Quarterly report on the strontium heat source development program, Advanced Systems and Materials Production Division for April--June 1978

Abstract

All of the remaining compatibility tests are proceeding as scheduled. Results of the 20,000-hr compatibility tests with nonradioactive SrF/sub 2/ show that, with one exception, attack of the specimens by the SrF/sub 2/ after 20,000 hr is no greater than after 6000 and 12,000 hr. The one exception involved Haynes Alloy 25 specimens tested at 1000/sup 0/C. These test specimens exhibited isolated subsurface voids to depths of 0.025 in., although the general surface attack was only about 0.001 inches. The cause of the void formation has not yet been determined. Tests with Hastelloy S and Hastelloy C-4 at 600 to 800/sup 0/C for 2500 hr show that oxidation of the two alloys adheres to the parabolic rate law. Both alloys from adherent oxide layers over the temperature range of interest. Intergranular attack, pitting, and subsurface void formation increase sharply with increased oxidation temperature with both alloys, and at 800/sup 0/C the depth of metal exhibiting oxidation damage is several times greater than the thickness of the oxide layer.