| NiCoCrAlY alloy has been widely used in surface protection of ae rospace components for their outstanding resistance to high-temperature oxidation.However,the high cost of commercial NiCoCrAlY alloy powder has become the bottleneck of civil industrial application,so it has the significant industrial application value to study how to prepare NiCoCrAlY alloy coating with low cost.The pure powder constituting the NiCoCrAlY alloy is inexpensive,and the price of mixed powder is 7.5times lower than that of the commercial powder.So it would be the certain scientific significance and industrial application value if the mixed powders are used as feedstock and then prepared NiCoCrAlY alloy coatings by a special process.Therefore,the study put forward to prepare powder pre-coatings with mixed Ni,Co,Cr,Al,Y by cold spraying and then NiCoCrAlY alloy coating was successfully prepared by in-situ diffusion synthesis.The mixed power of Ni,Co,Cr,Al,and Y was prepared with the ratio of 4:2:1.5:1:0.03 for 4 h.The mixed powder coating was prepared on the 310S heat-resistant steel?0Cr25Ni20?surface by low-pressure cold spraying technology,followed by in-situ synthesis induction remelting and vacuum diffusion.The phases,microstructure and composition of NiCoCrAlY alloy coatings were analyzed by XRD,SEM and EDS,respectively.The ability of situ synthesize NiCoCrAlY coatings of two technologies and the high temperature oxidation resistance of the alloy coatings were compared.Simultaneously,the friction and wear properties of the inductive remelted NiCoCrAlY coatings t hat showed the better effect of in-situ diffusion synthesis were investigated.The results showed that the microstructure of vacuum diffusion coating exhibited a"fish scale".The oxidation experiment showed the internal oxidation of the coating is more serious,and the overall oxidation weight gain of the coating is more obvious.When the oxidation time was 50 h,the oxidation weight gain of vacuum diffusion coating is 4.35 mg/cm2 at 950?,4.5 mg/cm2 at 1050?,which decreased by 7.4%and7.2%compared with the substrate,respectively.However,the microstructure of induction remelt coating is more dense,the pores inside the coating are significantly reduced and excellent metallurgical bonding is formed between coatings and substrate due to full diffusion and reaction between elements.In addition,the microhardness value can reach about 345 HV.The oxidation experiment showed when the oxidation time was 50 h,the oxidation weight gain of induction remelt coating is 3.4 mg/cm2 at950?,which decreased by 27.7%compared with the substrate and 21.8%compared with the vacuum diffusion coating with the same condition;the oxidation weight gain of induction remelt coating is 3.65 mg/cm2 at 1050?,which decreased by 24.7%compared with the substrate and 18.9%compared with the vacuum diffusion coating with the same condition.Combining the study of bonding state between coatings and substrate,morphology and high temperature oxidation resistance of coatings,the result showed that in-situ inductive remelting was a good method for preparing NiCoCrAlY alloy coating.The tribological performance of the induction remelted coating from room temperature?RT?to 800?was tested on a HT-1000 pin-on-disk type high temperature tribometer.The results showed that the wear rate of the induction remelted coating at RT,600?and 800?is very low.The wear resistance at 600?is significantly superior,characterized by wear rate of 0.2×10-4 mm3/?N?m?,which decreased approximately by 77.3%,98.4%,97.8%,71%than that of room temperature,200?,400?and 800?,respectively.The wear mechanisms of coatings at different temperatures are distinct.As the testing temperature elevates,the dominative wear mechanism changes from a mild regime of smear and adhesive wear at room temperature to the severer adhesion wear at medium temperature,then to slight scratch wear and partial abrasive wear at high temperature.The coatings exhibited good high-temperature wear resistance and had a good protection effect on the substrate. |
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