科研之友
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摘要
Laminated coatings of Al2O3-NiCrAl and Al2O3+13 wt% TiO2-NiCrAl were deposited on low carbon steel substrates by plasma spraying. The bond strengths of the coatings were measured by pull-off test, and the residual stresses in the outermost surface layers were measured by X-ray diffraction. The effect of additive SiO2 on bond strength and stress of the coatings in the two systems was compared with the results of our previous investigation of the ZrO2 system. The nature of liquid phase sintering of additive SiO2 in ceramic coatings is elucidated. The bond and transition layers in the laminated coatings can largely overcome the inherent mechanical and thermal incompatibilities between the oxide coating and metal substrate, therefore the residual stress can largely be relaxed and the coatings will possess good bond strength. However, when an appropriate additive is doped into refractory ceramic coatings, contact between ceramic and substrate, as well as within the coating, would be developed. Thus, the bond strength and stress can be further improved. Introduction of additive results in liquid phase sintering. The effect of additive of lower melting point would be very obvious in a system which possesses a higher melting point, such as the SiO,-doped ZrO2 coating. However, this effect would not be so apparent in ceramic coatings which possess a lower melting point, such as Al2O3 and Al2O(3) +13 wt% TiO2 systems. Because the molten droplets can stay long enough for spreading and full flattening, the contact can reach rather a good state. As a result, a suggestion is put forward that when the melting point of a ceramic coating is high, an additive should be introduced; and when the melting point of a sprayed coating is low, then no additive is necessary.
- 出版日期1997-2-15
- 单位华南理工大学
