Effects Of Heat Treatment Temperature On Microstructure And Mechanical Properties Of NiTi/（Al₃Ti+Al₃Ni）Laminated Composites

NiTi/（Al₃Ti+Al₃Ni）laminated composites were prepared by vacuum hot pressing sintering process and annealed at 750℃,850℃and 950℃.The composition,structure and fracture of the material were analyzed and observed by XRD,SEM and EDS at the microscopic level.The results show that the heat treatment has no effect on the structure of NiTi/（Al₃Ti+Al₃Ni）layered composites,and the NiTi layer,the reaction zone and the intermetallic layer（two-phase zone）structure before heat treatment are still maintained,but the heat treatment changes the thickness of the reaction zone.And promote the formation of Al₃Ni phase;from the Charpy impact fracture analysis,the sensitivity of the V-shaped fracture is more sensitive than the U-shaped fracture;The analysis carried out shows that,on the macroscopic view,the intermetallic compound layer in the fracture is relatively flat and bright,and the NiTi layer is dull and uneven.Microscopically,the intermetallic compound layer is in the form of uneven granules.After further enlargement,a typical"ice-like"feature is observed,showing a characteristic of apparent brittle fracture along the crystal.Dynamic compression（Hopkinson pressure bar）and static compression experiments were performed on the parallel lamination direction and the vertical lamination direction respectively in the mechanical properties,and the tensile test was performed in the parallel lamination direction and the hardness analysis was performed in the vertical lamination direction.Hopkinson pressure bar experiments show that the average compressive strength of the original sample,heat treatment samples of 750℃,850℃and 950℃in the vertical stacking direction is greater than the average compressive strength when colliding in the parallel stacking direction,It can be seen that whether the vertical lamination direction or the parallel lamination direction impacts,the compressive strength decreases as the heat treatment temperature increases,and the compressive strength reaches the lowest value at the highest heat treatment temperature;the static compression test shows that the heat-resistant composite material has lower compression resistance than the original composite material without heat treatment;The tensile test shows the characteristics of the ductile material and the maximum load is negatively correlated with the tensile strength and the heat treatment temperature.The hardness of the NiTi/（Al₃Ti+Al₃Ni）layered composite exhibits a periodic variation in the direction perpendicular to the lamination direction.The reaction zone reaches the highest value,followed by the two-phase zone,and finally the NiTi layer and the intermediate zone.The hardness of the sample after heat treatment still maintains this rule,but the hardness value decreases.