Federal State Unitary Enterprise “All-Russian Scientific-Research Institute of Aviation Materials” of National Research Center “Kurchatov Institute” (NRC “Kurchatov Institute” – VIAM), Moscow, Russia

A. A. Shiryaev, Senior Researcher, Candidate of Technical Sciences, e-mail: shiryaev_aa84@mail.ru
A. V. Zavodov, Senior Researcher, Candidate of Technical Sciences , e-mail: zavodovad@gmail.com
V. V. Avtaev, Senior Engineer, e-mail: darkee@mail.ru
N. A. Nochovnaya, Counselor to Director General, Doctor of Technical Sciences, e-mail: nochovnaya_viam@mail.ru

The article presents the results of thermal stability investigation for the structure and mechanical properties of rolled semi-finished products from metastable β-titanium alloy VT47 after hardening heat treatment and subsequent thermal exposure with the application of tensile stresses. It has been established that the change in the mechanical properties of the VT47 alloy during thermal exposure at tensile stresses close to the values of the longterm strength limit is due to the development of twinning processes in the secondary α phase lamellae. This is also actual for semi-finished products with 12 mm thickness wherein the formation of TiCr₂ nano-sized particles with lamellar morphology is observed in microvolumes of residual β phase, the particles belonging to the group of Laves phases (type C36). During the analysis of the mechanical properties after long-term exposure, a high correlation relationship (R² ≥ 0.89) was established between the yield strength (σ_0,2), integral work of destruction (W), uniform tensile elongation (δ_u) and stress applied during thermal exposure (σ³⁵⁰). The studies have shown that the application of stresses not higher than 0.7...0.8 of σ₁₀₀³⁵⁰ during thermal exposure at a temperature of 350 оС allows to retain a high level of the VT47 alloy plasticity. Based on the obtained results, it follows that the VT47 alloy has a high level of bulk thermal stability of mechanical properties (without taking into account the effect of surface oxidation) under load during thermal exposure within the recommended values, approximately corresponding to the level of the alloy creep strength values at the selected temperature. The level of mechanical properties thermal stability of the alloy VT47 corresponds to that of the metastable β-titanium alloys VT32 and VT35, and significantly exceeds the characteristics of the first generation metastable β-titanium alloy VT15.

This work was carried out as part of the implementation of complex scientific direction 9.2 “Titanium-based materials with regulated β structure” (“Strategic directions for the development of materials and technologies for their processing for the period until 2030”).

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