Role of boron on the Spark Plasma Sintering of an α-SiC powder

Abstract

This study deals with the role of non-oxide sintering aids such as boron carbide (B 4 C) or -free boron (B) plus free carbon (C) -on the Spark Plasma Sintering treatment of silicon carbide. The results so obtained clearly show that free boron plus free carbon additions lead to the higher densification rates. This favourable behaviour with regards to the densification kinetics is accompanied by the absence of any abnormal grain growth. At the opposite, boron carbide additions do not significantly raise the densification kinetic after SPS treatment of SiC in comparison to pure silicon carbide. In this case, TEM investigations point out the formation of a borosilicate vitreous phase due to the dissolution process of B 4 C in contact with a native superficial silica layer surrounding the SiC grains. The resulting liquid phase leads to an abnormal grain growth coupled with undensifying process.

Spark plasma sintering and pressureless sintering of SiC using aluminum borocarbide additives

“…The decrease of surface area during heating at 1500 • C and the reduction of the driving force for densification are believed to be the main reason for the increase of the sintering temperature. 23 The decomposition of SiO 2 during heating at 1500 • C and consequent depletion of a liquid phase is considered as another possible reason. TEM observation informed the absence of an amorphous layer in between SiC grains (Fig.…”

“…3(a)-(c) vs. (d)-(f)). Maitre et al reported that the densification of SiC was possible at 1950 • C under 100 MPa using SPS when adding boron and carbon additives 23. In contrast, the sintering of SiC was nearly completed at 1670 • C under 40 MPa pressure by using the Al 8 B 4 C 7 additive.…”

A ternary compound additive for vacuum densification of β-silicon carbide at low temperature

“…When these additives are added, the consolidation steps take place through liquid phase sintering, accompanied by the formation of an interphase at the grain boundaries. 6 However, the interphase shows lower corrosion resistance than SiC. 6 To obtain a high density and to minimize the degradation of corrosion resistance, consolidation of SiC has been achieved with non-oxide sintering aids, such as B-C 6,7 and Al-B-C 8,9 systems.…”

“…6 However, the interphase shows lower corrosion resistance than SiC. 6 To obtain a high density and to minimize the degradation of corrosion resistance, consolidation of SiC has been achieved with non-oxide sintering aids, such as B-C 6,7 and Al-B-C 8,9 systems. Boron has been shown to be a very efficient additive for low-temperature sintering of SiC, but liquid phases such as borosilicate glass 6 or melts of Al 8 B 4 C 7 9 were reported to form during heating, which may decrease corrosion resistance of the sintered SiC.…”

“…6 To obtain a high density and to minimize the degradation of corrosion resistance, consolidation of SiC has been achieved with non-oxide sintering aids, such as B-C 6,7 and Al-B-C 8,9 systems. Boron has been shown to be a very efficient additive for low-temperature sintering of SiC, but liquid phases such as borosilicate glass 6 or melts of Al 8 B 4 C 7 9 were reported to form during heating, which may decrease corrosion resistance of the sintered SiC. The fabrication of a fully dense SiC with a non-oxide additive in the absence of boron is very difficult at temperature as low as 1700 • C. Al and Al 4 C 3 have been shown to be effective sintering aids for SiC, thus SiC to which Al has been added can be sintered without pressure to high densities (>95% theoretical density) at temperature ≥1850 • C. 9 Recently, a ternary compound (Al 4 SiC 4 ) has received widespread attention because of its combination of unique properties, including a low crystal density (3.03 g/cm 3 ) and a high melting temperature (>2080 • C).…”