Materials Science Forum, Vol.357-3, 405-410, 2001
Internal stress superplasticity in an in-situ intermetallic matrix composite
Processing of NiAl-Cr based eutectic in-situ composite via internal stress superplasticity has been explored. The alloy is heat treated to produce spherodized Cr particles in NiAl matrix. Results of thermal cycling creep experiments indicate that internal stress of considerable magnitude are generated between the NiAl matrix and Cr particles, which aids the external applied stress in deforming the alloy in viscous manner. The origin of internal stress is attributed to the difference in thermal expansion behavior of the constituent phases. At low stresses, the thermal cycling creep rates are higher than the isothermal creep rates. However, the observed thermal cycling creep rates are an order of magnitude lower than values predicted by an internal stress superplasticity model based on micromechanics. The possible reasons for this discrepancy are discussed.