Investigation On Microstructure Characteristics And High Temperature Oxidation Resistance Of Cryomilled CoNiCrAlY Coatings By Laser Cladding

With the development of science and technology,the service temperature of the air turbine blade center area has reached more than 1150 degrees Celsius,and the service temperature of the gas turbine in military aircraft is even more than 1600 degrees Celsius.Based on the high temperature alloy material itself has not been able to withstand such a high temperature.The use of MCrAlY bonding layer and YSZ ceramic top structure design has become a worldwide widely used method.The MCrAlY?M=Co or Ni or both?can be used alone as heat-resistant alloy coating on the surface of the adhesive layer,and it also can be used as thermal barrier coatings.The use of laser cladding technology for preparation of MCrAlY coating was proved compared with the plasma spraying coating,electron beam physical vapor deposition technology to fabricate more compact,more high bonding strength,but has not yet developed specifically powder for laser cladding.It is reported in the literature are almost directly buy thermal spraying powder as cladding materials.In view of this,this paper carried out laser cladding preparation prior to CoNiCrAlY coating on CoNiCrAlY powders were ball milling process,the laser cladding was carried out on K438 alloy and A3 stainless steel by CO2 laser and semiconductor laser.Milling time and process parameters on the particle size of CoNiCrAlY on microstructure and high temperature oxidation resistance,and studied by using two kinds of lasers in two kinds of substrate cladding Co NiCrAlY ball milling coating microstructure difference.The results are as follows:?1?In 30 hours of milling range,CoNiCrAlY powder particle size in 0¹5 hours,20²5 hours decreased rapidly,and in 15 hours and 25 hours minimum at about 7um.15²0 hours,25³0 hours,particle size increased,but the size does not exceed the original particle size of CoNiCrAlY powder.?2?The milled CoNiCrAlY powder mainly consisted of ? phase?solid solution formed by Co-Ni-Cr?and ??-Ni3 Al,peak reduction of ?/??phase after ball milling.When milled to 5 h,10 h and 25 h with NiAl and Al₂O₃ formation,NiAl and Al₂O₃ hindered the decrease of CoNiCrAlY powder particle size.?3?Under reasonable parameters,increasing laser power can make the none-milled powder coating thickness increased significantly,while the milled coating thickness increased slightly after milling,none-milled coating thickness 2³ times as much as milled coating.Laser power cannot be increased the coating width increases,it is mainly determined by the spot size of the laser.?4?The high temperature property of the substrate affects the macro quality of the coating.Under same process parameters,The thickness of CoNiCrAlY coating prepared by ball milling on K438 was thicker than that of A3 steel.The type of laser can affect the thickness of coating,In the premise of not burning,short wavelength,high laser energy is conducive to form the coating.?5?Preparation of CoNiCrAlY coating with different milling time,the different preparation process parameters have no effect on the phase of the CoNiCrAlY coating.Mainly consists of ?-Co??-?Ni,Cr????-Ni3 Al and Cr2Ni3.At the same process parameters,with the decrease of the size of CoNiCrAlY powder,the content of??-Ni3 Al increased and the content of Cr2Ni3 decreased.?6?In the 1100 degrees Celsius oxidation,the milled CoNiCrAlY coating oxidation kinetics curve obey the parabolic law.10 h coating high temperature oxidation weight gain is relatively low,The antioxidadant of the remaining five groups of coating as followed: 30h>25h>20h>15h>5h,It showed that the oxidation resistance of CoNiCrAlY coating was positively correlated with the ball milling time.?7?I n the six groups of CoNiCrAlY coating prepared by different milling time,at 1100 degrees Celsius after high temperature oxidation,oxide coating surface layer only 10 h coating has shedding phenomenon.Other coating without shedding phenomenon,and the surface is smooth,with metallic luster.?8?The oxidation products of CoNiCrAlY coating with different milling time were composed CoO?Al₂O₃?Cr₂O₃??-?Ni,Cr??NiCr2O4?Ni3AlandNiO,with the increase of milling time,the content of Al₂O₃ and Cr₂O₃ decreased gradually.