Paragraph postulated that the observed cracking and powdering of the Tm.O./ Yb^O-may be the result of a "stress-corrosion" phenomenon common to some metallic systems. The required stresses would result from Increased densifIcatlon (sintering) during the testing cycle thereby producing high circumferential stresses and cracking. Intergranular attack (powdering) would be the result of both the tensile stresses and the iron contaminant from the Hastelloy X. The changes in color and translucency are believed related to the combined effect of impurity elements in the Tm_0_/Yb-0, and increased densifIcatlon thereof due to heat treatment. The mechanisms Involved are not understood and their study was beyond the scope of this program. The Yb-0-content of the Tm-O-had essentially no observable effect on the compatibility/incompatibility of the tested system. 3-9 SECTION 4 COMPATIBILITY OF HAYNES 25-Tm202/Yb20 4.1 INTRODUCTION Haynes 25 is a cobalt base alloy, which like Hastelloy X, possesses excellent resistance to oxidation at elevated temperatures and to corrosion by seawater. Its principal alloying constituents. In order of decreasing content, are: chromium, tungsten, nickel, iron and manganese. Chemical analysis of the Haynes 25 is given in Appendix A. Compatibility tests were performed on Haynes 25-Tm_0-/ Yb-0-at 600° and 1000°C for times up to 4000 hours. 4.2 EFFECT OF Tm203/Yb203 ON HAYNES 25
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