Influence of alloying elements on the kinetics of massive transformation in gamma titanium aluminides
- PDF / 2,390,388 Bytes
- 14 Pages / 606.24 x 786 pts Page_size
- 26 Downloads / 287 Views
11/9/03
3:35 PM
Page 2053
Influence of Alloying Elements on the Kinetics of Massive Transformation in Gamma Titanium Aluminides U. PRASAD and M.C. CHATURVEDI 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 70 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.
I. INTRODUCTION
TIAL-based two-phase titanium aluminide alloys have long been considered to be suitable candidates for hightemperature structural applications, mainly because of their high specific strength and modulus, and good hightemperature strength retention properties.[1–5] Unfortunately, these attractive properties are invariably accompanied by low room-temperature ductility and fracture toughness, and this restricts the usage of these alloys. Various efforts have been and are being made to overcome these drawbacks, to enhance the effective use of these alloys. A number of alloys of engineering importance based on Ti-(45-48)Al, with an appropriate combination of ternary and quaternary alloying elements (Cr, Mn, V, Nb, Ta, etc.), have been identified and developed through intensive research over the past two decades. These are two-phase alloys containing a2 and g phases. The proportion and morphology of the constituent phases in the microstructure can be varied significantly by altering the composition of the alloy and their processing techniques. The mechanical properties are strongly dependent on microstructure, and an optimum balance of all the mechanical properties can be achieved by controlling the proportion of different phases and also by controlling the grain size. The microstructural modifications can be brought about by varying the alloy chemistry and alloy processing and by thermal and thermomechanical treatments. U. PRASAD, Postdoctoral Fellow, and M.C. CHATURVEDI, Professor and Canada Research Chair, are with the Department of Mechanical Engineering, University of Manitoba, Winnipeg, MB, Canada R3T 5V6. Contact e-mail: [email protected] This article is based on a
Data Loading...
