STRUCTURE PROPERTY OBSERVATIONS FOR AL-TI-CR ALLOYS NEAR THE CUBIC (AL,CR)3TI PHASE

The nature of the six phases surrounding the cubic Al3Ti phase has been determined for Al-Ti-Cr alloys hot isostatically pressed at 1473 K. The cubic phase itself is stable from 7 to 13 at.% Cr for alloys with the titanium level at the stoichiometric 25 at.% and the field is at least 4 at.% wide in titanium. Hardness profiles for alloys containing 23, 25 and 27 at.% Ti indicate that the off-stoichiometric levels of titanium cause strengthening of the cubic phase, with a minimum in hardness near the tetragonal/cubic solvus at 8 at.% Cr and 25 at.% Ti. Excess titanium causes greater strengthening of the cubic phase than does a deficiency of titanium. Second phases such as Al3Ti, AlCr2 and TiCrAl embrittle the cubic matrix, as does the porosity that forms readily during conventional heat treatment. In general, hot isostatic pressing prevents the formation of porosity and improves the cracking resistance of Al-Ti-Cr alloys.