It is an effective strengthened technique to introduce a coating containing compressive stress on the surface of ceramic. In this work, the mixed slurry of alumina and quartz powder was coated on the pre-sintered alumina body, then the mullite-alumina coating with lower thermal expansion coefficient was synthesized in-situ after pressureless co-sintering. The pre-stressed strengthening of alumina was achieved by the residual compressive stress formed in the coating during the cooling process. The results indicate that, with the increase of the doping content of quartz in the coating, the flexural strength of pre-stressed alumina increases firstly and then decreases. The flexural strength of specimen realizes the highest value when the doping mass fraction of quartz is 15%, and the interface between the coating and the substrate bonds tightly. Under this condition, the flexural strength of the pre-stressed alumina ceramic is (549.44±27.2) MPa, which is 37.19% higher than that of the common alumina. When the doping mass fraction of quartz is higher than 15%, the flexural strength decreases due to the shrinkage stress mismatch in the sintering process. The effect of prestress enhancement weakens gradually with the increase of temperature. As the testing temperature reaches and exceeds 1000 ℃, pre-stressed alumina and common alumina possess approximately equal flexural strength. Pre-stressed alumina also exhibits better thermal shock resistance and damage tolerance due to the compressive stress formed in the coating
HAO Hongjian, LI Haiyan, WAN Detian, BAO Yiwang, LI Yueming. Enhanced Flexural Strength and Thermal Shock Resistance of Alumina Ceramics by Mullite/Alumina Pre-stressed Coating. Journal of Inorganic Materials, 2022, 37(12): 1295-1301 DOI:10.15541/jim20220238
Fig. 8
Theoretical relationship between residual compressive stress and substrate-to-coating thickness ratio in different pre- stressed aluminas
涂层残余应力与热膨胀系数差Δα正比、与涂层弹性模量Ec也存在正比关系。由于两者的竞争关系, 当石英含量大于20%时, 涂层残余应力计算结果增加已不明显。综上, 为实现一个高性价比的莫来石-氧化铝涂层增强氧化铝构件, 优化设计准则建议为：a)形成强界面且hs/hc>10; b) 相一致的烧结收缩匹配性; c) 涂层需要较高的弹性模量。
A processing approach has been identified and reduced to practice in which a residual stress profile can be designed such that cracks in a brittle material are arrested or grow in a stable manner. In the approach, cracks in the body encounter an increase in the magnitude of residual compression as the crack propagates. If correctly designed, the process increases strength and significantly decreases strength variability. This approach was demonstrated for a silicate glass, and multiple cracking was observed as a forewarning of the final failure. Normally, such glasses would fail catastrophically with the propagation of a dominant crack.
BERMEJOR, TORRESY, SÁNCHEZ-HERENCIAA J, et al.
Residual stresses, strength and toughness of laminates with different layer thickness ratios
A pre-stressing design and a simple fabrication technology to substantially improve the strength of ceramic components are presented. Residual surface compressive stress is generated in ceramic components by pressureless sintering of a green bulk coated with a thin layer of low coefficient of thermal expansion (CTE). The stress level can be controlled by changing the cross-section area ratio, Young's modulus ratio and CTE ratio of the coating. Pre-stressed ZrO2 ceramics coated with Al2O3 can achieve a flexural strength of 1330 +/- 52 MPa, 45% higher than their uncoated counterpart. Similarly, the flexural strength of building porcelain tiles is increased by 70%, from 67 +/- 3 MPa to 114 +/- 5 MPa. The damage tolerance of pre-stressed ZrO2 ceramics is excellent with a high residual strength of similar to 1200 MPa in a thermal shock test at 325 degrees C. This simple technique can improve the mechanical performance of ceramic components with no limitation of size and shape. (C) 2019 The Chinese Ceramic Society. Production and hosting by Elsevier B.V.
LIH Y, HAOH J, TIANY, et al.
Effects of residual stresses on strength and crack resistance in ZrO2 ceramics with alumina coating
Journal of Inorganic Materials, 2022, 37(4):467-472.
It is a worldwide challenge to simultaneously improve the strength and damage tolerance of ceramics, which is a core issue in the development of ceramics and a goal pursued by materials scientists. While the pre-stressed design has been widely used to improve the strength of concrete and glass for over a century, a little progress has been made for ceramic materials. In this paper, the research progresses of ceramic reinforcement are summarized, and a new pre-stressed design and model of high strength and high damage tolerance composite ceramics are proposed. The novel design focuses on the generation of residual compressive stresses on the surface of ceramic components to inhibit crack initiation and growth, and offset the external tensile stress, which can be applied to different fields such as structural ceramics, architectural ceramics, domestic ceramics and so on. This simple and economical technique with no limitation of size and shape in ceramic components has great application prospects.
LIN, ZHANGX Y, QUY N, et al.
A simple and efficient way to prepare porous mullite matrix ceramics via directly sintering SiO2- Al2O3 microspheres
Journal of the European Ceramic Society, 2016, 36(11):2807-2812.
Porous anorthite/mullite composite ceramics with different mullite contents were fabricated by foam-gelcasting method, using CaCO<sub>3</sub>, SiO<sub>2</sub>, α-Al<sub>2</sub>O<sub>3</sub> as raw materials. Effects of mullite content on bulk density, porosity, compressive strength, thermal conductivity and microstructure of the porous composite ceramics were researched. Mullite content has great effect on the apparent porosity of the porous anorthite/mullite composite ceramics. As a result of the appearance of liquid phase in the sintering, the sample shrunk, which is the main reason for the porosity decrease. Compressive strength and thermal conductivity increase with the mullite content under the condition of the similar porosity. Dense pore wall and rod-like mullite grain are benefit for compressive strength of porous anorthite/mullite composite ceramics. The apparent porosity of the prepared porous anorthite/mullite composite ceramics is in the range of 60.8%-75.2%, the compressive strength is between 12.94 MPa and 36.95 MPa, and the thermal conductivity is in the range of 0.30-1.33 W/(m·K).
JIANGY, CHANGL F, RUH Q, et al.
Microstructure and oxidation behaviors of dense mullite-silicon carbide-silicon coating for graphite fabricated by dipping-pyrolysis and reactive infiltration
Surface and Coatings Technology, 2018, 350:410-418.
XRD-based quantitative analysis of clay minerals using reference intensity ratios, mineral intensity factors, Rietveld, and full pattern summation methods: a critical review
Microstructure and oxidation behaviors of dense mullite-silicon carbide-silicon coating for graphite fabricated by dipping-pyrolysis and reactive infiltration
XRD-based quantitative analysis of clay minerals using reference intensity ratios, mineral intensity factors, Rietveld, and full pattern summation methods: a critical review
