Effect of microstructure on the tensile properties and impact toughness of TC21G titanium alloy

Based on TC21 alloy, the modified TC21G alloy with excellent comprehensive mechanical properties was designed. The influences of the double annealing process on microstructure and mechanical properties of TC21G alloy were investigated. The quantitative relationship between microstructure parameters, strength and impact toughness was established. Microstructural evolution with different double annealing conditions was characterized using SEM, TEM and EBSD. Results show that with reducing the cooling rate of first annealing, the size and content of the equiaxed and lamellar alpha phase both increased, and the width of the secondary alpha phase was increased, whereas the content of the fine acicular secondary alpha phase was decreased. Meanwhile, the fraction of high angle grain boundaries increased with reducing the cooling rate. The fine acicular secondary alpha phase was beneficial to improve the strength of TC21G alloy. Microstructural parameters of the equiaxed and lamellar alpha phase play a dominant role in improving ductility with reducing the cooling rate. Moreover, the crisscross lamellar and equiaxed alpha phase, the fraction of high angle grain boundaries are the main factors affecting impact toughness.