Enhancement of the Creep Resistance of Metals.
Final rept. 15 Sep 70-15 Sep 71,
MARTIN MARIETTA CORP DENVER COLO DENVER DIV
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Creep data are reported for three materials titanium 6Al-4V, Haynes 188, and 321 steel. In all threee cases, a specimen which had been prestressed below the proportional limit and whose surface layer had been eliminated creeps at much lower rates compared to untreated ones. The ratio, R, of creep rates in untreated and treated specimens decreases with stress and reaches a value of 1 at the proportional limit where the surface layer is completely reformed in the treated specimen. Ratios of 4 in titanium 6Al-4V at 600F, 14 in 321 steel at 1200F, and 14 in Haynes 188 at 1600F are reported at the lowest stresses investigated. The improvements are independent of method of prestressing in tension or in bending or by shot-peening and removal of surface layer stress room temperature stress relaxation or high temperature relaxation, chem-milling. A model is proposed to explain the mechanism by which such large improvements are obtained. This model considers a specimen as a composite of surface and core with workhardening and recovery occurring in both parts. Author
- Properties of Metals and Alloys