Rf Plasma Nitriding Research Articles

Investigating the structure and tribo-mechanical performance of PVD TiN on bearing TiN substrate constructed by rf plasma

Abstract Recent study was focused on conjoining rf plasma nitriding of titanium with TiN coating by rf plasma magnetron sputtering as a duplex treatment technique. To develop the tribo-mechanical characteristics and load bearing capacity of titanium substrate, rf plasma nitriding was engaged to predestine a bearing TiN layer on Ti base substrate. The PVD process was accomplished employing TiN target in argon plasma atmosphere. All PVD parameters were constant excluding the deposition time which was varied from 4 to 20 min with deposition rate of ∼60–65 nm/min. The effect of PVD TiN film thickness which was varied from 240 to 1300 nm on structure, tribo-mechanical and electrochemical performance of TiN/TiN duplex coatings was investigated. It was found, the duplex treatment expressively increased the PVD TiN/TiN coatings hardness (max: 2600 ± 47 HV0.025) and constricted the substrate plastic deformation. An enhancement in the adhesion in the duplex TiN/TiN samples compared to TiN/Ti was observed. Moreover, the wear, friction (reduced to nearly 0.2) and the corrosion performance were markedly upgraded for the duplex treated samples compared with pure Ti and PVD TiN/Ti.

Low temperature RF plasma nitriding of self-organized TiO2 nanotubes for effective bandgap reduction

Titanium dioxide is a widely studied semiconductor material found in many nanostructured forms, presenting very interesting properties for several applications, particularly photocatalysis. TiO2 nanotubes have a high surface-to-volume ratio and functional electronic properties for light harvesting. Despite these manifold advantages, TiO2 photocatalytic activity is limited to UV radiation due to its large band gap. In this work, TiO2 nanotubes produced by electrochemical anodization were submitted to plasma nitriding processes in a PECVD reactor. The plasma parameters were evaluated to find the best conditions for gap reduction, in order to increase their photocatalytic activity. The pressure and RF power density were varied from 0.66 to 2.66 mbar and 0.22 to 3.51 W/cm2 respectively. The best gap reduction, to 2.80 eV, was achieved using a pressure of 1.33 mbar and 1.75 W/cm2 RF power at 320 °C, during a 2-h process. This leads to a 14% reduction in the band gap value and an increase of 25.3% in methylene blue reduction, doubling the range of solar photons absorption from 5 to 10% of the solar spectrum.

Plasma nitriding of Ti6Al4V alloy for improved water erosion resistance

Water droplet erosion (WDE) is a severe problem encountered in the operation of gas turbines. The damage is caused when small water droplets hit the surface of the compressor blades at very high velocities. In this work, RF plasma nitriding of Ti6Al4V alloy was performed with the aim of improving its resistance to the WDE. Process parameters, including temperature and gas atmosphere, were varied to evaluate the influence of nitriding conditions on the WDE resistance. Structural and morphological changes of the samples were investigated by scanning electron microscopy (SEM), phase composition by X-ray diffraction, and cross-sectional hardness distribution by nanoindentation. Water droplet erosion tests were performed using a rig that simulates WDE at working conditions of the compressor blades. Each sample was subjected to 6 min of WDE tests. After every minute of the experiment the erosion area of the sample was evaluated by the optical microscope and the specific mass loss was determined. Damage was analyzed using SEM and confocal laser scanning microscopy. The results show significantly higher resistance against WDE of Ti6Al4V nitrided at low temperature, especially in the case of hydrogen-free nitriding atmosphere. The incubation time for these samples was extended four times, as compared to the bare substrates or to the samples nitrided at higher temperatures.

