Microstructure Investigation of WC-Based Coatings Prepared by HVOF onto AZ31 Substrate

Area of Science:

• Materials Science
• Surface Engineering
• Tribology

Background:

• Cermet coatings enhance substrate properties.
• Magnesium alloys offer lightweight advantages but require surface protection.
• High Velocity Oxy Fuel (HVOF) spraying is a key technique for applying dense coatings.

Purpose of the Study:

• To investigate the microstructure, phase composition, and residual stress of HVOF-sprayed cermet coatings on AZ31 magnesium alloy.
• To compare the characteristics of WC-Co-Cr, WC-Co, and WC-Cr3C2-Ni coatings.
• To understand the influence of the magnesium alloy substrate on coating properties.

Main Methods:

• Coating deposition using the High Velocity Oxy Fuel (HVOF) method.
• Microstructural analysis via optical microscopy (OM), scanning electron microscopy (SEM), and transmission electron microscopy (TEM).
• Phase analysis using X-ray diffraction (XRD).
• Residual stress measurement.

Main Results:

• All coatings exhibited satisfactory homogeneity.
• X-ray diffraction confirmed the presence of WC as the main phase in all coatings, with secondary phases like W2C, Co, W, Cr3C2, and Cr7C3 observed depending on the coating composition.
• Linear stress was compressive in all coatings. WC-Co and WC-Cr3C2-Ni coatings showed similar residual stress levels, lower than WC-Co-Cr.
• Shear stress was induced in the WC phase of the coatings, attributed to the low elastic modulus of the AZ31 magnesium alloy substrate.

Conclusions:

• HVOF spraying successfully produced homogeneous cermet coatings on AZ31 magnesium alloy.
• The coatings possess compressive residual stresses, beneficial for wear resistance.
• The magnesium alloy substrate significantly influences the stress state within the coating, inducing shear stress in the WC phase.