Nitrided Specimens Research Articles

Enhancing corrosion fatigue performance of 17-4 PH stainless steel by simultaneous aging and plasma nitriding

This study investigated the effects of simultaneous aging and low-temperature plasma nitriding on the corrosion fatigue performance of 17-4 PH stainless steel. Plasma nitriding was conducted under two temperatures of 400 and 500 °C and, for comparison, some other specimens were subjected to aging treatment at the same temperatures and times. Microstructural characterization by scanning electron microscope (FESEM) and electron backscatter diffraction (EBSD) confirmed similar structures at the core in the nitrided and aged specimens, thereby, the influence of nitrogen at the surface of 17-4 alloy could be carefully investigated. X-ray diffraction and grazing incidence X-ray diffraction (GIXRD) identified expanded martensite as the matrix within the nitrided layer, accompanied by CrN, Fe3N, and Fe4N phases. X-ray photoelectron spectroscopy (XPS) analysis revealed high nitrogen concentration, in regions very close to the surface, after nitriding at 500 °C. The N1s spectra shifted towards lower binding energies, indicating interaction between nitrogen and the matrix atoms, and the formation of nitrides in the nitrided layer. The nitrided thicknesses experienced close values at 400 °C (10 h) and 500 °C (5 h), provided at 400 °C the layer was mostly a supersaturated solid solution but at 500 °C it was composed of iron nitrides and chromium nitride. High hardness values of above 1600 HV0.1 were obtained after optimum plasma nitriding as the result of combined effects of solution strengthening induced by nitrogen atoms and the presence of dispersed nitride phases. EBSD results indicated residual stress within the nitrided layer, which would affect the corrosion fatigue resistance. Experimental findings demonstrated that both aging and plasma nitriding substantially enhanced the corrosion fatigue resistance of 17-4 PH stainless steel in 3.5 wt% NaCl. Moreover, simultaneous aging and plasma nitriding proved superior behavior in corrosion fatigue, primarily due to delayed crack initiation and improved fatigue resistance, without the risk of overaging which is detrimental to mechanical properties.

Effects of rare earth on nitriding microstructure and properties of a La-Ce micro-alloyed Q235RE steel

Accelerating nitriding is an interesting topic in chemical heat treatment of ferrous parts. In order to have a deeper understanding of the catalysis principles of rare earth in nitriding, a Q235 carbon steel and a Q235RE steel micro-alloyed with rare earth elements La and Ce were nitrided respectively by plasma nitriding and gas nitriding. The microstructure, phase constitution, and composition of the nitrided specimens were analyzed. The hardness profile of nitriding layer and the brittleness of surface compound layer were measured. The results demonstrate that the Q235RE specimens obtained a higher hardness and deeper effective hardening layer than the Q235 specimens without rare earth microalloying. The rare earth catalysis effects were presented as the acceleration of nitrogen diffusion and the inhibition of nitride precipitation in the diffusion layer of the Q235RE specimens. In addition, the surface compound layer of the Q235RE specimens showed higher toughness and better adhesion to the matrix than that of the Q235 specimens, which is considered to be strongly related to the rare earth elements diffused into the compound and the enhanced residual compressive stress in the layer.

Graphitic carbon nitride functionalized with NiO nanoaggregates: An X-ray photoelectron spectroscopy investigation

The design and synthesis of low-cost oxygen evolution reaction (OER) photoelectrocatalysts endowed with high activity and durability is of utmost importance for sustainable energy generation via solar-assisted water splitting. In this regard, and in the framework of our recent activities, we have focused on the electrophoretic deposition of graphitic carbon nitride (gCN) specimens containing dispersed NiO nanoaggregates on carbon cloth substrates. In the present study, the attention is devoted to the x-ray photoelectron spectroscopy characterization of a representative gCN–NiO specimen. In particular, we provide an analysis of C 1s, N 1s, O 1s, and Ni 2p regions, discussing in detail the main spectral features. The obtained results, that provide evidence for a direct electronic interplay between the single material components, may serve as a useful comparison for additional research on analogous materials for energy and environmental applications.

