EFFECT OF IRON ADDITIONS ON BETA-PHASE STABILITY WITH RESPECT TO ALPHA''-MARTENSITE IN V-28AL-17TI (WT-PERCENT)

The effect of iron additions (up to 7 wt.%) on the beta-b.c.c.-phase stability with respect to alpha" orthorhombic-martensite and the corresponding transformation volume change in a V-28Al-17Ti (wt.%) alloy has been studied using optical microscopy and X-ray diffraction. It was found that iron additions stabilize the beta-phase while the volume change remains positive and relatively high (3-4%). Using a liquid nitrogen refrigeration treatment and introducing cracks into the materials to further test beta-phase stability, and carrying out a thermodynamic analysis, it was found that an addition of 5 wt.% of iron gives rise to the optimum level of stability of the beta-phase. This, in turn, should ensure maximum transformation toughening effects when this alloy is used as a dispersed phase within a gamma-titanium aluminide matrix.