Pengaruh Rasio Laju Alir Gas Nitrogen-Hydrogen serta Gas Pressure pada RF Plasma Nitriding terhadap Surface Hardness Spesimen SUS304

RF Plasma nitriding was done on the specimen SUS304. This research had aim to obtain a high surface hardness value as a result of flow rate ratio of Nitrogen-Hydrogen. The experimental research consisted of three models. Each experimental model used varying parameters and constant parameters. Micro Vickers Hardness test was used for testing each specimen of the experimental models. The varying parameters of first experimental model were times of plasma nitriding, ie, 1 hour, 2 hours, 4 hours and 8 hours. The constant parameters were RF-Power Voltage = 250 Volts, DC-Bias Voltage = 500 Volts, N 2 = 100 (ml/min), H 2 = 20 (ml/min), Gas pressure (P) = 70 Pa and Heater Temperature (T) = 420 o C. The second experimental model contained three varying parameters of nitrogen gas pressure ie, 50 Pa, 60 Pa and 70 Pa. The constant parameters of second experimental model were time of plasma nitriding (t) = 8 Hours, RF-Power Voltage = 250 Volts, Heater Temperature (T) = 420 o C, N 2 = 140 (ml/min), H 2 = 20(ml/min). The first and second experimental models had same configuration. The third experimental model used three variations of nitrogen flow rate, ie, 140 (ml/ min), 160 (ml/min), 180 (ml/min). The constant parameters were time of plasma nitriding (t) = 4 hours, RF-Voltage = 250 volts, The Heater temperature (T) = 420 o C; H 2 = 20 (ml/min), DC-Bias Voltage = 500 Volts, the gas pressure (P) = 60 Pa. The configuration of third experimental model was different with the configurations in first and second experimental models. Surface hardness Values of first experimental model were 379 HV, 348 HV, 474 HV and 387 HV. Surface hardness values of second experimental model were 586 HV, 607HV, 249 HV. Surface hardness values of third experimental model were 313 HV, 574 HV, and 677 HV. from the results were known that nitrogen-hydrogen flow rate ratio into vacuum chamber and gas pressure influenced the surface hardness of SUS304 specimen. The highest surface hardness value of 677 HV was happened at gas pressure of 60 Pa, nitrogen flow rate of 180 (ml/min) and hydrogen flow rate of 20(ml/min).

Microstructure and wear properties of AISI M2 tool steel on RF plasma nitriding at different N2–H2 gas compositions

Wear behavior of quenched-tempered AISI M2 tool steel samples has been studied after plasma nitriding at different N2–H2 plasma gas flows containing 25, 50 and 75sccm N2. Plasma nitriding was performed at 450°C for 8h under floating potential using a plasma reactor equipped with a radio frequency power generator. Microstructure, phase composition, nitrided layer thickness, hardness and surface roughness of the samples were studied using optical microscopy, X-ray diffraction, microhardness and surface profilometry measurements. Dry sliding wear resistance of samples was determined by performing ball-on-disc wear testes. The results revealed formation of mainly a diffusion zone at the 25sccm N2–75sccm H2 gas flow and mono-phase ε-Fe2–3N compound layer at higher N2 concentrations. Plasma nitriding increases near surface hardness up to 50% (about 1600HV0.025) irrespective of the N2:H2 ratio, where nitrided layer depth and surface roughness increase with increasing the N2 flow rate in the plasma gas. Depending on the nitrogen content, sliding wear resistance may be improved between 20 and 90% with respect to the un-nitrided substrate. Among the nitrided samples the maximum and minimum wear resistance was obtained at plasma gases containing higher and lower H2 fractions, respectively. Decreasing wear resistance with increasing N2 flow rate in the plasma gas attributed to formation of the hard and brittle compound (white) layer on the sample surface and development of residual stress profiles.

Effect of Hydrogen in rf Plasma Nitriding on Al-6wt%Cu Alloy

Effect of Hydrogen in rf Plasma Nitriding on Al-6wt%Cu Alloy

Surface Hardening of Aluminium-Copper Alloy 2011 by RF Plasma Nitriding Process

In this work, an inductively-coupled rf plasma reactor was utilized in the nitriding process for surface hardness improvement of aluminium-copper alloy 2011. Substrate bias at 400V was used in the pre-sputtering step to eliminate the aluminium oxide on the samples. Plasma nitriding was carried out in a N2-H2 admixture at total pressure of 1 torr. The process length was varied from 9 to 36 hours while the input rf power and substrate temperature were varied from 100 to 300 W and kept at 400 oC, respectively. A negative bias voltage up to 400 V was used in the nitriding process. Glancing incident-angle x-ray diffraction (GIXRD) results showed the hexagonal crystal structure of AlN on samples. The roughness increased slightly when the voltage increase up to 400V and was investigated by Scanning Electron Micrograph (SEM). Electron Probe Microscopy Analysis (EPMA) and Energy Dispersive X-ray Analysis (EDX) were used to detect the N atoms in specimens. Significant increases of surface hardness are observed after plasma nitriding.

