Abstract
Abstract The thermodynamic optimization of Ti-X-Si systems requires that their respective binary systems be constantly updated. The most recent assessments of the Ti-Si phase diagrams used three sublattices to describe the Ti5Si3 phase. The stable version of this phase diagram indicated the presence of Ti(β)+Ti5Si3→Ti3Si and Ti(β)→Ti(α)+Ti3Si reactions in the Ti-rich corner, while the metastable version featured the presence of a Ti(β)→Ti(α)+Ti5Si3 reaction. The present investigation assessed these phase diagrams using two sublattices to describe the Ti5Si3 phase in order to simplify the optimization of Ti-X-Si systems.
Highlights
There is a technological interest in the Ti-Si system promoted by the beneficial effect of Si addition for the oxidation and creep resistance of Ti-X-Si alloys (Azevedo, 1996)
Employed an optimization method for the determination of the variables used for the thermodynamic description of the phases in order to assess the Ti-Si phase diagram from selected experimental data. They described, for instance, the Ti5Si3 phase as a nonstoichiometric compound containing three sublattices, (Ti)3(Ti,Si)2(Si,Ti)3, to represent its D88 crystal structure. Their calculated phase diagram was in good agreement with previous calculated (Murray, 1987) and experimental (Svechnikov et al, 1971) phase diagrams, presenting Ti3Si as the stable phase of the eutectoid reaction
The present work will calculate and compare the Ti-rich corner of the stable and metastable Ti-Si phase diagrams, using two sublattices, (Ti,Si)5(Si,Ti)3, to describe the Ti5Si3 phase, assuming that Ti3Si is the stable phase in the eutectoid decomposition of Ti(β) phase
Summary
There is a technological interest in the Ti-Si system promoted by the beneficial effect of Si addition for the oxidation and creep resistance of Ti-X-Si alloys (Azevedo, 1996). Employed an optimization method for the determination of the variables used for the thermodynamic description of the phases in order to assess the Ti-Si phase diagram from selected experimental data They described, for instance, the Ti5Si3 phase as a nonstoichiometric compound containing three sublattices, (Ti)3(Ti,Si)2(Si,Ti), to represent its D88 crystal structure. Their calculated phase diagram was in good agreement with previous calculated (Murray, 1987) and experimental (Svechnikov et al, 1971) phase diagrams, presenting Ti3Si as the stable phase of the eutectoid reaction. The present work will calculate and compare the Ti-rich corner of the stable and metastable Ti-Si phase diagrams, using two sublattices, (Ti,Si)5(Si,Ti), to describe the Ti5Si3 phase, assuming that Ti3Si is the stable phase in the eutectoid decomposition of Ti(β) phase. These results will be compared to previous calculated phase diagrams using three sublattices to describe the Ti5Si3 phase (Cost, 1998; Fiori et al, 2016)
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