Rapid Growth of TiNi intermetallic compound within undercooled Ti_(50)Ni_(50)alloy under electrostatic levitation condition

The undercooling dependence of the solidification mechanism was systematically explored by the electrostatic levitation(ESL)facility.During the experiments,the maximum undercooling reached up to 406 K(0.26 T_L)and the growth velocity of the primary TiNi phase was in-situ determined at various undercoolings.At the initial increase of alloy undercooling,the value of growth velocity sluggishly rose followed by a power function.In this case,the primary TiNi phase preferentially developed as the equiaxed dendrite,then the remnant liquid participated as Ti_(2)Ni andα-Ti phases on the grain boundary.Once the undercooling exceeded the critical value of 350 K,the growth velocity of the primary phase displayed a sharply increase tendency.Meanwhile,the TEM results demonstrated that the precipitation of the intermetallic Ti_(2)Ni compound was gradually restrained during the rapid solidification and the R-phase existing in the TiNi matrix at large undercooling implied that the martensitic transformation was incomplete.