Chapter 5 - Direct Sintered (Pressureless Sintered) SiC: DSSC

Abstract

Pressureless sintered SiC, also known as direct sintered SiC (DSSC), is a near-pure near-fully dense form of SiC that has been densified by simple pressureless sintering. DSSC is cheaper and simpler to manufacture than hot-pressed SiC (HPSC). Solid-state sintered DSSC (SSiC-DSSC) is densified by pressureless solid-state sintering, at >2000°C, typically with approximately1wt.% sintering aids. Liquid-phase sintered DSSC (LPS-DSSC) is densified by liquid-phase sintering at <2000°C, typically with approximately10wt.% sintering aids. The advantages and disadvantages of each are explored in detail. Some of the key issues for comparison of HPSC to DSSC are: (1) HPSC has limited shape complexity, DSSC has virtually no limitations to shape complexity; (2) HPSC is essentially net shape in the lateral plane, DSSC is not a net shape process; (3) DSSC is commonly 93%–98% dense and can generally only give densities near 100% at sintering temperatures that cause exaggerated grain growth (only HPSC can give both 100% density and fine-grain microstructures); (4) DSSC has much faster production throughput because pressureless sintering can be carried out in a continuous manner using a pusher or band-type furnaces (HPSC is a slow-throughput process); and (5) DSSC is a cheaper simpler process than HPSC. Thus there is no ‘faster better cheaper’ option with dense polycrystalline sintered SiC ceramics, whether HPSC or DSSC, there are always compromises to be made, whether in cost, shape complexity, density, or grain size. DSSC evolved from HPSC as SSiC-DSSC, and then LPS-DSSC diverged from SSiC-DSSC later. Today, DSSC is a mass-market product, and the ceramic of choice in the millions of ceramic body armour breastplates used by armies globally, and has numerous other applications also. DSSC is mass-market, and HPSC is a boutique technology. This chapter explores the evolution of DSSC from HPSC, the evolution of both SSiC-DSSC and LPS-DSSC into the highly evolved forms they have attained today, and comprehensively examines the DSSC technology in a depth not previously documented in a review.