materials Article Laser Surface Alloying of Austenitic 316L Steel with Boron and Some Metallic Elements: Properties Michal Kulka 1, * , Daria Mikolajczak 2 , Piotr Dziarski 1 and Dominika Panfil-Pryka 1   Citation: Kulka, M.; Mikolajczak, D.; Dziarski, P.; Panfil-Pryka, D. Laser Surface Alloying of Austenitic 316L Steel with Boron and Some Metallic Elements: Properties. Materials 2021, 14, 2987. https://doi.org/10.3390/ ma14112987 Academic Editor: Mikhail Zheludkevich Received: 20 April 2021 Accepted: 28 May 2021 Published: 31 May 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 Institute of Materials Science and Engineering, Poznan University of Technology, Pl. M.Sklodowskiej-Curie 5, 60-965 Poznan, Poland; piotr.dziarski@put.poznan.pl (P.D.); dominika.panfil-pryka@put.poznan.pl (D.P.-P.) 2 WSK Poznan Ltd., Unii Lubelskiej Street 3, 61-249 Poznan, Poland; daria.mikolajczak02@gmail.com * Correspondence: michal.kulka@put.poznan.pl Abstract: Austenitic 316L stainless steel is known for its good resistance to corrosion and oxidation. However, under conditions of appreciable mechanical wear, this steel had to demonstrate suitable wear protection. In this study, laser surface alloying with boron and some metallic elements was used in order to improve the hardness and wear behavior of this material. The microstructure was described in the previous paper in detail. The microhardness was measured using Vickers method. The “block-on-ring” technique was used in order to evaluate the wear resistance of laser-alloyed layers, whereas, the potentiodynamic method was applied to evaluate their corrosion behavior. The produced laser-alloyed layers consisted of hard ceramic phases (Fe 2 B, Cr 2 B, Ni 2 B or Ni 3 B borides) in a soft austenitic matrix. The significant increase in hardness and wear resistance was observed in the case of all the laser-alloyed layers in comparison to the untreated 316L steel. The predominant abrasive wear was accompanied by adhesive and oxidative wear evidenced by shallow grooves, adhesion craters and the presence of oxides. The corrosion resistance of laser-alloyed layers was not considerably diminished. The laser-alloyed layer with boron and nickel was the best in this regard, obtaining nearly the same corrosion behavior as the untreated 316L steel. Keywords: laser surface alloying; laser boriding; 316L steel; hardness; wear resistance; corro- sion resistance 1. Introduction The main disadvantage of AISI 316L austenitic stainless steel is its relatively low hardness (about 200 HV) which causes the limited use of this material. It would be difficult to harden the austenitic steel using the typical heat treatment, i.e., quenching and tempering, because of the extended stability of an austenitic structure to the room temperature [1]. Therefore, the only way to harden such a steel is via adequate surface treatment in order to produce hard and wear resistant surface layers. It is relatively easy using the physical techniques of surface treatment, especially if the surface is saturated with nitrogen, carbon or boron under glow discharge conditions [2–31]. Such techniques are also called plasma or ion processes [32]. In this case, the activation of the surface is carried out during the first step of the process, i.e., sputter cleaning of the surface. This pre-treatment causes removal of the passive layer, consisting of oxides, from the surface. Among these processes, the most important are: low-temperature plasma gas nitriding (LTPGN), high-temperature plasma gas nitriding (HTPGN), low-temperature plasma gas carburizing (LTPGC), low-temperature plasma gas nitrocarburizing (LTPGNC), cathodic plasma electrolytic nitriding (CPEN) or plasma paste boriding (PPB). The conventional thermo-chemical treatment, i.e., boriding [33–43], nitriding [44–49] or carburizing [50–52] as well as producing the TiN coatings by physical vapor deposition (PVD) [53,54], requires the mechanical or chemical removing these oxides before these processes. It is relatively difficult due to the susceptibility of austenitic steel to re-passivation. The new possibilities, especially in increasing the depth of surface layers produced, appear in the case of laser Materials 2021, 14, 2987. https://doi.org/10.3390/ma14112987 https://www.mdpi.com/journal/materials