INCREASED STRENGTHENING OF AUSTENITIC ALLOYS THROUGH DUAL AGING

Abstract

A study of the effect of solution treatment, single and duplex isothermal aging heat treatments on an Fe-Ni-Ti-Al austenitic alloy hardened by ..gamma..' precipitation is reported. Sequential heat treatments were performed and studied in order to develop a systematic process for achieving very high strength austenite through thermal processing alone. Room temperature tensile tests were carried out. Alloys receiving double aging treatments were found to achieve mechanical properties superior to those aged at a given temperature. An optimum level of yield strength (172 Ksi) along with good elongation (20%) was obtained from a two-step aging process. Structural examination indicated that overaging was retarded by secondary aging. The formation and growth of cellular precipitates were suppressed. Resistivity changes were measured on wire specimens to study the early stages of precipitation. Resistivity peaks were observed during secondary aging indicating evidence of secondary precipitation.