Investigation On Microstructure And Mechanical Property Of Ti-62A Alloy Plate

The effects of heat treatment on tensile properties and the damage tolerance behavior of Ti-62A alloy 30mm plate are investigated. The relationships between microstructure, tensile properties, fracture toughness and rate of fatigue crack propagation (FCG) of the alloy are researched systematically. The crack propagation of FCG and plane strain fracture is revealed by OM and SEM.The experimental results show that the typical microstructure of the plate as rolled is lamellar structure. The microstructure inα/βsolution and aging condition is lamellar structure. With increasing solution temperature, the primary a (αp) phase content decreased, and the thickness of the secondary a (as) phase increased in the same aging condition. The microstructure inβsolution and aging condition is widmanstatten structure. In the same solution treatment condition, the thickness of as phase increased when the aging temperature and aging time increased.For the lamellar structure, the strength decreased by the factors that make the thickness of as phase increased, such as the increased of solution/aging temperature and aging time. But there are some anomalies, when the aging temperature increased, the tensile strength increased and then decreased, reached the maximum at 560℃.Fracture toughness and the yield strength of the alloy showed the opposite trend when the solution temperature and aging temperature changed. When the yield strength increased, fracture toughness decreased. The fracture toughness and the yield strength of the alloy showed the same trend when aging time changed.Compared the three typical microstructure in this paper, widmanstatten structure has the highest strength and fracture toughness, but ductility is the lowest. Large plastic deformation of a colonies is observed in both sides of the plane strain fracture crack. The plane strain fracture crack propagation path is most tortuous. Lamellar microstructure has good tensile properties and damage tolerance properties. Slight plastic deformation of as phase is observed in both sides of the plane strain fracture crack. The tortuous level of plane strain fracture crack in lamellar structure is between the other two structures. Equiaxed structure has the best ductility, lowest strength and KIC. The crack bypass or pass through the equiaxed a-phase. In equiaxed structure, the crack propagation path is relatively straight.Compared with lamellar structure, widmanstatten structure has lower fatigue crack growth rate. In lamellar structure, the fatigue crack directly through theαp phase. Secondary cracks were found in the interface of as phase,αp phase and in theαp phase. The crack propagation path is relatively straight. The crack parallel to, perpendicular to or has a certain angle with the a colonies in widmanstatten structure. The crack propagation path is more tortuous than that in the lamellar structure.