| The failure of die is becoming more and more common,eighty percentage failure of die is reflected as local wear and fatigue of mold surface,which seriously affects the normal production,re-production of the mold takes an army of time and money,the development of remanufacturing technology has taken an effective way for mold repair,among which thermal spraying technology is widely applied in the remanufacturing engineering.In the Cr12 steel substrate Ni60B-WC/Co coating was prepared with various proportions of material composition by high velocity oxygen fuel(HVOF),using the L8(27)of the regression orthogonal experimental design,and the optimal coating preparation process was verified by experiments.The microstructure and phase composition of the coatings was characterized by metallographic microscope(OM),scanning electron microscopy(SEM)and X ray diffraction(XRD),Microhardness and wear properties of the coating was measured by microhardness tester and friction and wear tester.The results show that:(1)The mathematic model of relative wear,microhardness,porosity and coating material ratio and spraying distance were established respectively,under the condition of satisfying the constraint conditions,the limit value of the objective function is obtained,and the best coating preparation process is obtained.(2)The impact of WC content,Co content and spraying distance on the wear of the coating properties and microhardness is significant,and the regression equation between the factor and porosity was not significant.It's on the impact of the degree of wear properties:WC content>spraying distance of>Co content,the degree of impact on the micro hardness:WC>Co content>spraying distance.The extremum of the objective function under the constraint conditions,each component of the mass fraction of W(Ni60B)=51.3%,w(WC)=35.9%,w(Co)=12.8%,spraying distance of 320mm,the relative wear of the coating is 0.0264,coating wear resistance performance is best.(3)The coating is well bonded with the substrate.The Ni60B bonded phase is completely melted and the WC hard phase particles are semi molten state.The coating and the substrate are mainly mechanical bonding.There are no large pores and cracks and the coating is compact.The porosity of 4#coating samples is the highest,which is 0.866%,the coating phase analysis,the coating is mainly composed of WC phase phase-Ni and Ni3Si2,CrB2,CrmCn,W2C and ? phase(Co3W3C)dispersion composition etc.The results prove that the WC of the coating has a certain degree of decarburization decomposition during spraying.(4)The microhardness of the coating samples is greater than HV0.2851,the substrate is HV0.2277,and the coating is 3 to 5 times of the substrate.The wear mechanism of the coating was mainly related to the content of hard phase and binder phase,WC and other hard phase content is high,the binder content is low,the wear mechanism of the coating is mainly abrasive wear.On the contrary,the main wear mechanism is fatigue spalling.The maximum friction coefficient of the coating is 0.72.The friction coefficient of 6#sample is 0.64,which is less than that of other samples.The wear resistance of the coating is the best.(5)Adopt wear-resisting performance the best coating preparation technology for experimental verification,the corresponding relative wear coating and microhardness of the actual measured values are in conformity with the theoretical calculation;at the same time,the bonding strength of the coating is above 65MPa,the coating corrosion potential is higher than that of the matrix,is about-0.65 V,the corrosion current density of the matrix to be small,about 0.7*10-5 A/cm2,the corrosion resistance of the coatings was significantly higher than that of Cr12 steel. |
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