Effect of Adjusted Gas Nitriding Parameters on Microstructure and Wear Resistance of HVOF-Sprayed AISI 316L Coatings

Abstract

Gas nitriding is known as a convenient process to improve the wear resistance of steel components. A precipitation-free hardening by low-temperature processes is established to retain the good corrosion resistance of stainless steel. In cases of thermal spray coatings, the interstitial solvation is achieved without an additional surface activation step. The open porosity permits the penetration of the donator media and leads to a structural diffusion. An inhomogeneous diffusion enrichment occurs at the single spray particle edges within the coating’s microstructure. A decreasing diffusion depth is found with increasing surface distance. The present study investigates an adjusted process management for low-temperature gas nitriding of high velocity oxy-fuel-sprayed AISI 316L coatings. To maintain a homogeneous diffusion depth within the coating, a pressure modulation during the process is studied. Additionally, the use of cracked gas as donator is examined. The process management is designed without an additional surface activation step. Regardless of surface distance, microstructural investigations reveal a homogeneous diffusion depth by a reduced processing time. The constant hardening depth allows a reliable prediction of the coatings’ properties. An enhanced hardness and improved wear resistance is found in comparison with the as-sprayed coating condition.

Low-Temperature Plasma Nitriding for Austenitic Stainless Steel Layers with Various Nickel Contents Fabricated via Direct Laser Metal Deposition

“…Recently, low-temperature plasma nitriding was also applied to the plasma-sprayed and cold-sprayed AISI 316L stainless steel coatings [24][25][26][27]. In addition, HVOF-sprayed stainless steel coatings were treated by gas nitriding and nitrocarburizing at low temperatures [28][29][30]. As results indicate, the low-temperature nitriding for these coatings produced the S-phase, thereby enhancing the wear resistance, similar to bulk austenitic stainless steels.…”

The Effects of Modifying the Activity of Nitriding Media by Diluting Ammonia with Nitrogen

“…Kogan and Solodkin [ 10 , 11 ] started from the expression of the relationship that allows the determination of the concentration of nitrogen in the ε phase, an expression that takes into account the nitride masses, m γ’ and m ζ ’ , respectively, as well as their molar masses, M γ ’ and M ζ , respectively; the result is a simplified reaction that links the concentration of nitrogen in the ε phase, [N] ε , to the molar participation of Fe 2 N nitride, N ζ , in the composition of ε nitride: …”

“…The analysis of the equilibrium in the Fe-N system allows obtaining information regarding the phase composition of the nitrided layers obtained under strict conditions of temperature and nitrogen concentration in the furnace chamber atmosphere [ 1 , 2 , 3 , 4 , 5 ]. The adjustment of the nitrided layer phase composition can be set by altering the nitrogen potential of the atmospheres used: by maintaining it at the level of nitrogen solubility in a certain phase, one is able to control the phase composition of the layer [ 6 , 7 , 8 , 9 , 10 , 11 ]. Thus, a nitrided layer can be obtained, which in the areas adjacent to the surface is composed exclusively of solid solution α N , or γ ’ , or ε (with a certain concentration of nitrogen), depending on the requirement (operational destination of the nitrided product).…”

Impact of Mechanical Processes as a Pre-Sulphonitriding Treatment on Tribology Properties of Selected P/M Tool Steels

“…Thermo-chemical treatment, such as nitriding or sulphonitriding, is another type of operation widely used in industrial conditions based on the diffusion change of the chemical composition of SL in order to obtain the required functional properties of a workpiece [11,12,13,14,15]. In this process, a nitrided layer is achieved, as in the case of the classical nitriding method.…”