Relationships between interstitial content, microstructure and mechanical properties in fully lamellar Ti-48Al alloys, with special reference to carbon

Carbon effects on microstructural and mechanical properties of Ti-48Al fully lamellar alloy are studied for increasing concentrations from 20 to 6000 wt.ppm. The lamellar structure is obtained for alloys slowly cooled (35 degreesC/mn) from 1350 degreesC. Carbon in solid solution increases lattice parameters of the alpha (2) phase. In the experimental conditions of this study, the solubility limit of carbon is 3000 wt.ppm. For higher carbon contents, Ti2AlC (H phase) precipitates in the gamma phase, leading to grain size decrease. Carbon in solid solution increases the alpha (2) Volume fraction, microhardness, yield stress and decreases the minimum creep rate. Precipitation of the H phase does not modify these parameters except yield stress which increases still further. Comparison is made with previous results obtained from alloys with similar contents of either oxygen or nitrogen. Emphasis is put on the importance of alpha (2) phase hardening by solute interstitial elements on the mechanical properties of lamellar alloy. (C) 2001 Published by Elsevier Science Ltd. All rights reserved.