Abstract:
NiAl-TiO
2/Bi
2O
3 nanocomposite coatings were prepared by atmospheric plasma spraying, where nanostructured TiO
2/Bi
2O
3 feedstock powders were prepared by high-energy ball milling and spray drying. The influence of nanostructured TiO
2/Bi
2O
3 with different mass ratios on microstructure, mechanical and tribological properties of composite coatings was investigated. The results show that all composite coatings possessed dense microstructure and uniform distribution of the phases. The coatings by using nanostrctured TiO
2/Bi
2O
3 composite powders performed the typical bimodal microstructure and displayed higher adhesive strength to substrate (>40 MPa). The composite coating with addition of monolithic TiO
2 feedstock powders displayed poor tribological properties at low/mid temperatures. The combination of TiO
2 and Bi
2O
3 improved plasticity and tribological properties of the coatings at low/mid temperatures, and further enhanced the lubricious behavior of composite coatings at high temperatures. For its composite coatings, the wear rate were below 7×10
-5 mm
3/(N·m) in the whole test temperatures and the friction coefficient was about 0.1 at 800 ℃. With the Bi
2O
3 content increasing, the hardness of composite coating decreased and resulted in higher wear rate. The sliding process promoted the formation of Bi
4Ti
3O
12 and NiTiO
3 at 800 ℃, which formed a continuous and complete glaze layer together with TiO
2 and NiO on worn surfaces and resulted in excellent tribological properties of composite coatings at high temperature.