Densification mechanisms and microstructural evolution leading to high density processing of prealloyed powders in supersolidus liquid phase sintering

Supersolidus liquid phase sintering is used to achieve near theoretical densities with relatively coarse powders in a short period of time. However, this inherent advantage is seldom realized in commercial practice due to the complex relation between different parameters such as the heating rate, particle size, grain size, sintering temperature, liquid volume fraction, and sintering time.;The current work isolates the sintering mechanisms using a wide range of alloys. Using model experiments and a combination of quenching and sintering studies, it has been shown that grain sliding is involved during particle fragmentation. A stereological model is developed, which relates the mean liquid film thickness between the grains to contiguity, grain size, and the liquid volume fraction. The model shows excellent correlation with experimentally determined values and offers guidelines for particle tailoring to enhance densification. An improved and realistic capillary-induced densification model is also developed based on experimental observations.;The processing of an austenitic steel is systematically studied by isolating the interaction between the parameters such as sintering temperature, liquid volume fraction, and sintering time. Using boron containing additives, it is shown that refined microstructures with enhanced mechanical properties and better corrosion resistance are possible.;The study shows that grain coarsening plays a significant role in the design of processing cycle for attaining high densities in SLPS, besides affecting the mechanical properties. The grain coarsening study, in the domain of high solids volume fraction, shows that the coarsening rate constant increases with increasing the liquid fraction and varies linearly with the inverse 2/3 power of the mean liquid film thickness. The results are used to estimate the time scale for particle fragmentation and compare well with dilatometric observations.;The results provide a detailed insight into the overall understanding of SLPS mechanisms and the relationship between the material and process parameters. The experimental approach used for processing stainless steel is a guideline for developing new alloys.