H.C. Lin

A comparison of the cavitation erosion resistance of TiNi alloys, SUS304 stainless steel and Ni-based self-fluxing alloy

Abstract Cavitation erosion of TiNi shape memory alloys, SUS304 stainless steel (SS) and Ni-based self-fluxing alloys has been investigated in freshwater and 3.5xa0wt.% NaCl solution according to the ASTM G32-85 standard method. After 300xa0min of cavitation erosion, the cumulative weight loss of SUS304 SS is 45 times, whereas that of Ni-based self-fluxing alloy is 15 times the value of TiNi alloys. TiNi alloys and SUS304 SS exhibit a working-hardening behavior in the early cavitation stage, and thereafter maintain constant hardness during further cavitation. However, the Ni-based self-fluxing alloy exhibits no hardening phenomenon during cavitation test. The thermoelastic martensitic transformations of TiNi alloys have important effects on their erosion characteristics. The variants accommodation, pseudoelasticity of SIM and high work-hardening rate can improve the erosion resistance of TiNi alloys. Cavitation erosion of all these alloys in freshwater is similar to that in 3.5xa0wt.% NaCl solution under the same testing conditions.

Damping characteristics of TiNi binary and ternary shape memory alloys

Abstract High damping materials are currently attracting much attention in engineering applications. TiNi shape memory alloys (SMAs) could exhibit high damping capacity, as well as excellent shape memory effect and superelasticity. The high damping capacity of TiNi SMAs is mainly related to the hysteretic movement of martensite variants, twin planes and parent–martensite interfaces. The addition of a third element has a substantial effect on the damping capacity of TiNi SMAs. In this paper, the damping characteristics of the binary and ternary TiNi SMAs are systematically investigated. Also, effects of alloy’s microstructures and crystal defects on damping characteristics of TiNi SMAs are discussed.

Recent development of TiNi-based shape memory alloys in Taiwan

Abstract TiNi-based alloys are considered to be the most important shape memory alloys (SMAs) because of their salient shape memory effect (SME), pseudoelasticity (PE) and high damping capacity (HDC). Recent investigations focus on their transformation behaviors, thermal-mechanical treatments, manufacturing processes, and industrial applications based on the characteristics of SME, PE and HDC. The two-stage martensitic transformations of B2↔R-phase↔B19′ and B2↔B19↔B19′ have been clarified for both TiNi binary and ternary alloys. The deformation behaviors have been investigated by cold-rolling, hot-rolling and wire drawing. Both SME and PE can be improved by thermal-mechanical treatments, and the damping characteristics of TiNi and TiNiX SMAs have been systematically studied. Both B19′/B19 martensite and R-phase have high damping capacities due to the easy stress-induced movement of twin boundaries. The high temperature SMAs, Ti–Ni–X with X=Au, Pd and Zr alloys, have also been intensively studied. The ion nitriding technique has been used to improve the wear and corrosion resistance of TiNi and TiNiX SMAs. TiNi thin films have been successfully fabricated using the sputter-deposition technique. These investigations on the TiNi-based SMAs have attracted much attention and their important characteristics will be applied widely in the near future.

Wear characteristics of ion-nitrided Ti50Ni50 shape memory alloys

Abstract The wear characteristics of Ti 50 Ni 50 shape memory alloy can be improved by ion nitriding. Both TiN and Ti 2 Ni compound layers are produced by 700–800°C ion nitriding. The thickness of TiN/Ti 2 Ni compound layers and the specimens surface hardness increase with increasing nitriding temperature. Main adhesive and minor abrasive wear mechanisms are observed for the TiN/Ti 2 Ni compound layers against a Cr-steel ball. The friction coefficient and weight loss of 700–800°C nitrided Ti 50 Ni 50 alloy are quite low before the TiN/Ti 2 Ni compound layers have been worn out. The thicker TiN/Ti 2 Ni compound layers can sustain higher wear loads and hence have better wear resistance. The mass transfer from TiNi martensite to Cr-steel ball and from Cr-steel ball to TiN/Ti 2 Ni compound layers occurs because of their significant difference in hardness.

A study on the wire drawing of TiNi shape memory alloys

Abstract Drawn wires of TiNi shape memory alloys (SMAs) have been studied systematically using DSC, microhardness, SEM and tensile tests. Severe work hardening during the drawing process is observed and hence interannealing is necessary. Multi-pass drawing around the Ms temperature is recommended. The defects induced by cold drawing depress martensitic transformation but promote the R-phase transformation. Defect recovery and recrystallization during interannealing are responsible for the decrease of drawing stress. At the same time, surface oxide film thickness is another important factor related to drawing stress. A thin surface oxide film can be used as a lubricant during the drawing process, however, thick oxide films tend to exhibit cracks and spalling which decrease the drawing surface quality, shape memory effect and pseudoelasticity of TiNi SMAs. MoS 2 is shown to be an effective lubricant for the wire drawing of TiNi SMAs.

