Creep of dispersion strengthened materials : a critical assessment

Experimental investigations into the creep behaviour of dispersionstrengthened materials, with emphasis on dislocation creep in nickel and aluminium base alloys, are reviewed. Points of interest are the "anomalously" high stress dependence of the creep rates, the role of grain boundaries, and the loss of strength at high temperatures. Theoretical attempts to explain the creep behaviour in terms of interactions between dislocations and dispersoid particles are extensively discussed. It is concluded that recent models based on an attractive dispersoid-dislocation interaction bear great promise for explaining some phenomena which are not understood on the basis of more classical dislocation climb theories. For the purpose of creep data extrapolation, it follows that the "threshold stress" concept is only an approximation which must not be used uncritically. Further considerations regarding models for the effects of grain boundaries on deformation and fracture are briefly presented. The importance of a theoretical understanding of dispersoid effects for designing optimum alloys is stressed, and areas for further work are outlined