Effect of Cool-heat Cycles on the Welded Joints' Phase Transformation Temperatures of TiNi SMA in PPRBW Han Lijun Zhu Junjie Han Lihong Zhao Xihua Ph.D., Faw volkswagen,Changchun 130011, China.This paper studies the effect of cool heat recycle on the phase transformation temperatures of the TiNi shape memory alloy welded joints of the precise pulse resistance butt welding by using TEM,DSC, X ray diffraction measures, and discusses the principles from microviews. Experimental results show that cool heat recycle times have great effect on the phase transformation temperatures. The start and finish temperatures of the phase transformation of M→A are promoted with cool heat recycle times increasing, due to the change of dislocation density and the separate out and growth of intermetallic compounds. On cool heat recycle being about 1 000 times, the phase transformation of M→A→R takes places for these reasons, which delays the austenite transformation temperatures and makes it serious for temperature hystersis phenomena, then come to stability. The physicals model that dislocation affects phase transformation temperatures is given.TiNi shape memory alloy; cool heat cycle; phase transformation temperature; R phase transformation