Studies On Microwave Sintering Cobalt-based Alloy Functional Coating On Ceramic

Cobalt-based self-fluxing alloy powder and alumina ceramic powder aremicrowave sintered on alumina ceramic in order to make functional gradient coating.Measure the microwave-absorbing characteristics of powder, relative density, thermalshock resistance and inoxidizability of coat specimens sintered with different powdersizes and different structure and proportion of powder in gradient coating by SEM,EDS micro test tools during research.Powder particle size decrease with the increasing of ball-milling time, powdershave obvious agglomeration after36h ball-milling.The tendency of metal powderheated microwave-absorbing is that absorbing microwave ability increase with ball-milling time increase and absorptivity approach saturation during heating process,temperature rise slowly. Lump organizations are bigger and more asymmetrical in coatspecimen sintered by primitive powder while this phenomenon is completely oppositein coat specimen sintered by24h ball-milling powder. The amount of shrinkageporosity and desquamating near bonding surface decrease with ball-milling timedrawing near24h and increase with ball-milling time exceeding24h far away. Relativedensity of specimens increase with ball-milling time lengthening but decline slightlywhen ball-milling time reach to36h and48h. Thermal shock resistance of specimensimprove when milling time surpass12h and deprave when milling time reach to36hand48h.The same as the inoxidizability of coat specimens.The best ball-milling time is24h.After comparison with specimens different in structure and proportion of powderin gradient coating we find that the relative density of gradient coating specimens aregreat higher than specimen without gradient coating, and relative density improveslightly with compositional gradient lessening in coat. Shock resistance of gradientcoating have the varying law that the cobalt-based alloy powder specimen with fourlayers compositional gradient lessening in coat is worse while the specimen with two layers which alloy powder count half in endothecium and pure cobalt-based alloypowder in exothecium is better.Combination between coating and matrix become better when sinteringtemperature rise.Under the microwave selective heating condition there are manyglobular offwhite organizations which have more cobalt-based alloy elements andmany gray black organizations which have more Al2O3elements in SEMmicrotopography of specimens. From XRD analysis results of transition layer ofspecimens we conclude that there are Al13Co4mesophase in some specimens.Therelative density increase and thermal shock resistance improve with sinteringtemperature rising, while they get down after temperature is over1200℃.The samerule as inoxidizability of coating specimens.The best sintering temperature is1200℃.Coating specimens get better uniformity and combination, the relative densityincrease and thermal shock resistance improve with sintering time lengthening, whilethey get down when sintering time is over30min. The same rule as inoxidizability ofcoating specimens. The best sintering time is30min.