A study on the machinability of a Ti49.6Ni50.4 shape memory alloy

Abstract The machinability of a Ti 49.6 Ni 50.4 shape memory alloy (SMA) has been studied by using a mechanical cutting test. There is a wide hardened layer in front of the cutting edge of the Ti 49.6 Ni 50.4 SMA which comes from the effects of strain hardening and cyclic hardening. Meanwhile, Ti 49.6 Ni 50.4 fragments can adhere on the diamond blade. The longer the cutting time, the more adhesion the Ti 49.6 Ni 50.4 fragments have. These features cause the Ti 49.6 Ni 50.4 SMA to exhibit more difficult cutting characteristics than 18-8 stainless steel and Ti 50 Al 50 alloy. From the viewpoint of cutting energy, the effect of applied load is more important than that of cutting speed and there is an optimal cutting load for the cutting of Ti 49.6 Ni 50.4 SMA.

An investigation of unbalanced-magnetron sputtered TiAlN films on SKH51 high-speed steel

Abstract A thin coating of TiAlN was deposited on SKH51 high-speed steel using an unbalanced-magnetron sputtering process. The chemical composition, microstructure and mechanical properties of deposited TiAlN films were investigated. The Ti/Al ratio of TiAlN films can be successfully predicted from the sputtering parameters, involving the applied target currents, the yielding of targets impinged by Ar ions and the target configurations. When Ti atoms are partially replaced by Al atoms during the deposition, TiAlN films are identified as a δ-TiN structure and have the preferred texture of the (200) plane. The more internal stress occurring within the deposited TiAlN films is suggested to result in adhesion of TiAlN films inferior to that of TiN films under the same sputtering condition. TiAlN film with a 50% Ti fraction exhibits an excellent cutting performance due to the slight adhesion of SKS-95 steel fragments during the cutting process.

A comparison of slurry erosion characteristics of TiNi shape memory alloys and SUS304 stainless steel

Abstract The slurry erosion characteristics of three TiNi shape memory alloys and SUS304 stainless steel using the liquid/solid impingement have been systematically studied. Experimental results show that more resistant TiNi alloys and less resistant SUS304 stainless steel exhibit ductile behavior and the maximum erosion has observed at 30°. The surface morphologies exhibit many long furrows and ridges at low impingement angles. The exponent in the relation e = kV n varied between 2 and 3 for impingement angles between 15° and 90°. Work hardening of surface is observed on the surface of all tested materials. The work hardening layer and thin platelet formation increase with angle of impingement. The SIM formation and pseudoelastic behavior of TiNi B2 phase, and variant accommodation and SIP formation of TiNi martensite, make important contributions to the slurry erosion resistance of TiNi alloys.

Gas nitriding of an equiatomic TiNi shape memory alloy: II. Hardness, wear and shape memory ability

Abstract Ti 50 Ni 50 shape memory alloy was gas nitrided to modify the surface conditions. The surface hardness, wear characteristic, transformation temperature and shape memory ability of gas-nitrided Ti 50 Ni 50 alloy were investigated. Experimental results indicate that the surface hardness is increased owing to the formation of TiN and Ti 2 NiH 0.5 compounds. The Ti 50 Ni 50 specimens nitrided at 700–900°C show improved wear characteristics, but those nitrided at 600°C cannot be effectively improved owing to surface cracks appearing in nitrided layers. Martensitic transformation temperatures are depressed slightly owing to the constraining effect originating from the nitrided layers, and/or the penetration of N and H atoms into the Ti 50 Ni 50 matrix. The shape recovery is also slightly reduced because the nitrided layers do not exhibit a shape memory effect, and the constraining effect will also depress the shape recovery of the Ti 50 Ni 50 matrix.

Aging effect on the low temperature internal friction relaxation peak in a Ti49Ni51 alloy

The internal friction relaxation peak appearing around 200 K in TiNi alloys is associated with the interaction of twin-related dislocations with the pinning agents. The 200 K relaxation peak in the 400 °C aged Ti 49 Ni 51 alloy appears at the R-phase and martensite but not at the B2 phase, since there is no twin-dislocation available in the latter. The sources of the pinning agents are due to the quenched-in vacancies or Ti 11 Ni 14 precipitate-vacated lattice sites in the matrix. It is found that 400°C aging will significantly affect the relaxation characteristic in Ti 49 Ni 51 alloy. These aging effects on the 200 K relaxation peak in Ti 49 Ni 51 alloy will be systematically investigated in this study.