Three-dimensional Multi-particle Finite Element Simulation Of Isostatic Pressing And Sintering Of Pure Tungsten Powder

In this paper,three dimensional multi particle finite element method(3D-MPFEM)was utilized to numerically reproduce the cold isostatic pressing(CIP)followed by solid phase sintering and the hot isostatic pressing(HIP)process of pure tungsten powder at a particulate scale level.The effects of initial packing structures,pressure,temperature and particle size ratio on the densification behavior of the tungsten powder during CIP-sintering and HIP were systematically investigated.Various macroscopic and microscopic properties including relative density,overall/local stress distributions,deformation status,pore filling behavior as well as densification mechanisms were characterized and analyzed.The obtained innovative results are as follows.During CIP and solid phase sintering,high performance tungsten components with high relative densities can be realized by properly control of various parameters,including the initial packing structure,CIP pressure and sintering temperature.The initial packing structure before CIP plays an important role in determining the properties of both green compact and sintered part after compaction and sintering.Detailed analyses of individual particles revealed the internal stress distribution of particles with different degree of deformation,where the particles with larger deformation tend to generate a greater stress concentration during CIP and sintering;the stress distribution at different location within each particle was also characterized and analyzed,results indicated that a close relationship exists between the stress concentration and release process of individual particles and their initial packing structure before CIP;when compared with particles in random initial packing structure,much lower levels of stress were found in the core of the particles in orderly dense packing structure during both CEP and sintering.For HIP,the results show that the HIP process of tungsten powder can be numerically reproduced from particulate scale and high performance components can be obtained by properly controlling the HIP conditions such as pressure and temperature.The pressure and temperature during HIP play a dominant role in determining both the final properties of the components and the microscopic properties of individual particles;the higher the HP temperature,the lower the pressure required for the tungsten powder mass to achieve densification.Also,different particle size ratios of the tungsten powder mass can affect both the macro-and microscopic properties of the compacts during and after HIP;the larger the particle size ratio,the higher the concentration of stresses on small particles,and the larger the difference between the deformation degree of large and small particles.