The effect of trace element additions on the grain boundary composition of Ir + 0.3% W alloys

Abstract
Iridium alloys are currently used as cladding and post-impact containment material for radioactive fuel in radioisotope thermoelectric generator heat sources. In this application, the cladding must exhibit at least 15% elongation during high temperature impact (h.t.i.), which for purposes of this study will denote an overall elongation rate of 85 m/s with a gauge length of 1.27 cm in the temperature range 1200—1500 °C. Liu & Inouye (1976) have reported that doped Ir + 0.3% W normally fails intergranularly during h.t.i., with elongation between 3 and 15 %. Intergranular failure at lower temperatures and strain rates has been reported by others, and has been attributed to the presence of impurities or precipitates at the grain boundaries. Hecker et al . (1979) and White et al . (1979) have recently studied the composition of grain boundaries in Ir and Ir + 0.3% W by using Auger electron spectroscopy (A.e.s.). They were unable to find any impurity segregated to the grain boundaries, and concluded that intergranular fracture is intrinsic to Ir, and not related to impurities.

This publication has 0 references indexed in Scilit: