The effect of alloying elements, Nb and Mn on massive transformation in Ti-45Al based alloys was studied. The alloy samples were heat treated at 1350 °C for 30 minutes and subsequently cooled to room temperature by furnace cooling, air cooling, and water quenching. The microstructural evolution in various alloys was investigated by a detailed microstructural characterization of the heattreated samples by optical, scanning, and transmission electron microscopy. It was observed that the volume fraction of the massively transformed gamma in water-quenched samples increased from nil in the Mn-free alloy to ϳ70 pct in the alloy containing 2 at. pct Mn. Nb had a minimal effect on the extent of transformation. The effects of Nb and Mn have been rationalized on the basis of the site occupancy of the alloying elements and their possible influence on the phase boundaries and grain size. An attempt has also been made to elucidate the mechanism of massive transformation in these alloys. Based on the results obtained, the influence of Mn and Nb on the kinetics of massive transformation is presented and discussed and, the CCT diagrams for different alloys used in this study are proposed.

No abstract

The phenomenon of grain growth in the a phase eld and the effect of annealing time/grain size on the formation of lamellar microstructure upon subsequent cooling was studied in Ti -45Al -2Nb -0 . 4Mn and Ti -45Al -2Nb alloys. The grain size of both alloys increased with annealing time and the grain growth exponent of Ti -45Al -2Nb -0 . 4Mn and Ti -45Al -2Nb at 1350 C was observed to be 0 . 52 and 0 . 38, respectively. The difference in the grain growth exponent values has been attributed to the initial grain size and the grain boundary morphology. Interlamellar spacing in the lamellar microstructure, which formed upon furnace cooling from the a phase eld, was also observed to increase with increase in annealing time, i.e. interlamellar spacing increased with increase in grain size.MST/5845

The influence of minor elements, viz., C, B and P, present either individually or in combination, on HAZ micro-fissuring susceptibility of Inconel718 Superalloy was studied. The microfissuring susceptibility was evaluated by hot ductility testing in a Gleeble 1500 system and by the measurements of cracks in HAZs around electron beam welds. It was then correlated to the microstructure of the alloys and the segregation of minor elements to the grain boundaries. It was observed that B affected the HAZ micro-fissuring susceptibility very adversely, but the influence of C was only marginal. The addition of P to the B containing alloy made it more susceptible. However, the addition of C to both the B, and B and P containing alloy was beneficial in reducing the HAZ micro-fissuring susceptibility. The influence of minor elements could be reasonably explained by the segregation and/or formation of precipitates on grain boundaries. Superalloys 2ooo Edited by T.

No abstract