Effect of low-temperature plasma nitriding on the sliding wear behavior of 17–4PH stainless steel in high temperature water

Plasma nitriding significantly enhances the tribological performance of 17–4 precipitation hardening (PH) stainless steel. However, the wear resistance of plasma-nitrided 17–4PH stainless steel in high temperature water remains unpredictable due to the complex interaction between wear and corrosion under such conditions. In this study, we conducted a wear test on nitrided 17–4PH stainless steel in high temperature water to evaluate its wear behavior. Our findings demonstrate that nitriding treatment improves wear resistance. Additionally, the wear mechanism shifts from delamination wear to oxidational wear after nitriding. The interaction between wear and corrosion was revealed. The subsurface of the worn scar undergoes plastic deformation, which accelerates corrosion. However, the oxide scale formed by corrosion can act as a lubricant to mitigate wear. For non-nitrided specimen with lower hardness, delamination cracks initially form in the subsurface, with the crack surfaces subsequently oxidizing and filled with debris. Material loss results from the peeling of the delamination. In contrast, for nitrided specimens with higher hardness, the subsurface of the worn scar is composed of an oxidation layer that detaches under mechanical wear, leading to material loss.

Surface melt nitriding and strengthening mechanism of plasma torched M50 bearing steel

This paper presents a new plasma torch nitriding technology for the first time to realize the surface nitriding of bearing steel for strengthening. By adjusting the plasma torch current parameters in the range of 120–160 A, M50 bearing steel was carried out at a nitriding speed of 2 s/cm2. After nitriding, the nitrogen content was increased from 0.00732 wt% in the original M50 steel up to 0.416 wt%, and the thickness of the nitrided layer was up to 2.51 mm. FeN0.076, Fe2N and Fe3N phases were formed in the steel, which was beneficial to increase the hardness and strength of bearing steel. The Vickers hardness of the original M50 bearing steel was 241 HV0.2. However, the highest surface hardness of specimen after nitriding was increased up to 778 HV0.2, which was attributed to the effect of sub-surface hardness strengthening within 2 mm from the depth of nitride surface. The average wear coefficient and the volumetric wear rate of the specimen after nitriding were decreased by about 32 % and 70 %, respectively. TEM observation showed that after nitriding, the structure of nitrided layer was martensite. The precipitates in the steel changed from large-sized, irregular and aggregated carbides (M23C6, M4C3 and M2C) to small-sized, spherical and uniformly distributed carbon‑nitrogen composite precipitates (M23(C, N)6, M7(C, N)3) in the steel sub-surface, but no obvious precipitates were formed on the surface of nitrided specimens. At depths of 1 mm and 2 mm, the size of the precipitates was reduced by about 68 % and 41 %, respectively, and the area of the precipitates was reduced from 18.4 % to 2.3 % and 3.7 %, respectively, compared to the original M50 bearing steel. It was concluded that the nitrided layer were strengthened synergistically with nitrogen solid solution, nitrogen-containing precipitates and martensite.

