Creep deformation is characterized in terms of temperature, the applied load and the resultant steady-state creep rate. A correlation is often sought to describe accelerated test data and to provide a means of predicting performance in service. Since prediction often involves extrapolation outside the data range, there is concern for possible transitions in creep behavior. Rate dependent transitions in creep behavior are common for many commercial alloys, and research over the years has provided an understanding of some of the basic mechanisms involved. This understanding has led to definition of conditions under which different mechanisms are active and, thus, bounds at which transitions will occur. In this paper, the major transition mechanisms are briefly discussed and their significance to long-term extrapolation of creep properties is demonstrated.

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