Papers by Author: Yun Qing Ma

Abstract: The effects of Nb addition on microstructures, Young’s moduli, tensile properties of Ti-30Ta-xNb (x = 21, 24, 27, 30, wt. %) alloys were investigated in this study. The results show that dual phases containing β phase and a little α" martensite were observed when x = 21 and 24, whereas single β phase is present when x = 27 and 30. A minimum Young’s modulus of 52.13 GPa was obtained in Ti-30Ta-21Nb alloy. Ti-30Ta-xNb alloys exhibit high strength-to-modulus ratios, showing their great potentials to develop as new candidates for biomedical applications.

Abstract: The effects of trace boron on microstructure and mechanical properties of β type Ti-9V-3Al-3Cr-3Zr-3.5Mo (wt. %) alloy have been investigated in this study. Upon the addition of 0.02 wt. % boron, the grain size of the B-modified alloy was almost four times smaller than that of the B-free alloy. Accordingly, the tensile strength and elongation of B-modified alloy increased from 712 MPa and 14.6 % to 813 MPa and 17.9 %, respectively, mainly due to the effect of grain refinement.

Abstract: The phase equilibria at 900 °C and B2/L21 order-disorder transition in the Ni-Mn-Ga ternary system were investigated by analyzing the equilibrated alloys and diffusion couples using a combination of techniques. It was confirmed that a bcc single phase region exists in a wide composition range at 900 °C, and the critical temperatures of B2/L21 order-disorder transition were determined in Ni-50 at.% section, which exhibits a maximal ordering transition temperature of 796 at Mn content of 25 at.%. The obtained results will be helpful for the preparation and annealing of Ni-Mn-Ga alloys in the specific temperature.

Abstract: The rare earth element Gd is added to Ni53Mn22Co6Ga19 high-temperature shape memory alloy to refine the grain size and adjust the distribution of γ phase, and their microstructure, martensitic transformation behaviors, mechanical and shape memory properties were investigated. The results show that the grain size is obviously decreased and the γ phase tends to segregate at grain boundaries with increasing Gd content. Small amounts of Gd-rich phase were formed with 0.1 at.% Gd addition. The martensitic transformation temperature abruptly increases with 0.1 at.% Gd addition, then almost keeps constant with further increasing Gd content. The addition of 0.1 at.% Gd is proved to be beneficial to both tensile stress and strain before fracture, but negative to the shape-memory effect.

Abstract: Recently Ni-free Ti-based shape memory alloys have been actively studied for biomedical applications in order to replace Ti-Ni alloys which bear the possibility of Ni-hypersensitivity. In this paper, The Ti-(40-65) Ta (wt. %) alloys have been studied with regard to their microstructure, mechanical and shape memory properties, as well as the effect of heat treatment on their shape memory behaviors. The results show that Ti-40wt. %Ta exhibits single orthorhombic structure (''), Ti-55wt. %Ta mainly '' and a little BCC structure (β), and Ti-65wt. % Ta mainly β and a little '' at room temperature. The tensile strengths of Ti-Ta alloys are all over 550 MPa, and the elongations over 17%. The Young’s modulus of Ti-Ta alloys ranges from 66 to 75 GPa, which are closer to the modulus of human bone as compared with that of Ti-6Al-4V alloy. The maximal shape memory strain of 3.32% was obtained in Ti-55wt. %Ta alloy quenched at 1273 K followed by aging at 723 K for 10min. The obtained results will be beneficial for developing Ti-Ta alloys for biomedical applications.

Abstract: A strong need exists to develop new kinds of high-temperature shape-memory alloys. In this study, two series of CoNiGa alloys with different compositions have been studied to investigate their potentials as high-temperature shape-memory alloys, with regard to their microstructure, crystal structure, and martensitic transformation behavior. Optical observations and X-ray diffractions confirmed that single martensite phase was present for low cobalt samples, and dual phases containing martensite and γ phase were present for high cobalt samples. It was also found that CoNiGa alloys in this study exhibit austenitic transformation temperatures higher than 340°C, showing their great potentials for developing as high-temperature shape-memory alloys.