Abstract: The functional performance of Cu-Al-Mn shape memory alloys originates from their reversible martensite transformation,while the complex thermal cycles involved in laser powder bed fusion（L-PBF） may significantly affect the phase transformation behavior and phase stability. A Cu₇₁Al_17.5Mn_11.5 shape memory alloy was fabricated by L-PBF,and its temperature-induced solid-state phase transformation behavior was systematically investigated using in situ transmission electron microscopy（TEM） and in situ X-ray diffraction（XRD）. The results show that the L-PBF-fabricated Cu₇₁Al_17.5Mn_11.5 alloy mainly consists of a β-phase matrix,together with a small amount of lamellar structures composed of α and β phases. In situ TEM observations reveal that no significant morphological changes occur in either the lamellar structures or the matrix during heating up to 1 073 K. After rapid cooling,the lamellar structures exhibit diffraction features characteristic of the αphase,while the matrix undergoes a martensitic transformation to form 18R martensite. In situ XRD results indicate that theα phase completely dissolves into the β phase at approximately 1 173 K. After annealing,the grains coarsen markedly,with most grains transforming into coarse equiaxed grains,accompanied by an increased fraction of high-angle grain boundaries. This study elucidates the microstructural evolution of L-PBF-fabricated Cu-Al-Mn alloys under dynamic thermal conditions and its influence on mechanical performance,providing a theoretical basis for process optimization and material design.