The Influence of Hot-Rolled Temperature on Plasma Nitriding Behavior of Iron-Based Alloys

Experiments were performed with an aim of studying the effect of hot-rolled temperature (600 and 900°C) on radio frequency (rf) plasma nitriding of Fe93Ni4Zr3 alloy. Nitriding was carried out for 10 min in a nitrogen atmosphere at a base pressure of 10−2 mbarr. Different continuous plasma processing powers of 300–550 W in steps 50 W or less were applied. Nitrided hot-rolled specimens were characterized by optical microscopy (OM), X-ray diffraction (XRD) and microhardness measurements. The results reveal that the surface of hot-rolled rf plasma nitrided specimens at 600°C is characterized with a fine microstructure as a result of the high nitrogen solubility and diffusivity. Moreover, the hot-rolled treated samples at 600°C exhibit higher microhardness value than the associated values of hot-rolled treated samples at 900°C. The enhancement of microhardness is due to precipitation and predominance of new phases (γ and e phases). Mainly, this conclusion has been attributed to the high defect densities and small grain sizes of the samples hot-rolled at 600°C. Generally, the refinement of grain size plays a dramatic role in improvement of mechanical properties of tested samples.

Duplex treatment of 304 AISI stainless steel using rf plasma nitriding and carbonitriding

Surface of 304 AISI austenitic stainless steel has been modified using duplex treatment technique of nitriding and carbonitriding. A thick modified nitrided layer, of approximately 20 µm, has been achieved when rf inductively coupled plasma was adjusted at 450 W for processing time of only 10 min. After performing the nitrided layer, the nitrided samples were carbonitrided using the same technique at different acetylene partial pressure ratios ranges from 10% to 70%, the balance was pure nitrogen. Different amount of nitrogen and carbon species are diffused underneath the surface through the nitrided layer during carbonitriding process and are found to be gas composition dependent. The treated samples were characterized by glow discharge optical spectroscopy, X-ray diffractometry, scanning electron microscopy and Vickers microhardness tester. The microstructure of the duplex treated layer indicates the formation of γ́-Fe 4N, Fe 3C, CrN and nitrogen-expanded austenite (γ N). The thickness of the duplex treated layer increases with increasing the acetylene partial pressure ratio. The surface microhardness of duplex treated samples has been found to be gas composition dependent and increased by 1.29 fold in comparison to the nitrided sample.

MicroRaman study of the effect of oxide layer on nitriding of Ti–6Al–4V

Ti–6Al–4V samples were subjected to nitrogen ion implantation and low pressure RF plasma nitriding in a PIII equipment after chemical etching in Kroll's reagent. The samples were characterized by optical microscopy, AFM, microRaman, XRD and micro hardness measurements. From microRaman, oxides of titanium were found in the inter-granular β region whereas the oxide on the α region was extremely thin. The oxide on the β region was found to be amorphous and from intensity dependent Raman spectra, it was found to have a layered structure. The top layer was rutile and the inner layer anastase. Presence of Ti 2O 3 was also found. After PIII treatment at 600 °C, microRaman showed the presence of nitride in both the regions and the oxide was absent in the β regions. Also, from intensity dependent Raman spectra, it was found that in-take of nitrogen by β regions was higher. The oxide layer remained unaffected after plasma nitriding. Nitride presence in the α was established by microRaman. Even though Raman spectra from β regions were nearly the same as that of oxide, presence of nitrogen was indicated by the spectra. XRD studies of implanted and nitrided samples showed the prsence of TiN and Ti 2N in implanted sample and presence of Ti 2N in the nitrided sample. The β regions were found to have higher microhardness values after PIII and nitriding treatments. This is attributed to the deeper diffusion of nitrogen in these regions.

