Effects Of Isothermal Aging On Microstructure And Mechanical Performances Of Stellite 6 Claddings

High temperature friction wear is faced by most key equipment and/or parts which served at high temperature.Damage due to high temperature friction wear would be harmful for their safe and cost-effective running.This issue could be partly solved by applying wear-resistant claddings.However,the high temperature stability of the cladding,such as microstructure,mechanical properties,is critical to material selection.In this work,plasma arc surfacing and manual electric arc welding technologies were employed to produce wear-resistant claddings with Stellite 6 alloy powder and electrode,on the surface of 304 stainless steel.After cladding,the samples were isothermally aged at 700 for up to 1000 h.The thermal mechanical process of the filler metals were ?analyzed in advance by using JmatPro software.And the microstructures of the as cladded and as aged samples were characterized by using optical scope,scanning electronic microscope,energy spectrum and XRD.The hardness and friction wear behaviors of the samples were tested at room temperature,600 ??700 ? and 800 ?.The relationship between the microstructure and mechanical properties were analyzed.Though both the electrode and alloy powder are Stellite 6,they have difference in C content.Based on JmatPro software,the phase evolution during temperature increase and decrease were predicted.The results indicate that for the two materials,after cooled from liquid to room temperature,the microstructures mainly consist of?-Co,the content exceeds 50%.And whatever at room temperature or 600~800?,The carbides in Stellite6 alloy powder is more than that in Stellite 6 electrode.In addition,temperature increase would promote?-Co??-Co phase transformation.The microstructural characterization shows a typical dendritic feature for the both kinds of claddings.The primary phases include Co-rich solid solution and eutectic structures consisting of Cr-rich carbides and Co,the eutectic distributed in interdendritic.During isothermal aging,the?-Co gradually transformed to?-Co,and M7C3 transformed to M23C6.Moreover,very fine particle like M23C6 were found to precipitate in Co solid solution.And linearly distributed M23C6particles were found at the stack fault of?-Co.The martensite transformation in Stellite6 alloy powder cladding was quicker than that in Stellite 6 electrode cladding.The results of hardness test indicate that,the cladding could remarkably improve the hardness of the substrate.The hardness of the cladding decreased with temperature increase.At the temperature range of 600~800 ?,the hardness of the both claddings decreased about 20%.And the hardness at this temperature range show a stable feature.Thermal aging was found to be beneficial in increasing the room temperature hardness,while to be harmful for the high temperature hardness.It might be related with the redissolution of particle like carbides at high temperature.Moreover,the hardness of Stellite 6 alloy powder cladding was higher than that of Stellite 6 electrode cladding at the all testing conditions.Similarly,the wear performance of Stellite 6 alloy powder cladding was much better than that of Stellite 6 electrode cladding at the all testing conditions.The result indicates that the cladding produced by Stellite 6 alloy powder had more stable mechanical performance than that produced by Stellite 6 electrode.