Preparation And Characterization Of NiTi Shape Memory Alloy Particles Reinforced Cu Matrix Composites

The NiTi alloy has excellent super-elasticity,shape memory effect and wear resistance,which is the mostly investigated shape memory alloy at present.However,the shape memory effect of NiTi alloy is mainly driven by temperature,resulting in low response frequency.At the same time,the NiTi alloy exhibits poor processing performance and high cost,which greatly limit its practical application.Cu has many advantages,such as excellent conductivity,thermal conductivity,good corrosion resistance and processability.But Cu has some disadvantages,such as low mechanical strength and poor wear resistance.In this thesis,NiTi particles reinforced Cu matrix composite was prepared by combining NiTi alloy and Cu,in which NiTi particles are used to improve the mechanical properties of Cu matrix,and Cu matrix is used to improve the processing properties of the composite.Then the microstructure,phase transformation behavior and mechanical property of the composites are studied in detail.In this thesis,NiTi particles/Cu composites are prepared by spark plasma sintering.The effects of NiTi particle size,NiTi particle content and cold rolling on the microstructure,phase component,martensitic transformation behavior and mechanical properties of the composites are investigated.The results show that the pure Cu and NiTi particles/Cu composites prepared by spark plasma sintering have compact microstructure and no obvious sintering holes.NiTi particles are widely distributed in Cu matrix,and NiTi particles react with Cu matrix.The interfacial reaction in small-size NiTi particles/Cu composite is intense.The main product of interfacial reaction is Cu₂Ti phase.After cold rolling,the grains of Cu matrix in NiTi particles/Cu composite are refined,and the cracking happened at the interface between NiTi particles and Cu matrix.Compared with the initial NiTi particles,the martensitic transformation of NiTi particles/Cu composite is weakened,and the martensitic transformation of the rolled composite is further weakened.With the increase of NiTi particle content,the martensitic transformation of NiTi particles/Cu composite increases gradually.When NiTi particle content is the same,large-size NiTi particles composite shows stronger martensitic transformation than small-size NiTi particles composite.Compared with the sintered pure Cu,the mechanical strength of NiTi particle/Cu composite is significantly improved.With the increase of NiTi particle content,the strength of NiTi particle/Cu composite is gradually increased,but the plasticity is gradually decreased.When the content of NiTi particles is the same,the large-size NiTi particles/Cu composite shows better mechanical properties.After rolling treatment,the mechanical strength of pure Cu and 20wt%NiTi particles/Cu composite is improved,but the mechanical properties of30wt%and 40wt%NiTi particles/Cu composites are weakened.