Rockwell-C Indentation Research Articles

Effect of bias voltage on the erosion performance of TiAlSiN coatings on TC6 substrate by high power impulse magnetron sputtering

TiAlSiN coatings were deposited on TC6 substrates by high power impulse magnetron sputtering at various bias voltages for the improvement of titanium alloy anti-sand erosion performance. The effect of bias voltage on the composition, microstructure and mechanical properties were investigated by X-ray photoelectron spectroscopy, X-ray diffractometer, transmission electron microscopy, scanning electron microscopy, Rockwell-C indentation, scratch testing and nano nanoindentation. The erosion performance was evaluated at the impingent angles of 30° and 90° respectively in a sand blasting tester. With the application and increase in bias voltage, the discharge current increases from ∼87 A to ∼210 A. The coatings exhibit face center cubic structure, mainly composed of the (Ti,Al)N nanocrystallites and Si3N4 matrix. The preferred orientation shifts from (200) to (220) in the range of 0∼−150 V, but goes back to (200) at −200 V. The surface nodular defects and deposition rate are gradually reduced, yet the sectional structure becomes much denser. The residual stress is compressive and continually grows, whereas the adhesion strength, hardness (H), Young's modulus (E) and H/E ratio gradually increase before decreasing, arriving at maximum values of ∼68 N, ∼37.53 GPa, ∼339.9 GPa and 0.11 respectively at −150 V. The erosion resistance of the TiAlSiN coatings is consistent with these mechanical changes at various bias voltages and is also optimal at −150 V, which is ∼14 times that of TC6 substrate. The failure mechanism comes from coating brittleness nature, fractured chips and microcracks, regardless sand erosion angles, yet the driving forces are different.

Analysis of Diffusion Coefficients of Iron Monoboride and Diiron Boride Coating Formed on the Surface of AISI 420 Steel by Two Different Models: Experiments and Modelling.

In the present work, two mathematical diffusion models have been used to estimate the growth of the iron monoboride and diiron boride coating formed on AISI 420 steel. The boronizing of the steel was carried out with the solid diffusion packing method at a boronizing temperature of 1123 K-1273 K. Experimental results show the two-coating system consists of an outer monoboride and an inner diiron boride coating with a predominantly planar structure at the propagation front. The depth of the boride coating increases according to temperature and treatment time. A parabolic curve characterizes the propagation of the boride coatings. The two proposed mathematical models of mass transfer diffusion are founded on the solution corresponding to Fick's second fundamental law. The first is based on a linear boron concentration-penetration profile without time dependence, and the second model with time dependence (exact solution). For both models, the theoretical law of parabolic propagation and the average flux of boron atoms (Fick's first fundamental law) at the growth interfaces (monoboride/diiron boride and diiron boride/substrate) are considered to estimate the propagation of the boride coatings (monoboride and diiron boride). To validate the mathematical models, a programming code is written in the MATLAB program (adaptation 7.5) designed to simulate the growth of the boride coatings (monoboride and diiron boride). The following parameters are used as input data for this computer code: (the layer thicknesses of the FeB and Fe2B phases, the operating temperature, the boronizing time, initial formation time of the boride coating, the surface boron concentration limits, FeB/Fe2B and Fe2B/Fe growth interfaces, and the mass transfer diffusion coefficient of boron in the iron monoboride and diiron boride phases). The outputs of the computer code are the constants εFeB and εFe2B. The assessment of activation energies of AISI 420 steel for the two mathematical models of mass transfer is coincident (QFeB=221.9 kJ∙mol-1 and QFe2B=209.1 kJ∙mol-1). A numerical analysis was performed using a standard Taylor series for clarification of the proximity between the two models. SEM micrographs exhibited a strong propensity toward a flat-fronted composition at expansion interfaces of the iron monoboride and diiron boride coating, confirmed by XRD analysis. Tribological characterizations included the Vickers hardness test method, pin-on-disc, and Daimler-Benz Rockwell-C indentation adhesion tests. After thorough analysis, the energies were compared to the existing literature to validate our experiment. We found that our models and experimental results agreed. The diffusion models we utilized were crucial in gaining a deeper understanding of the boronizing behavior of AISI 420 steel, and they also allowed us to predict the thicknesses of the iron monoboride and diiron boride coating. These models provide helpful approaches for predicting the behavior of these steels.

