Skip to content
6CCVD Research

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

At a Glance

Section titled “At a Glance”
MetadataDetails
Publication Date2021-06-19
JournalMaterials
AuthorsYu. G. Chabak, V. G. Efremenko, Miroslav DĆŸupon, Kazumichi Shimizu, V.I. Fedun
InstitutionsPryazovskyi State Technical University, Muroran Institute of Technology
Citations10
AnalysisFull AI Review Included

Executive Summary

Section titled “Executive Summary”

This research validates the use of Pulsed-Plasma Deposition (PPD) followed by heat treatment (HT) to significantly enhance the wear resistance of Gray Cast Iron (GCI) via a high-chromium carbide coating.

  • Coating Structure and Hardness: A 210-250 ”m thick composite coating was formed, consisting of 48 vol.% Cr-rich carbides (M7C3, M3C) embedded in a martensite/retained austenite matrix (48 vol.% martensite, 4 vol.% austenite). Microhardness was dramatically increased to 980-1180 HV.
  • Metallurgical Bonding: PPD induced melting of the GCI substrate, creating a strong metallurgical bond via an 8-25 ”m transitional layer formed by the counter-diffusion of C, Cr, and Mn atoms.
  • Abrasive Wear Performance: The coating exhibited 3.0-3.2 times higher abrasive wear resistance compared to both non-heat-treated and heat-treated GCI substrates.
  • Dry-Sliding Performance: Volume loss under dry-sliding was reduced by factors ranging from 1.2 times (vs. steel ball) up to 1208.8 times (vs. diamond cone), demonstrating superior performance against hard counter-bodies.
  • Critical Limitation: The as-deposited coating, initially mostly austenitic, generated high internal tensile stress (calculated at 5832 MPa) upon cooling, leading to solidification cracking. These cracks locally accelerate wear under high-stress contact.

Technical Specifications

Section titled “Technical Specifications”
ParameterValueUnitContext
Substrate MaterialGray Cast Iron (GCI)N/AComposition: 2.95 wt.% C, 1.45 wt.% Si, 0.95 wt.% Mn.
Cathode MaterialHigh-Cr White Cast IronN/ASource material: 27.39 wt.% Cr, 2.34 wt.% C.
Coating Thickness210-250”mAfter Pulsed-Plasma Deposition (PPD).
Transitional Layer Width8-25”mFormed at coating/substrate interface.
PPD Discharge Voltage4.0kVStored in 1.5 mF capacitor.
PPD Discharge Current~18kAPeak current during pulsed arc discharge.
Post-Plasma Heat Treatment950°CHolding temperature for 2 hours, followed by oil-quenching.
Coating Microhardness (HT)980-1180HVRange from top surface to interface.
Substrate Microhardness (Initial)223 ± 25HVAverage microhardness of ferrite grains.
Carbide Volume Fraction (HT)48.2vol.%Cr-rich carbides (M7C3, M3C) in the final coating.
Martensite Volume Fraction (HT)47.6vol.%Matrix phase in the final coating.
Abrasive Wear Resistance Increase3.0-3.2timesCompared to GCI substrate (stable wear process).
Dry-Sliding Volume Loss (vs. Diamond Cone)0.49 x 10-3”m3Lowest volume loss achieved by the coating.
Calculated Tensile Stress (As-Deposited)5832MPaStress attributed to the mostly austenitic structure causing cracking.

