| MCrAlY(M=Ni,Fe or Co)coatings,as a type of thermal protective coatings used on superalloy,have been widely applied in aircraft and gas turbine blade or other high temperature components.It shows excellent oxidation,corrosion resistance and mechanical properties.Conventional preparing method of MCrAlY coatings mainly include high velocity oxy-fuel spraying(HVOF),air plasma spraying(APS),low pressure plasma spraying(LPPS),electron beam physical vapor deposition(EB-PVD),magnetron sputtering(MS).Arc ion plating(AIP)is one of most extensive PVD techniques applied in industry.It exhibits high ionization rate and high particle energy,this characteristics enable the AIP method to deposit denser and more well-bonded coatings and to a large extent to overcome the line-of-sight effect.Hence it has a remarkable advantage in terms of depositing on the complex geometries substrate like turbine blades.Due to those advantage,in this paper,Ni CoCrAlYTa coatings were prepared on the supperalloy-K423 A by arc ion plating.After studying the influence of technological parameters on deposition of NiCoCrAl YTa coating,the coatings under-50 V,-100 V and-150 V were prepared based on the optimized parameters of arc current and pressure.Then the effect of vacuum heat treat on the phase structure and the element distribution of the coatings were analyzed;The oxidation resistance and the thermal shocking of the coatings were studied emphatically;Meanwhile,the protection and degradation mechanism of the coating were also explored.The results are as follows:(1)The bias voltage had most significant effect on porosity of the coatings,the density of the coating were increased with the increase of bias voltage;The composition changes from alloy cathode target to alloy coating deposited by arc ion plating,the Al content in the NiCoCrAlYTa coating decreased in comparison with the target composition.(2)The density of the coating after vacuum heat treatment was improved,meanwhile,the vacuum heat treatment promote the element diffusion between the coating and the substrate,which produce the metallurgical bonding in the coating/substrate interface;the vacuum heat treatment is not able to change the phase composition,however,can increase the degree of crystallinity and make the crystalline grain bigger.Besides,after vacuum heat treatment,Al and O accumulate on the surface of the coating,forming a thin layer of Al2O3 scales.(3)The oxidation resistance of the NiCoCrAlYTa coating decreases with the increase of bias voltage before oxidation for 100h:-50 V coating still show excellent oxidation resistance,however,the internal oxidation occurred in the-100 V coating and-150 V coating,leading to the complete degradation of-100 V coating and-150 V coating and making the substrate oxidized after oxidation for 200 h.The spallation mass from K423 A,-50 V,-100 V,-150 V is2.45mg/cm2,0.146mg/cm2,0.757mg/cm2 and 0.611mg/cm2 respectively,the rate of mass gain from-50 V,-100 V and-150 coating after oxidation for 200 h is 0.0601g/m2·h,0.1090g/m2·h,0.1095g/m2·h respectively.(4)Essentially,the influence of bias on the oxidation resistance of the coating is the influence of Al content and porosity of the coating on the oxidation resistance of the coating.As the pores in the NiCoCrAlYTa coating prepared by arc ion plating can disappear after exposed in high temperature environment,hence Al content is the determining factor which influences the oxidation resistance of the coating.The coating begins to degrade when the Al content decrease below a critical value.(5)NiCoCrAlYTa coating by arc ion plating shows excellent thermal shock property,the coating under the bias voltage of-50 V,-100 V and-150 V were all not spalled after thermal shock,however,some cracks are formed in the coatings,moreover the number of these cracks is reduced with increase of the bias voltage,which indicates that the thermal shock of the coating is improved with increase of the bias voltage. |
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