Hit has made important progress in ultra-high toughness nano-ceramics

Important progress in the field of ultra-high toughness nano-ceramics

Recently, the project team of Professor Zheng Yongting, Institute of Composites and Structures, School of Astronautics, HIT has made important progress in the field of ultra-high toughness, columnar crystal nano-alumina based ceramics. In this study, the internal microstructure of powders can be controlled at micro and nano scale during the rapid cooling process of ceramic melt, and the geometric characteristics of grains can be controlled during powder sintering process, which provides a new technical principle for the development of ultra-high toughness nano-ceramics.

Alumina ceramics have excellent electrical properties, mechanical properties, chemical stability, is one of the most widely used ceramic materials. However, its low fracture toughness severely limits its application in a wider range of fields, so enhancing the fracture toughness of alumina ceramics has become one of the hot spots in current research.

Zirconia toughened alumina (ZTA) ceramic material is a kind of multiphase fine ceramic material formed by introducing a certain amount of phase change material zirconia into the alumina parent matrix. Due to the hardness of alumina and the toughness of zirconia, these two materials form an excellent complex of high strength and toughness, which has higher flexural strength and fracture toughness at room temperature, and thus has excellent wear resistance. Therefore, this kind of multiphase ceramic material not only has the characteristics of high toughness and strength of zirconia ceramics, but also has the advantages of high hardness of alumina ceramics, and with the improvement of the comprehensive mechanical properties, its wear resistance has also been greatly improved.

Among them, the preparation of ZrO2 / Al2O3 composite powders with excellent properties is an important prerequisite for the preparation of alumina based ceramics with high toughness. At present, the preparation technology of composite powder includes mixing method, sol-gel method, coprecipitation method and precipitation wrapping method. The key is to ensure that the particle fineness of ZrO2 is small and the particle size distribution is narrow. It is also necessary to ensure the uniform dispersion of ZrO2, so that Al2O3 particles can wrap ZrO2, in order to produce a good toughening effect.

Professor Zheng Yongting's project team initiated the "Al-O2 ultra-high temperature combustion synthesis + melt rapid water cooling" method, developed a new ultra-high temperature melt water cooling atomization equipment, synthesized alumina/zirconia metastable micron powder (Figure A), the internal microstructure of the powder is shown in Figure B, in the sintering densification process, Alumina based ceramics with high-density multistage zirconia nanostructure and submicron columnar crystal were induced in situ (Figure C, D), which can realize the synergistic toughening of multistage nanostructure, columnar crystal and zirconia T-M phase transition, and greatly improve the mechanical properties of ceramics. The product has high hardness (HV20GPa) and excellent toughness (16MPa• M1/2), and its technical principle can be widely used in the production and manufacturing of advanced ceramics with high performance.

Compared with the traditional nanocomposite ceramic process method, the research results have the following advantages: the product has multistage high-density, fine and uniform nanostructure, the grain size is about 500 nm, and the intragrine nano-reinforced phase is about 50 nm; A large number of sub-micron columnar crystals grow spontaneously inside the ceramic, and the columnar crystals are closely bonded to the matrix atomically, and the strengthening and toughening effect is significantly improved. Economical and efficient, low cost, suitable for industrial mass production; Powder synthesis and sintering process green environmental protection, no pollution, to avoid the pollution problem caused by the liquid phase production process of nano powder; The raw material of nanometer ceramics is spherical and micron solid solution powder, which avoids the problems of nanometer powder easy agglomeration, difficult dispersion and forming difficulty, and greatly reduces the difficulty and cost of forming process.

In addition, the project team has achieved a number of research results in the technology of "ultra-high temperature combustion synthesis + melt rapid water-cooling atomization". In the previous stage, supersaturated solid solution micron powder and nano-eutectic powder of alumina/zirconia have been successfully prepared, and the high-density nano-structure equiaxed nano-ceramics have been sintered. In the nonlinear phase transformation process far from the equilibrium state, the precision control of advanced ceramic microstructure has been realized. The related achievements have been published in the journal of European Ceramic Association and American Ceramic Association, and 9 national invention patents and 1 international patent have been authorized.