Phase stabilization of plasma-sprayed alumina coatings by spraying mechanically blended alumina–chromia powders

ABSTRACT

A study of phase stabilization is performed on atmospheric plasma-sprayed alumina–chromia coating applied on low-carbon steel substrates. Alumina–chromia mixture with varying amounts of chromia content (1 wt.% to 6 wt.%) is used for this purpose. X-ray diffraction (XRD) analysis is carried out to investigate the different phase compositions of the coatings. Quantification of the different phases present in the coatings is performed by subsequent use of Rietveld refinement method. Surface morphology, microhardness, and wear behavior of the different coatings are also observed. Rietveld analyses performed on coatings ensure the stabilization of metastable phases present in the alumina coatings by chromia addition. Significant increase of the α -alumina and (Al_xCr_1-x)₂O₃ content is observed in alumina coatings with 4 wt.% chromia content. This is supported by the improved hardness and wear-resistant properties of the alumina coatings containing 4 wt.% chromia. The minimum surface roughness of the coating is also observed for alumina coatings with 4 wt.% chromia content among all the alumina coatings with different chromia content. The formation of alumina–chromia solid solution and solidification of α-alumina are found to be the reasons behind the enhancement in mechanical properties of the coating.

KEYWORDS:

• Atmospheric plasma spraying (APS)
• alumina
• chromia
• coating
• rietveld refinement
• microhardness

Acknowledgments

The authors would sincerely thank Dr. P. P. Bandyopadhyay of the Department of Mechanical Engineering, IIT Kharagpur, India, and the staff and members of the Materials Testing and Manufacturing (MTM) Lab, IIT Kharagpur, West Bengal, India, for their involvement in the work. Mr. Devesh Tomar (Territory manager) of Hindalco Industries Limited (Aditya Birla Group), Delhi, India, is also thanked for providing the feedstock material. They are also grateful to Sophisticated Instrumentation Centre (SIC) for FE-SEM, X-ray diffraction (XRD) facility, Central Workshop and AMP Laboratory of IIT Indore for necessary tests and fabrication works.