Improving the wear performance of TC6 Titanium alloy by ion nitriding treatment

TC6 titanium alloy, also known as Ti-6Al-1.5Cr-2.5Mo, is one of the most widely used titanium alloys in the aerospace industry due to its high specific strength, corrosion resistance and excellent mechanical properties. However, its poor wear resistance limits its application in some situations, such as aircraft actuators. To improve its wear resistance, this paper performs ion nitriding treatment on TC6 titanium alloy for aircraft cylinder and studies its wear performance. The ion nitriding test is conducted for 16 h at 820 °C using a bell-type titanium alloy ion nitriding furnace. The nitrided specimen is divided into three parts: nitrided layer, diffusion layer, and substrate layer. The nitrided layer was 4.11 μm thick and consisted of TiN and Ti2N phases. The diffusion layer was 13.69 μm thick and mainly composed of a gap solid solution formed by N element solid dissolved in α-Ti. After nitriding, the surface hardness of the specimen increased to 1105.2 HV, which is 2.37 times higher than that of the matrix. The hardness-affected layer is about 200 μm thick. The wear rate is reduced by 99.78% compared with that of the matrix, indicating that ionic nitriding greatly improves the wear resistance of TC6 titanium alloy. The wear mechanism of the nitriding specimen differs from that of the matrix, mainly due to abrasive wear, while the wear mechanism of the matrix is a combination of adhesive wear and abrasive wear.

Formation of Plasma-Nitrided Barrier Layers Against Hydrogen Absorption and Diffusion in Pure Iron

Hydrogen embrittlement is a serious problem for steels such as high strength steels. Reducing hydrogen absorption into steels is required for the prevention of hydrogen embrittlement. In order to improve the hydrogen absorption resistance into steels, a nitriding treatment is one of the effective ways among surface modifications because nitriding may increase the overpotential for the hydrogen evolution reaction on the surface and decrease hydrogen diffusivity in nitrided layers. In this study, the phase structure in the nitrogen compound layers for the pure iron specimens was controlled by plasma nitriding with different types of plasma gas and gas composition. The influence of ε-Fe2-3N and γ’-Fe4N phases on hydrogen absorption into the inside of the pure iron matrix through the nitrided layers was evaluated. During the hydrogen permeation tests, the plasma-nitrided specimens showed small permeation current values compared to the as-polished specimen when it reached the steady state. Especially, hydrogen absorption and permeation for the specimen with the compound layer containing ε-Fe2-3N were extremely inhibited. Hydrogen absorption and permeation behaviors in the nitrided pure iron specimens were discussed in terms of the catalytic activity and hydrogen diffusivity.

Fatigue behaviors of 40Cr steel bars after nitriding-ultrasonic impacting compound strengthening treatment

In this study, 40Cr steel specimens were subjected to a combination of nitriding and ultrasonic impacting compound strengthening treatments under different impact forces (50, 70, and 90 kg). Consequently, the fatigue life and failure mechanisms of the treated specimens were investigated. The results indicate that the fatigue life of nitride subjected specimens improved compared with the specimens without the nitride treatment. Further, the fatigue life of nitride specimens following the ultrasonic impacting treatment first increased and then decreased with increasing the impact force. The nitriding-ultrasonic impacting compound strengthened specimens with the impact force of 50 kg exhibited the highest fatigue life. In addition, a critical impact force was obtained within the range of 70–90 kg. Fatigue cracks were initiated on the surface for an impact force of less than 70 kg, and they were initiated around the inclusion of Al2O3-CaCO3 on the fracture as the impact force was greater than 90 kg. Finally, the fatigue crack initiation mechanisms of the nitriding-ultrasonic impacting compound strengthened specimens were elucidated in terms of the surface crack, surface roughness, hardness, and residual stress. This study is expected to provide new clues for the optimization of surface strengthening processes of mechanical workpieces.

Experimental Study on ELID Grinding of Silicon Nitride Ceramics for G5 Class Bearing Balls

