Abstract
In this paper, by using the hot-pressed sintered technology, pure Si 3 N 4 ceramics and Si 3 N 4 composite ceramics containing different volume fraction(hBN) are prepared with the sintered catalyst of Al 2 O 3 and Y 2 O 3 (total 10vol%) by HIGH MULTI 5000 multi-functional high temperature sintering furnace. And the phase compositions, microstructure and mechanical properties of specimen were studied. The results show that, based on the hot pressing sintering process, the α-Si 3 N 4 is all changed into β-Si 3 N 4 . Addition of hBN into Si 3 N 4 inhibits the growth of the crystal grain and makes the ceramic materials generate hBN segregation zone in internal materials, which causes the addition of hBN that cannot improve the physical mechanical properties effectively just because the serious stress concentrates and fatigue break down. In addition, compared with other sintering process, the physical and mechanical properties of Si 3 N 4 prepared by hot-pressing sintering are better than other methods. Improvement of sintering temperature and time can refine the crystal grain and be a helpful densification. The changed β-Si 3 N 4 grain completely forms an intertwined structure and increases the physical and mechanical properties of Si 3 N 4 . Meanwhile, Y 2 O 3 and Al 2 O 3 additives are melted and filled into Si 3 N 4 particles at the high temperature, leading to a significant drop of the porosity and the increase of density.
Highlights
Si3N4 ceramic occupies an important position in engineering ceramic, because it has excellent comprehensive performances such as high strength, high temperature resistance, oxidation resistance, wear resistance, heat shock resistance and so on
Pure Si3N4 ceramic material is limited in engineering because it’s very fragile and rigid
For heat-pressing sintered sample, the density and open porosity are measured by Archimedes principle method; the hardness is measured by Vickers; the bending strength is measured by three point bending test; the fracture toughness is measured by indentation method; the detailed test method is shown as follows: (1)Density and open porosity The density and open porosity of the heat-pressing sintered Si3N4-hBN sample are measured by Archimedes principle method
Summary
Si3N4 ceramic occupies an important position in engineering ceramic, because it has excellent comprehensive performances such as high strength, high temperature resistance, oxidation resistance, wear resistance, heat shock resistance and so on. It is widely used in mechanical, chemical, oceanographic engineering, aerospace and other important areas. By deflection of the crack and bridging of the layer, the main crack growth resistance will increase greatly, and the fracture toughness property and flaw tolerance will be greatly increase, too In this regard, Saito T et a l[2]and Liu H et al[3] adopt BN as an additive of ceramic material and product Si3N4 ceramics matrix layered composites which shows perfect fracture toughness. What’s more, the rule of corresponding layered composite materials mechanics performance which is compared with other sintering methods is investigated
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