【作者】 唐达培；

【导师】 高庆；

【作者基本信息】 西南交通大学 ， 固体力学， 2009， 博士

【摘要】 金刚石膜是一种性能极其优异的多用途功能材料,在机械加工、航空航天、微电子制造等众多领域具有广泛的应用前景。但金刚石膜在制备过程中,过高的残余应力容易引起膜开裂破坏这一问题尚未得到很好地解决。本文以直流电弧等离子体喷射法制备自支撑金刚石厚膜为研究对象,以等离子体炬内外复杂的电、磁、热、力多场耦合变量以及金刚石膜热-力耦合条件下的应力为研究目标,对等离子体的流动和传热以及自支撑金刚石厚膜在制备中各个阶段的应力进行数值模拟,并揭示大尺寸金刚石厚膜发生开裂破坏的原因及其影响因素。主要的研究工作如下:1.以沉积金刚石膜的磁控直流等离子体炬为研究对象,在经典的纳维叶-斯托克斯（Navier-Stokes）流动方程和能量方程中引入多项源项,包括因外磁场和内部自感应磁场引起的洛伦兹力、辐射冷却、焦耳热以及Ar-H₂混合等离子体因温度、压强、电场及浓度等梯度引起的对流扩散等,并结合组分质量守恒、广义欧姆定律及麦克斯韦方程组,建立了炬内等离子体的磁流体动力学（MHD）多场耦合模型。对FLUENT软件成功地进行了二次开发,有效地对所建MHD耦合模型中所涉及的流场、温度场及电磁场进行了仿真。得到了在有与无外磁场情形下,等离子体炬内的速度场、温度场和电流密度场,以及炬出口的速度和温度沿径向的分布。2.基于上述等离子体炬内的MHD多场耦合模拟计算结果,将炬出口处的速度、温度等参数的出口条件作为炬外沉积腔内等离子体射流的入口条件,建立了等离子体射流的计算流体动力学模型。利用二次开发后的FLUENT软件对沉积腔内金刚石膜上方的等离子体射流的流动和传热进行数值模拟。得到了等离子体射流的速度场及温度场,同时还得到了金刚石膜上表面温度沿径向的分布,为本文其后对金刚石膜的热-力耦合分析奠定了基础。3.运用膜/基系统在冷却过程中的瞬态热-力耦合模型,考虑了温度与应变之间的耦合效应,对膜/基系统在冷却过程中的温度场和热应力场,以及冷却到室温时的热残余应力场进行了有限元数值模拟。在模拟中,膜/基系统冷却时非均匀温度场的初始条件来自于本文在实际制备条件下的多场耦合计算结果,这使得在热应力场和热残余应力场的模拟结果中,不仅体现了膜/基材料热膨胀系数差异的影响,还体现了膜/基系统内各点温度非均匀性的影响,故所模拟计算的应力结果更加真实准确。基于金刚石膜的热应力场和热残余应力场的模拟结果,分析研究了金刚石膜脱落或开裂破坏的原因,对实际的破坏现象进行了较合理地解释。4.采用单元“生死”技术,对脱离基体时的自支撑金刚石厚膜内热残余应力的再分配进行了研究,定量地得到了金刚石膜热残余应力的释放情况,对求算本征应力提出了有益的意见。5.研究了金刚石膜热残余应力和开裂破坏的一些影响因素,其研究成果对于金刚石膜残余应力的合理控制、制备工艺的改进和成品率的提高等,均有较大的参考价值。更多还原

【Abstract】 The unique characteristics of diamond film make it extremely attractive for numerous applications in machining, aerospace, microelectronics and so on. But during the process of producing diamond film by chemical vapor deposited technology, such as DC arc plasma jet, the problem of film cracking caused by excessive residual stresses has not been well solved yet. The objective of this work is to study the complicated multi-field coupling variables of electricity, magnetism, heat, mechanics inside and outside the plasma torch, and the stresses in diamond film based on thermal-mechanic coupling. The flowing and conducting heat of plasma were simulated, and the stresses existed in the various stages of self-standing diamond thick film were also simulated. Moreover, the cause and influence factors of diamond film cracking were revealed.The principal researches are as the follows:（1） A coupling magneto-hydrodynamic （MHD） model of magnetic controlled DC plasma torch, which was used for diamond film deposition, was presented. The model includes Navier-Stokes and energy equations modified by the addition of some source terms, which reflect the Lorentz force due to self-induced and external magnetic fields, radiative cooling, joule heating, and the diffusive and convective enthalpy fluxes due to the temperature, pressure, electric field, and concentration gradients of Ar-H₂ mixture plasma. In addition, the mass conservation and species conservation equation, generalized ohm’s law, and Maxwell’s equations were also modeled. By reprogramming the software FLUENT, the author effectively simulated the fluid field, temperature field and electromagnetic field in the MHD coupling model. These fields in the torch were obtained respectively with and without external magnetism, and the radial distributions of velocity and temperature at the outlet of the torch were also obtained.（2） Based on the results of these fields mentioned above ,a computational fluid dynamics model was established for the plasma jet spraying from the torch to the deposition chamber by taking the outlet conditions of velocity and temperature at the torch exit as their inlet conditions of the plasma jet. The flowing and conducting heat of plasma jet over the diamond film were simulated by using the reprogramming software FLUENT. The velocity field and temperature field of plasma jet were obtained, and the radial distribution of temperature on the upside of diamond film was also obtained, which laid a foundation for analyzing the thermal-mechanic coupling in the diamond film later.（3） A transient thermal-mechanic coupling model was adopted in the cooling process of film/substrate system. In this model, the coupling effect between temperature and strain was considered. A finite element simulation was made about the temperature field and thermal stresses fields during the cooling process of film/substrate system and about the thermal residual stresses fields at indoor temperature. The uneven initial temperature condition used for the simulation during the cooling period of the film/substrate system came from the calculated result of the coupling multi-field on real production condition. Both the thermal expansive coefficient difference of film/substrate material and the non-uniformity of temperature at each point in film/substrate system were reflected in the simulated results of thermal stresses and thermal residual stresses. Therefore, the simulated results of stresses are more accurate. Based on these simulated results, the cause of detachment and cracking of diamond film were analyzed, and the actual damage phenomenon was rationally explained. （4） The redistribution of thermal residual stresses in self-standing thick diamond film was studied by using "life or death element" technology while the film separated from substrate. So, the release of thermal residual stresses was obtained quantitatively. A useful suggestion about how to compute intrinsic stresses was made.（5） Some influence factors of residual stresses and cracking damage of diamond film were studied. These research achievements have considerable reference values for the control of residual stresses, the improvement of producing technology, and the increase of diamond film finished product ratio.更多还原