【2h】

Lattice continuum and diffusional creep

机译:晶格连续体和扩散蠕变

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摘要

Diffusional creep is characterized by growth/disappearance of lattice planes at the crystal boundaries that serve as sources/sinks of vacancies, and by diffusion of vacancies. The lattice continuum theory developed here represents a natural and intuitive framework for the analysis of diffusion in crystals and lattice growth/loss at the boundaries. The formulation includes the definition of the Lagrangian reference configuration for the newly created lattice, the transport theorem and the definition of the creep rate tensor for a polycrystal as a piecewise uniform, discontinuous field. The values associated with each crystalline grain are related to the normal diffusional flux at grain boundaries. The governing equations for Nabarro–Herring creep are derived with coupled diffusion and elasticity with compositional eigenstrain. Both, bulk diffusional dissipation and boundary dissipation accompanying vacancy nucleation and absorption, are considered, but the latter is found to be negligible. For periodic arrangements of grains, diffusion formally decouples from elasticity but at the cost of a complicated boundary condition. The equilibrium of deviatorically stressed polycrystals is impossible without inclusion of interface energies. The secondary creep rate estimates correspond to the standard Nabarro–Herring model, and the volumetric creep is small. The initial (primary) creep rate is estimated to be much larger than the secondary creep rate.
机译:扩散蠕变的特征在于,作为空位的源/汇的晶界处晶格面的生长/消失,以及空位的扩散。这里发展的晶格连续体理论代表了一个自然而直观的框架,用于分析晶体中的扩散以及晶格在边界处的生长/损失。该公式包括对新创建的晶格的拉格朗日参考构型的定义,传输定理以及对于多晶体的分段均匀,不连续场的蠕变速率张量的定义。与每个晶粒相关的值与晶界处的正常扩散通量有关。 Nabarro-Herring蠕变的控制方程式是通过具有成分特征应变的扩散和弹性耦合得出的。考虑了空位成核和吸收引起的体扩散耗散和边界耗散,但发现后者可以忽略不计。对于晶粒的周期性排列,扩散从形式上与弹性解耦,但是以复杂的边界条件为代价。如果不包含界面能,则偏应力多晶的平衡是不可能的。次要蠕变速率估计值对应于标准的Nabarro-Herring模型,并且体积蠕变很小。初始(初级)蠕变速率估计要远大于次级蠕变速率。

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