Investigation of the surface properties of modified 5140 steel by pulse plasma technology

Key Words: Pulse plasma, AISI 5140, surface modification, linear wearThe pulse plasma technology which is a new process of surface modification have been developed for the production of materials, tools and machine parts with required surface properties, such as wear and corrosion resistance. Pulsed plasma system with improved surface properties of AISI 5140 steel is expensive and hard to find the availability of steel rather than groups studied.The surfaces of AISI 5140 steel were modified by a newly developed pulse plasma technique. The surfaces of the samples were modified by a mixture of air, C3H8 and oxygen gases by using plasma pulse technique. The samples were investigated in optical microscope and modified coating layer thicknesses were measured. It was determined that pulse plasma process parameters affect the thickness of modification layer and its microstructure. In this study, the microstructure and surface properties of pulse plasma treated AISI 5140 steel was evaluated.Fe3C, Fe7C, Mo, MoC, Cr, ? -Fe, ? -Fe phases were detected in modification layer taken from X-ray analysis. Microstructural hardness measurements were taken from surface to core and different values were measured depending on various parameters. The hardness of steel sample was measured as 228 HV0.05 before pulse plasma treatment. Its value was increased to 990 HV0.05 after the treatment. After wear study, several analysis techniques such as X-ray diffraction and scanning electron microscope (SEM) and EDS were utilized to reveal the nature of this improvement. It is found that the hardness of the surface of the samples after treating was 2-3 times increased.Wear test was done in CSM-linear wear test machine with 0,15m/s constant sliding speed under 1N, 2N, and 3N loads for 500m. It was observed that friction coefficient and wear value were changed in accordance with load. Friction coefficient values of modified specimens were lower than that of non-modified ones. Wear resistance was increased in modified samples.