0435380 - ÚFM 2015 RIV DE eng J - Journal Article
Hasegawa, M. - Nomura, T. - Haga, H. - Dlouhý, Ivo - Fukutomi, H.
Microstructural control of Ti-46Al-7Nb-0.7Cr-0.2Ni-0.1Si alloy by heat treatment.
International Journal of Materials Research. Roč. 105, č. 11 (2014), s. 1075-1083. ISSN 1862-5282. E-ISSN 2195-8556
Institutional support: RVO:68081723
Keywords : titanium aluminides * phase transformation * microstructure
Subject RIV: JG - Metallurgy
Impact factor: 0.639, year: 2014
http://www.hanser-elibrary.com/doi/abs/10.3139/146.111115

The effects of holding temperature, time and cooling rate on the microstructure of Ti-46Al-7Nb-0.7Cr-0.2Ni-0.1Si (at.%) alloys are studied. Three kinds of segregations are found in the as-cast material. In back scattered elektron images these segregations are observed as dark regions formed by the solidification process, bright regions with irregular shaped blocks and imaged regions of lighter kontrast formed by the cooling process from b phase to a phase and from a phase to (b + c) two phase or (a + b + c) three phase, respectively. Addition of small amounts of Cr, Ni and Si to the Ti-45Al-7Nb alloy shifts the (b + c) two phase state and (a + c + b) three phase state to a lower Nb concentration range. While cooling from the a single phase state to the (b + c) two phase or (a + b + c) three phase states, sequential type phase transformation occurs. The amounts of Cr, Ni and Si are too small to induce the pearlitic mode of transformation. Therefore, the sequential mode of the ternary alloy containing Nb occurs. The microstructures change depending on the cooling rate from a single phase region. Massive transformation occurs in the range of 300 K s–1 to 50 K s–1. However, the a phase is partially retained at the cooling rate of 300 K s–1. A fully lamellar structure appears at cooling rates lower than 10 K s–1.
Permanent Link: http://hdl.handle.net/11104/0239282