Study On Martensitic Transformation Of Ti-based Amorphous Composites

This dissertation selected Ti–Ni–Cu composition with larger glass forming ability as the research object, on this basis, we carried out Nb, Zr and Sn addition.Ti–Ni–Cu–Nb and Ti–Ni–Cu–Zr glass composites were prepared by copper mold casting method and single-roll melt spinning technique, and Ti–Ni–Cu–Zr–Sn alloy were prepared by Arc smelting method. The phase composition, martensitic transformation behavior and transformation temperature were examined by the XRD, DSC and electrical resistivity methods.Moreover, the effect of alloy compositions, cooling rate and annealing treatment on the phase composition and marentsitie transformation characteristics is explored.The results showed that: Nb for 4at.% and Zr for 4at.% and 5at.% promote the martensitic phase transformation in the Ti–Ni–Cu–Nb/Zr alloy, which includes B2 and B19 phase and undergoes B2–B19 one-stage phase transformation on colding and heating. Nb for 4at.% promote to precipitat β–Nb phase, significantly reduce the Ms and ΔT. Ms of Ti–Ni–Cu–Zr alloy firstly decrease, then increase, with increasing the content of Zr, and phase transition hysteresis ΔT are just reverse. Ti50Ni25Cu25 as–casted alloy undergoes B2–B19 phase transformation.Ti45Ni25Cu25Zr5 as–casted alloy undergoes B2–R–B19’ two-stage phase transition. Martensitic phase transformation points of casting alloy are significantly reduced, phase transition point and the hysteresis are stable after aging at 300℃ and 500℃. Further, that has a stable phase transformation process.Ti–based metallic glass composites can be prepared by copper mold casting method and melt spinning technique. Nb elements reduce the formation of amorphous alloy, however, the Zr elements for 4at.% and 5at.% can improve the ability of amorphous formation. After aging treatment, Ti–based metallic glass composites have the crystallization behavior to precipitat crystal phase.Ti–Zr–Cu–Ni–Sn alloy mainly cotains B2 phase, tP4–TiCu phase and(Ni, Ti)phase, Sn elements promote the generation of dendritic phase tP4–TiCu phase.Three kinds of alloy with Sn for 3.1at.% only undergoe one-stage phase transition on heating.Which has stable phase transition.Cu element increase As by gradually taking the place of Ni element. Ti50Ni25Cu16Zr6Sn3 alloy with Sn for 3% undergoes B2–R–B19’ two-stage phase transition,Ti50Ni16Cu25Zr6Sn3 alloy undergoes B2–B19 one-stage phase transition. Ms,Mf and transformation hysteresis of alloy with Cu replacing Ni for 9at.% decrease.