An experimental assessment of the effects of heat treatment on the microstructure of Ti-47Al-2Cr-2Nb powder compacts

作者：Berteaux O^*; Popoff F; Thomas M

来源：Metallurgical and Materials Transactions A-Physical Metallurgy and Materials Science, 2008, 39A(10): 2281-2296.

DOI：10.1007/s11661-008-9578-2

A detailed and systematic microstructural characterization has been carried out on a Ti-47Al-2Cr-2Nb (at. pct) intermetallic alloy processed by powder metallurgy (PM). Heat-treatment parameters such as isothermal temperature, holding time, and cooling rate were varied in order to produce a series of near-gamma, duplex, and fully lamellar microstructures. These were then quantitatively analyzed in terms of grain size, surface fraction, lamellar spacing, second-phase spatial distribution, and serrated grain boundary morphology. Owing to these extensive quantitative image analyses, several unusual microstructural features occurring in this well-known TiAl-based alloy were identified and assessed. First, a dissolution of the smallest gamma grains was emphasized in subtransus conditions as the isothermal temperature or holding time was increased. Second, the competition that occurs between the alpha double right arrow alpha + gamma transformation and the direct-ordering alpha double right arrow alpha(2) reaction upon cooling from above the alpha-transus temperature is mainly governed by the reduction in chemical free energy. Third, new grains were found to nucleate upon cooling, which is presumably induced by a minimization of interfacial energy at prior alpha grain boundaries. Finally, new gamma grains were formed as a result of the coarsening of primary gamma lamellae under furnace-cooled (FC) conditions.

• 出版日期2008-10