Spark plasma sintering of a lunar regolith simulant: effects of parameters on microstructure evolution, phase transformation, and mechanical properties

The spark plasma sintering (SPS) process is a potentially effective in-situ resource utilization (ISRU) technology for consolidating lunar regolith in order to produce structural components for future space exploration. This study examined the fundamental mechanisms of the effects of SPS conditions on microstructure evolution, phase transformation, and mechanical properties. For this purpose, a lunar regolith simulant (FJS-1) was selected and sintered for a total of 16 cases based on four primary SPS testing parameters: temperature, applied external pressure, dwell time, and heating rate. The Taguchi design method was used to examine the effects and sensitivity of each testing parameter. Laboratory tests were conducted in multiple length scales, including density, porosity, optical microscopy, scanning electron microscopy aided by energy-dispersive spectroscopy, transmission electron microscopy, nanoindentation, and strength testing (in both compressive and flexural). Taguchi analysis results of SPS parameters and sintering mechanism discussion indicated that the sintering temperature is the dominant factor changing microstructure heterogeneity and densification during the SPS process. The contribution of applied pressure to the surface and the grain boundary diffusion rate and the nucleation rate indicated that the applied pressure may have enhanced both phase transformation and homogeneity during the sintering process. Strength of the sintered samples were approximately 10 times greater than those of a typical plain concrete. The collective results indicate that the SPS technology, a potentially viable ISRU method, can be used to produce property-specific and application-targeted building components on the lunar surface.