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SCREENING AND SELECTION OF CANDIDATE SHEET ALLOYS. PART 2
Final technical rept.
TITANIUM METALS CORP OF AMERICA NEW YORK
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Three alloys were selected as being suitable for addition of elements designed to bring about precipitation hardening Ti-17V-10Cr-3Al, Ti-8Mo-8V-7. 5Fe-3Al and Ti-15Mo-5Fe-3Al. Addition of 0.5-1Si to Ti-17V-10Cr-3Al followed by water quenching from solution temperatures of around 2000F and aging at 1150- 1250F, produced Vickers hardness increases of up to 100 points upon aging without visible microstructural change. Although precipitation hardening of a stable beta alloy was thus achieved, grain growth and embrittlement were encountered because of the high temperatures required to dissolve the silicide. Work was then redirected toward development of two other types of alloy a moderate strength stable beta alloy, and a high strength metastable beta alloy hardenable by alpha precipitation. Two stable beta alloys, Ti-17V-10Mn-3Al and Ti-8Mo-8V-6Fe-3Al, and two metastable beta alloys, Ti-17V-4Fe-3Al and Ti-8Mo-8V- 2Fe-3Al were evaluated. However, the stable beta alloys had brittle welds, and work on these was discontinued. They were replaced by stabilized alloys, metastable alloys aged at 1100-1200F to suppress the maximum aging response and reach a strength plateau. Four such alloysTi-8Mo-8V-5Co-3Al, Ti-17V-7.5Co-3Al, Ti-17V-2Fe-2Co-3Al and Ti-8Mo-8V-2Fe-3Al - were evaluated in this condition. Ti-8Mo-8V-2Fe-3Al proved to be best of the high strength metastable beta candidates. On a basis of smooth and notched tensile properties at room temperature and 600F, creep stability and stress corrosion resistance, Ti-8Mo- 8V-2Fe-3Al was selected for mill production.
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