The Effect of Heat Treatment on the Mechanical Properties of Ti-10V-2Fe-3Al

Abstract

The effect of heat treatment on strength and fracture toughness of Ti-10V-2Fe-3Al, a near β titanium alloy, was studied. Fatigue properties were also investigated using heat treated specimens specified by Aerospace Material Specifications.
(1) Aging at 490°C for 8 h after solution treatment at 760°C gives the best combination of strength and fracture toughness. However, aging under the same conditions after solution treatment at 785°C decreases ductility. This is considered to have occurred because the treatment at 785°C produces small amounts of primary α phase, which contributes to ductility, than that at 760°C, resulting in a larger amounts of secondary α phase, which contributes to strength.
(2) Agings treatments at 400°C for 8 h and 600°C for 8 h after solution treatment at 760°C cause embrittlement and overaging, respectively. The embrittlement caused by 400°C aging may not come from ω phase but rather from the existence of very fine secondary α particles.
(3) Fracture toughness obtained under as-solution treated condition is lower than that estimated from the relationship between strength and fracture toughness for materials produced with aging after solution treatment. Therefore, an adequate aging is indispensable for obtaining the high strength and high fracture toughness expected from this alloy.
(4) By aging at 490°C for 8 h, a fatigue strength as high as 666 MPa can be obtained. Low cycle fatigue strength is given by the equation;
Δε_t=4.589(N_f)^-1.24+0.0514(N_f)^-0.136
Fatigue crack growth rate is given by the equation
da/dN=3.54×10^-9(ΔK)^3.62
and ΔK_th is 4.4 MPm.