Effect of the Multiscale Lamellar on Mechanical Properties of TC21 Titanium Alloy

TC21 titanium alloy with high strength and toughness was selected, and the heat treatment process of "Step-quenching" was used to regulate and optimize the multi-scale lamellar microstructure and its mechanical properties. The microstructure morphology, fracture morphology and cross-section crack propagation morphology of multi-scale lamellar microstructure were investigated by SEM and TEM. The results show that the isothermal quenching temperature has a strong influence on the a phase precipitation behavior and the mechanical properties of the alloy. The samples were solution treated at 930 degrees C for 1 h, and then step-quenched at temperature of 0 degrees C to 600 degrees C for 2 h, and cooled to room temperature. With the increase of temperature, the width of secondary alpha lath phase gradually increases, and the hardness first increases and then decreases slightly, among which the hardness at 400 degrees C being the highest. The samples were solution treated from 880 degrees C to 960 degrees C for 1 h and aged at 400 degrees C for 2 h with water cooling to room temperature. Thus, coarse lamellar, multi-scale lamellar and fine lamellar microstructures were obtained, and the hardness and strength of the alloy increase successively. However, due to its tortuous crack propagation path and crack deflection characteristics, the multi-scale lamellar microstructure shows excellent crack propagation resistance (K-Q=104 MPa.m(1/2)), which is significantly higher than those of the coarse lamellar (K-Q=67 MPa.m(1/2)) and the fine lamellar microstructure (K-Q=33 MPa.m(1/2)).