This study has focused on analyzing the impact of material characteristics and grinding conditions on the surface roughness in ELID grinding of ceramic materials intended for bearing balls. The main research objective was to examine the feasibility of achieving the required surface roughness for G5 class bearing balls through a high-efficiency and high-precision ELID grinding process. Three types of silicon nitride specimens and two types of grinding wheels with cBN and diamond abrasives were prepared for the experiments. An HP (high-pressure) specimen was fabricated through high-temperature and high-pressure sintering at 1700 °C for 2 h, containing a composition of Y2O3 and MgO in Si3N4, while GPS 1hr and GPS 6hr specimens were prepared using gas-pressure sintering for 1 h and 6 h, respectively. From the experimental results, it has been confirmed through surface morphology and surface roughness analysis that material characteristics and grinding parameters affect the surface roughness of silicon nitride ceramics during the grinding process. The surface ground with a #2000 diamond wheel is at a level that can satisfy the required surface roughness, 0.014 um or less in G5 class bearing balls. Based on the analysis of surface morphology and roughness in grinding processes, the #325 cBN wheel exhibited excellent performance in rough grinding, while the #2000 diamond wheel demonstrated highly effective surface finishing performance, indicating that the combination of these two abrasives can be effectively utilized for high-efficiency and high-precision nanosurface machining of silicon nitride ceramics.

New White Etch Cracking resistant martensitic stainless steel for bearing applications by high temperature solution nitriding

White Etch Cracking (WEC) is a severe and unpredictable failure mode that has been frequently observed in, among others, bearings for wind energy applications. In this work a novel, patented, WEC resistant bearing steel solution is developed through high temperature solution nitriding, followed by a custom heat treatment. Conventional medium carbon, 13 wt% Cr martensitic stainless steels were subjected to the novel process to obtain a nitrogen-rich case. A series of soft annealing, austenitization, cryogenic and tempering treatments converted the nitrogen-rich region into a fine-grained case containing nano-sized precipitates. Test bearings and tribometer specimens were treated with the same sequence of treatments. These specimens were tested under two different accelerated WEC failure promoting conditions. In contrast to standard through-hardened bearing steel the nitrided specimens showed no WEC formation, not even after prolonged testing.

Improving tribocorrosion resistance of a medical grade CoCrMo alloy by the novel HIPIMS nitriding technique

In this work, tribocorrosion performance of the High Power Impulse Magnetron Sputtering (HIPIMS) nitrided (F75) CoCrMo alloys was examined with the help of sliding wear corrosion experiments carried out in Hank's solution. Results indicate that under Open Circuit Potentials (OCP), both nitrided and the untreated specimens exhibited near similar Sliding-Wear-Corrosion coefficient (KSWC) values (6.52 × 10−15 and 3.95 × 10−15 m3N−1m−1 respectively). However, the benefits of HIPIMS nitriding were evident under accelerated corrosion (anodic potentials) and passivating conditions. KSWC values of the nitrided specimens were an order of magnitude lower (6.41× 10−15 m3N−1m−1) than the untreated specimens (3.4 × 10−14 m3N−1m−1), indicating that nitrided surfaces had higher resistance against tribocorrosive mechanisms. This superior performance was attributed to the formation of a nitrided microstructure consisting mainly of expanded austenite (ƔN) without the formation of the detrimental CrN phase, which resulted in high hardness and sustained resistance to corrosion. A rationale for lower synergy between wear and corrosion and its relation to the nitride microstructure has been presented.

The effects of load on the microstructure and wear behavior of Co–27Cr–22Fe alloy processed by high-temperature nitriding

In this study, high-temperature nitriding was used to improve the surface hardness and wear resistance of Co–27Cr–22Fe alloy in a thermogravimetric analyzer. The high-temperature nitriding treatments were performed at 1200 °C for 3 and 10 h. Subsequently, at room temperature, the dry sliding wear test was carried out, and the possible effects of load on friction performance and microstructure of different specimens were investigated. The results show that the microstructure of as-received specimens is composed of γ-Co and MC carbides, while the microstructure of the nitrided specimens contains γ-Co, MC carbides, acicular AlN, and granular (Ti, Nb)N. The thickness of the nitriding layer is 375 μm and 708 μm for nitriding 3 h and nitriding 10 h, respectively. An improvement in microhardness (∼425 HV) was attained for nitrided specimens. For the as-received specimens, the wear rate decreases with increasing load. The as-received specimen exhibits better wear resistance than the nitrided specimen under a high load (∼30 N). The wear mechanism under different loads was mainly abrasive wear, accompanied by adhesive wear. For the nitrided specimens, the specimens show different wear mechanisms under varying loads. Under low load (∼5 N and ∼15 N), the high-temperature nitriding improves the wear resistance, and it exhibits abrasive wear and oxidative wear. Under high load (∼30 N), the wear resistance of the nitrided specimen was significantly reduced, and the wear mechanism is mainly abrasive wear, fatigue wear, and oxidative wear.

