Study On Particle-reinforced TiNi Shape Memory Alloy Composites

Nanowires and nanoparticles have ultra-large elastic strain limits and ultrahigh yield strengthes.Materials scientists consider that the reinforced composite materials should have super mechanical properties.However,all the existing research results are disappointing,the extraordinary mechanical properties of nanowires or nanoparticles can't be achieved in the reinforced composites.For example,freestanding nanowires have ultra-large elastic strain?4-7%?,but its elastic strain is limited?less than 1.8%?.Recently,our group has found that the nanowires embedded in the matrix deformed by lattice shear shows ultra-large elastic strain,and its composite materials have high mechanical properties.Therefore,the component systems of such nanowire composites are limited.If the particles formed by conventional aging or spheroidizing annealing methods could have large elastic strain and ultrahigh yield strength in the matrix deformed by lattice shear,it is expected to be widely available.From these above discussions,we have recently explored the elastic deformation behavior of the particles embedded in the matrix deformed by lattice shear.The corresponding research contents and results are as follows.In-situ Nb particles/TiNi shape memory alloy composite and Ti₂Ni particles/TiNi shape memory alloy composite were fabricated by spheroidizing annealing or conventional aging methods.Using in-situ high-energy X-ray diffraction technique,it is demonstrated for the first time that the precipitation particles?Ti₂Ni?and spherical particles?Nb?in the TiNi matrix deformed by lattice shear show larger elastic strain than that deformed by dislocation slip,Meanwhile,they also present the elastic deformation instantaneity,Locality,elastic strain distribution non-uniformity,elastic strain relaxation and other characteristics.Based on the Characteristics that Ti₃Ni₄ particles dissolve in the process of cold drawing and then separates out in conventional aging,Ti₃Ni₄ nanoparticles/nanocrystalline TiNi shape memory alloy composite was fabricated for the first time.The preliminary findings are as follows:Ti₃Ni₄ nanoparticles are uniformly distributed in nanocrystalline TiNi memory alloy matrix,and the composite material exhibits excellent mechanical properties.