Compatibility of Strontium Compounds with Superalloys at 900 and 1100°C

The compatibility of three strontium compounds (SrTiO₃, Sr₂TiO₄, and SrO) with three superalloys (Haynes alloy No. 25, Hastelloy C, and Type 316 stainless steel) was studied at 900 and 1100°C for periods up to 10 000 h. The Sr₂TiO₄ was compatible under all test conditions, and only slight reaction occurred between SrTiO₃ and the three superalloys. A 2- to 4-mil reaction zone developed between SrO and both Haynes alloy No. 25 and Hastelloy C at 900°C. At 1100°C the reaction was more extensive and also occurred with Type 316 stainless steel; however, the reaction rates became negligibly slow after 5000 h. For commercially produced Hastelloy C or C-276, the reaction with SrO appears to be related to the presence of one or more intermetallic phases. In laboratory heats containing very low silicon but relatively high carbon or in those containing very high silicon, these intermetallics did not form and no attack was observed. A reduction in the room-temperature mechanical properties of Haynes alloy No. 25, Hastelloy C, and Type 316 stainless steel was noted after heat treating at 900 or 1100°C. A further reduction in ductility was found in some of the samples exposed to SrO.