materials Article Comparison of Different Cermet Coatings Sprayed on Magnesium Alloy by HVOF Ewa Jonda 1, *, Leszek Latka 2 and Wojciech Pakiela 1   Citation: Jonda, E.; Latka, L.; Pakiela, W. Comparison of Different Cermet Coatings Sprayed on Magnesium Alloy by HVOF. Materials 2021, 14, 1594. https://doi.org/10.3390/ ma14071594 Academic Editors: Frank Czerwinski and Guillermo Requena Received: 1 February 2021 Accepted: 20 March 2021 Published: 24 March 2021 Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affil- iations. Copyright: © 2021 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). 1 Department of Engineering Materials and Biomaterials, Silesian University of Technology, Konarskiego St. 18a, 44-100 Gliwice, Poland; wojciech.pakiela@polsl.pl 2 Faculty of Mechanical Engineering,Wroclaw University of Science and Technology, Lukasiewicza St. 5, 50-371 Wroclaw, Poland; leszek.latka@pwr.edu.pl * Correspondence: ewa.jonda@polsl.pl Abstract: In the present study, two different cermet coatings, WC–CrC–Ni and Cr 3 C 2 –NiCr, manu- factured by the high-velocity oxy-fuel (HVOF) method were studied. They are labeled as follows: WC–CrC–Ni coating—WC and Cr 3 C 2 –NiCr coating—CrC. These coatings were deposited onto a magnesium alloy (AZ31) substrate. The goal of the study was to compare these two types of cermet coating, which were investigated in terms of microstructure features and selected mechanical properties, such as hardness, instrumented indentation, fracture toughness, and wear resistance. The results reveal that the WC content influenced the hardness and Young’s modulus. The most noticeable effect of WC addition was observed for the wear resistance. WC coatings had a wear intensity value that was almost two times lower, equal to 6.5·10 −6 mm 3 /N·m, whereas for CrC ones it was equal to 12.6·10 −6 mm 3 /N·m. On the other hand, the WC coating exhibited a lower value of fracture toughness. Keywords: HVOF spraying; magnesium AZ31 alloy; microstructure; hardness; instrumented inden- tation; fracture toughness; wear resistance 1. Introduction The development of modern technology forces a permanent search for structural solutions tending to the improvement of a product’s efficiency and quality, i.e., to the minimization of dimensions, an increase in reliability, and the maintenance of dimensional stability during its exploitation. Low density and relatively high strength represent ma- terial selection criteria for specific applications in industry. The materials that meet the abovementioned requirements include alloys of magnesium, titanium, and aluminum. The magnesium alloys, in addition to the combination of low density (1.7 g/cm 3 )[1] and high dimensional density, are also characterized by a good damping capacity, low casting shrinkage, good castability, and the possibility to apply them to the manufacturing of machinery and equipment that operate in temperatures reaching 300 ◦ C. The application of magnesium alloys is not restricted to the automotive industry only, but also to the manu- facturing of airplanes, computers, helicopters, home appliances, and office equipment as well as the chemical industry, aeronautics, radio engineering, and the power industry. A disadvantage of these materials is their low resistance to abrasive wear and corrosion. Al- ternative solutions to this issue include the application of surface engineering technologies to improve the applicative properties of the materials discussed herein [2–5]. The prospective solutions aimed at increasing the usable properties of magnesium alloys and, in consequence, the improvement of their applicative attractiveness include the methods of thermal spraying of coatings. The benefits resulting from the application of coatings include, without limitation, the possibility of regeneration and restoring the usable properties of machines and equipment that operate under conditions of abrasive, erosive, and corrosive wear as well as the combination of the beneficial properties of the Materials 2021, 14, 1594. https://doi.org/10.3390/ma14071594 https://www.mdpi.com/journal/materials