EFFECT OF HIP TEMPERATURES ON THE MICROST RUCTURE AND MECHANICAL-PROPERTIES OF CARBIDE DISPERSED TI-48AL-1MN MECHANICALLY ALLOYED COMPACTS

The effect of hot isostatic pressing (HIP) temperature on the microstr ucture and mechanical properties of Ti-48 mol%Al-1 mol%Mn compacts fab ricated by mechanical alloying was investigated. N-heptane was used as a process control agent for the mechanical alloying. The compacts HIP treated at 1173, 1373 or 1573 K showed an ultra-fine equiaxed grain s tructure, i.e., a microduplex structure, consisting of TiAl (gamma) an d Ti2AlC phases, and their average grain sizes were 185 nm, 510 nm and 1.5 mu m, respectively. The gamma phase was considered to be formed b y an alpha-->gamma massive transformation during heating. On the other hand, the compacts HIP treated at 1623 or 1673 K showed quite differe nt microstructures from the above HIP compacts. The 1623 K-HIP compact was composed of equiaxed gamma grains, whose size was approximately 1 1.5 mu m, rectangular shaped Ti2AlC particles, and a small amount of t he grain boundary nucleated alpha phase. Although the 1673 K-HIP compa ct showed a microstructure similar to the 1623 K-HIP compact, the gamm a grains were coarsened to be approximately 27.8 mu m in diameter and the Ti2AlC particles were more elongated rectangles. Furthermore, the amount of the grain boundary nucleated ct phase was increased and the lamella alpha phase nucleated at gamma twin boundaries was observed in the 1673 K-HIP compact. Mechanical properties determined by compressi ve testing at various temperatures made clear that the compacts HIP tr eated at 1173, 1373 or 1573 K have good workability at elevated temper atures and those HIP treated at 1623 or 1673 K have good high temperat ure strength. These mechanical properties were influenced significantl y by the microstructure, especially by the grain size and morphology o f the Ti2AlC phase.