Nitride Surface Research Articles

Analysis of Pre-Treatment Processes to Enable Electroplating on Nitrided Steel

Nitrided steel is being used to increase the lifetime and wettability of selective soldering nozzles. In this environment, the liquid solder wets to the surface of the nozzle to enable control of the solder flow during the soldering process. Pre-treatment is a key step in the processing of parts for electroplating. Pre-treatment usually involves degreasing and acidic pickling steps in order to remove adsorbed oil-based compounds and oxides respectively. These steps ensure a well-structured and adherent electroplated coating to the part.Surface treatments such as nitriding alter the surface composition of steels and thereby change the conductivity/surface activity. Typically, a nitrided surface contains a dual-phase surface layer followed by a diffusion zone consisting of the formed nitrides and finally a transition zone to the bulk material. Generally, this surface treatment is performed to harden materials without the risk of dimensional changes. For a selective soldering application, it reduces the dissolution of material into the solder during operation while also improving the wetting of the nozzle.The electroplated coatings for the selective soldering nozzles consist of 10 microns of nickel and 10 microns of tin. This structure allows for near-instant wetting and use of the nozzle. Furthermore, the electroplated layers provide corrosion protection for the nozzle ensuring no oxide or scale layers will form that may require flux for cleaning.A range of chemical and electrochemical pre-treatment steps were explored to prepare and optimally activate the nitride-hardened steel surfaces for electroplating. The processes included: hot degreasing and electrolytic degreasing with alkaline detergents; electrolytic descaling in a solution containing sodium hydroxide; chemical pre-descaling process with potassium permanganate; varying the compositions of pickling in inorganic acids; different formulations for nickel strike electrolytes for plating onto ferrous alloys.Mass loss measurements provided an estimation of the thickness of the material removed due to acid pickling. Scanning electron microscopy was employed to assess changes in the surface due to the pre-treatment. Open circuit potential measurements were applied to measure the surface activity before any pre-treatment and also the change in surface conductivity/activity post-treatment. Nanoindentation measurements were used to assess the change in surface hardness as a result of the nitriding treatment and also to check for the presence of the remaining hardened nitrided layer after pre-treatment. Glow discharge optical emission spectroscopy was utilised to study the elemental depth profile of the nitrided parts. Crystalline structure was studied through x-ray diffraction. After pre-treatment, a Woods nickel strike was applied to prepare the surface for further electroplating with bright tin. SEM analysis of the cross-sections of the coated specimens was used to analyse the coating microstructure. Thickness of the electrodeposited coatings were confirmed with x-ray fluorescence. Thermal shock tests were performed to confirm that the adhesion of the coating was sufficient.Approximately half of the nitrided layer was removed by pre-treatment in order to activate the surface for electroplating. More severe pre-treatment was required compared to electroplating non-hardened parts to activate the surface. Surface conductivity/surface activity was altered as measured by OCP resulting from the pre-treatment.This work has analysed the surface modification of nitride-hardened steels during the pre-treatment steps required to initiate electroplating and has shown that it is possible to prepare nitride-treated steels for electroplating. The results can be used to develop more optimal pre-treatment processes for electroplating nitrided steels.

(Invited) Towards GaN Passivation: Identification of GaN Surface/Interface States

