Microstructure and Wear Behavior of TIG Surface-Alloyed AISI 4140 Steel

Abstract

In this study, AISI 4140 steel surfaces were alloyed with preplaced SiC/C powders using a tungsten-inert gas (TIG) heat source. The effects of different production parameters on the microstructure, hardness, and wear resistance of the alloyed surfaces were investigated. Following the surface alloying, conventional characterization techniques such as optical microscopy, scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), and X-ray diffraction (XRD) were used to study the microstructure of the alloyed surfaces. Hardness measurements were performed across the alloyed zones, and wear properties of the alloyed surfaces were evaluated using a block-on-disc wear test method. The collected data suggest that alloyed zones solidify into different microstructures depending on the production parameters. The alloyed surfaces exhibited an increase in hardness and wear resistance; this was attributed to the presence of harder phases and graphite. Lamellar or layered crystal structures of graphite have good lubricity and decrease coefficient of friction. Hardness values of the alloyed surfaces varied between 670 and 1165 HV. The minimum mass loss was observed in the sample that was alloyed with a 0.0581 cm/s process speed, 0.5/0.2 g/s powder feed rate, and a 29.1 kJ/cm heat input. The exhibited mass loss ratio was attributed to M3C, M7C3, and FeSiC carbides in the microstructure. The results conclude that TIG can be used effectively for surface alloying with SiC/C powders to improve the wear resistance of the AISI 4140 steel surface.