Effect of Plasma Nitriding and Oxidation on the Corrosion Resistance of 304 Stainless Steel in LiBr/H2O and CaCl2-LiBr-LiNO3-H2O Mixtures

The effect of plasma nitriding and oxidation on the corrosion resistance of AISI 304 type stainless steel in LiBr/H2O and CaCl2-LiBr-LiNO3-H2O mixtures at 80 °C has been evaluated by using potentiodynamic polarization curves and electrochemical impedance spectroscopy techniques (EIS). Steel was plasma treated at 500 °C during 8 h under different atmospheres, nominally 20% N2 + 80% H2, 100% N2 and 100% O2. X-ray diffraction analysis (XRD) showed the presence of a CrN layer in nitrided specimens, whereas scanning electronic microscopy analysis revealed that specimen treated in the 20% N2 + 80% H2 atmosphere showed the thickest nitride layer. Specimens nitrided in the 20% N2 + 80% H2 atmosphere had the noblest open circuit potential value in both solutions, whereas potentiodynamic polarization curves indicated the formation of a passive layer. These specimens exhibited the lowest corrosion and passivation current density values. Corrosion process was under charge transfer control in both solutions regardless of the plasma treatment. The type of corrosion suffered by the steel under all treatments was the pitting type of corrosion. Pits density was the lowest for nitrides steels rather than that for untreated or pre-oxidized ones.

Improvement of Ti-6Al-4 V alloy in terms of mechanical and tribological properties by oxidation and nitriding

In this study, we aimed to compare the mechanical properties and tribological properties of specimens after different thermal treatments. We treated specimens in oxidation and nitriding with argon in the chamber with 900 °C and 950 °C respectively. The results of the microhardness showed that the oxidized specimens were observed the highest value of 788VHN (0.05). We found that comparing to oxidized specimens (CoF=0.6 ± 0.09), the nitrided specimens showed lower coefficient of friction (CoF=0.52±0.06). There was around two times improvement of microhardness comparing to untreated specimens. And oxidized specimens (1.61±0.29 μm3/Nmm) showed five times lower value of wear rate than nitrided specimens (4.12±0.79 μm3/Nmm), and around ten times lower value of wear rate than nitrided with mechanic pump (9.54±0.68 μm3/Nmm). We concluded that oxidation could help to achieve the enhancement of hardness and wear properties, but with thinner layer on the surface. Nitriding with diffusion pump increased the efficiency of Ar+ and N+ diffusion than only with mechanic pump.

Effect of hydrogen on microstructure and mechanical properties of plasma-nitrided pure titanium by cathodic cage plasma nitriding

Surface modification technologies have been applied for the improvement of surface properties, and low temperature nitriding in the mixed N2-H2 atmospheres by cathodic cage plasma nitriding (CCPN) is identified to be an effective way to enhance the mechanical properties of Ti and its alloys. However, little attention was paid on the absorbed H2 in the nitrided specimen under different H2 proportion and the consequent deleterious influence. In this paper, the influence of different H2/(N2 + H2) ratio on microstructure of the nitrided Ti specimens by CCPN were investigated by XRD, EDX, SEM, respectively. And the surface structure of the compound layer is consisted of an outer layer of δ-TiN over the inner layer of ε-Ti2N, formed on the top of diffusion layer consisting of mainly of α-Ti solid solution enriched with nitrogen. It is found that the thickness of compound layer on Ti increases with the introduction of H2. And the N-rich top layer of TiN layer with coarse grain structure is resulted by the combined effect of the introduction of H2 and the plasma action. The surface mechanical properties of nitrided layer were also measured by microhardness tester and tensile test. The results show an average surface hardness of 900 HV0.2–1100 HV0.2 of the nitride surface compared to that of Ti (200 HV0.2 in average). And the surface hardness of nitrided Ti samples increases with the increasing H2 concentration. However, the tensile properties are badly deteriorated independent of hydrogen concentration with the introduction of H2 due to the generation of titanium hydride during nitriding process.

