剪切熔化和高温脆化：理论及其在钛加工中的应用
Shear melting and high temperature embrittlement: theory and application to machining titanium
摘要：
我们描述了一个动态的相变发生在高温和极高的剪切速率下的剪切带。随着温度的升高，位错变形和晶界滑动被高度局部化的纳米带中的非晶化所取代，这允许大规模应变和断裂。其机理类似于剪切熔化，并导致高温下液态金属的脆化。模拟结果表明，无位错滑移系、低导热系数和接近熔点的温度是形成超导体的必要条件。前两个表现出体心立方钛合金，我们表明，最后一个可以通过实验来实现添加低熔点元素：特别是我们使用不溶性稀土金属（REM）。在高剪切下，REM与钛混合，降低剪切带内的熔点并触发剪切熔融转变。这又产生热量，由于不良的热传导，热量保持在剪切带中。材料沿剪切带断裂。我们展示了如何利用这种转变，在创建新的钛基合金，改善切削性能。
英文摘要：
We describe a dynamical phase transition occurring within a shear band at high temperature and under extremely high shear rates. With increasing temperature, dislocation deformation and grain boundary sliding is supplanted by amorphization in a highly localized nanoscale band, which allows massive strain and fracture. The mechanism is similar to shear melting and leads to liquid metal embrittlement at high temperature. From simulation, we find that the necessary conditions are, lack of dislocation slip systems, low thermal conduction and temperature near the melting point. The first two are exhibited by bcc titanium alloys, and we show that the final one can be achieved experimentally by adding low-melting point elements: specifically we use insoluble rare earth metals (REMs). Under high shear, the REM becomes mixed with the titanium, lowering the melting point within the shear band and triggering the shear-melting transition. This in turn generates heat which remains localized in the shear band due to poor heat conduction. The material fractures along the shear band. We show how to utilize this transition in the creation of new titanium-based alloys with improved machinability.
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