Effect of heat treatment on structure and properties of sheet semi-finished product made of heat-resistant alloy based on titanium and doped with rare-earth metal

Abstract

This paper is a continuation of studies on the effect of microalloying with gadolinium, a rare earth metal, on the structure formation and properties of a titanium alloy under thermal action. It was previously shown that the introduction of gadolinium into an experimental heat-resistant alloy promotes cast structure transformation and reduces the size of structural components, and affects the rate of growth and nucleation of particles. It has been established that additional alloying of gadolinium has no significant influence on the microstructure formation of hot-rolled sheets made of the heat-resistant experimental alloy after annealing at 950 °C. The structure is represented by equiaxial particles of the primary α-phase, secondary α-phase of lamellar morphology and a small amount of β-phase. It has been established that the ordering processes occur in primary α-phase particles and α2-phase particles are formed during isothermal aging at 700 °C for 100 h with the formation of silicides at the α-β interface. It is shown that the α2 phase is formed in the body of the primary α-phase particles, and its border regions are free from precipitations that is due to their aluminum depletion as a result of β→α transformation. It has been established that the silicide particle size is reduced as the gadolinium content in the alloy increases. The average particle size is 0,2–0,3 μm in the alloy with 0 % Gd, and it is reduced to 0,05–0,1 μm in the alloy with 0,2 % Gd. It was shown that the introduction of 0,2 % of gadolinium into the heat-resistant titanium alloy leads to a decrease in the gas-saturated layer depth, and to an increase in the cyclic durability and short-term strength at 700 °C by 30 %.