Mechanical properties and microstructure of silicon nitride fabricated by pressureless sintering

The effect of Al2O3-MgO additives on the microstructure of spark plasma sintered silicon nitride

“…The microhardness of the produced ceramics insignificantly increases from 1957 HV to 1985 HV with an increase in the sintering temperature from 1550°C to 1650°C despite on the increase in density and the grain growth. Although, both SPSed samples are characterized by higher microhardness as compared with the pressureless sintered silicon nitride with a microhardness equal to 1511 HV with the same type and amount of additives described in our previous work [26].…”

“…The microstructure of this silicon nitride is duplex and quite different compared to the described material and mostly consists of the equiaxed α-grains, while the secondary elongated β-grains can also be distinguished. The advantages and disadvantages of this material have been described elsewhere [26]. Different type of microstructure indicates a difference in the mechanisms of microstructure evolution for both corresponding sintering methods.…”

“…Fine α -silicon nitride powder (92 wt%) was mixed with 2 wt% selfmade MgO and 6 wt% Al 2 O 3 (A16 SG, 600 nm) using vibratory disc mill Retsch RS-200. Other details were reported previously [21][22][23][24][25][26][27][28]. A new innovative technology has been used to produce a nanoscale highpurity powder of magnesium oxide.…”

“…Their microhardness, densities, and average grain size are summarized in Table 1. The silicon nitride ceramics produced by SPS at 1550°C is marked in Table 1 as SPS155, ceramics SPSed at 1650°C is denoted as SPS165 and ceramics pressureless sintered at 1880°C is referred as SN18 [26], respectively. Both ceramics demonstrate almost the same type of microstructure.…”

“…The lack of the surface porosity was observed for both investigated ceramics. The equiaxed α-Si 3 N 4 grains connected randomly with each other and formed fine-grained microstructure that could be benefit for the various high-temperature applications of silicon nitride ceramics [26,28].…”