Numerical investigation of the WC re-precipitation impact on the residual stress state in WC20 wt.-%Co hardmetal
Numerical investigation of the WC re-precipitation impact on the residual stress state in WC20 wt.-%Co hardmetal
复制标题
DOI：
10.1016/j.ijrmhm.2019.105003
复制
发表时间：
2019-11-01
影响因子：
3.6
通讯作者：
Broeckmann, Christoph
中科院分区：
文献类型：
--
作者：
Kayser, Wolfgang;van Kempen, Stanley;Broeckmann, Christoph
在WC-Co硬质合金中，在液相烧结过程的冷却阶段，碳化物和粘结相之间会形成严重的微应力。这些微观残余应力的主要原因是各组成相的热膨胀系数的差异。还存在关于元素钨的溶解和再沉淀是否可能是残余应力随温度形成的额外驱动因素的讨论[1, 2]。为了进一步研究再沉淀效应对硬质合金中残余应力状态的影响，结合了 Thermocalc/DICTRA [3] 扩散建模功能的数值方法与利用有限元方法的温度相关非线性力学分析相结合。这种组合可以定性估计再沉淀对硬质合金最终残余应力状态的影响。此外，还研究了硬质合金中残余应力状态的温度依赖性，考虑或不考虑粘结剂中 W 和 C 的溶解和再沉淀。基于 WC20wt.-%Co 硬质合金的 EBSD 图像导出了详细的 2.5D 代表性体积单元，用于机械有限元模拟。在力学分析中，钴粘合剂被建模为具有各向同性硬化的温度依赖性弹粘塑性各向同性材料。碳化物被建模为纯正交各向异性弹性材料，具有弹性常数的温度相关描述。 DICTRA 结果通过两个等效的热膨胀系数作为附加内部载荷应用于机械模型。通过对有和没有再沉淀效应获得的模型结果进行比较，可以定性地检查再沉淀效应对残余应力状态的影响。最后，将模型结果与通过中子衍射获得的 WC20wt.-%Co 硬质合金样品中残余应力状态的实验测量结果进行比较。
In WC-Co hardmetals severe micro stresses form between the carbide and binder phases during the cooling stage of the liquid phase sintering process. The main cause of these micro residual stresses is the difference in the coefficients of thermal expansion in each of the constituent phases. There have also been discussions as to whether or not the solution and re-precipitation of elemental tungsten may be an additional driver for the temperature-dependent formation of residual stresses [1, 2]. To further investigate the influence of the re-precipitation effect on the residual stress state in hardmetals, a numerical approach combining the diffusion modelling capabilities of thermocalc/DICTRA [3] is applied in conjunction with temperature-dependent nonlinear mechanical analysis utilizing the finite element method. This combination allows for a qualitative estimate of the re-precipitation effect on the final residual stress state in hardmetals. Additionally, the temperature dependence of the residual stress state in hardmetals is investigated, with and without consideration of the solution and re-precipitation of W and C in the binder.A detailed 2.5D representative volume element based on EBSD images of a WC20wt.-%Co hardmetal has been derived for use in mechanical FE simulation. In the mechanical analysis, the cobalt binder is modelled as temperature-dependent elastic-viscoplastic isotropic material with isotropic hardening. Carbides are modelled as purely orthotropic elastic materials with temperature-dependent description of the elastic constants. The DICTRA results are applied as additional internal loads to the mechanical model via two equivalent coefficients of thermal expansion. A comparison of model results obtained with and without re-precipitation effect permits the impact of the re-precipitation effect on the residual stress state to be examined qualitatively.Finally, the model results are compared to experimental measurements of the residual stress state in WC20wt.-%Co hardmetal specimens, obtained via neutron diffraction.