Study on aluminum phosphate binder and related Al2O3–SiC ceramic coating

Refractory and wear-resistant Al2O3–SiC ceramic coatings have been fabricated on A3 steel using alumina (Al2O3), silicon carbide (SiC), aluminum phosphate binder (inorganic binder), and other additives as starting materials. The powder X-ray diffraction (XRD), thermogravimetric analysis/differential thermal analysis (TG/DTA), and scanning electron microscopy (SEM) techniques are applied to investigate the chemical compositions of the in-house synthesized aluminum phosphate binder and the morphologies of the fabricated ceramic coatings after abrasion test. The XRD results indicate that monoaluminum phosphate (Al(H2PO4)3) is the most effective binding phase in the synthesized aluminum phosphate binder. The TG/DTA analysis shows that two phase transformations occur at 100.7 and 217.7 °C when the synthesized aluminum phosphate binder is heated in a range 60–1000 °C and the binder after heat treatment is a mixture of several phases. The wear test results show that the wear durability of the A3 steel covered with Al2O3–SiC ceramic coatings is about two times that of the uncoated A3 steel. The results also indicate that the wear properties of Al2O3–SiC ceramic coatings are dependent on fabrication conditions such as the weight ratio of ceramics (Al2O3 and SiC) to the binder (RCB), the distribution of particle size of ceramics, the density of the aluminum phosphate binder, and the Al/P atomic ratio in the aluminum phosphate binder. Upon the above results, optimal fabrication conditions for achieving good wear resistance of Al2O3–SiC ceramic coatings are suggested in this paper.