两种TC4钛合金板材的显微组织均匀性及力学性能各向异性研究

Study on Uniformity of Microstructure and Anisotropy of Mechanical Properties of TC4 Titanium Alloy Sheets with Two Microstructures

研究了不同轧制工艺对TC4钛合金板材显微组织及力学性能的影响,结果表明,采用β热变形工艺可获得片层α相+残余β相组成的片层组织,而采用α+β热变形工艺可获得等轴初生α相+片层次生α相+残余β相组成的等轴组织。力学性能测试结果表明:等轴组织TC4钛合金板材的强度-塑性匹配高于片层组织TC4钛合金板材的,而片层组织TC4钛合金板材的冲击、断裂韧性更高。进一步分析了两种TC4钛合金板材的显微组织性能均匀性及力学性能各向异性,结果表明:两种TC4板材沿厚度(ND)方向的显微组织及力学性能均匀性较好,而沿板材轧向(RD)和横向(TD)上存在一定程度的各向异性。原因如下:板材中存在<0001>α//TD的α相织构,导致TD方向位错滑移阻力增大,使TD方向的强度高于RD方向的;板材沿RD方向存在明显的组织流线,导致裂纹穿晶扩展过程阻力增大,使TD-RD方向的冲击、断裂韧性高于RD-TD方向的。

The effects of rolling processes on the microstructure and mechanical properties of TC4 titanium alloy sheet are studied.The results indicate that the lamellar microstructure consisting of lamellarαand residualβphases is obtained byβphase field deformation,and that the equiaxed microstructure consisting of equiaxedα,lamellarαand residualβphases is obtained byα+βphase field deformation.The mechanical test results show that the match between the strength and plasticity of TC4 sheet with equiaxed structure is better than that with lamellar microstructure,while the impact and fracture toughnesses of TC4 sheet with lamellar structure are better.The uniformity of microstructure and mechanical properties of TC4 sheets with the two microstructures is further analyzed.The results indicate that the microstructure and mechanical properties along the normal direction(ND)of two types of TC4 sheets show higher uniformity,and that the anisotropy of tensile strength and fracture toughness in the sheets along the rolling direction(RD)exists.The texture of<0001>α//TD direction in the TC4 sheet would increase the slip resistance of dislocations in the transverse direction(TD),resulting in higher strength in the TD than in the RD.There is obvious flowline microstructure along the RD in the TC4 sheet,which increases the resistance of crack transgranular propagation,resulting in higher impact and fracture toughnesses in the TD-RD direction than those in the RD-TD direction.