Preparation And Mechanical Properties Of Laser Cladding Layer On High Temperature Friction Surface

Due to operating in harsh environments,many engineering friction pairs,such as the piston pin-hole friction pair,are prone to structural/surface damage that can result in equipment downtime or even scrapping.Manufacturing new components for these parts is costly and has a long cycle time,which contradicts sustainable development goals.By utilizing remanufacturing technology to regenerate critical components,costs can be reduced by 50%,energy can be saved by 60%,and materials can be conserved by 70%.Laser cladding（LC）technology has comprehensive advantages in high interfacial bonding strength and a small heat-affected zone,meeting the stringent repair requirements of high-end components.It is also environmentally friendly and cost-effective,with repair costs only 1/5th of the replacement price,making it the most valuable remanufacturing technology.Additionally,LC technology can prepare functional coatings on inexpensive metal surfaces to meet service requirements,replacing expensive bulk alloys and achieving cost reduction,energy savings,and consumption reduction goals.However,due to the"hot and cold quickly"characteristics of LC process,the surface formed by direct cladding is rough,and there are often defects such as cracks,pores,and stress,which hinder the wide application and promotion of this technology.Based on the above engineering background,taking the high-power piston pin-hole friction pair as an engineering case,LC technology is used to prepare Fe,Ni,and Co-based three cladding layers on the surface of the 42CrMo piston substrate.At the same time,the"turning+ultrasonic burnishing"process is used to cut and surface strengthen the prepared cladding layer.Compared with the forging 42CrMo material currently used in engineering,the three cladding samples are analyzed for their surface integrity,mechanical properties,and high-temperature friction performance.The main research content and conclusions include:（1）A comparative study is conducted to investigate the effect of ultrasonic burnishing（UB）treatment on the surface integrity of three types of cladding layers.While turning can reduce the surface roughness of the cladding layer,it cannot alter the structure and internal characteristics of the cladding layer.In contrast,the surface integrity of the three types of cladding layers is significantly improved with UB treatment compared to the turning samples.The roughness parameter Ra decreased from 1.1-1.2μm to 0.1-0.2μm,and a compressive stress layer is formed on the surface of the samples.The porosity decreased,and the grain size is refined,with a refined layer of 200μm.The microhardness was increased,with the Co-based turning sample having a microhardness of 664.1 HV_0.5,which was 102.28%higher than the control sample.The Co-based UB sample has a further increase of 13.81%in microhardness(755.8 HV_0.5)compared to the turning sample.The primary mechanism of ultrasonic burnishing surface strengthening is attributed to the ultrasonic plasticity of the surface material and sub-surface material under high-frequency impact load,resulting in easier deformation and greater plastic deformation.（2）Using the nanoindentation method,the mechanical properties of the three types of cladding layers are analyzed after ultrasonic burnishing treatment.The results showed that the UB treatment can improve the elastic modulus,nano-hardness,and creep resistance of the three types of cladding layers.The mechanism of improved creep resistance of the cladding layer with UB treatment is attributed to the fact that the creep mechanism of the cladding layer is dislocation migration,and the UB treatment increased the surface dislocation density of the cladding layer,hindering deformation.The improvement in the mechanical properties of the cladding layer after UB treatment is attributed to the improvement in surface integrity,namely,grain refinement,increased hardness,and residual stress,all of which contribute to enhancing the resistance to deformation and strength of the samples.（3）A comparative study is conducted to investigate the high-temperature tribological properties of the three types of cladding layers.The friction coefficient,wear loss,and wear morphology of the three types of cladding samples are experimentally tested and compared.Compared to the control samples,the friction coefficient and wear loss of the three types of cladding samples subjected to turning treatment are significantly reduced,and the three types of cladding samples subjected to UB treatment showed further reductions,which is attributed to the improved surface quality and mechanical properties of the cladding samples.Among them,the Co-based cladding sample exhibits the best high-temperature wear resistance.Meanwhile,the wear mechanisms of the three types of cladding layers are both abrasive wear and adhesive wear.