Diffusive and displacive phase transitions in Ti–Fe and Ti–Co alloys under high pressure torsion

• Published in: Journal of alloys and compounds 2018-02, Vol.735, p.2281-2286
• Main Authors: Straumal, B.B., Kilmametov, A.R., Ivanisenko, Yu, Mazilkin, A.A., Valiev, R.Z., Afonikova, N.S., Gornakova, A.S., Hahn, H.
• Format: Article
• Language: English
• Subjects: Cobalt base alloys; Decomposition of solid solution; Eutectoid temperature; Ferrous alloys; High-pressure torsion; Intermetallic compounds; Intermetallic phases; Iron compounds; Lattice parameters; Mass transfer; Phase transitions; Solid solutions; Studies; Titanium alloys; Titanium base alloys; Titanium compounds; Ti–Co alloys; Ti–Fe alloys; Torsion
• ISSN: 0925-8388; 1873-4669
• DOI: 10.1016/j.jallcom.2017.11.317

The high pressure torsion (HPT) of Ti–4 wt. % Fe and Ti–4 wt. % Co alloys has been studied. Before HPT, the samples were annealed above and below the temperature of eutectoid transformation. After quenching, the first samples contained a mixture of α and β phases. The latter samples contained a mixture of α-Ti saturated with Fe or Co and respective intermetallic phases TiFe. During HPT the high-pressure ω-phase formed in all samples. The amount of ω-phase was higher when the initial samples contained the α+β mixture then in the case of α+TiFe or α+Ti2Co mixture. Most probably, the martensitic β→ω transformation occurs easier than the α→ω one. The amount of ω-phase was higher in Ti–Fe alloy than in the Ti–Co alloy for both initial states. It seems that cobalt additions disadvantageously change the lattice parameters in Ti for martensitic β→ω and α→ω transformations. The phase transformations with mass transfer (diffusive ones) also take place by HPT of Ti–Fe and Ti–Co alloys. Both α-based solid solutions partially decomposed after HPT. After HPT, the lattice parameters of α-phase containing cobalt or iron changed towards those of pure α-Ti. It has been observed for the first time that the composition of TiFe phase also changes after HPT. [Display omitted] •High pressure torsion (HPT) of Ti–Fe and Ti–Co alloys leads to the formation of ω-phase.•The amount of ω-phase was higher in initial samples with α+β mixture then in those with α+TiFe or α+Ti2Co mixture.•The amount of ω-phase was higher in Ti–Fe alloy than in the Ti–Co alloy for both initial states.•Both α-based solid solutions partially decomposed after HPT.