Effect of heat wave at the initial stage in spark plasma sintering

Abstract

Thermal effects are important considerations at the initial stage in spark plasma sintering of non-conductive Al2O3 powders. The generalized thermo-elastic theory is introduced to describe the influence of the heat transport and thermal focusing caused by thermal wave propagation within a constrained space and transient time. Simulations show that low sintering temperature can realize high local temperature because of the superposition effect of heat waves. Thus, vacancy concentration differences between the sink and the cross section of the particles increase relative to that observed during pressure-less and hot-pressure sintering. Results show that vacancy concentration differences are significantly improved during spark plasma sintering, thereby decreasing the time required for sintering.

Sintering driving force of Al2O3 powders at the initial stage of pulse electric current sintering under thermoelastic diffusion

“…When ignoring the influence of the concentration, only considering the coupling effect of strain and temperature, the Eqs. (2)-(4) degraded into the generalized thermoelastic theory (GT) as follows (Zhang et al 2016):…”

“…For the condition of a high heat rate under pressure, the vacancy concentration difference ΔC of PECS in consideration of the intrinsic Laplace stress, the thermal stress, and the additional applied pressure is proposed as follows (Zhang et al 2016):…”

“…The influence of temperature gradient and strain are considered in the main concentration diffusion equation. Therefore, the driving forces of mass migration during neck sintering consists of three parts: (1) the neck vacancy concentration gradient affected by intrinsic Laplace stress, additional pressure, and thermal stress (Zhang et al 2016); (2) the temperature gradient caused by the non-uniform temperature distribution at the neck (Olevsky and Froyen 2009); and (3) the concentration gradient resulting from the influence of the temperature and stress fields.…”