The Preparation And Characterization Of The Nickel-based Ternary Intermetallic Alloys

Based on the theories of alloying and multiphasing of transfer metallic silicide alloys,the Ni₃(Al_1-x,Si_x)ordered alloy and Laves phase Ti₂Ni₃Si/NiTi multiphase alloy are prepared by Non-Consumable-Electrode vacuum Arc Melting,mechanical alloying add hot-pressing sinteri add heat treatment,respectitively.The investigation and part performances of the melted alloy,powder alloy and sinter alloy are performed by using the XRD,OM,SEM, DSC,EDS methods and so on.About the Ni₃(Al_1-x,Si_x)order alloy,We focus on the influence of composition scale of Al, Si element on its microstructure,properties and evolution on the phase transform.It shows that the casting structure of the Ni₃(Al_1-x,Si_x)alloy transforms from the thick denrite at first to close to the tiny equiaxed crystalline With the Si content increasing and then gradually becomes the short needle morphology with a little grain boundaries,at last it transformes the thick long needle or strip.The morphology and structure of the grain boundaries are increasing.The average micro-hardness of the alloys is increasing with the Si content increasing.The casted Ni₃(Al_1-x,Si_x)alloy has worse plasticity and brittleness in room temperature;Fractures of the alloy are always brittle cleavage fracture,when x=0,tile alloy is composed of single-phase, when x=0.25～0.75,obtaining the compacted Ni₃(Al,Si)based of as-casted complex;when x adds up to 0.75,it begins to have Ni₃₁Si₁₂phase,when x=1,the strcuture is Ni₃Si matrix and content of he Ni₃₁Si₁₂phase is relatively increasing After annealled at 900℃,the Ni₃₁Si₁₂phase is completely transformed to Ni₃Si,which proves that the Ni₃₁Si₁₂phase is the metastable phase.About the Laves phase Ti₂Ni₃Si/NiTi multiphase alloy,We focus on the evolution of particle morphology,microstructure,grain size and microstrain of the mixture of Ti,Ni and Si elemental powders during MA have been investigated.It is found that the mechanical composite powders with extremely fine Ti-Ni-Si nanocrystalline prepared by MA.The influence of milling time on Ti-Ni-Si lamella spacing of composite powders is estimated on the basis of the model of MA established from the theories in this paper,The temperature of powders during MA is also analysized,from which it is inferred that the temperature rising due to milling of the milled powders was not enough to drive the reaction between Ti,Ni and Si.It supplies the theoretic thereunder for prepareing Ti-Ni-Si composite powders by MA method.The influence of the density and strcture of the sinter by using the high temperature sintering technics are researched.And the rule of the density changing of the sinter is theoretically analyzed also in the paper.Through the study of the sintering behavior of the composite powders,the results show that the Ti,Ni and Si reactant phases is sufficient fined by MA which obvious promotes the sintering densification and refinement of the structure. The longer prolonging the sintering time is,the higher promotes the density of the as-sintered specimen at the end.