Novel experimental strategy towards temperature inhomogeneity during spark plasma sintering of metallic glasses

Abstract

Despite the importance of temperature distribution in spark plasma sintering of metallic glasses, its quantification has been experimentally laborious. This work proposes an experimental strategy to determine the sintering temperature by establishing a quantitative relationship between the temperature-thermal signal. We reproduced the thermal profiles of spark plasma sintering by isothermal annealing and found a correlation between annealing temperature and isothermal crystallization time. This strong correlation indicates the temperature-dependent structural evolution of glassy powders. Using isothermal crystallization time as the measuring gauge, we correlated the annealing temperature to the sintering temperature and obtained the sample temperature map. The sample temperature is at least 19 ​°C higher than the nominal temperature of 425 ​°C measured by the thermocouple. Meanwhile, the sample temperature shows a hump-shaped pattern closely correlated with the current density. The maximum temperature of 453 ​°C occurs on the sample/punches contact surfaces. Temperature heterogeneity within the sample induces diverse microstructures and porous structures. We elucidate that the temperature inhomogeneity is intrinsic, given the presence of contact interfaces. Contact resistances affect the current distribution and heat transfer, resulting in a larger temperature gradient than the traditional powder metallurgy process.

Keywords

• Metallic glass
• Spark plasma sintering
• Temperature inhomogeneity
• Isothermal crystallization time
• Current distribution