Wear performance under dry and lubricated conditions of duplex treatment TiN/TiCrN coatings deposited with different numbers of CrN interlayers on steel substrates

Cold work steels are used in harsh conditions including high load, wear, corrosion, and mechanical stresses that can easily lead to degradation and wear of the material. Generally, multilayer ceramics coatings are attractive candidates to develop engineering components by combining positive characteristics of different coatings. In this study, the TiN/TiCrN coatings with the different number of CrN interlayers were successfully deposited on nitrided and non-nitrided DIN 1.2379 steel, and their wear behavior was investigated at dry and lubrication conditions under different loads. The relationship between coating architectures and coating characteristics was explored. The microstructure and composition of the specimens were studied using X-ray diffraction (XRD), scanning electron microscopy (SEM) with Energy dispersive X-ray analysis (EDX) and Atomic force microscopy (AFM).The nano-hardness were measured by nanoindenter, respectively. The adhesion and tribological behavior were evaluated using the Rockwell-C indentation and reciprocating tribometer tests, respectively. The results reveal that the nitrided samples with the TiN/TiCrN coatings with the different number of CrN interlayer showed much better wear resistance than the non-nitrided coatings at dry conditions. On the other hand, nitrided and nitride + coated TiN/TiCrN with the different number of CrN interlayer specimen showed better wear resistance at lubricated conditions. In addition, the fact that uncoated and nitrided steels have higher wear resistance at lubricated conditions than coated samples shows that TiN/TiCrN coatings are not proper even with a lubricant additive over a certain load value.

Effect of diffusion annealing on wear and cohesion behaviours of boronized AISI 1040 steel

AISI 1040 grade steel is a commonly used steel in industry. In this study, pack boriding of AISI 1040 steel was carried out in Ekabor-II powder at different temperatures (900 °C and 950 °C) for 4 h holding time, which was followed by Diffusion annealing process (DAP) for 4 h at different temperatures (950 °C and 1000 °C). The morphology of the boride layers generated on the steel surfaces was investigated using optical and SEM microscopes following boriding experiments. The micro-hardness tester was used to assess the hardness values, and the XRD method was used to determine the phases generated on the layer. In XRD analysis, a boride layer consisting of the Fe2B phase was shown to form as a single-phase structure following the DAP at 1000 ℃ for 4 h. While the original hardness of AISI 1040 steel was 233 HV0.05, the hardness increased up to 1950 HV0.05 using the Boriding process and DAP. Wear tests were carried out using the ball-on-disc method at a sliding speed of 0.3 m/s, under a load of 10 N, at a sliding distance of 500 m in a dry environment. The Daimler-Benz Rockwell-C indentation test was used to study the adhesion capabilities of the boride layer. Wear resistance increased with boriding process and diffusion annealing temperatures. It was discovered that high Diffusion annealing temperatures resulted in the best adhesion and wear resistance.

Carbon-fibre-reinforced-PEEK and silicon doped amorphous carbon as a potential tribopair for implant application

ABSTRACT Studies pertaining to the evaluation of temperature rise in bio-tribopairs are scarce. The present work analyses the application of Si-doped amorphous carbon (Si:a-C) and carbon-fibre-reinforced-PEEK (CFRPEEK) as a potential metal-on-polymer acetabular articulation. The structure of the materials was studied using XRD and Raman spectroscopy and the mechanical behaviour of the Si:a-C film was evaluated using nanoindentation test and Rockwell-C indentation test. Si incorporation resulted in improved hardness and elastic modulus of a-C film along with appreciable H/E and H3/E2 attributes. The structure of Si:a-C film presented SiC phase with reduced sp2 clustering which results in lower graphitisation. CFRPEEK showcased crystalline structure with disorderness induced due to the introduction of carbon fibre. What is more, during lubricated sliding, the temperature rise in the sliding interface was obtained using thermocouple installed in the CFRPEEK counterbody near the sliding vicinity. The results showed low friction coefficient due to the formation of SiOx phase during sliding with low temperature rise having coefficient of 2.1. Si:a-C film underwent low fracture with patches of delamination and CFRPEEK suffered fibre pull-out and tearing. Further studies on the biological activities such as cell adhesion and bacterial adhesion can mainstream the application of these materials for implants.