Modification of Diffusion Layers by Laser Shock Peening

The article deals with a possibilities of an enhancement of functional properties of highly stressed components by specific combination of surface technology. Two surface technologies such as plasma nitriding and laser shock peening were selected for the experiment. Those technologies were applied upon steel 42CrMo4 frequently utilized in manufacturing of strained components. Properties obtained by applied surface technologies were tested by following experimental methods. The chemical composition was verified by optical emission spectrometer Tasman Q4 Bruker. The surface morphology was inspected by scanning electron microscope TESCAN MIRA 4. The microstructure of heat treated as well as of nitrided specimens was observed by opto-digital microscope Olympus DSX500i. The microhardness profiles were measured by microhardness tester LM247 AT LECO. The friction coefficient was tested on tribometer Bruker UMT 3 TriboLab. For an assessment of the surface wear resistance the profilometer Talysurf CLI 1000 and Contour GT were utilized. The experimental results show that although the proposed surface technology combination manifests itself to be disadvantageous, both technology LSP, as well as plasma nitriding, applied separately, can lead to a significant wear reduction.

Improvement of Silicon Nitride Turbine Blade Impact Resistance Under Uniaxial Compression Loading

Abstract The inside-out ceramic turbine (ICT), a novel microturbine rotor architecture, uses monolithic ceramic turbine blades held in compression by a rotating structural shroud instead of traditional superalloy turbine blades in order to increase its maximum turbine inlet temperature (TIT) and cycle efficiency. Previous work has shown that this microturbine architecture has potential to be viable for long-term operation in normal operating conditions. However, foreign object damage (FOD) has been a major concern for ceramic turbine rotor past development efforts, and its effects on the ICT ceramic turbine blades lifespan have not been studied thus far. An experimental approach was used to characterize the effect of the ICT configuration on ceramic turbine blade impact resistance: spherical steel impactors were fired toward silicon nitride specimens simulating blade boundary conditions for both traditional and inside-out turbine layouts. Preload levels ranging from 100 MPa to 400 MPa were applied on the inside-out layout specimens to determine its effect on impact resistance. Results indicate that the inside-out turbine configuration increases the resistance to FOD over a traditional turbine configuration. For the specific conditions of this study, the specimens resisted to over five times the impactor energy when fixed at both ends. Also, results show that applying a higher compression preload on the specimens helps to resist higher energy impacts by about 50% when far from the buckling limit.

Effect of Nitriding Process on Wear Behavior of Dual Phase (Ferrite+Martensite) Ductile Cast Iron

