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A high Nb content Al_3 Ti alloy was prepared by spark plasma sintering technology to study the effects of 315 ℃and 645 ℃ pre-sintering and different reaction sintering temperatures at 885-1130 ℃ on the microstructure of Al_3 Ti alloy. The microstructure transformation process at different sintering temperatures was analyzed and the schematic diagram of microstructure transformation was drawn. The results show that after the pre-sintering treatment at 315 and645 ℃,the surface oxide of the raw material particles dissolves,and the solid phase diffusion occurs and a small amount of Al_3 Ti is generated to make the phase boundary passivation. The liquid-phase sintering and grain growth occurs in the reaction sintering process at 885-1130 ℃,the peritectic reaction between molten Al and refractory Ti and Nb2 Al results in the formation of Al_3 Ti and Al_3 Nb,and the formation of Al2 Ti is attributed to the fact that the Al_3 Ti phase hinders the diffusion of Al element and reduces the Al content of the reaction with Ti. With the increase of sintering temperature,the reaction rate is accelerated and the alloying process and grain growth of the reaction materials is rapidly completed,resulting the improvement of the crystallinity of Al_3 Ti and Al_3 Nb.