Effect Of Nb Additions On Phase Formation In Ll(2) Type Al3ti-8mn-Based Alloys

The microstructure of a monolithic Ll(2)Al(67)Mn(8)Ti(25) compound changes significantly when modified with a small amount of Nb (0.2 similar to 4.0at%) and with corresponding adjustments to the Ti and Al contents. In 32 experimental alloys near the Al3Ti-8Mn composition region of the Al-Ti-8Mn-Nb quaternary system, five multiphase regions, Ll(2)+Al2Ti, Ll(2)+DO22, Ll(2)+Ll(0), Ll(2)+Al2Ti+DO22 and Ll(2)+Al2Ti+Ll(0) formed adjacent to the original Lit single phase. When Ll(2) content keeps constant, the plate-like or netty Al2Ti phase precipitates appear with the decrease of Al/Ti ratio. The ripple-like Ll(0)AlTi phase may appear in the alloys contained higher Nh contents. A room temperature constitutional diagram near the Al3Ti-8Mn region of Al-Ti-Nb-8Mn quaternary system has been determined.