120°模具室温8道次ECAP变形TA1纯钛的组织与性能

Microstructure and Properties of TA1 Pure Titanium Processed by 8 ECAP Passes Using a 120° Die at Room Temperature

采用两通道夹角Φ=120°,外圆角ψ=20°的模具,在道次间未退火的条件下实现TA1纯钛BC方式8道次室温ECAP(Equal Channel Angular Pressing)变形,制备表面光滑无裂纹的变形试样。研究纯钛室温ECAP变形组织结构的演变和特征,测定变形试样的力学性能。结果表明:随着室温ECAP变形道次的增加,原始粗大的α相等轴晶由最初几道次形成的板条和孪晶经过自身和相互交割形成亚晶,以及剧烈变形形成的位错胞状结构,通过位错的相互作用和重组逐渐演变成大角度晶界的超细晶等轴组织。获得平均晶粒尺寸约200nm的TA1纯钛试样,其屈服强度和抗拉强度分别由275和407MPa提高到710和791MPa,并保持较高的塑性,延伸率为19.0%。

Commercial pure titanium billets, grade 1 （TA1）, were successfully processed by equal channel angular pressing （ECAP） for 8 passes via route BC at room temperature using a Φ=120° and ψ= 20° die. The as-processed Ti billets were smooth and free of any visible surface cracks. Special attention was paid on the microstructure evolution and mechanical properties of the ECAP samples at room temperature. The microstructure examination of the ECAP processed billets reveals that, with the pass of ECAP increasing, the initial and coarse equiaxed grains evolve into gradually the ultrafine grains with high-angle boundary composed of the subgrains and the dislocation cells, which are formed from the band structures, deformation twins and high density dislocations produced within initial several passes through the dislocations interacting and recombining. After the 8th ECAP pass, the original grains are refined to about 200 nm, and the yield strength and ultimate tensile strength is increased to 710 and 791 MPa from original 275 and 407 MPa, respectively. Meanwhile, a higher ductility of 19.0% elongation still is maintained.