Kanryu Inoue

Martensite transformation temperatures and mechanical properties of ternary NiTi alloys with offstoichiometric compositions

Abstract Effects of ternary additions, Co and Cr, on martensite transformation temperatures and mechanical properties of offstoichiometric NiTi alloys were investigated. Martensite transformation start temperature (M s ) and austenite transformation start temperature (A s ) were determined by means of differential thermal analysis (DTA) in the temperature range between 77 and 423 K. Mechanical properties of yield stress and work-hardening coefficient were investigated using B2-stabilized NiTi alloys, whose alloy compositions were based on Ni-49 mol% Ti. It has been shown that (1) M s and A s considerably decrease with decreasing Ti concentration on the Ti poor side of stoichiometry (the concentration of Ti is less than 50 mol%); (2) M s and A s change slightly when Ti concentration is more than 52 mol%, where the alloys are in the two phase region; and (3) M s and A s decrease with increasing Cr and Co content with a constant Ti concentration. In the present analysis for evaluating the effect of ternary additions on M s , we use M s change by adding 1 mol% of ternary elements. M s changes by Cr addition are −65 K mol% −1 on the Ti rich side and −46 K mol% −1 on the Ti poor side. M s changes by Co addition are −15 K mol% −1 on the Ti rich side and −30 K mol% −1 on the Ti poor side. Both Cr and Co atoms are suggested to locate Ni sites preferably if only M s changes are considered. Characteristic stress-strain curves have indicated that the stress induced martensitic transformation (SIMT) occurred at 77 K. Above room temperature, work hardening coefficient at a permanent strain of 1% was found to be between 2 and 11 GPa. It should be emphasized that yield stress and work hardening coefficient increase with increasing test temperature between room temperature and about 650 K in most alloys. This strength anomaly is not related to SIMT but to precipitation hardening and/or anomalous dislocation motion, probably in a similar manner to B2-type CoTi.

Thermal Properties of Diamond-Particle-Dispersed Cu-Matrix-Composites Fabricated by Spark Plasma Sintering (SPS)

Diamond-particle-dispersed copper (Cu) matrix composites were fabricated from Cu-coated diamond particles by spark plasma sintering (SPS) process, and the microstructure and thermal properties of the composites fabricated were examined. These composites can well be consolidated in a temperature range between 973K and 1173K and scanning electron microscopy detects no reaction at the interface between the diamond particle and the Cu matrix. The relative packing density of the diamond-Cu composite increases with increasing sintering temperature and holding time, reaching 99.2% when sintered at a temperature of 1173K for a holding time of 2.1ks. Thermal conductivity of the diamond-Cu composite containing 43.2 vol. % diamond increases with increasing relative packing density, reaching a maximum (654W/mK) at a relative packing density of 99.2%. This thermal conductivity is 83% the theoretical value estimated by Maxwell-Eucken equation. The coefficient of thermal expansion of the composites falls in the upper line of Kerner’s model, indicating strong bonding between the diamond particle and the Cu matrix in the composite.

Magnetic-Field-Induced Martensitic Transformation in Ni2MnGa-Based Alloys.

The magnetic controllability of the thermoelastic martensitic transformation, which is the origin of the shape-memory effect, has been investigated. We have carried out neutron diffraction measurem...

Microstructures and Mechanical Properties of 6061 Al Matrix Smart Composite Containing TiNi Shape Memory Fiber

6061 Al-matrix composite with TiNi shape memory fiber as reinforcement has been fabricated by vacuum hot pressing to investigate the microstructure and mechanical properties. The yield stress of this composite increases with increasing amount of prestrain, and it also depends on the volume fraction of fiber and heat treatment. The smartness of the composite is given due to the shape memory effect of the TiNi fiber which generates compressive residual stresses in the matrix material when heated after being prestrained. Microstructual observations have revealed that interfacial reactions occur between the matrix and fiber, creating two intermetallic layers. The flow strength of the composite at elevated temperatures is significantly higher than that of the matrix alloy without TiNi fiber.

Magnetic instability of the Co sublattice in the Ho1−xYxCo3 system

Abstract X-ray thermal expansion, magnetic and electrical resistivity measurements of the pseudo-binary Ho 1− x Y x Co 3 system with PuNi 3 -type structure have been performed in a wide temperature range. Temperature-induced itinerant-electron metamagnetism has been observed in the concentration range 0.0⩽ x ⩽0.4 where the Co sublattice is in the strong ferromagnetic state at low temperatures. The transition was found to be sharper in the diluted compounds with a lower value of the transition temperature, which is in accordance with the nature of the observed effect. The temperatures of the spin-reorientation transition have been determined from low-field magnetisation measurements and the magnetic phase diagram of this system has been constructed.

Alloys Design of PdTi-Based Shape Memory Alloys Based on Defect Structures and Site Preference of Ternary Elements

Defect structures and site preference of ternary elements in B2-type PdTi alloys are evaluated in order to design PdTi-based smart materials using the pseudo-ground state analysis (or analysis performed at near zero Kelvin). It has been found that this analysis can predict types of defect structures in these alloys which are of antistructure (substitution) type regardless of alloy compositions. Substitution behavior predicted is as follows: (1) most elements belonging to groups 1A through 5A occupy Ti sites only; (2) most elements belonging to groups 6A through 8A occupy Pd sites only; and (3) the others studied occupy either sites when these sites are unfilled with the corresponding constituent elements (Pd or Ti). Moreover, effects of both offstoichiometry and 3dtransition elemental additions on martensitic transformation start temperature (MS) in PdTi alloys are evaluated as a function of electron-atom ratio (e/a). It has been found that M, is strongly related to the e/a value when 3d electrons of ternary additions are taken into account, although the effect of e/a on M, differs if their substitution behavior is different. Changes in M, per e/a are estimated to be 900 K when Pd-site substitution elements, such as Cr, Mn, Fe, Co, and Ni are added, while changes in M, per e/a are 790 K when Ti-site substitution elements such as V are added. This suggests that M, is influenced not only by the e/a value but also by atomic configurations.

