MONOTONOUS AND CYCLIC CREEP IN A HEAT-RESISTANT 16CR-10W-4MO-TIAL NICKEL-BASED ALLOY - TRANSMISSION ELECTRON-MICROSCOPY STUDY OF MICROSTRUCTURE

A transmission electron microscopy (TEM) study of the dislocation stru cture developed in a nickel-based 16Cr-10W-4Mo-TiAl heat-resistant all oy was performed. Specimens subjected to monotonic or cyclic creep at 1023 K were investigated. Two distinctly different arrangements of dis locations were found after monotonic creep. At low applied stresses, n umerous dislocation loops around gamma' particles indicate that the mo tion of dislocations is strongly influenced gamma' precipitates. In th e range of high applied stresses. pronounced slip bands form which are composed of several closely spaced (sic)111 slip planes, The cutting of gamma' particles by dislocations is observed frequently and the dis location motion does not seem to be considerably hindered by precipita tes. The distribution of dislocations after cyclic creep can be charac terized as a mixture of the dislocation structures representative of l ow and high applied stress regions in monotonic creep. Two different d islocation arrangements are discussed in terms of the creep mechanism and the response of the alloy to cyclic creep loading.