Papers by Keyword: Porous NiTi Alloy

Abstract: In this paper, the porous NiTi alloys were prepared by microwave sintering, and the effects of NH₄HCO₃ contents on the microstructure of the porous NiTi alloys were studied. The microstructure of the porous NiTi alloys was investigated by optical microscopy, Archimedes drainage method, surface roughmeter and X-ray diffraction. The results showed that the porous NiTi alloys were mainly composed of NiTi, Ni₃Ti, Ti₂Ni and Ni, and the diffraction peaks of the non-equiatomic phases (Ni₃Ti, Ti₂Ni and Ni) increased with increasing the NH₄HCO₃ contents. At the same time, the porosity, pore size and surface roughness of the porous NiTi alloys increased with the increase of the NH₄HCO₃ contents.

Abstract: In this paper, porous NiTi alloy prepared by powder metallurgy method was oxidized at high temperature. The effect of oxidation temperature and time on quality of oxidation layer of porous NiTi was studied. The component and morphology of oxidation layer before and after oxidation at high temperature were analyzed by XPS and SEM. The behavior of Ni ion release of porous NiTi alloy was observed. The results showed uniform and thick oxidation layer was formed on the surface of porous NiTi alloy after oxidation at 550°C for 1h. XPS analysis showed the oxidation layer mainly composed of TiO₂, and the thickness of the film was about 180nm higher than that before oxidation. The research on the behavior of Ni ion release showed the Ni release after oxidation can be significantly reduced at simulated body fluid due to TiO₂ layer.

Abstract: Porous NiTi alloys were prepared by powder metallurgy method using NH₄HCO₃ as space-holder. The effect of sintering temperature on pore characteristic, phase composition and compressive property of porous NiTi alloys was studied by XRD, SEM, EDS and a universal testing machine. The results show with the increase of sintering temperature the porosity of porous NiTi alloys first increases and then decreases, but the content of NiTi phase, compressive strength and modulous of sintered products continuously increase. When sintered at 980°C for 2h, the porous NiTi alloys have higher porosity of 53.6%, better compressive strength of 173.7MPa and elastic modulous of 4.2GPa. The phases of sinter products are mainly composed by TiNi, Ti₂Ni, and TiNi₃ phases.

Abstract: Porous NiTi shape memory alloys were fabricated by thermal explosion method using different Ti and Ni powder as initial materials. The effect of process parameters including heating rate, and particle size of Ti on pore characteristic and phase composition was analyzed. Microstructure, phase composition, and mechanical properties were studied by SEM, XRD, and compression test, respectively. The mechanism of thermal explosion reaction was studied. The results show higher heating rate and smaller Ti particle size result in higher porosity and bigger pores. The thermal explosion reaction starts with the melting of a eutectic between β-Ti(Ni) and Ti2Ni and the main phases of as-reacted products are TiNi phase which are the desired phases. NiTi2 and TiNi3 phases are also present in small amounts. The content of TiNi phase increases with increasing heating rate or decreasing Ti particle size. The compressive strength and Young’s modulus of compacts decrease with the increase of the porosity.

Abstract: One internal friction peak associated with the B2↔B19’ transformation appears on the cooling curve of porous NiTi shape memory alloy and the dense NiTi alloy shows the maximum peak. The tan δ value increased with the increasing of strain amplitude and the decreasing of frequency. Tan δ value of porous alloy mainly comes from the energy absorbing of the matrix at the small strain amplitude, however, if the strain amplitude is large, the tan δ value comes from the energy consumption that overcomes the friction between folds and the plastic contribution.

Abstract: The machining performance of porous NiTi shape memory alloys prepared using powder metallurgical production technique has been investigated experimentally in the grinding operation. Grinding force ratio, specific grinding energy, surface characteristics were detected. The result reveals that, much difference of grinding characteristics exists among three kinds of NiTi alloy because of the pore rate and the mechanical performance induced by TiH2. Under the experimental conditions, the integrated effects of predominant plastic flow and slight brittle fracture were taken for porous NiTi alloy during grinding. Additionally, the grinding parameters should be chosen carefully, otherwise the surface quality deteriorates and even the microcrack perhaps appears.