Search for a command to run...
Problem. Currently, in the field of research on alloys based on orthorhombic Ti 2AlNb aluminide, there are no data on the relationship between heat treatment modes, structural parameters, and mechanical characteristics to ensure a balance of strength and ductility. Aim. To establish the relationship between heat treatment modes, microstructural characteristics (O-phase sizes, α2-phase volume fraction) and mechanical characteristics at room temperature, as well as to determine the heat treatment mode that provides the best balance of strength and ductility for the VTI-4 alloy. Methods. In this work, the method of isothermal multidirectional forging was applied to form a fine-grained globular structure in order to improve the ductility characteristics of the alloy. Subsequent two –stage heat treatment was carried out in the α2+β+O-phase region. Mechanical characteristics were determined by tensile testing. Results. The influence of quenching and aging temperature on the size and volume fraction of α2 and O-phase particles was investigated. The choice of heat treatment modes aimed at forming a structure that ensures high strength and ductility properties of the VTI-4 alloy is substantiated. It was established that when heating for quenching to T=900 °C, O-phase precipitates are retained at triple junctions along β-grain boundaries; during subsequent aging, O-phase particles and interlayers are formed, the thickness of which increases with rising temperature, leading to a decrease in strength and ductility. It was also established that heating for quenching from the upper part of the α2+β+O-phase region (T=960 °C) preserves the globular microstructure, leading to the dissolution of O-phase particles and, accordingly, saturating the β-phase with alloying elements. Increasing the quenching temperature also reduces the volume fraction of α2-phase particles and prevents the formation of O-phase interlayers along β-grain boundaries during aging in the temperature range of 760–800 °C. Conclusions. The study of the influence of aging temperature in the range of 760–840 °C revealed that the lower the temperature, the smaller the thickness of O-phase particles, the higher the strength, and the lower the ductility. The optimal heat treatment mode was determined: quenching at T=960 °C for τ=2 h and aging at T=800 °C for τ=6 h. After such heat treatment, the wrought VTI-4 alloy demonstrates high strength and ductility (σ0.2=1180 MPa, σв=1300 MPa, δ=6.2 %).