GaN has been emerging as the next technological semiconductor after silicon and has already secured its superiority in the niche of power electronics with a rapidly growing interest since the advent of electric vehicles. To enable GaN to concur more microelectronic applications, one major barrier has yet to be surpassed. Rather limited control has so far been achieved over the density of GaN interface states. To achieve it, native and process-induced surface states need to be fully identified. Photoluminescence (PL) has been the most commonly used method in the study of GaN defects, and it typically shows a wide sub-bandgap peak centered at 2.2 eV that has been called the yellow luminescence (YL) band. Despite 30 years of studies, the debate as to whether this is a bulk or surface defect has not been settled. Present deep level characterization methods have not provided clear enough evidence. Theoretical studies attempted to associate this luminescence with various bulk defects, e.g., Ga-vacancies, O or O-C complexes,[1] while various optical spectroscopy studies, point to a surface origin.[2]Here, we report results of using an optical spectroscopy method based on surface photovoltage before and after a mild anneal in vacuum. The method is capable of showing the energy distribution of charge density trapped in surface states and thus of monitoring changes thereof. Using the method in air on untreated GaN reveals two peaks over the same ranges of the yellow and blue peaks observed by PL. After a mild anneal at 170 C for 24 hrs in vacuum, the “yellow” charge density peak was absent. Exposure to air was then observed to fully restore the “yellow” charge density peak. This observation clearly points to the involvement of an airborne molecule, a constituent of air, as the source for charge in the yellow-luminescence-related state. If this deep level were a bulk defect, it would not be able to interact with air. This observed interaction with air thus provides a first direct evidence that the yellow luminescence-related defect is a surface state. Experiments of controlled exposure to the various air constituents to identify the related airborne molecule are currently ongoing. The same method is now used in a search for passivation method for this surface state.The method we use is based on the following model. Illumination using sub-band gap photon energies excites electrons from the surface states over the surface potential barrier, consequently, reducing the surface band bending, and this change is observed as photovoltage (Fig. 1). We have already shown how this photovoltage can be used for calculation of the surface charge distribution in GaN HEMT.[3] In the case of bulk crystal, the model is slightly different, and a quantitative relation may be obtained between the measured photovoltage and the surface state charge distribution. Quantitative calculation requires knowledge of the surface band bending in equilibrium, which may not always be reliably obtained. However, when the spectrum is acquired using low photon flux, assuring the change in the band bending is small compared with the equilibrium band bending the surface charge density is practically relative to the derivative of the photovoltage, and thus, qualitative distribution may be obtained.[4]Figure 2 exemplifies the use of the model presented here to obtain a qualitative charge density spectrum. It shows surface charge density obtained using the model from the photovoltage spectrum shown as inset.This method is then used in Fig. 3 to compare three spectra of the same sample: In air (red), in vacuum (green) - the yellow peak is slightly reduced, and after heating up to 450 K for 24 h in vacuum (blue) - the yellow peak is practically gone.These results suggest that the charge in the yellow-luminescence-related state is contributed by a non-inert constituent of air, and this interaction may not be possible unless this state is a surface state. In the talk, preliminary results on the chemical identity of this air constituent will be presented.[1] Van de Walle et al., Microscopic origins of surface states on nitride surfaces, J. Appl. Phys. 101, 081704 (2007).[2] Shalish et al., Yellow luminescence and related deep levels in unintentionally doped GaN films, Phys. Rev. B 59, 9748 (1999).[3] Turkulets et el., Surface states in AlGaN/GaN high electron mobility transistors: Quantitative energetic profiles and dynamics of the surface Fermi level, Appl. Phys. Lett. 115, 023502 (2019).[4] Turkulets et al. The GaN(0001) yellow-luminescence-related surface state and its interaction with air. Surfaces and Interfaces 38, 102834 (2023). Figure 1

DFT Simulations on the Nitrogen Reduction Reaction Activity of Transition Metal Nitride and Oxynitride

Transition metal nitride (TMN) is a promising material towards the energy related applications including catalysis and energy storage.1 The sluggish nitrogen reduction reaction (NRR) due to the high energy input to activate N2 remains a significant challenge for NRR electrocatalysts. The surface N of TMN can be a solution to this with initial N vacancy formation via hydrogenation steps and ammonia formation. In addition, with a small amount of surface oxygen present in the catalyst surface, the resulting oxynitride seems very interesting and active towards NRR.2 But the mechanism behind this is not yet understood.In this study, we first focused on the modelling of the structure of metal nitride (ZrN) and oxynitride (ZrOxNy/ZrN) surfaces. The structure of oxynitride is obtained by running molecular dynamics (MD) calculations at both room temperature and experimental deposition temperature (90°C and 750°C). NRR reaction is then studied via the Mars-Van Krevelen (MvK) mechanism with introducing surface N vacancy and subsequent N2 adsorption and N filling. With computing the reaction energy and activation barriers of key reaction steps on both ZrN and ZrOxNy/ZrN, we can find a clue on how surface N of TMN helps to activate N2 and the role of small amount of surface oxygen on activating N2. To study the origin of small amount of oxygen, reaction energies and full reaction pathway along the deposition process are computed and plotted. Finally, dopant effect will be modeled with transition metal dopants (e.g. Cu and Hf) at surface region to study any localized electronic effect on NRR.These results can be useful to design and deposit ZrN acting as effective NRR electrocatalysts.