Surface treatment of Ti–6Al–4V alloy by rf plasma nitriding

The Ti–6Al–4V alloy was treated by inductively coupled rf plasma nitriding. Theeffects of plasma-processing time in the range of 5–35 min on the microstructureand the mechanical properties of the plasma-nitrided Ti–6Al–4V sampleswere studied. The plasma power input was adjusted at 450 W and pureN2 gas was introduced to establish a treatment pressure of8.0–8.4 × 10−2 mbar. The characteristics of the nitrided layers have been investigated by microhardnesstesting, surface roughness measurements, optical microscopy, and x-ray diffraction. The resultsshow that the surface microhardness increases as the plasma-processing time increases toreach 2000 HV0.1 at a plasma-processing time of 35 min. A high nitriding rate of2.81 µm2 s−1 at a plasma-processing time of 25 min was achieved. The formation of the hard phases TiN,Ti2N, and Ti(N) in the Ti–6Al–4V surfaces are found to be the reason for the increasedmicrohardness. Surface energy, yield strength and Young’s modulus for the nitridedTi–6Al–4V alloy were calculated from the Vickers microhardness data.

Duplex treatment of AISI 304 austenitic stainless steel using rf nitriding and dc reactive magnetron sputtering of titanium

In this work, duplex treatment has been carried out using radio frequency (rf) plasma nitriding process and direct current (dc) magnetron sputtering of titanium. Nitriding of AISI 304 stainless steel, using rf plasma technique, created a thick modified layer of approximately 20 μm for short plasma processing time of 10 min. After nitriding process, a thin titanium nitride film has been deposited using dc magnetron sputtering of titanium for different nitrogen/argon gas pressure ratios. The treated samples were characterized via glow discharge optical spectroscopy, X-ray diffractometry, scanning electron microscopy, profile meter and Vickers microhardness tester. The elemental composition, thickness and microhardness values of the duplex treated layers are found to be gas composition dependent. The data shows that the microhardness of the duplex treated layer increases to 1.42 fold relative to the associate value of the nitrided one. Moreover, high deposition rate of 110 nm/min is obtained.

Surface improvement and biocompatibility of TiAl 24Nb 10 intermetallic alloy using rf plasma nitriding

The present work describes the surface improvement and biocompatibility of TiAl 24Nb 10 intermetallic alloy using rf plasma nitriding. The nitriding process was carried out at different plasma power from 400 W to 650 W where the other plasma conditions were fixed. Grazing incidence X-ray diffractometry (GIXRD), Auger electron spectroscopy (AES), tribometer and a nanohardness tester were employed to characterize the nitrided layer. Further potentiodynamic polarization method was used to describe the corrosion behavior of the un-nitrided and nitrided alloy. It has been found that the Vickers hardness (HV) and corrosion resistance values of the nitrided layers increase with increasing plasma power while the wear rates of the nitrided layers reduce by two orders of magnitude as compared to those of the un-nitrided layer. This improvement in surface properties of the intermetallic alloy is due to formation of a thin modified layer which is composed of titanium nitride in the alloy surface. Moreover, all modified layers were tested for their sustainability as a biocompatible material. Concerning the application area of biocompatibility, the present treated alloy show good surface properties especially for the nitrided alloy at low plasma power of 400 W.

Effect of rf plasma nitriding time on electrical and optical properties of ZnO thin films

ZnO thin films were prepared by thermal oxidation of metallic Zn films and nitrided by an inductively coupled rf plasma. The effects of successive plasma processing cyclic times on structural and optical properties as well as electrical resistivity were examined by different characterization techniques. A small amount of nitrogen was detected at the film–substrate interface. The grain size decreased slightly as the treatment time increased. The surface roughness of examined films increased while the thickness decreased with increasing plasma treatment time. The electrical resistivity decreased about four orders of magnitude when the sample nitrided for 15 min. However, the transmittance increased as the plasma treatment time increased. The optical band gap increased from 2.76 to 3.02 eV with increasing plasma treatment time from 0 to 15 min.

A study on rf plasma nitriding at a constant power in different H 2–N 2 mixtures at different temperatures

Austenitic stainless steel AISI 304 has been nitrided by radio frequency (rf) plasma containing various nitrogen–hydrogen gas mixtures, in order to study the effect of hydrogen on structure and magnetic properties of the formed compound layer. The thermal temperature has been measured at the vicinity of the samples. The compound layer thus produced has been characterized using, X-ray diffractometer and vibration sample magnetometer. Providing the total pressure of nitrogen and hydrogen is held constant, the addition of hydrogen up to 50% gives new structural phases. The magnetization values of the plasma treated samples are strongly dependent on the percentage of H 2 in the gas phase. An excessive amount of hydrogen (∼75%) on the other hand, retards the nitriding process. The surface temperature of the sample and plasma condition is crucial factors for nitriding process.

