Study On The Partial Phase Equilibrium From1000℃to1150℃and The Solidification Behavior In The Nb-Ni-Ti Ternary System

Nb-Ni-Ti is the important and basic system for hydrogen permeation materials, applied high-temperature alloy, superconducting alloy and shape memory alloy. But the research mainly concentrated in the solid phase equilibrium. However, the design of the new Nb base casting hydrogen permeation materials in Nb-Ni-Ti system needs the support of information associated with liquid phase equilibrium. The fundamental basic parameter is L(?)β(Ti,Nb)+TiNi three-phase eutectic transformation. Establishing a comprehensive phase equilibrium relations related to L(?)β(Ti,Nb)+TiNi three-phase eutectic transformation and studying the solidification behaviour. Controling the composition and volume fraction of the two phases in eutectic structure, the size and shape of eutectic structure, in order to maximize the hydrogen penetration ability of Nb-Ni-Ti alloy membrane and ensure adequate mechanical properties, make the study on the Nb based hydrogen permeation alloy reliable.In this work, alloy balance structure analysis are used, by using optical and scanning electron microscopic observation, X-ray diffraction, differential scanning calorimetry to study the phase equilibrium relations from1000℃to1150℃related to L(?)β(Ti,Nb)+TiNi three-phase eutectic transformation and solidification behavior of alloy-in Nb-Ni-Ti ternary system. The results obtained are as follows:There is always the β(Ti,Nb)+TiNi phase region from1000℃to1150℃. It can provide more choices for the design of component and the volume fraction of β(Ti,Nb)+TiNi two-phase eutectic organization.But the β(Ti,Nb)+TiNi phase region will narrow with the increasing of temperature.From1000℃to1100℃, existing two three-phase regions:β(Ti,Nb)+TiNi+liq and β(Ti,Nb)+TiNi+XB on both sides of theβ(Ti,Nb)+TiNi phase region.But there are two different compositions (3(Ti,Nb)+TiNi+liq three-phase regions on both sides of the β(Ti,Nb)+TiNi phase region at1150℃.Withing the rising of the temperature in the β(Ti,Nb)+TiNi+liq three-phase regions.The Nb content of β(Ti,Nb) gradually increases, the Ti content of (3(Ti,Nb) gradually decreases, while the Ni content at the β(Ti,Nb) basically unchanges.The content of the Nb at liquid increases.The constituent of TiNi basically unchanges.And the β(Ti,Nb)+TiNi+liq three-phase regions will close to the ligature of Nb-TiNi.The maximum content of Nb at the TiNi can run up to11.1at.%at1100℃. The lattice constant of the (3(Ti,Nb) will decline gradually from0.3292nm to0.3280nm with the content of Ti at the (3(Ti,Nb) rising in the (3(Ti,Nb)+TiNi phase region at1000℃. The content of Nb at the Ti2Ni is3.6at.%at950℃.The temperature reacting L(?)β(Ti,Nb)+TiNi three-phase eutectic transformation is about1040℃-1150℃.For the eutectic reaction L(?)Ti2Ni+P(Ti,Nb) in a subsequent, the temperature is increased form942℃in the binary system to950.5℃in the ternary system with the addition of the third component Nb.