Key Methodologies

Section titled “Key Methodologies”
  1. Substrate and Cathode Selection: GCI specimens were used as the substrate. The cathode for the Electrothermal Axial Plasma Accelerator (EAPA) was a 5 mm rod of high-Cr white cast iron (27.4 wt.% Cr) to ensure a high-chromium coating.
  2. Pulsed-Plasma Deposition (PPD): Performed in air using an EAPA. The process involved 10 high-current pulses (~18 kA, 4.0 kV) which eroded the cathode. The erosion products (microdroplets and ions) were transferred by the plasma flow to the GCI target surface (50 mm distance).
  3. Plasma-Induced Melting: Numerical modeling confirmed that the plasma flow heated the substrate surface rapidly (up to 2350 °C), causing melting to a depth of up to 15 ”m. This molten layer mixed with the plasma material, ensuring strong metallurgical bonding.
  4. Post-Plasma Heat Treatment (HT): Specimens were held at 950 °C for two hours, covered in coal to prevent oxidation, and then oil-quenched. This HT promoted the precipitation of stable Cr-rich M7C3 carbides and the transformation of austenite to hard martensite.
  5. Microstructural Analysis: X-ray Diffraction (XRD) confirmed the phase transformation (austenite to martensite/carbides). Scanning Electron Microscopy (SEM) and EDS mapping revealed the elemental gradient (Cr and Mn decreasing, C increasing toward the substrate) and the formation of the carbide network.
  6. Tribological Testing:
    • Three-Body Abrasion: Tested using Al2O3 particles (0.5-0.6 mm diameter) under a 20 N load against a rubber roller.
    • Dry-Sliding: Reciprocating tests (5 N load) were conducted against three counter-bodies: 100Cr6 steel balls, SiC balls, and diamond cones, to evaluate performance under varying contact stresses and hardnesses.

Commercial Applications

Section titled “Commercial Applications”
  • Tooling and Die Manufacturing: Strengthening wear-loaded tool steels, die forms, and molds used in cold stamping and forming processes, particularly for hybrid car bodies, where GCI is commonly utilized.
  • High-Performance Sliding Components: Application in mechanical engineering components, such as cylinder liners or sliding bearings, where GCI’s inherent low abrasive resistance is a limitation.
  • Rolling Equipment: Components subjected to high friction and abrasive conditions, leveraging the coating’s high hardness and superior resistance to three-body abrasion.
  • Hard-on-Hard Contact Systems: Use in systems where contact occurs against hard ceramic materials (like SiC), as the coating demonstrated significantly lower adhesion and volume loss against SiC compared to steel.
  • Surface Hardening of Castings: General surface modification technique for structural GCI components where increased service life is required due to wear, offering a composite structure superior to simple case hardening.
View Original 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 ”m) 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.

Tech Support

Section titled “Tech Support”

Original Source

Section titled “Original Source”

References

Section titled “References”
  1. 2006 - Damping and tribological properties of Fe-Si-C cast iron prepared using various heat treatments [Crossref]
  2. 2018 - Wear behaviour of grey cast iron with the presence of copper addition
  3. 2020 - Effects of quench-tempering and laserhardening treatment on wear resistance of gray cast iron [Crossref]
  4. 2015 - Effect of bionic coupling unitsŚł forms on wear resistance of grey cast iron under dry linear reciprocating sliding condition [Crossref]
  5. 2017 - Effect of alternate biomimetic coupling units on dry sliding wear resistance of grey cast iron [Crossref]
  6. 2018 - Lubricating property of cast iron combined with two-scale unit structure by biomimetic laser treatment [Crossref]
  7. 2018 - A bio-inspired concept to improve crack resistance of gray cast iron [Crossref]
  8. 2017 - Application of the Q-n-P-treatment for increasing the wear resistance of low-alloy steel with 0.75 %C [Crossref]
  9. 2014 - In-situ surface hardening of cast iron by surface layer metallurgy [Crossref]
  10. 2015 - Improved fatigue wear resistance of grey cast iron by localized laser carburizing [Crossref]

Reads Similar to This

Robust Pt-based nanogap electrodes with 10 nm scale ultrafine linewidth Tungsten Carbide Nanolayer Formation by Ion Beam Mixing with Argon and Xenon Ions for Applications as Protective Coatings A Versatile Sacrificial Layer for Transfer Printing of Wide Bandgap Materials for Implantable and Stretchable Bioelectronics