Enhancement of steel surface properties through pulse plasma technique

The surfaces of AISI 4140 steel were modified by a newly developed pulse plasma 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. It was seen that number of pulse, battery capacity and nozzle distance are the important factors affecting layer thickness and microstructure.Samples were held in liquid nitrogen and then exposed to SEM and EDS investigations. As a result, thin grains and small white wolfram oxide grains coming from wolfram electrode were detected. Other elements were calculated by EPMA and SEM analyses.Fe3N, W, W3O, W308 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 180 HV before pulse plasma treatment. Its value was increased to 1050 HV after the treatment.Retained stress values of some specimens were measured by means of X-rays by tilting. The compression stresses were calculated in coating layers.Wear test was done in CSM-linear wear test machine with 0.15 m/s constant sliding speed under 5N, 7N, and 9N loads for 200 m. 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.Worn surfaces of specimens were studied by SEM, AFM and EDS analyses techniques.