HYDROXYAPATITE/Si-DOPED TiN INTERLAYER COATINGS AS POTENTIAL CANDIDATES FOR SURFACE MODIFICATION OF MEDICAL-GRADE 316 LVM STAINLESS STEEL FOR BIOIMPLANT APPLICATIONS

Hydroxyapatite (HAp) was deposited by plasma spraying technique with TiSiN adhesive interlayer on the medical-grade 316 LVM stainless steel. The surface topographies of HAp and HAp/TiSiN were evaluated using X-ray diffraction (XRD), Raman spectroscopy, atomic force microscopy (AFM), scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS). The important mechanical properties of the films such as hardness ([Formula: see text]) and elastic modulus ([Formula: see text]) were determined by the nanoindentation test. Lastly, the adhesion and anti-scratch behaviors of the films were evaluated by Rockwell-C indentation and nanoscratch test, respectively. The elemental analysis showed the values of Ca/P (at.%/at.%) ratio to be 1.80 and 1.59 in HAp and HAp/TiSiN coatings, respectively. The mechanical properties of HAp film with TiSiN interlayer were greatly improved from 1.23[Formula: see text][Formula: see text][Formula: see text]0.26[Formula: see text]GPa to 10.6[Formula: see text][Formula: see text][Formula: see text]1.12[Formula: see text]GPa for hardness and from 18[Formula: see text][Formula: see text][Formula: see text]3[Formula: see text]GPa and 29.8[Formula: see text][Formula: see text] 5[Formula: see text]GPa for elastic modulus, respectively. The results of the Rockwell-C indentation test showed a significant reduction in HAp coating delamination with TiSiN interlayer which can be categorized with HF2 or HF3 Daimler–Benz quality ranking. What is more, the nanoscratch profile of HAp coating showed wider scratch with evidence of deformation at the edges which got significantly reduced with the TiSiN interlayer. The results are suggestive of improved mechanical properties, viz. hardness and elastic modulus, and improved adhesion strength of HAp coating with TiSiN interlayer.

Comparison and Analysis of Diffusion Models: Growth Kinetics of Diiron Boride Layers on ASTM A283 Steel

Hard-coated surfacing of a few micrometers is widely applied to increase the efficiency of tools, e.g., for cutting, forming, and casting applications. Therefore, the base thermodiffusion surface treatment is a practical solution to these issues by hardening surface layers with interstitial elements such as carbon, nitrogen, and boron. In particular, within this study, the growth kinetics of an iron boride layer on ASTM 283 steel were investigated with two diffusion models of the powder-pack boriding technique in the temperature range of 1123-1273 K with different treatment periods. The first model, called the steady-state diffusion model, used the modified version of the mass balance equations at the Fe2B/substrate growth interface, the parabolic growth law, and the solution of Fick's second law without time dependence. At the same time, the second diffusion model was based on Goodman's method, also called the integral heat balance method. Afterward, the diffusion coefficient of boron in the Fe2B phase was calculated by fitting the experimental data to the models. Nevertheless, the estimated value for the activation energy of ASTM A238 steel in both diffusion models was coincident (168.2 kJ∙mol-1). A mathematical analysis was implemented by means of a power series (Taylor series) to explain this similarity. The SEM examinations showed a solid tendency to saw-tooth morphology at the growth interface with the formation of the Fe2B layer, whose presence was verified by XRD analysis. The tribological characterizations, including the tests of Rockwell-C indentation, pin-on-disc, and Vickers hardness test method, were used to analyze the antiwear features of the Fe2B layers. Finally, this value of energy was compared to the literature for its experimental validation.