Characterisation of PI 3 and RF plasma nitrided austenitic stainless steels using plan and cross-sectional TEM techniques

Type 304 and 316 austenitic stainless steels treated with plasma immersion ion implantation (PI 3™) and RF plasma nitriding have been studied with transmission electron microscopy (TEM). A range of TEM specimen preparation techniques have been used to enable characterisation of the nature of the treated surface layers. Plan view TEM specimens, prepared by thinning from the back, highlighted the removal by sputtering of original surface features in steels during PI 3 processing, while the less energetic RF plasma nitriding retained the original surface features. All treatments resulted in the formation of an austenite phase heavily expanded by the high levels of interstitial nitrogen. Decomposition of this expanded austenite into CrN and α Fe occurred at higher treatment temperatures, and was found to nucleate at the grain boundaries preferentially. Conventional cross-sectional TEM specimens also showed the importance of the surface as a nucleation site for this transformation. The transformation process and the products of expanded austenite decomposition were the same regardless of the treatment process used. The expanded austenite layer was aligned with the underlying steel, with no orientational difference across the interface observed. Focused ion beam milling has the ability to consistently section treatment depths of several micrometers, although further work is necessary to produce through-section specimens thin enough for EELS and EFTEM analysis.

RF plasma nitriding of a severely deformed high alloyed steel

The effect of severe plastic deformation by high pressure torsion (HPT) on radio frequency plasma nitriding of X5CrNi1810 steel was investigated. The results reveal that HPT enhances the effect of nitriding at 350 °C leading to doubling of the nitrided layer thickness. This layer was shown to consist of expanded austenite and possibly some iron nitrides.

The influence of surface microcracks and temperature gradients on the rf plasma nitriding rate

Rf plasma nitriding processes have been used recently for surface treatment. 304 Austenitic stainless steel has been nitrided using an inductively coupled rf plasma. High rates of nitriding and relatively high microhardness have been achieved. The effect of plasma power and plasma processing time on the rate of nitriding and the microstructure was investigated. A high nitriding rate of 3 μm 2/s and a microhardness value of 1800 HV0.1 were achieved under optimum plasma conditions. The interpretation is based on a new approach that the microcracks in the surface, at a certain ambient temperature and plasma, can create traps for the active nitrogen species. The nitrogen concentration and temperature gradient can also draw some of the nitrogen species towards the bulk side. The microhardness can be explained in terms of the high concentration of nitrided phases created under the surface of the treated samples.

Structural properties of austenitic stainless steel in the initial state and after rf plasma nitriding

Mossbauer spectroscopy, TEM, electrical resistivity and magnetic measurements are used for investigation of structural changes of X5CrNi189 austenitic stainless steel sheet induced by rf plasma nitriding carried out at 400°C for 24 h. The initial structure formed by small grains of austenite and α′-martensite changes after nitriding into expanded austenite close to the surface and austenite with minor contents of ferrite/CrN in the bulk.

Effect of rf plasma nitriding power density on microhardness, structure, and magnetic properties of 304 austenite stainless steel

Structural phases, microhardness, and magnetic properties of nitrided 304 austenite stainless steel prepared using different rf plasma power densities ranging from 78·5 to 138 W cm-2 torr-1 have been investigated. The results of X-ray diffraction revealed that the structural phases of the nitrided layers are strongly dependent on the nitriding plasma power density. Fe2–3 N, Fe4 N, CrN, and α ferrite are the main phases formed in the treated layers which can be easily identified. The hysteresis loops of the samples were measured using a vibrating sample magnetometer, from which the saturation magnetisation Ms , remnant magnetisation Br , coercive field Hc , and magnetic susceptibility χ, were evaluated. The highest values of Ms , Br , Hc , and χ were obtained when the samples were nitrided at around 106 W cm-2 torr-1. This behaviour can be explained in terms of the high precipitation of CrN and Fe4 N at this nitriding plasma power density.