The Positive Effect of Hydrogen Alloying on the Phase Tailoring and Mechanical Properties of Sintered Ti-13Nb SMAs
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, B. YUAN
, and Y. GAO
The effect of hydrogen alloying on phase tailoring and mechanical properties of the sintered Ti13Nb (at pct) shape memory alloy (SMA) was investigated. It was found that hydrogen addition changed the microstructure of the sintered Ti-13Nb-(0-31)H (at pct) alloys gradually from a + b dual phase to single b phase due to the lowered transition temperature of b phase to a phase by hydrogen action. The reduction of a phase precipitation in the alloy reduced the amount of Nb squeezed out from the Nb-depleted a phase, and consequently decreased the mean Nb content in the b phase. Thus, the Ms temperature of Ti-13Nb alloy was successfully increased from lower temperature to near room temperature, which consequently enhanced the recoverable strain of the alloy by easier martensitic transformation. The sintered Ti-13Nb-18H alloy presented a Ms temperature of 22 C and a remarkable recoverable strain of 3.9 pct at room temperature, which is the highest value ever reported in the sintered Ti-Nb based SMAs. Meanwhile, the Ti-13Nb-18H alloy exhibited a fracture strain of 23.1 pct and a fracture strength of 1321 MPa, both better than that of the Ti-13Nb alloy, which was attributed to the hydrogen atoms in the alloy which caused solid solution strengthening and also increased the content of the b phase with higher plasticity. https://doi.org/10.1007/s11661-019-05411-w The Minerals, Metals & Materials Society and ASM International 2019
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INTRODUCTION
ALTHOUGH NiTi SMAs have been successfully utilized in biomedical applications due to their excellent superelasticity, shape memory effect, good corrosion resistance, and high strength,[1] the high content of Ni in the alloys, which is considered allergenic and carcinogenic,[2–4] has hindered their wider acceptance. Thus, considerable efforts have been made to develop Ni-free Ti-base shape memory alloys. The Ti-Nb based and TiMo based alloys, made up of non-toxic b-stabilizing elements with excellent biocompatibility, have been reported to present shape memory effect and superelasticity (or recoverable strain).[5–8] Among them, Ti-Nb based SMAs exhibit a recoverable strain of over 4 pct,[9] which is adequate for bone implant requirement. However, the elastic modulus of these superelastic Ti-Nb based SMAs is much higher than the bone (6 to 26.6 GPa),[10] which may lead to causal bone loss or osteoporosis of the patient due to stress shielding effect. So it is necessary to develop porous Ti-Nb based SMAs
Z. XU, B. YUAN and Y. GAO are with the School of Materials Science and Engineering, South China University of Technology, Guangzhou, 510641 P.R. China. Contact e-mail: [email protected] Manuscript submitted March 26, 2019.
METALLURGICAL AND MATERIALS TRANSACTIONS A
to decrease the elastic modulus. Furthermore, the porous structure can be easily tuned to favor tissue or cell in-growth and enhance biocompatibility.[11] Powder metallurgy (PM) is an effective method in preparing porous alloys and controlling their pore characters, such as porosity and pore shape.
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