Publication 13-CNA-020
Effects of The Laplace Pressure and of Gas Pressure on Isostatic Pressing and Free Sintering of Cylindrical Specimens
L. Galuppi
Industrial Engineering Dept.
University of Parma, Parma, Italy
laura.galuppi@unipr.it
L. Deseri
D.I.M.S., Mechanical and Structural Engineering Dept.
University of Trento, Trento, Italy
luca.deseri@ing.unitn.it
Abstract: Unlike previous recent contributions [20], the influence of the gas pressure in pores and of local capillary stresses acting at the surface of one pore or particle (called interstitial stress or Laplace pressure) during sintering of
pre-compacted metallic (micro/nano)-powdered cylinders is here analyzed. In this paper, the isostatic pressing loading mode, which also covers the case of free sintering, is considered.
The role of the Laplace pressure is twofold.
- First of all, during the sintering process such a pressure influences the evolution of the porosity and, for instance, its residual value at a given time. It is worth emphasizing that threshold pressures are determined below which the sintering
stress is actually not negligible; the duration of the process is indeed heavily affected by such a stress whenever the residual porosity is prescribed. In turn, such a duration would be underestimated otherwise. Furthermore, industrial processes often entail loading pressures lower than the thresholds mentioned above, especially of "small" grain sizes.
- In the case of isostatic pressing with non-null external load, the loading parameter may be tuned in such a way that, at some stage of the process, i.e. when a "critical porosity" is reached, its value may equate the Laplace pressure. Henceforth, the porosity would remain constant. A stability analysis allows us to conclude that, the equilibrium is unstable at such a value and hence the sintering may keep on going. It follows that in order to have stability of sintering either the loading parameter must be high enough with respect to the Laplace pressure or it must be zero, which would give rise to (stable) free sintering.
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