| Metal materials have many excellent performances, while also having some disadvantages such as being susceptible to corrosion of gas, water and some chemical medium in the using process, abrasion due to the mutual movement, oxidation caused by the high operating temperature.The preparation of ceramic coating on metal surface can organically combine the features of ceramic material with the characteristics of metal material to obtain the composite products which not only have good strength and toughness, processability, electrical and thermal conductivity of metal, but also have the excellent properties such as high temperature resistance, wear resistance and corrosion resistance, and thus possess the comprehensive advantages of the two materials. It has an important engineering significance to develop the surface protection and enhancement technology such as metal-based ceramic coating to improve the abrasion resistance and corrosion resistance of products in conditions of high temperature, high speed, high pressure and harsh working environment.In metallurgy and electric power industries, many devices and pipes are in long-term poor operating condition. To solve the problem of erosive wear, domestic and foreign scholars have put forward the ideas of enamel coating and glass-ceramic coating. However, these measures have limited effects.Li2O-ZnO-Al2O3-SiO2(LZAS) glass-ceramics have low softening temperature and adjustable thermal expansion coefficient within a certain temperature range (3.6-20×10-6K-1, 20-500℃). Accordingly, functionally gradient materials (FGM) theories were adopted to the design and manufacture of coating materials in this paper, and the idea of preparing Y-TZP/LZAS gradient coating on Q235 steel substrate by enameling method was put forward. The researches in this paper give scientific support to overcome the low strength and toughness of glass-ceramic coating, and have important academic value to develop the metal-matrix ceramic coating surface protecting and intensifying technology.There have been few studies on preparation of LZAS system glass-ceramic by sintering method. Therefore, heat treatment process and sintering behavior of LZAS glass-ceramics were investigated by using X-ray diffraction, scanning electron microscopy and shrinkage rate. The results showed that the nucleation temperature and nucleation time played an important role on crystallinity. Crystallization temperature had a significant effect on type, size and size uniformity of crystals. The major crystalline phase of the LZAS glass ceramic was γⅡ-LZS when the specimens were crystallized at low temperature. The major crystalline phase was changed into β-quartz solid solution and yo-LZS when the specimens were crystallized at high temperature. With the increase of crystallization temperature, there were two kinds of phases transition in the heat treatment process for the LZAS system glass ceramics:cristobalite to β-quartz solidsolutions, γⅡ-LZS to yo-LZS. The one-step heat treatment process of LZAS glass ceramic was also investigated. There were few chages on type and morphology of precipitated crystal phase but the decrease in quantity of crastal compared to two-step heat treatment. The Sintering mechanism of LZAS glass-ceramics belonged to viscosity flow sintering. Densification was accompanied by crystallization during the sintering process. There existed a fact that densification dominated the early stage of sintering process and crystallization dominated the later stage. These phenomena promoted densification of specimens.In order to improve the toughness of LZAS glass-ceramics, Y-TZP/LZAS glass-ceramics composites were prepared with different content of 3Y-TZP by pressureless sintering. The effect of 3Y-TZP content on phases, microstructure and mechanical properties of composites were investigated by using X-ray diffraction, scanning electron microscopy and performance tests. The results revealed that adding 3Y-TZP particales into the glass-ceramic matrix increased the vosity of glass phase and reduced the sinterability. The viscous flow sintering was the singtering mechanism of the Y-TZP/LZAS glass-ceramics composites; During sintering, galss-ceramic and 3Y-TZP remained independent, and there was no reaction with each other. With the increase of 3Y-TZP content, the hardness, bending strength and fracture toughness of composites increased. The composite containing 15vol% 3Y-ZTP had desirable properties in comparision to the other composites. The composite containing 20vol% 3Y-ZTP had worse bending strength and fracture toughness because of failing to density. The mechanism for improving fracture toughness was crack pinning, crack deflection and transformation toughening by existing t-ZrO2 during fracture.Based on the physical, composition distribution and propety parameter models of Y-TZP/LZAS gradient coating, the residual stresses and contact stresses were investigated by using finite element software. The results show that the optimal coating could be obtain corresponding to the following parametrs:the composition gradient exponent m=1, the nuber of graded layers=3-5, the coating thickness=1-1.5 mm, the volume difference of 3Y-TZP in various graded layers=5-8%.Finally, based on the theoretical research in the previous chapters, Y-TZP/LZAS glass-ceramic gradient coatings on Q235 steel substrate were successfully fabricated by enameling method. The singtering process and microstrucure were also investigated by means of viscosity-temperature test, wetting ability test and SEM. The results indicated that the interfaces combined closely, there were no crack defects. The reaction between SiO2 and Fe oxides insured strong adhesion between LZAS glass-ceramic and Q235 steel. The reaction products were Fe2SiO4 and FeSiO3. With the increase of 3Y-TZP content, the microhardness and fracture toughness of graded coating increased along the thickness direction. The existing residual press stress of gradient coatings was measured by X-ray diffraction approach. The enhancement of toughness of graded coatings could be attributed to crack pinning, crack deflection and transformation toughening by existing t-ZrO2. The bonding strength between coating and Q235 substrate was up tol6.3 Mpa. Thermal cycling times was more than 30 when the graded coating underwent thermal cycling test at 300℃. The graded coatings had preferable thermal shock resistance.
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