Micro residual stresses in hard metals

以碳化钨钴硬质合金为例，建立了一个有限元模型，该模型能够精确预测液相烧结非均质金属基复合材料中的II型残余应力。基于温度相关的，晶体-（粘）塑性本构描述的钴粘结剂，正交各向异性的热弹性本构配方的碳化钨和体积变化的影响的第二类残余应力响应的考虑，引起的碳化钨的沉淀，追求以下目标：1。根据冷却历史和硬质合金的显微组织特征，精确预测残余应力和内应力的发展。2.从烧结温度冷却过程中碳化钨从粘结剂中析出的影响的定性研究。3.基于电子背散射衍射数据（EBSD）和聚焦离子束（FIB）技术的多个三维模型的调查的基础上的模拟结果的统计验证。4.通过对具有不同加工历史的硬质合金进行残余应力测量来验证模拟结果。5.识别导致最小残余应力状态的显微组织特征和冷却循环的组合。为了实现上述目标的本构关系的实施到l有限元软件Abaqus通过使用不同的用户定义的子程序。晶体（粘）塑性模型的参数来自于对由代表性钴粘结剂合金制成的单晶的温度依赖性力学实验。有限元模型是由EBSD数据通过一个自主开发的软件，检测晶体取向和钴/碳化物边界自动导出。通过执行基于实际工艺参数的多个模拟，可以预测微观结构内的残余应力分布，并且可以导出用于优化制造工艺的信息。模拟结果进行了验证，通过测量不同的加工历史，使用X射线和中子衍射技术在硬质合金的残余应力。除了更准确地预测碳化钨材料中的残余应力状态外，该模型还将有助于更好地理解这些材料中产生残余应力的机制。

Using the example of tungsten carbide cobalt hardmetals a finite element model is developed which enables the precise prediction of type II residual stresses in liquid phase sintered, heterogeneous metal matrix composites. Based on a temperature dependent, crystal-(visco)-plastic constitutive description of the cobalt binder, an orthotropic thermo-elastic constitutive formulation of the tungsten carbide and the consideration of the influence of volume changes on the type II residual stress response, caused by precipitation of tungsten carbide the following objectives are pursued: 1. The accurate and precise prediction of the residual stresses and the development of the internal stresses depending on the cooling history and the microstructural features of the hardmetal. 2. The qualitative investigation of the influence of precipitation of tungsten carbide out of the binder during the cooling from sintering temperature. 3. The statistical validation of the simulation results based on the investigation of multiple 3D models based on electron backscatter diffraction data (EBSD) and focused ion beam (FIB) techniques. 4. Verification of the simulated results by residual stress measurements performed on hard metals with varying processing history. 5. Identification of a combination of microstructural features and cooling cycle which leads to a minimal residual stress state. For achieving the above mentioned targets the constitutive laws are implemented into the l finite element software Abaqus by the use of different user defined subroutines. The parameters for the crystal-(visco)-plastic model are derives form temperature dependent mechanical experiments on single crystals made of a representative cobalt binder alloy. Finite element models are automatically derived from EBSD data by a self-developed software which detects the crystal orientation and cobalt-/-carbide boundaries. By performing multiple simulations, which are based on realistic processing parameters, the residual stress distribution within the microstructure is predicted and information for the optimization of the manufacturing process can be derived. The simulation results are verified by measuring the residual stresses in hard metals with varying processing history using X-Ray and neutron diffraction techniques. Besides a more accurate prediction of the residual stress state in tungsten carbide materials, the model will lead to a better understanding of the mechanisms causing residual stresses in these materials.