Effect Of Forging And Heat Treatment Processing On Mechanical And Ballistic Properties Of TC21 Titanium Alloy

TC21 titanium alloy is a new alpha+beta alloy with high strength, ductility and toughness which developed in China. This paper carried out study on the quasi-static, dynamic and ballistic performance of TC21 titanium alloy under different forging technique and heat treatment processing as armor application background, and systematic study damage characteristic with different microstructures under the 12.7mm armor-piercing incendiary(API). Effect of microstructures on quasi-static, dynamic mechanical, ballistic property and damage characteristic was investigated. The main results and conclusions are as follows:The α+β region forged TC21 alloy obtain bimodal microstructure which β region forged TC21 alloy achieve lamella microstructure. The α+β region forged TC21 alloy has higher dynamic strength but lower dynamic failure strain than the β region forged TC21 alloy. In the ballistic impact experiment, the α+β region and β region forged TC21 alloy show similar ballistic impact property. The analyze of damage characteristic show that: In the bimodal microstructure, spall fragments induced by ductile hole formation is the failure mode; while in the lamellar microstructures, the TC21 targets fail by the type of brittle fragmentation. The failure mechanism involved in these two types microstructure of TC21 alloy is facilitated by initiation and propagation of adiabatic shear bands and cracks induced by adiabatic shear bands.Varying thermal treatment processings for TC21 alloy resulted in four kinds of microstructures, there are 900℃/1h/AC+ 600℃/4h/AC bimodal microstructure(B1), 925℃/1h/FC+600℃/4h/AC bimodal microstructure(B2), 900℃/6h/SFC equiaxed microstructure(E) and 1000℃/1h/FC lamella microstructure(L). On quasi-static condition, bimodal microstructure B1 show highest strength, equiaxed microstructure E show best ductility and lamella microstructure has the lowest strength and ductility. Necking phenomenon has been observed in bimodal microstructure B1, B2 and equiaxed microstructure E, which not appear in lamella microstructure L. On dynamic condition, equiaxed microstructure E and lamella microstructure L show highest criticality failure strain rate, equiaxed microstructure E absorb most energy before failure, where lamella microstructure L take second place, higher then bimodal microstructure B1, B2. All of the four microstructure can observe the strain rate hardening effect. The results of forced shear test taken on the hat shaped sample show that equiaxed microstructure E and lamella microstructure L has lower adiabatic shear sensitivity then bimodal microstructure B1, B2. Ballistic impact experiment show that, the ballistic performance of lamella microstructure L is best, where equiaxed microstructure E take second place, better then bimodal microstructure B1, B2. The damage characteristic of all four microstructures is plugging, the process of fragmentation has taken place during the separation of the block and target due to the low ductility of lamella microstructure L. Adiabatic shear bands have been found in all of the targets for alloys with different microstructures, and confined to the location near the crater surface with shallow extension depth.