RESEARCH ON INCREASING THE HARDENING OF A GEAR REDUCER USING PLASMA TECHNOLOGY

Different case hardening methods are used to increase the hardening of machine-building products and their resistance to abrasion, temperature and corrosion. The most modern methods include plasma nitriding technology. This method can be applied for the following parts: crankshaft, gears, piston parts, etc. A common characteristic feature of workpiece that undergo case hardening is that their mechanical processing after hardening is difficult or impossible due to high hardness and complex geometric shape. Plasma nitriding is the process of low-temperature common case hardening for highly loaded gears. When nitriding, a diffusion layer with very hard complex nitride precipitation with a thickness of several microns is formed on the surface of the gear wheel, which greatly increases the technical performance of the part. [1] This article summarizes the state of knowledge in the field of plasma nitriding technology equipments and surface nitriding of gears, provides a overeview of the current state of research in the field of nitrided gears. Keywords: hardening, plasma nitriding, nitriding, gears, mechanical processing, reducer.

A Photonic Label-Free Biosensor to Detect Salmonella spp. in Fresh Vegetables and Meat

This paper presents a method that can be used to detect and identify Salmonella spp. in fresh meat and vegetable samples using a photonic biosensor with specialized bioreceptors. Detection was based on photon transduction. Silicon-nitride-based resonant cavities were used to capture the change in light response when there is specific binding of the immobilized antibody to the sensor surface against the target antigen. A control immobilization experiment was conducted to validate the immobilization process on the biosensor surface prior to biofunctionalization for Salmonella spp. detection. This experiment involved immobilization of pre-selected antibodies on silicon nitride surfaces. Two types of antibodies were suitable. The first was a specific polyclonal antibody with superior antigen-binding capacity across a wide range of concentrations. The second was a monoclonal antibody designed for effective binding at lower concentrations. Rigorous validation was performed. The outcomes were compared with those of the habitual method used to detect Salmonella spp. (reference method). Replicates from different batches of contaminated meat and vegetable samples were analyzed. This comprehensive approach provides a methodologically robust, highly sensitive, and accurate way of rapidly detecting Salmonella spp. in food samples. It has potential implications for improved food safety and quality control.

Silicon Nitride Surface Modification by Ion Bombardment with Physisorbed Hydrofluorocarbons: Theoretical Assessment

Silicon Nitride Surface Modification by Ion Bombardment with Physisorbed Hydrofluorocarbons: Theoretical Assessment

Studies of the Solid Particle Erosion Resistance of 30 L Steel with Different Types of Surface Modification

Earlier studies have shown that 30 L steel, used for the manufacture of hydraulic machinery equipment elements, has greater resistance to cavitation wear than 20 GL steel. This paper presents the results of experimental studies of the solid particle erosion resistance of 30 L structural steel samples with different surface modifications based on nitriding and boriding processes. The characteristics of the modified near-surface layers were determined. The results of the solid particle erosion resistance tests carried out according to the ASTM G76-13 standard are presented. The research results demonstrated that boriding processes worsen the solid particle erosion resistance of 30 L steel at flow impact angles of 30° and 90°. All the considered variants of surface nitriding at an impact angle of 90° do not worsen the solid particle erosion resistance of 30 L steel samples, while at an impact angle of 30°, they increase the solid particle erosion resistance by at least 10–20%.

Effects of gas mixture on active screen plasma nitriding and post-oxidation of a 4140 steel

Plasma nitriding, followed by post-oxidation, is a surface treatment used to enhance the properties of steel parts. The primary objective of such treatments is to develop a magnetite-rich oxide phase on the previously nitrided surface, aiming to achieve increased wear and corrosion resistance. The active screen plasma treatment method offers an alternative to direct plasma treatments, where parts are shielded from direct exposure to active species. This approach helps prevent defects caused by electric arcing and reduces the risk of increased porosity. However, due to differences in kinetics between active screen and direct plasma methods, the parameters commonly used in direct plasma treatments are not suitable for achieving the desired outcomes with active screen plasma. In this study, we applied plasma nitriding and oxidation to AISI 4140 hardened and tempered steel workpieces using the active screen method, varying the O2:H2 ratio in the gas mixtures. Treated workpieces were subjected to reciprocating wear tests. Our findings demonstrate that for the active screen post-oxidation step to be successful, it is essential to increase the O2 content compared to the reference treatment parameters used for non-active screen methods. The highest O2 content investigated (40 %) facilitated the development of magnetite oxides over the nitrided surface. This resulted in remarkable improvements in wear resistance and a favorable reduction in the friction coefficient during our tribological tests.

Improved Stability of Graphene-Coated CMOS ISFETs for Biosensing.

