMA), X-ray diffraction analysis and transmission electron microscopy (TEM). Then, the three alloys Ti–35Pt–10Ir, Ti–22Pt–22Ir, and Ti–10Pt–32Ir (at%) close to the phase boundary but in the single phase of Ti(Pt, Ir) were prepared by the arc melting method. The shape memory effect and crystal structure were investigated by compression loading–unloading tests and high-temperature X-ray diffraction analysis, respectively.Highlights► The partial isothemal section at 1523 K was determined in Ti–Pt–Ir. ► The high-temperature shape memory effect of Ti(Pt, Ir) was investigated. ► The shape recovery ratio was 72% in Ti–10Pt–32Ir after deformation at 1123 K. ► Ir addition to TiPt is effective to improve shape memory effect of TiPt.

The effects of adding Zr to TiPd alloys on martensitic transformation and strain recovery were investigated. The martensitic transformation temperature decreased with Zr addition, but Mf was 718 K for Ti–50Pd–5 at% Zr. The shape recovery ratio was improved by the addition of 5 at% Zr, reaching 94.3% after deformation at 653 K. The effects of adding Zr are discussed in terms of its solid-solution hardening effect.Highlights► The martensitic transformation temperature of TiPd decreased with Zr addition. ► The shape recovery ratio was improved by the addition of 5 at% Zr. ► Shape recovery of 94.3% was obtained in Ti–50Pd–5Zr alloy after deformation at 653 K. ► The high strength of martensite and the parent phases by solid-solution hardening by Zr suppressed plastic deformation and improved strain recovery.

Composition and temperature dependence of the crystal structure of IrTi with Ti content of 46–61 at.% was investigated using high-temperature X-ray diffraction analysis. Single-point energy calculations and geometry optimization were carried out based on first-principles calculations to understand the phase stability and transformation. Using X-ray diffraction analyses, a CsCl-type B2 structure was found in Ir-61 at.% Ti at room temperature; on the other hand, an orthorhombic structure in the alloys with Ti content below 58 at.%. The atomic positions obtained through first-principles calculations suggested a distorted L10 structure refined as a new orthorhombic (Cmmm #65) structure. The orthorhombic structure changed to almost a tetragonal structure with rising temperature and finally to a distorted B2 structure above 873 K in Ir-46–58Ti alloys.Highlights► Composition and temperature dependence of the structure of IrTi was investigated. ► The new orthorhombic structure was found in the alloys with below 58 at.% Ti. ► A distorted L10 structure is refined as a new orthorhombic structure with Cmmm #65. ► The orthorhombic structure changed to a distorted B2 structure above 873 K.

Martensitic transformation behavior and shape memory properties of Ti-50at%Pt were investigated using high-temperature X-ray diffractometry and loading–unloading compression tests. The structure of the parent and martensite phases was identified as B2 and B19, respectively. Changes in the lattice parameters of the martensite phase were investigated as a function of temperature. Applying the lattice parameter changes, the volume strain between B19 and B2 phases at 1473 K was estimated at 2.5%. The compression test was carried out at room temperature and at 1123 K. Strain was precisely measured using a strain gage for the test at room temperature and a CCD camera for the test at 1123 K. Strain recovery was observed during unloading at room temperature and at 1123 K, which was below the martensite temperature. Shape recovery was investigated for the samples tested at room temperature and at 1123 K by heating at 1523 K for 1 h. It was found that the strain recovery rate was 30–60% for the samples tested at room temperature and about 11% for the samples tested at 1123 K.

Dislocation character and operative slip systems in α-Nb5Si3 were examined by transmission electron microscopy. Two-phase alloys comprised of (Nb) and α-Nb5Si3 were used in this study. Although few dislocations were present in the α-Nb5Si3 phase of a pre-deformed alloy, many developed after 15% of compressive deformation at 1673 K. Two types of the Burgers vectors were identified for α-Nb5Si3: <100] and 1/2 < 111]. The glide planes of dislocations were defined by the cross products between the Burgers vectors and the line vectors of the dislocations, by which the slip systems that operate in α-Nb5Si3 at 1673 K were determined as {011)<111], {100)<010], and {001)<100].

The isotherms of the Ir–Ni–Al in the composition range up to 50 at% Al are presented at 1573 K. The phase constitution and microstructure of the Ir–Ni–Al alloys were examined using X-ray diffractometry (XRD), scanning electron microscopy (SEM) with an electron probe microanalyzer (EPMA), and transmission electron microscopy (TEM) after heat treatment at 1573 K for 168 h. The B2-NiAl and B2-IrAl phases connected with each other at 1573 K. The highest solubility limit of Ir into Ni3Al was about 3.5 at% in the tested alloys. Then, a wide fcc + B2 and a narrow fcc + L12 and B2 + L12 two-phase region appeared in the isothermal section. In part of the B2 phase, a martensitic transformation from the B2 to the L10 phase was observed.

To design an alloy with high strength around 1773 K and good ductility at room temperature, the microstructure, the compression strength and the creep properties at 1773 K of the Ir–Al alloys with an fcc and B2 two-phase structure were investigated. High-temperature mechanical properties are discussed in terms of microstructure.

To design high-temperature materials with good creep properties at 1773 K, the creep behavior of Ir–Ni–Al alloys was investigated. The phase constitution and microstructure of the Ir–Ni–Al alloys were examined using X-ray diffraction analysis (XRD) and scanning electron microscopy (SEM) with energy dispersive X-ray spectroscopy (EDS). Compression creep tests were then carried out with some of the Ir–Ni–Al alloys at 1773 K under 30 MPa. The deformation mechanism was discussed in terms of solid-solution hardening and precipitation hardening.