Stress sintering

The densification rate for the diffusion-controlled mechanisms may be expressed as a general form, which is given by 

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Recently, the sintering driving force has been modified to the so-called sintering stress [4,5] (or, in other terminology, sintering pressure... 

The initial sintering stress is dependent upon only the dihedral an e. The application of stress on a string of particles will affect the chemical potential at the grain boundary and, more important, determine the sintering rate. The chemical potential of a surface atom is given by [9]... 

Thermal stress in FGM has been studied because it is important to avoid the fracture due to thermal shock. However, the defects in the powder compacts during sintering is caused by sintering stress, which arises from surface tension. Therefore, the structure of FGM made by sintering should be designed with both thermal stress and sintering stress taken into consideration. Analysis of the sintering process of FGM powder compacts has not been conducted. 

Sintering can be described as the deformation process of viscous porous bodies under the action of the sintering stress, which is an apparent hydrostatic stress [4-6]. Based this theory, the constitutive equation for sintering is given by... 

Let us express the shrinkage behavior of powder mixtures MCI composed of Ml and Cl, and MC2 composed of M2 and C2 by the shrinkage curve of each component shown in Figure 1. It is assumed that there is no reaction between the metals and the ceramics. The powder mixtures are described as two porous bodies mechanically engaging with each other. Using this assumption, the sintering stress of the mixtures may be given by... 

The finite element method with the sintering stress taken into account has been formulated [4,6]. In this case, the equilibrium equation is given by dojj dSjj ... 

Smaller pores between nanoparticles cause higher internal sintering stress (by orders of magnitude) and therefore allow densification at lower temperatures. 

De Jonghe, L. C. Rahaman, M. L. (1984). Pore shrinkage and sintering stress. Journal of the American Ceramic Society, 67, C-214-15. 

Svoboda, J., Riedel, H. and Zipse, H., Equilibrium pore surfaces, sintering stresses and constitutive equations for the intermediate and late stage of sintering — I. Computation of equilibrium surfaces, Acta Metall. Mater., 42, 435-43, 1994. 

De Jonghe, L. C. and Rahaman, M. N., Sintering stress of homogeneous and heterogeneous powder compacts, Acta Metall., 36, 223-29, 1988. 

Zuo, R., Aulbach, E. and Rodel, J., Experimental determination of sintering stresses and sintering viscosities, Acta Mater., 51, 4563-74, 2003. 

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