基于铀的激光氮化机理研究和数值模拟

Numerical Simulation and Mechanism Research on Laser Nitriding of Uranium

针对工件铀的表面激光氮化工艺,考虑铀的固-液相变过程中各物理参数随温度的变化,结合计算流体软件FLUENT中流体体积函数(VOF)模型计算气-液相界面处的降膜解吸传质过程。进行了铀的瞬态激光氮化传热传质耦合数值仿真,仿真分析研究了不同工艺参数下瞬态温度场和流场的分布,同时获得渗氮量在铀表面和深度上的分布。分析结果表明,因激光局部加热引起的表面张力梯度导致的Marangoni对流对铀表面氮化过程中的传热和传质有很大的影响。其中渗氮量在不同工艺参数下的数值结果与试验结果相吻合,验证了数值模型的可行性,为激光氮化的理论分析和工艺指导提供了理论和方法。

The numerical model based on transient laser nitriding process of uranium was established by using the computational fluid software FLUENT. Physical parameters related to temperature were considered during phase transition. The process of gas-liquid falling film desorption was calculated with fluid volume function （VOF） model. The time-dependent distributions of the temperature, the width and depth of melt pool were derived. Moreover, the lateral and depth profiles of nitrogen across the laser spot were calculated. It was found that the gradients of interracial tension due to local heating would lead to Marangoni convection, which had significant influence on the formation of surface and the process of mass transport in the laser nitriding of uranium. The simulation results matched with the experimental data well. The simulation gave a better insight into the physical processes and dependencies of the coating formation for the uranium-nitrogen system. This would provide references for theory analysis and allow an optimization of the coating synthesis.