Effect of zirconia content on mechanical and thermal properties of mullite–zirconia composite

Abstract

Mullite-zirconia composites were prepared by adding various zirconia contents in the mullite ranging from 0 to 30 wt-% and sintering at 1400-1600uC for 2 h. The phase composition examined by X-ray diffraction showed that mullite was the major phase combined with developed t-ZrO 2 and m-ZrO 2 phase as a function of zirconia content, especially at 1600uC, wherein m-ZrO 2 predominated. Density increased when the zirconia content and sintering temperature were increased ranging from 2?2 to 3?53 g cm 23 . The morphology of mullite grain showed elongated grains, whereas dispersed zirconia showed equiaxed and intergranular grains. Flexural strength was continuously improved by adding zirconia during the sintering temperature ranging from 1400 to 1500uC, whereas flexural strength was initially improved up to 5 wt-% of zirconia addition and deteriorated with more than 5 wt-% of zirconia content during sintering between 1550 and 1600uC. The maximum strength, 190 MPa, was obtained when sintering mullite with 30 wt-% of zirconia content at 1500uC. The degradation of strength at high sintering temperature may be a result from more occurrence of m-ZrO 2 phase. Thermal expansion of sintered specimens indicated linear change and hysteresis loop change. The hysteresis loop obtained with increased zirconia content resulted in the t-m phase transformation. Martensitic start temperature M s was determined to be 530uC for 15 wt-% zirconia sintered at 1500uC, implying that the t-m phase transformation occurred.

Microstructure and properties of (1 − x)La0.9Ca0.1CrO3/x ZrO2(x = 0–30 wt-%) composites

“…The stomata of uniform size and dispersive distribution can disperse and consume thermoelastic strain energy and suppress the nucleation and growth of hot cracks, thereby improving the thermal shock resistance of materials. The difference of mechanical strength corresponds with the density, porosity and phase composition of materials, which Hemra and Aungkavattana 7 also proved. Second, ZrO 2 particles may not react with LCCO particles at high sintering temperatures for not too long time in air, and they are used as hard particles to hinder the grain growth.…”

“…1–5 Using ZrO 2 grains to achieve the aim of phase transformation toughening is one of the most effective ways to improve the toughness and thermal shock resistance of ceramics (as demonstrated in Refs. 6 and 7), which refers to making use of the martensite phase transformation from tetragonal to monoclinic phase in a certain temperature range that occurred in the partially stabilised ZrO 2 grains added in the ceramic matrix, 8 accompanied by the volume change of 3–5%. The microcracks and phase transformation mechanisms induced by stress can explain this.…”

Reaction sintering of alumina/mullite nanocomposites from nano-sized starting powders

“…Importantly, some research work in the field of composites containing mullite as the matrix or the second phase emphasises that the distribution of second phase plays an important role to an enhancement of mechanical properties. [5][6][7] Therefore, it would be beneficial to be able to control the microstructure of the composites by ceramic processing. Direct addition of mullite into alumina cannot effectively tailor the microstructure after sintering.…”

Thermophysical properties and processing of ceramics

“…Hemra et al . 1 report the effect of zirconia content on the mechanical and thermal properties of mullite–zirconia composites. The thermal expansion of sintered specimens showed linear and hysteresis loop changes: Hysteresis loop obtained with increased zirconia content resulted in the t–m phase transformation.…”

“…Ceramics researchers have been widely interested in mullite because of its excellent properties such as low thermal expansion coefficient, low thermal conductivity, high-temperature strength, and phase stability at high temperatures. Hemra et al 1 report the effect of zirconia content on the mechanical and thermal properties of mullite-zirconia composites. The thermal expansion of sintered specimens showed linear and hysteresis loop changes: Hysteresis loop obtained with increased zirconia content resulted in the t-m phase transformation.…”