Evaluation of the Microstructure, Tribological Characteristics, and Crack Behavior of a Chromium Carbide Coating Fabricated on Gray Cast Iron by Pulsed-Plasma Deposition

Abstract

The structural and tribological properties of a protective high-chromium coating synthesized on gray cast iron by air pulse-plasma treatments were investigated. The coating was fabricated in an electrothermal axial plasma accelerator equipped with an expandable cathode made of white cast iron (2.3 wt.% C–27.4 wt.% Cr–3.1 wt.% Mn). Optical microscopy, scanning electron microscopy, energy-dispersive spectroscopy, X-ray diffraction analysis, microhardness measurements, and tribological tests were conducted for coating characterizations. It was found that after ten plasma pulses (under a discharge voltage of 4 kV) and post-plasma heat treatment (two hours of holding at 950 °C and oil-quenching), a coating (thickness = 210–250 µm) consisting of 48 vol.% Cr-rich carbides (M7C3, M3C), 48 vol.% martensite, and 4 vol.% retained austenite was formed. The microhardness of the coating ranged between 980 and 1180 HV. The above processes caused a gradient in alloying elements in the coating and the substrate due to the counter diffusion of C, Cr, and Mn atoms during post-plasma heat treatments and led to the formation of a transitional layer and different structural zones in near-surface layers of cast iron. As compared to gray cast iron (non-heat-treated and heat-treated), the coating had 3.0–3.2 times higher abrasive wear resistance and 1.2–1208.8 times higher dry-sliding wear resistance (depending on the counter-body material). The coating manifested a tendency of solidification cracking caused by tensile stress due to the formation of a mostly austenitic structure with a lower specific volume. Cracks facilitated abrasive wear and promoted surface spalling under dry-sliding against the diamond cone.

Abrasive Wear of High-Carbon Low-Alloyed Austenite Steel: Microhardness, Microstructure and X-ray Characteristics of Worn Surface

“…According to the results obtained, it is possible to make some general conclusions: The microhardness values of the worn surface of B-mode samples are noticeably greater than those of A-mode samples; The microhardness of the worn surface of all samples is higher than that of many industrial-wear-resistant hardfacings [ 41 ], and at the same level or higher than that of chromium carbide plasma fabricated coatings [ 42 , 43 ]. …”

“…The microhardness of the worn surface of all samples is higher than that of many industrial-wear-resistant hardfacings [ 41 ], and at the same level or higher than that of chromium carbide plasma fabricated coatings [ 42 , 43 ].…”

Microstructure-Properties Characterization of Selective Laser Melted Biomedical Co-28Cr-6Mo Alloy

“…The wear tests were performed in dry conditions and in simulated body fluid (SBF) containing (mM/liter): Na + : 145.0, K + : 4.0, Mg 2+ :1.0, Ca 2+ : 2.5, Cl -: 127.0, HCO3 -: 24.0 [21]. The volumetric wear was measured as described in [22], using wear track profiling by the "Micron-beta" profilometer, Micron-System, (five replicate tests).…”