A polymer-assisted graphene transfer method is used to transfer sheets of monolayer and multilayer graphene onto the passivation layer of ion-sensitive field effect transistor arrays. The arrays are fabricated using commercial 0.35 μm complementary metal-oxide-semiconductor (CMOS) technology and contain 3874 pixels sensitive to pH changes on the top silicon nitride surface. By inhibiting dispersive ion transport and hydration of this underlying nitride layer, the transferred graphene sheets help address non-idealities in the sensor response while retaining some pH sensitivity due to the presence of ion adsorption sites. Improvements in hydrophilicity and electrical conductivity of the sensing surface after graphene transfer, as well as in-plane molecular diffusion along the graphene-nitride interface, also greatly improve spatial consistency across an array, allowing for ∼20% more pixels to remain within operating range and enhancing sensor reliability. Multilayer graphene offers a better performance trade-off than monolayer graphene, reducing drift rate by ∼25% and drift amplitude by ∼59% with minimal reduction in pH sensitivity. Monolayer graphene offers slightly better temporal and spatial uniformity in performance of a sensing array, which is associated with the consistency in layer thickness and a lower defect density.

Growth of AlN coating on Al-6061 alloy surface

The objective of the study was to grow uniform nitride coatings over Al-6061 alloys to resist fluorine diffusion. This paper discusses a process of carrying out surface nitridation of an Al-6061 alloy substrate. Through this method, a dense aluminum nitride coating can be grown on Al-6061 alloy with complete area coverage of the samples having complex geometries. The method uses nitrogen gas alone as the nitrogen carrier, and not ammonia derivatives used in conventional processes. Magnesium powder was also used in the process to reduce the protective alumina layer on the alloy and to facilitate the aluminum nitride growth. The process led to uniform coating coverage over the flat sample surfaces as well as over the surfaces of drilled holes in the sample. The coatings were stable when subjected to several 400 °C thermal cycles.

Adsorption of uranium (VI) from aqueous solutions using boron nitride/polyindole composite adsorbent

AbstractTurbostratic boron nitride (tBN) surface is modified with polyindole (PIn) by a facile polymerization technique and the uranyl adsorption efficiency of this mesoporous hybrid is investigated. The successful surface modification is confirmed by FT‐IR, Raman, XRD, TEM, SEM, EDX, EDS mapping XPS, BET, and zeta potential techniques. The batch experiments are performed in various temperatures (T), contact times (t), pH, and initial solution concentrations (C0) to evaluate its adsorption performance. The optimum adsorption performance is achieved at pH = 5.0–5.5, T = 307 K, t = 10 min, C0 = 18 mg L−1. These experimental results are evaluated using Freundlich, Redlich–Peterson, and Langmuir isotherm models, which presents equivalent regression coefficients. Maximum adsorption capacity (qm) of the nanoadsorbent (tBN/PIn), determined by the Langmuir isotherm, is 315.29 mg g−1. The adsorption kinetics of uranyl ions on tBN/PIn are in harmony with the pseudo‐second order model. tBN/PIn nanoadsorbent provides high adsorption efficiency even at exceptionally low UO22+ concentration range (4–40 mg L−1) and low adsorbent mass (0.005 g). XPS analysis results show that 0.05% of uranium is adsorbed on tBN/PIn via mainly U‐O coordination. The results of present study demonstrate that tBN/PIn can a potential adsorbent for removing uranium from aqueous solutions.

Opportunity to achieve an efficient SiC/SiO2 interface N passivation by tuning the simultaneous oxidation modes during the SiC surface nitridation in N2 + O2 annealing

We investigated a possible guideline to design the SiC surface nitridation process for an efficient interface N passivation in high-temperature N2 + O2 annealing, based on the understandings of SiC surface nitridation kinetics. Based on the findings of the time-dependent transition of the simultaneous SiC surface oxidation mode from passive to active during the annealing with reduced O2 partial pressure condition, it was proposed that an efficient SiC surface nitridation is achievable by following these steps: triggering the passive-to-active transition of the simultaneous surface oxidation by tuning the thermodynamic conditions and SiO2 thickness, and terminating the surface reaction at the beginning of the active-oxidation-dominant period by controlling the annealing time. It is confirmed that the observed interface passivation would be attributable to the N introduction to SiC/SiO2 interface, suggesting an opportunity to achieve an efficient interface N passivation following the proposed guideline.

