Surface properties of AISI 4140 steel modified by pulse plasma technique

Abstract

The pulse plasma process is a kind of surface modification technique. In this study, the microstructure and mechanical properties of pulse plasma -treated AISI 4140 steel were studied. Four different sample -plasma gun nozzle distances and three different pulses were chosen for the surface modification at a constant battery capacity of 800 mf. The samples were subjected to optical microscope, SEM and EDS analyses, microhardness testing and X-ray diffraction (XRD) analysis. The columnar and fine grained structures were formed in modified layer. New and hard phases were formed on the modified layer. Hence, the hardness increased five times after pulse plasma treatment. The amount of wear for all specimens was evaluated by using the reciprocating wear (linear wear test machine) test with a 0.15 m/s constant sliding speed under 5, 7, and 9 N loads along a 200 m sliding distance. A WC ball (with 6 mm diameter) was used in this test. The friction coefficient and wear rate were changed in accordance with the applied load. The friction coefficient values decreased and the wear resistance increased in the surface -modified specimens compared to the non-modified ones. The wear rate and the friction coefficient were changed with the wear debris and load. The debris was increased by the resistance to wear of surface. The worn surfaces of the specimens were studied by using atomic force microscopy (AFM), scanning electron microscopy (SEM) and electron dispersive spectroscopy (EDS). The abrasive wear was shown on worn surface. (C) 2019 The Author. Published by Elsevier B.V.