In this study, it was aimed to improve the surface hardness by applying gas nitriding treatment to dual-phase ductile cast iron and to produce ductile cast irons with a good strength-ductility combination. Thus, it has been tried to develop a ductile cast iron with high wear resistance, strength, and ductility. Ductile cast iron specimens with a dual-phase microstructure consisting of ferrite + martensite were produced by oil quenching at 70 °C after intercritical austenitizing at 800 ⁰C in the ferrite + austenite zone. Instead of the tempering process, nitriding treatment was applied to the dual-phase ductile cast iron specimens at 560 °C for 540 minutes. The tempering process required to be applied to the martensitic structure was also performed by the nitriding process and a hard 10 µm thick nitride layer was obtained on the surface. Optical microscope and XRD analysis were performed for microstructural characterization of nitrided dual-phase ductile cast iron specimens. The wear properties were tested with a tribometer. For comparison reasons, microstructural characterization and wear tests were also performed on non-nitrided dual-phase ductile cast iron. In ductile cast iron, microstructures consist of a hard nitride layer (10 µm white layer) on the surface and a ferrite + tempered martensite (43% martensite volume fraction) structure in the center can be produced by oil quenching from intercritical austenitizing and nitriding treatment. Surface hardness of 510 HV in nitrided dual-phase ductile cast iron, 193 HV in dual-phase ductile cast iron, and 353 HV in austempered KGDD were obtained. The lowest weight loss and coefficient of friction were obtained in nitrided dual-phase ductile cast iron. The highest weight loss and friction coefficient values with wear were obtained in dual-phase ductile cast iron. The wear resistance of nitrided dual-phase ductile cast iron is 2 times higher than that of dual-phase ductile cast iron and austempered ductile cast iron.

Nitriding behavior and mechanical properties of AerMet100 steel and first-principles calculations of phase interfaces

In this paper, quenched AerMet100 steel specimens are plasma nitrided at different temperatures (from 440 °C to 500 °C), and their microstructures and mechanical properties are investigated. Surface layer hardness variation induced by plasma nitriding is also analyzed and correlated with microstructural characteristics and concentration distributions of carbon and nitrogen. Results show that wear resistance of AerMet100 steel after nitriding treatment exhibits various degrees of improvement compared with the un-treated specimen. Especially for the nitrided specimens from 460 °C to 500 °C, volume wear rate is reduced by more than 88%. Such great improvement is mainly attributed to the absence of brittle ε-Fe2-3N phase and the presence of a thick gradient nitrided layer. The interfacial properties of γ′-Fe4N(111)/α′N(011) are investigated by first-principles calculations. Six interface models with different γ′-Fe4N(111) termination and stacking sites are investigated to clarify their effects on the interfacial adhesion. The Fe-terminated Bridge site model exhibits a stronger adhesion tendency after relaxation, which can be regarded as the strongest interface. We found that the alloying additives benefit the γ′-(Fe,M)4N(111)Fe/α′N(011) interfacial adhesion in the order Si < Zr < Cu < Al < Ni < Mn < Co < Nb < Ti < V < Mo < Fe < Cr. Wherein, only Cr can be regarded as enhancers, and doping with Cr and Si are the most prominent representatives of strengthening and weakening effects, respectively. In addition, the bonding characteristics of two representative interface structures doped with Cr and Si are further studied. Density of states (DOS) and crystal orbital Hamilton population (COHP) analysis indicate that the significantly improved interfacial adhesion of Cr-doped is mainly due to the significant improvement of the enhanced Fe-Fe bonding. These results may provide some important inspirations for future experimental work of preparing high-performance nitrided layer.

Effect of nitriding conditions and operation temperatures on dry sliding wear properties of the aluminum extrusion die steel in the industry

Hot work tool steels are widely preferred in the hot extrusion of aluminum alloys. Nitriding of die steels in the aluminum extrusion industry is a well-accepted surface hardening method against surface wear and deformation. In this study, substrate material (DIN 1.2344 steel) is diffusion coated by salt bath nitriding method for 1 h, 2 h, and 3 h. The effect of different nitriding conditions on hardness, tensile and impact properties, wear behavior, and coefficient of friction is studied. Diffusion hardened surface is examined with different characterization techniques. The effect of nitriding time on diffusion layer thickness, tensile properties, impact energy, and wear resistance properties are investigated. It is shown that increasing nitriding time enables thicker diffusion layers that modify the adhesive's wear mechanism to abrasive. Increased nitride layer thickness resisted friction much more compared to less nitrided specimens. On the contrary of wear resistance, tensile properties are reduced due to the diffusion layer’s notch effect.