A recent article published in Nanomaterials demonstrated the use of WMoTaNb refractory high-entropy alloy as a reinforcement material to strengthen laser-cladding 316L stainless steel.
Image Credit: ANUPONG RAJSUPA/Shutterstock.com
Background
316L stainless steel is an essential component of modern industry because of its high mechanical strength, good corrosion resistance, and low cost. It is widely utilized for corrosion-resistant coatings in engineering sectors such as marine, aerospace, and nuclear. However, its poor hardness and wear resistance limit its broader applications.
Cemented carbide is generally added to 316L stainless steel matrix to enhance surface hardness and poor wear resistance. However, the carbides are not adequately compatible with stainless steel substrates, leading to weak bonding.
Recently, high-entropy alloys (HEAs) have emerged as innovative solutions for the above issues.
HEAs are mainly made of five or more elements with outstanding hardness, oxidation resistance, and extreme-temperature durability. Among various HEAs, WMoTaNb and WMoTaNbV refractory HEAs (RHEAs) exhibit excellent metallurgical bonding with 316L stainless steel while enhancing its mechanical properties.
This study proposed the fabrication of WMoTaNb RHEAs/316L composite coatings using laser cladding.
Methods
WMoTaNb HEAs and 316L stainless steel powder mix were procured commercially for laser cladding on a 45 steel plate with a size of 100×100×15 mm3. A coaxial powder-feeding laser setup was used to fabricate the laser-cladding specimens from these raw materials under argon protection.
The microstructure of the prepared coatings was characterized using a scanning electron microscope (SEM), while their phase structure was analyzed using a transmission electron microscope (TEM) with an energy-dispersive X-Ray spectrometer (EDS). The phase composition of WMoTaNb and 316L powders was determined using high-energy synchrotron X-Ray diffraction (S-XRD).
The coating’s microhardness was measured with a digital Vickers microhardness tester with a load of 300 grams and an indentation time of 15 seconds, and nanoindentation hardness was measured under a constant holding load of 10 mN. The nanoindentation position selection on the coating cross-section was done using a 5×10 array. The indentation morphology was analyzed through SEM.
Finally, the wear resistance of coatings was examined by a friction and wear tester consisting of an Al2O3 friction pair, with each sample tested twice.
Results and Discussion
The microhardness and wear resistance of WMoTaNb RHEAs/316L metallic composite coatings were analyzed compared to those of the laser-cladding 316L coatings. Individually, the 316L stainless steel exhibited a single-phase FCC structure, while WMoTaNb powder exhibited a BCC structure with high sphericity, which helped enhance the flowability of these powders.
WMoTaNb/316L composite coating comprised a BCC-structured Fe-based solid solution, intermetallic compounds with a hexagonal structure, and FCC-structured carbides. Consequently, the coating’s microstructure (XRD, EDS, and TEM results) exhibited a Fe-based dendritic solid solution phase, a hexagonal Fe2X (W, Mo, Ta, and Nb) Laves interdendritic phase, and an FCC (Ta, Nb)C interdendritic granular phase.
The cross-sectional SEM images of the WMoTaNb/316L composite coating revealed its exceptional metallurgical bonding with the substrate, free from cracks or porosity. However, some partially melted WMoTaNb powders existed in the coatings because of the high melting point of WMoTaNb RHEA.
The microstructure images of the coating-substrate interface showed highly oriented planar crystals developing normally to the substrate direction due to different temperature gradations and solidification rates in the molten pool.
Based on the cross-sectional morphology, different hardness zones were recognized: the WMoTaNb/316L composite coating zone, heat-affected zone (HAZ), and 45 steel substrate zone. Among these, the WMoTaNb/316L composite coating exhibited a surface hardness of approximately 460 HV0.3, significantly higher than that of the substrate and laser-cladding 316L coating.
Significant fluctuations were observed in the friction coefficient curve of the composite coating after the occurrence of friction, friction coefficient ranging from 0.65 to 0.75. Alternatively, the friction coefficient of the 316L coating changed gradually and stabilized at approximately 0.82 in the stable wear stage.
The wear resistance of WMoTaNb/316L composite coatings was superior to that of 316L coatings, with adhesion, oxidation, and abrasion being the main wear mechanisms at room temperature.
Conclusion
The researchers successfully demonstrated the fabrication of WMoTaNb/316L composite coatings with good metallurgical bonding to the substrate and no visible defects.
The enhanced microhardness of WMoTaNb/316L composite coatings was attributed to a significant network of high-strength Laves phases, resulting in nearly twice the hardness of 316L coatings and improved wear resistance.
This study provides valuable insights for designing and fabricating 316L stainless steel coatings with enhanced hardness and wear resistance, exploring the feasibility of using RHEAs as reinforcement materials in stainless steel systems.
More from AZoM: Metal Film Coatings for Mirrors
Journal Reference
Yan, A. et al. (2024). High-Entropy Alloy Activating Laves-Phase Network for Multi-Component Metallic Coatings with High Hardness. Nanomaterials. doi.org/10.3390/nano1412101
Disclaimer: The views expressed here are those of the author expressed in their private capacity and do not necessarily represent the views of AZoM.com Limited T/A AZoNetwork the owner and operator of this website. This disclaimer forms part of the Terms and conditions of use of this website.