粉末致密化过程数值模拟研究现状

Research Status of Numerical Simulation of Powder Densification Process

粉末冶金技术具有成本低、能耗低、材料利用率高等优点,在材料制备与加工过程中能在较大的范围内调节工艺,因而在机械、航空、医疗等领域得到了广泛应用。粉末冶金方法主要包括粉末的制取、混合、成形和烧结四个主要步骤,其中成形和烧结是致密化过程,更是制备高性能复合材料的决定性阶段。但传统粉末冶金实验方法不便于观察粉末致密化过程的动态变化,更加难以深入地研究成形和烧结过程中粉末颗粒的重新排布和变形等微观机制。计算机数值模拟技术可以实现粉末压制成形和烧结过程的可视化。因此近几年,国内外的学者们对粉末的压制过程进行了大量数值模拟研究,而对烧结过程的模拟尚且较少。不同的学者因具体的研究对象不同,使用的理论模型和建模方法也各不相同。本文简述了国内外粉末冶金过程数值模拟的理论模型,包括以弹塑性为主的椭圆屈服模型和一致本构模型,注重颗粒特性和流变特性的流变学理论,以及以内时度量反映非线性应变大小的塑性内时理论等,论述了常用的建模方法,包括体现可变形性的有限元法、基于颗粒特性的离散元法和将两者结合的多粒子有限元法。另外,简单阐述了目前粉末热压烧结过程存在的关键问题以及研究现状,以期为粉末冶金的数值模拟研究提供参考。

Powder metallurgy technology has the advantages of low cost,low energy consumption and high material utilization rate.In addition,process parameters can be adjusted in a larger range during the process of powder metallurgy.Therefore,it has been widely used in machinery,avia-tion,medical treatment and other fields.The manufacturing process can be divided into four steps,including powder preparation,mixing,compaction and sintering,among which the last two are critical for densification and decisive for the performance of composite material.However,it is hard to observe the dynamic densification changes of powders directly for traditional experimental method,which makes it more difficult to investigate the micro-mechanism of particle rearrangement and deformation.Still,computer numerical simulation can reach visualization during the compaction and sintering stages.In recent years,there have been surging researches of numerical simulation on powder compaction,but few on sintering.Theoretical models and modeling methods varies with each research object,from person to person.In this paper,theoretical models of numerical simulation in powder metallurgy are briefly described,involving ellipsoidal yield criterion and unified constitutive model both based on elastoplasticity behavior,rheological theory focusing on particle and rheological properties,endochronic plasticity theory with endochronic mea-surement reflecting the magnitude of nonlinear strain,etc.Common modeling methods including finite element method reflecting deformability,discrete element method based on particle characteristics,and multi-particle finite element method combining the above two,are also discussed.In addition,the chief problems and status of current powder sintering process are clarified.This review is expected to be referable for the numerical simulation of powder metallurgy.