Design and Preparation of WC Composite Powders and Coatings with in-situ Synthesis Al2O3

Nanostructured WC-Co-Al powders with in-situ synthesis Al2O3 were synthesized from submicron structured WC-12Co powder and Al powder using a ball-milling method. XRD analysis shows that the average sizes of WC grains are 93.1, 39.0 and 44.8 nm after milling for 10, 30 and 50 h, respectively. When they are sprayed by high velocity oxygen fuel (HVOF) thermal spraying, WC-Co-Al powders are more easily flattened than WC-12Co powder without ball-milling. The porosity of WC-Co-Al coating is only 0.57% which is much lower than that of WC-12Co coating with a value of 1.62%. During spraying Al reacts with oxygen, which effectively inhibits the decarburization of WC, and Al2O3 hard ceramic particles are in situ generated in coatings. The HV0.1 microhardness of WC-Co-Al coating is 12.98 +/- 0.73 GPa, about 36% higher than that of WC-12Co coating, which is mainly owing to the enhancement effect of Al2O3 particles, nanocrystallization of WC phase and lower porosity.