Evaluation of Ti 3 Si Phase Stability from Heat-Treated, Rapidly Solidified Ti-Si Alloys
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ection I: Basic and Applied Research
Evaluation of Ti 3 Si Phase Stability from Heat-Treated, Rapidly Solidified Ti-Si Alloys Alex Matos da Silva Costa, Gisele Ferreira de Lima, Geovani Rodrigues, Carlos Angelo Nunes, Gilberto Carvalho Coelho, and Paulo Atsushi Suzuki
(Submitted May 6, 2009; in revised form July 5, 2009) Ti-base alloys containing significant amounts of silicon have been considered for high temperature structural applications. Thus, information concerning phase stability on the Ti-Si system is fundamental and there are not many investigations covering the phase stability of the Ti3Si phase, specially its dependence on oxygen/nitrogen contamination. In this work the stability of this phase has been evaluated through heat-treatment of rapidly solidified Ti-rich Ti-Si alloys at 700 °C and 1000 °C. The rapidly solidified splats presented nanometric scale microstructures which facilitated the attainment of equilibrium conditions. The destabilization of Ti3Si due to oxygen/nitrogen contamination has been noted.
Keywords
silicides, Ti alloys, Ti-Si system, Ti3Si
1. Introduction Due to their high mechanical strength and low density (55% of steels), Ti-based alloys have been considered for structural applications at temperatures near 700 °C. Several of these alloys have compositions with significant amounts of Si[1-5] and thus, accurate knowledge of the phase relations in the Ti-Si system, especially in the Ti-rich region is of fundamental importance. The Ti-Si phase diagram shown in Fig. 1[6] indicates the following stable solid phases in the Ti-rich region: (1) terminal aTi-hcp and bTi-bcc solid solutions; (2) Ti3Si; (3) Ti5Si3; and (4) Ti5Si4. Among the investigations of this system, there are few focusing on the stability of the Ti3Si phase. Wakelkamp et al.[7] carried out experiments with Ti-Si alloys and proposed that oxygen contamination played an important role on destabilizing this phase. Suryanarayana et al.[8] carried out heat treatment at Alex Matos da Silva Costa, Carlos Angelo Nunes, and Paulo Atsushi Suzuki, Departamento de Engenharia de Materiais (DEMAR), Escola de Engenharia de Lorena (EEL), Universidade de Sa˜o Paulo (USP), Caixa Postal 116, 12600-970, Lorena, Sa˜o Paulo, Brazil; Gisele Ferreira de Lima, Departamento de Engenharia de Materiais, Centro de Cieˆncias Exatas e de Tecnologia, Universidade Federal de Sa˜o Carlos, Rod. Washington Luiz, Km 235, Caixa-Postal: 676, 13565-905, Sao Carlos, Sa˜o Paulo, Brazil; Geovani Rodrigues, UniFoa, Centro Universita´rio de Volta Redonda, Nu´cleo de Pesquisa, Campus Treˆs Poc¸os, Avenida Paulo Erlei Alves Abrantes, 1325, Bairro treˆs Poc¸os, 27240-560, Volta Redonda, Rio de Janeiro, Brazil; Gilberto Carvalho Coelho, Departamento de Engenharia de Materiais (DEMAR), Escola de Engenharia de Lorena (EEL), Universidade de Sa˜o Paulo (USP), Caixa Postal 116, 12600-970, Lorena, Sa˜o Paulo, Brazil and UniFoa, Centro Universita´rio de Volta Redonda, Nu´cleo de Pesquisa, Campus Treˆs Poc¸os, Avenida Paulo Erlei Alves Abrantes, 1325, Bairro treˆs Poc¸os, 27240
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