Influence Of Heat Treatment On The Performances Of HVOF Thermal Sprayed WC-12Co Coatings

Ordinary WC-Co cermets are not good at the corrosion resistance in molten pure zinc. CoxWyCz (η) has a positive role in improving the durability, in order to strengthen the durability of the WC-Co cermets and to prolong the service life of galvanizing equipment in this paper, a further way to generate more η in the low carbon WC-12Co coatings was through the use of post-spraying heat treatment in an inert atmosphere (Ar), the samples were separately heat treated at550℃(HT1)750℃(HT2),950℃(HT3) and1150℃(HT4) for1hour, and the influence of heat treatment on the phase, microstructure, wear-resistance and durability in molten pure zinc of coatings were researched. The conclusions as follows:With the increase of heat treatment temperature, W2C, Co and W phases in the WC-12Co coatings, were reduced to form the η-phase (Co3W3C、Co2W4C and Co6W6C). The hardness, brittleness and wear-resistance of coatings were firstly increased and then decreased with the increase of heat treatment temperature. The highest hardness, lowest porosity and best wear-resistance were found in the HT3cermet. When the heat treatment temperature was different, the abrasive-wear and sliding-wear failure mechanisms of WC-12Co coatings were different. The abrasive-wear mechanism of HT1coating was the rapid abrasion wear, sliding-wear mechanism was mainly the adhesion wear with a litter abrasive wear. The abrasive-wear mechanism of HT2coating was the rapid fall-off of WC particles, sliding-wear mechanism was the serious adhesion wear. The abrasive-wear mechanism of HT3coating was the slow and mean abrasion wear, sliding-wear mechanism was the adhesion wear. The abrasive-wear mechanism of HT4coating was the rapid abrasion wear, sliding-wear mechanism was serious plastic deformation.The major factors which affect the durability of molten pure zinc of WC-12Co coatings were η-phase, carbon content, porosity, toughness and residual stress. The corrosion resistance of cermets in molten pure zinc according to the performance from good to bad was listed as follows, Coating HT1> Coating HT3> as-sprayed cermet> Coating HT4> Coating HT2, however, the HT3cermet presented the best corrosion resistance during the2-week corrosion time.Through comprehensive assessment of all the WC-12Co coating with heat treatment or not, the results indicated that the coating being heated at950℃for1 hour has optimal performance.