Effect of plasma nitriding on electrodeposited Ni–Al composite coating

In this study plasma nitriding is applied on nickel–aluminum composite coating, deposited on steel substrate. Ni–Al composite layers were fabricated by electro-deposition process in Watt’s bath containing Al particles. Electrodeposited specimens were subjected to plasma atmosphere comprising of N₂–20% H₂, at 500 °C, for 5 h. The surface morphology investigated, using a scanning electron microscope (SEM) and the surface roughness was measured by use of contact method. Chemical composition was analyzed by X-ray fluorescence spectroscopy and formation of AlN phase was confirmed by X-ray diffraction. The corrosion resistance of composite coatings was measured by potentiodynamic polarization in 3.5% NaCl solution. The obtained results show that plasma nitriding process leads to an increase in microhardness and corrosion resistance, simultaneously.     

Plasma nitriding response at 400 °C of the single crystalline Ni-based superalloy MC2

Plasma nitriding of MC2, a single crystalline (γ/γ′) Ni-based superalloy, was performed at 400 °C for 1 and 4 h. Owing to its monomodal γ′ particle size distribution, MC2 was used as a model material in an attempt to investigate the behavior of precipitates during the nitriding of a γ matrix. The nitrogen profiles, the morphology, and the nature of the phases in the nitrided layer were characterized by glow discharge optical emission spectroscopy, scanning electron microscopy, and X-ray diffraction. The γ matrix appeared to be nitrided similarly to the γ solid solution in austenitic stainless steels with the development of an expanded γ_N phase. The amount of nitrogen in the γ matrix varies from ~30 at.% at the surface till ~20 at.% at the interface with the non nitrided matrix. On the contrary, the γ′ precipitates accommodate no more than few at.% of nitrogen. This disparity modifies the morphology and the average γ channel width increased by ~25 %.     

Kinetic features of the process of nitriding of (α + β) -titanium alloys

The kinetic features of nitriding of (α + β) -titanium alloys caused by their phase-structural state and the surface phenomena are investigated both analytically and experimentally. The influence of the temperature and time parameters of treatment on the depth of the nitrided layer is analyzed. It is shown that, as the β-phase content of alloys increases, the degree of saturation of their surface zone with nitrogen decreases. This is caused by its lower solubility in the β-phase than in the α-phase, more intense diffusion into the bulk of the specimen, and the formation of a deeper hardened zone.     

Effects of conventional and active screen plasma nitriding on properties of electroless Ni–B coating

Abstract

In the present study, the properties of nitrided electroless Ni–B coatings prepared by conventional plasma nitriding and active screen plasma nitriding were investigated. For this purpose, electroless Ni–B coatings were deposited from an alkaline bath on AISI 4140 substrates. Then, some of the prepared coatings were plasma nitrided by conventional method and the other ones by active screen method under the same conditions. Microstructure, morphology, microhardness and wear resistance of the coatings were evaluated. Based on the results, post-treatments change the amorphous as deposited coating structure to a crystalline one, which increases microhardness and wear resistance. Employing plasma nitriding treatment on the coatings results in higher microhardness and superior wear resistance than conventional heat treatment. The sputtering of iron atoms during plasma nitriding process can be the main reason for these results. In addition, active screen plasma nitriding demonstrates less surface roughness and superior wear resistance than conventional plasma nitriding.     

Investigating the wear characteristics of engineered surfaces: low-temperature plasma nitriding and TiN + MoS x hard-solid lubricant coating

Significant progress has been made in the past decade in plasma nitriding with a majority of the research work focusing on improving hardness and wear resistance of the nitrided surface through the reduction of nitriding temperature, pressure or time. Hard-solid lubricating coatings have also been extensively studied for lowering the wear rate and coefficient of friction of traditional hard coatings such as TiN by the combined effect of hardness and solid lubrication. In this study, the wear characteristics of low-temperature plasma-nitrided steel substrate performed using a Saddle-field fast atom beam source and TiN + MoS _x hard-solid lubricant coating deposited by a closed-field magnetron-sputtering technique have been investigated. The thin hard layer in plasma-nitrided substrates exhibited much higher hardness and lower wear compared to the untreated substrate in pin-on-disc wear testing. In addition, the study of the wear track morphology of the nitrided samples evidenced significant reduction of deeper ploughing and plastic deformation due to higher hardness and load supporting of the nitrided layer. On the other hand, due to the incorporation of MoS₂ in TiN coating, the wear resistance and coefficient of friction were greatly improved in TiN + MoS _x coating compared to pure TiN coating. In contrast to TiN coating, a relatively smoother wear track with less abrasive wear also supported the beneficial effects of adding MoS₂ in TiN coating.