Study On Preparation Of High Performance Cemented Carbide Spraying Powder For HVOF And Its Basic Mechanism

In order to improve the wear resistance of some key components such as the high-strength steel piston rod for undercarriage under the harsh working environments, the components are coated by a wear-resistance coating in aircraft manufacture. As an effective surface treatment process, the excellent wear-resistance coatings, made from cemented carbide powder, are usually fabricated by HVOF. However, high-quality coating depends on the performances of the thermal spraying powders.In this paper, in order to acquired high-quality powders, WC-10Co-4Cr cemented carbide powders were produced by a new granulating and speedy high temperature sintering process. A coating made from the self-made cemented carbide powders was obtained by HVOF. The effects of slurry preparation, spraying granulation, derosination process and speedy high temperature sintering process on properties of powders and the performances of the coating were investigated. The conclusions can be shown as follows:1) Through the comparative study of powder properties, the proper process of slurry preparation and spray granulation is adhesive being PEG4000, solid content being65～80%, inlet/outlet temperature being220℃～260℃/100℃～120℃, speed of atomizer being6000-8000r/min. A kind of WC-10Co-4Cr cemented carbide powder was obtained by the centrifugal spray drying process.2) Based on the thermal analysis of WC-10Co-4Cr cemented carbide solid powder whose particle size is100μm, its core temperature can raise to the high sintering temperature after0.02s in a high temperature environment.3) After the high temperature sintering, the bond of WC-10Co-4Cr composite powder shift from mechanical bond to metallurgical bond, the fluidity and apparent density increase remarkably; with the increase of sintering temperature, the fluidity, apparent density, and compactness of powders and the smoothness of surface increase; with the feed rate increases, the degree of liquid phase sintering of powder reduces; a speedy high temperature sintering theory of the powder was present;4) Using the self-made powder, a type of coating with very low porosity and high micro-hardness was fabricated by HVOF. The perfect combination between coating and substrate indicates that the self-made powder was suitable for HVOF.5) A proper WC-10Co-4Cr cemented carbide powder is fabricated by the new process of agglomeration and speedy high temperature sintering which is a short process technology and good economy.