基于等通道转角挤压的V-5Cr-5Ti合金晶粒细化机理研究

Grain refinement mechanism of V-5Cr-5Ti alloy based on equal channel angular pressing

摘要:

研究了等通道转角挤压（ECAP）技术处理V-5Cr-5Ti合金的可行性，并分析了后续退火处理对合金硬度和微观组织的影响规律，进而探讨了合金的晶粒细化机理。ECAP采用相关模具在万能试验机上进行，在真空炉中进行退火，利用维氏硬度计进行硬度测试，采用X射线衍射（XRD）分析相结构，光学显微镜（OM）观察微观组织。研究结果表明，在室温下V-5Cr-5Ti合金可以顺利进行两道次ECAP过程，后续配合950℃以上温度退火，晶粒尺寸可以从约100μm被细化到约30μm。V-5Cr-5Ti合金的晶粒细化机理不同于传统体心立方合金，在挤压过程中，原始晶粒发生自转动，原始晶界清晰可见，未被碎化，但晶内出现大量的剪切滑移带。在后续退火过程中，细小晶粒在原始晶粒内部的剪切滑移带上形成，最终原始晶界和形成的细小晶界逐渐难以区分，形成整体的细晶组织。

Abstract:

The hardness and grain refinement mechanism of V-5Cr-5Ti alloy by equal channel angular pressing (ECAP) and annealing treatment were studied. ECAP was tested using pressing die using universal material testing machine. The annealing was done in vacuum heat treatment furnace. The hardness was tested using Vickers hardness tester. The phase structure was identified using X-ray diffraction (XRD). The microstructure was observed using optical microscope (OM). The results indicated that the grain size of V-5Cr-5Ti alloy can be refined from ~100μm to ~30μm after ECAP two times and annealed above 950℃. Different from the traditional grain refinement mechanism of B.C.C alloy, the grains of V-5Cr-5Ti alloy are rotated on itself at ECAP process, and a lot of shearing glide bands are formed in coarse grains. With the annealing temperature increasing, fine grains are formed gradually at shearing glide bands and the initial grain boundaries are still clear. Finally, the fine grains are formed completely above 950℃, and the initial grain boundaries become blurred gradually.