Aluminum nitride surface acoustic wave resonators with high Qf product by optical lithography

Aluminum nitride surface acoustic wave resonators with high Qf product by optical lithography

Material Influence on the Micropitting and Wear Resistance of Nitrided External and Internal Gears

Abstract Due to increasing performance requirements and sometimes tribologically challenging operating conditions in gears (such as those found in wind turbines), alternative heat treatment processes to quenching and tempering or case hardening are becoming more and more important. Nitriding can significantly increase the load-carrying capacity of gears compared to the quenched and tempered initial state. The nitrided surface layer is characterized by a hard compound layer on the surface that is just a few micrometers thick and a diffusion zone that extends deeper into the material. The structure of the compound layer of iron and alloy element nitrides is primarily decisive for the wear behavior of nitrided components. Previous studies on nitrided gears with regard to micropitting and wear focus primarily on a systematic variation of the compound layer on gears made of nitriding steel 31CrMoV9. Results on the influence of the base material on the micropitting and wear resistance of nitrided gears are not yet available. In systematic load and speed stage tests, nitrided gears made from a quenched and tempered steel (42CrMo4) and a material with an alternative alloy composition (34CrNiMo6) were examined in addition to the reference (nitriding steel 31CrMoV9). Both external and internal gear pairings were tested, with the alternative materials showing more favorable tribological behavior in some cases. The results are presented and categorized according to the current state of the art. Finally, recommendations for the practical use of nitrided gears are derived.

Synergistic flame retardant modification of bio‐based nylon 56 by graphitic carbon nitride and melamine cyanurate

AbstractTo address the flammability drawbacks of nylon 56 and expand the application range of bio‐based nylon 56, melamine cyanurate (MCA) was employed through self‐assembly in a solvent with graphitic carbon nitride surface treatment. Modified MCA (CNMCA)composition and morphology were investigated. CNMCA created with surface treatment and polyamide 56 (PA56) prepared with unmodified MCA had their flame retardant functions and mechanical properties investigated and compared. x‐ray diffraction (XRD) and Fourier transform infrared (FT‐IR) spectroscopy confirmed the successful microencapsulation of g‐C3N4 on the MCA surface. Further characterization of the unmodified MCA and CNMCA was performed using scanning electron microscopy (SEM). The SEM images revealed a significant reduction in the degree of agglomeration in CNMCA compared to conventional MCA, resulting in a more uniform dispersion in the PA56 matrix. Additionally, PA56/CNMCA achieved a UL94 V‐0 rating and a limiting oxygen index (LOI) value of 30.1%. Notably, compared to pure PA56, PA56/CNMCA30 exhibited the most promising synergistic effect, leading to a separate reduction of 45.45% in the total heat release rate (THR) and 13.62% in the total smoke release (TSR). Consequently, with the same flame retardant addition (10 wt%), the CNMCA flame retardant showed superior dispersion in the bio‐based nylon 56 matrix compared to traditional MCA. Due to the physical isolation of g‐C3N4, the synergistic effect of MCA and graphitic carbon nitride imparted better mechanical properties and flame resistance to nylon 56.Highlights MCA/g‐C3N4 hybrids were prepared and applied in bio‐based nylon 56 for the first time. The MCA/g‐C3N4 hybrid has better dispersion than MCA. PA56/MCA/g‐C3N4 flame retardant composites have better flame retardant and smoke suppression properties than PA56/MCA.

Insight into the Dynamic Evolution of Co3Mo3N Bimetallic Nitride Surface during Ammonia Synthesis

Insight into the Dynamic Evolution of Co₃Mo₃N Bimetallic Nitride Surface during Ammonia Synthesis

Наукоёмкие технологии в материаловедении: высокотемпературное сквозное азотирование жаростойкой стали

