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Structural studies have been performed on precipitation hardening discovered in L12-ordered Ni3(Al,Cr) containing 0.2 to 3.0mol% of carbon using transmission electron microscopy (TEM). Fine octahedral precipitates of M23C6 appeared in the matrix by aging at temperatures around 973K after solution treatment at 1423K. TEM examination revealed that the M23C6 phase and the matrix lattices have a cube-cube orientation relationship and keep partial atomic matching at the {111} interface. After prolonged aging or by aging at higher temperatures, the M23C6 precipitates then adopt a rod-like morphology elongated parallel to the <100> directions. Deformation at temperature below 973K, typical Orowan loops were observed surrounding the M23C6 particles. At higher deformation temperatures, the Orowan loops disappeared and the morphology of dislocations at the particle-matrix interfaces suggested the existence of attractive interaction between dislocations and particles. The change of the interaction modes between dislocation and particles with increasing deformation temperature can be considered as a result of strain relaxation at the interface between matrix and particles.