Phase Stability and Mechanical Properties of Ti-Ni Shape Memory Alloys Containing Platinum Group Metals

In order to develop Ti-Ni base shape memory alloys (SMAs), the effects of ternary additions on phase constitution and mechanical properties were investiga ted for TiNi alloys containing some platinum group metals: Ir, Rh and Pt. All the al loys fabricated were made by Ar arc melting method using high purity elemental materials fol owed by hot-forging at 1173-1673K in Ar and furnace cooling. Then X-ray diffraction analysis a nd tensile tests were carried out at room temperature (RT). It was found that, whe n the amount of ternary is lower than 10mol%, all the additions reduce martensitic transf ormation temperature ( Ms) of TiNi and B2 phase becomes stable. Besides monoclinic, L1 0 and B19 phases appear for TiNi containing 40-50mol%Ir, 30-50mol%Rh and 20-50mol%Pt, respectively. The t ensile ductility at RT decreases with increasing the amount of terna ry additions, and the ductility becomes very limited when monoclinic (TiIr), L1 0 (TiRh) and B19 (TiPt) phases appear in the Ti-Ni-Ir, Ti-Ni-Rh and Ti-Ni-Pt systems, respectively . Strength strongly depends on Ms and crystal structure of the apparent phase. Small work hardening is recognized in all the alloy systems. Introduction Ti-Ni SMAs exhibit several smart functions represented by shap e memory effect and superelasticity. The applications of the Ti-Ni alloys are, how ever, still limited mainly because the martensitic transformation temperature ( Ms) is below 400K in the binary systems [1]. Then, in order to expand the applications related with SMAs, shape memory alloys actuated at higher temperature than binary Ti-Ni are required. Several investigations have been done for the improvement of actuation temperature of Ti-Ni by a lloying additives [2-4]. Most of additional elements such as Co, Fe, Mn, Cr and V reduce Ms. On the other hand, some refractory metals such as Hf and Zr and platinum group meta ls (PGMs) such as Pd and Materials Science Forum Online: 2003-08-15 ISSN: 1662-9752, Vols. 426-432, pp 2333-2338 doi:10.4028/www.scientific.net/MSF.426-432.2333

Mechanical properties of smart metal matrix composite by shape memory effects

The thermomechanical behavior of TiNi shape memory alloy fiber reinforced 6061 aluminum matrix smart composite is investigated experimentally and analytically. The yield stress of the composite is observed to increase with prestrain given to the composite. Analytical model is developed by utilizing a shape memory alloy constitutive model of exponential type for the thermomechanical behavior of the composite. The model predicts that the composite yield stress increases with increasing prestrain, and the key parameters in affecting the composite yield stress are prestrain and matrix heat treatment. The model predicts reasonably well the experimental results of the enhanced composite yield stress.

Cold rolling of B2 intermetallics

Abstract Cold-rolling behavior was investigated for B2 intermetallics in terms of chemical compositions (constituent elements and ternary addition), long-range ordering and environments. B2 intermetallics used were NiTi, FeCo and FeAl alloys and cold-rolling behavior was evaluated through Vickers hardness tests at room temperature as a function of reduction of thickness. The effects of compositional deviation from the stoichiometry and Co addition were studied for B2-stabilized NiTi alloys. It was found that reduction to failure is lowered with increasing the compositional deviation from the stoichiometry, i.e. with decreasing Ti content, and Co addition raises both the reduction to failure and hardness. The effects of order–disorder transformation were studied for V-added FeCo alloys, and it was found that the reduction to failure is lowered and the work-hardening rate is raised by ordering. The effects of wet environment and ternary addition were studied for FeAl alloys with or without Mn or Cr. It was found that hardness-reduction relationship slightly depends on environment and ternary addition, and largely depends on Al content. However, formation of cracks and/or burrs is much affected by the environment and the ternary additions in a complex manner. It is summarized for B2 intermetallics that cold-rolling behavior is largely affected by chemical compositions of constituent phases and ordering, and slightly by the environment.

Synthesis of New Structural and Functional Materials by SPS Processing

Capabilities of synthesizing new structural and functional materials by SPS processing were indicated by exemplifying the synthesis of nano-structured alumina with high bending strength or high transparency, Al/diamond composites with high thermal conductivity and zirconia(3Y)/ SUS410L FGM. In the synthesis of alumina, the bending strength of more than 720MPa was attained by choosing suitable SPS conditions. It was also indicated that SPS processing could easily synthesize Al/diamond composites with high thermal conductivity of more than 400W/(m･K), suggesting elaborate control of interface between Al and diamond in SPS consolidation. Further, zirconia(3Y)/SUS410L FGM could easily be fabricated by SPS. Mechanical weakness in the zirconia(3Y)-rich layers of the FGM was shown from the analysis of stress state based on Raman scattering method. It is suggested that the designing of the layer staking in FGM based on the Raman scattering analysis is effective for the improvement of the weakness in the FGM.