THE EFFECT OF HOT ROLLING ON THE MECHANICAL PROPERTIES AND EVOLUTION OF THE MICROSTRUCTURE OF VT20 ALLOY AND TIB-REINFORCED COMPOSITES BASED ON TiB

Microstructural changes and mechanical properties of titanium alloy VT-20 and a composite based on it containing 3 wt are investigated. % TiB2 in the initial charge subjected to hot rolling at a temperature of 800 °C with an accumulated degree of deformation of 80 %. In the initial cast state, the matrix is characterized by a two–phase structure (α + β), and the reinforcing phase in the composite is represented by TiB boride fibers with an average length of about 25 ‒ 30 microns and a length–to-diameter ratio of L/D ≈ 10 ‒ 12, which provides higher strength, but at the same time leads to embrittlement. Hot rolling leads to the grinding of the structure of the VT-20 alloy and the composite based on it. Intense fragmentation of TiB fibers is observed in the composite: the average length decreases approximately to 4-5 microns, the L/D value decreases to 2 ‒ 3, while the borides are distributed more evenly throughout the sample volume. The change in structure is accompanied by a significant increase in mechanical properties: at room temperature, the strength of the rolled composite reaches 1130 MPa compared to 1000 MPa for the initial alloy, which is explained by the grinding of borides along the length and structure of the matrix, which leads to hardening. At a temperature of 700 °C, the composite retains a significantly higher tensile strength (290 MPa versus 180 MPa for alloy), while the elongation of the composite is lower, but remains acceptable for many high-temperature applications (180 % for composite versus 320 % for alloy).