The topicality of the research is occasioned by exaggeration of working conditions of products used at high temperatures and made of heat-resistant sheet alloys, including in particular austenitic chromium-nickel steels. When steel parts under load are operated in an oxidizing atmosphere and aggressive environments, besides resistance to electrochemical and gas corrosion, they require increased strength, hardness, and heat resistance. The increase in the characteristics of these proper-ties is achieved by three-dimensional and surface hardening techniques, which include the nitration process. The applica-tion of traditional technologies of furnace gas nitriding for chromium-nickel steels is complicated due to the problems of the low rate of the nitrogen saturation, which significantly increases the process time, and the formation of chromium nitrides, which negatively affects corrosion and heat resistance. The development of new technologies for nitrogen hardening of high-alloyed chromium-containing steels is carried out in the direction of saturation process intensification and regulation of the phase composition of the nitrided layer to minimize the formation of chromium nitrides. The article is aimed at defin-ing rational technological options and modes of gas austenitic nitriding of austenic steel, making it possible to increase strength characteristics at RT and higher temperatures without sacrificing its heat resistance. Thermodynamic modeling of the phase composition based on the CALPHAD technique shows that primary ways for minimizing the release of chromium nitrides on the nitrided surface are to increase the concentration of titanium in steel and to reduce the activity of the saturat-ing gas atmosphere, which is achieved by inert gas dilution of nitrogen. Experimental studies were carried out on sheet samples of 1.5 mm thick austenic steel of the type X18N10T with a standard (0.5%Ti) and increased (1%Ti) titane content. The experiments were carried out on a laboratory installation for high-temperature nitriding (900.1200 °); pure nitrogen and mixtures of nitrogen with argon were used as saturating media. Two-stage processes consisting of nitrogen hardening in nitrogen followed by argon afterburning were also investigated. Metallographic analysis showed that at the same nitrid-ing temperature, the amount of chromium nitrides decreases in experimental steel with an increased titanium content, and dilution of nitrogen with argon reduces the temperature of chromium nitride release. According to the study of saturation process kinetic, the time of through-the-thickness nitriding of a sheet sample under different saturation modes was deter-mined, as well as the duration of de-nitriding annealing, calculated on the basis of the known thickness of the chromium nitride zone. It was found that the dispersion hardening of the zones of internal nitriding with titanium nitrides leads to an increase in the strength characteristics of steels both at RT and higher temperatures compared to the characteristics of base steel 08X18N10T after typical heat treatment, while the greatest hardening effect is achieved due to through-the-thickness nitriding of steel with 1%Ti. Recommended options for the processes of through-the-thickness nitriding of 1.5 mm sheet of experimental steel: tn=1050 ℃, N2, 16 h; tn= 1100 ℃, 50%N2 + 50%Ar, 22 h; tn=1100 ℃, N2, 5 h + tann=1200 ℃, Ar, 9 h. The temporary passive hardness of nitrided steel at RT increases by 45...50%, and when tested at 800 ℃ - by 40... 65%, de-pending on the process mode. Through-the-thickness nitriding makes it possible to raise the working temperature of steels by 100.150 ° with the same long-term strength. The heat resistance at 900 ℃ remains at the level of non-carbonated steel after two-stage processes that ensure maximum chromium nitrides removal from the surface at the annealing stage.

Quantification of carboxylic binding sites on functionalized silicon nitride surface through X-ray photoelectron signal and fluorescence labelling

The wet-chemical functionalization of inorganic surfaces by organic bifunctional interlayers is a viable method towards the realization of optical (bio-)sensing devices. A detailed description of the organic-inorganic interface and a quantification of the surface functional group density is desirable, as they will determine the interaction of the transducer surface with the bioreceptor, thus final sensor efficiency. By characterizing surfaces at different sample preparation stages, we demonstrate that X-ray photoelectron spectroscopy (XPS) can be used to identify different coexisting carbon species at the interface as well as to quantify the packing density of the bifunctional interlayer. As a model system for proof-of-concept, the silicon nitride surface was functionalized with a dodecanoic acid molecule bearing a carboxylic end group, and the molecular packing density was quantified both via standard fluorescence-based labelling and XPS attenuation. Our combined approach identifies the fraction of bioreceptor-accessible and -inaccessible binding sites on the functionalized surface. This information will help to optimize the formation of dense layers of immobilized bioreceptors at the transducer surface.

Enhancing the tribological properties of TA1 pure titanium by modulating the energy of pulsed laser nitriding

Surface nitriding of titanium and titanium alloys is a commonly used method to enhance their wear properties. In this work, the pulsed laser was used to nitride TA1 commercially pure titanium and the microstructure and wear properties of the nitride layers prepared with different pulsed laser energies was investigated. The nitride layers prepared by laser nitriding are bi-layered with the upper layer being an N-element enriched layer (mainly composed of TiN) and the lower layer being an N-element diffusion layer [mainly composed of α(N)-Ti]. With the rise in laser energy, the nitrogen-rich layer gradually thickens and the mechanical properties improved to provide good wear resistance. Therefore, the nitride layer prepared with laser energy of 400 mJ has the best wear resistance, whereas the nitride layer prepared with laser energies of 100, 200, and 250 mJ fails completely during the wear test.

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.