诱发钛合金塑性增强的分步超塑性成形法

介绍了分步超塑成形法,从成形方式上探索一种增强材料塑性的途径。分步超塑成形过程中,分别以恒速度与最大m值法,分两步先后作用于拉伸试样,通过控制初始变形方式的变形量以及各步间隙时间等,来促使材料内部产生晶粒细化、组织结构改善等,从而增强材料塑性。实验比较了单步拉伸成形与分步拉伸成形,以及分步成形中恒速法的预应变量对金属延伸率与组织的影响。结果表明:未经特殊细化处理的TC6钛合金分步拉伸,其恒速变形的工程应变为2.0时,可获得延伸率为2053%,而同温度下单步恒速与最大m值法拉伸的延伸率为753.9%与1347%;TC4钛合金在分步拉伸中恒速应变量为1.5时,可获得2147%的大延伸率。可见分步成形显著诱发了塑性增强。此外,预应变量决定着拉伸试样的晶粒组织大小。

A Stepped Superplasticity Deformation Method Inducing Plasticity Enhancement of Titanium Alloy

A novel concept of stepped superplasticity deformation (Stepped-SPD) was proposed for exploring a way from superplasticity deformation process to enhance the metal plasticity. In that Stepped-SPD process, the constant speed deformation and the maximum m superplasticity deformation ( Max m SPD) were adopted superlatively to finish the tension of samples through two steps. The strain of the first step and clearance time between two steps in Stepped-SPD were controlled in order to facilitate the grain refinement and structure improvement which induced plasticity enhancement. In these experiments, stepped tension deformation was compared with single-step tensile deformation and the influences of pre-strain of the first step in Stepped-SPD on elongation and microstructure were analyzed. The results for TC6 alloy without grain refinement treating show that the Stepped-SPD tensile method obtains the best SPD capability, with an elongation of 2053% corresponding to the pre-strain of 2.0, whereas the Max m SPD and constant speed tensile method produces the biggest elongations of 1347% and 753.9%, respectively. The elongation for TC4 titanium alloy using stepped tensile test is 2147% corresponding to the pre-strain of 1.5 in the first deformation step. Thus, it is indicated that the Stepped-SPD induces the plastic enhancement in comparison with the single-step deformation. Moreover, the pre-strain determines the grain size of the tensile sample in Stepped-SPD.