The sub-structure of powder-metallurgy material was investigated at 1523 to 1623K, using stresses ranging from 35 to 120MPa. Experimental data showed that the apparent creep behaviour was different to that of pure metals: the stress exponent was equal to about 7 and the activation energy for creep (502kJ/mol) was higher than that for self-diffusion (416.5kJ/mol). An analysis of the data revealed a threshold stress which depended strongly on temperature. The creep sub-structure revealed the presence of frequent interactions between dislocations and nm-sized particles within the interiors of equiaxed sub-grains whose average size decreased with increasing stress. The dislocation-dispersion particle configurations resembled those in dispersion-strengthened alloys. It was suggested that these particles were introduced as a result of powder-metallurgy processing, and that their interaction with moving dislocations gave rise to the threshold stress creep behaviour which was observed.

Threshold Stress Creep Behaviour in Ta. Z.Lin, F.A.Mohamed: Philosophical Magazine A, 2002, 82[8], 1479-94