Study On The Technology Of Nano-ceramic Metallic Matrix Gradient Material

The bonding forces and thermal shock resistance can be improved through weaken the stress concentration existing in the bonding layer between metal and ceramic, by metal-ceramic gradient composites. FeNiAl alloy powder at a specific proportion was prepared in advanced. Also nano Al₂O₃ powder was used as raw material in our experiment. The samples were prepared with different composition alloy powder. Through a mass of experiments, pressureless sintering in protecting atmosphere was determined as the optimized process parameter. In this article, the mechanical properties, microstructure and abrasion mechanism of FeNiAl/Al₂O₃ gradient ceramic layer were the emphasis.A Sintering was carried out in a box furnace at 1150¹200℃ for 1h in Ar atmosphere. The FeNiAl/Al₂O₃ gradient composite layer based on 45 steel has a favorable surface topography. And the ingredient shows a gradient distribution, which contributes to improving the thermal shock resistance and abrasion resistance.Both microstructure and phase constituent of samples were investigated by SEM, EDAX and XRD. We draw the conclusions as followed: FeNiAl/Al₂O₃ gradient composite layer presents a splinter shaped, from the matrix to the surface of ceramic layer, along the thickness direction, the content of Al₂O₃ increased, while that of Fe-Ni-Al alloy decreased gradually, shows a gradient distribution of ingredient. The structure has a characteristic with macroscopical inhomogenous and microcosmic continuity. Additionally, a new phase FeAl₂O₄ was observed in the interface between gradient composite layer and 45 steel, which indicated there exists chemical reaction between the element in ceramic and Fe, at the same time, mutual diffusion between them.The micro-hardness, thermal shock resistance and abrasion resistance were respectively studied by numeral micro-sclerometer, circular calefaction and slippaging abrasion. The capability variation rule of bonding layer was also analysed. It was indicated:The micro-hardness increased with the content of AI2O3 from substrate to surface along the direction of ceramic layer thickness, but declined in the AI2O3 ingredient section near surface. The micro-hardness reached its maximum in the area contained 70wt% AI2O3.The thermal shock resistance of composite layer was preferable and was as three times as common ceramic coating. The addition of FeAINi transition bottom and component gradient had some effect on improvement of thermal shock resistance. The failure mode of thermal shock behaved as shedding of ceramic layer. The intensity fell gradually with the times of thermal circulation. At last the damage mode behaved as slice shedding along the grain.The properties of the abrasion resistance of gradient composite layer is fine and it is 16-25 times as strong as the substrate of 45 steel. It proved that gradient composite layer conduced to abrasion resistance. FeAlNi/AhC^ gradient composite layer with specific component (about 30wt%FeAlNi) had better abrasion resistance than that of AI2O3 coating. FeAlNi/A^Oa gradient composite layer presented different friction action under different load. The greater load, the higher abrasion rate it had and the worse abrasion resistance.The SEM of abrasion surface shows that the gradient variety along the direction of thickness of composite layer made the coating presented a friction abrasion mechanism, which behaved as grain shedding, crack emergence and crack spread, during the wearing process.