INVESTIGATION OF CORROSION AND ADHESION BEHAVIORS OF BORONIZED ASP® 2012 STEEL

Tool steels are extensively used in sheet metal forming dies in order to prolong the life of dies and reduce the cost of production. Powder metallurgy tool steels are also alternatively preferred because of their low-risk metallurgical behavior owing to their compositions by which bulk steel would be difficult to produce, such as high amount of carbides or high alloying elements. Such advantage is desired if the steel has a narrow range of fine grain sizes and is less metallurgically affected by the heat treatment process due to having large surface area of fine grains. In this study, ASP® 2012 powder metallurgy steel containing high amounts of Si, Cr, Mo and W was selected for boronizing by the boron-giving thermochemical process. The boride layers on the surface of ASP® 2012 tool steel were metallographically characterized by various characterization techniques including adhesion strength test, SEM and XRD. The effects of corrosion kinetics and chemical composition of steel on the amount and types of boride layers formed on P/M steel of ASP® 2012 after powder-pack boriding were investigated. The results indicate that, according to the Rockwell-C indentation test, the best adhesion in the boride layer was obtained in samples borided at 850°C for 4 h, while the worst adhesion was obtained in ASP® 2012 steel boronized at 950°C for 4 h. Corrosion rates of boronized ASP® 2012 steel were decreased compared to nonboronized ASP® 2012 steel.

Effect of plasma nitriding ion current density on tribological properties of composite CrAlN coatings

CrAlN coatings were synthesized on pre-plasma nitrided M2 high speed steels using different ion current densities. The effect of plasma nitriding pretreatment on the microstructures and tribological properties of composite CrAlN coatings had been studied. The results showed that the nitriding efficiency could be significantly enhanced by higher ion current density. The thickness of nitrided layer increased from 43 μm to 63 μm with the increase of ion current density. The nitrided layers without either compound layer or grain boundary precipitation were produced with all experimental ion current densities. Radial cracks also appeared at the Rockwell-C indentation edge of the composite CrAlN coating due to the conformal effect. Moreover, radial cracks of the composite coatings originated from the hard and brittle nitrided layer. The highest interfacial adhesion of the composite CrAlN coating reached 105 N. Furthermore, the wear resistance of CrAlN coating was improved by combining nitriding pretreatment with coating deposition, and the composite coating (PN4/CrAlN) possessed the superior wear resistant.

Properties and Growth Kinetics of the Boride Layer of a Boriding-Strengthened Fe-Based Powder Metallurgical Material

The Fe-based powder metallurgical material was directly sintered by the packed powder boriding method to obtain specimens with the boride layer. These materials were treated at 1123, 1223, and 1323 K for 3, 5, 7, and 10 h, the morphology and thickness of the boride layer were examined with SEM. The phase composition of the boride layer, was analyzed with X-ray diffractometer, and the Rockwell-C indentation test was used to estimate the quality of the bonding strength between the boride layer and substrate. The growth kinetics of the layer was fitted to obtain the plot of thickness variation dynamics. The boride layer thickness is 35–183 μm. The biphase (Fe2B+FeB), and single-phase Fe2B boride layers are obtained at 1323 K and at 1123 and 1223 K, respectively. The quality of the bonding strength of the boride layer obtained at 1223 K for 5 h is approved by the HF3 grade according to the specifications. The diffusion activation energy of B atoms in this experiment is 164 kJ/mol. The sintering temperature and boriding time are closely related to the thickness of the boride layer, and the relationship between the boriding time and the thickness of the boride layer is parabolic. The squared thickness and boriding time are linearly related and consistent with the Arrhenius formula. The microhardness of the boride layer is significantly higher than that of the substrate. The number of defects in the layer is growing with time. The characteristic comb-tooth shape of the boride layer is gradually passivated, and the tip is not obvious until the front edge of the layer is relatively flat. This phenomenon is more pronounced at high temperatures.

Effect of microstructure on the adhesion strength of TiBx coating on Ti6Al4V substrate

TiBx coatings were deposited on Ti6Al4V and Si (100) wafer substrates by D.C. magnetron sputtering with various target-to-substrate distances (T.S. distances) from 50 mm to 200 mm. The influence of T.S. distance on the microstructure, hardness and adhesion strength of TiBx coatings and Ti6Al4V substrate system was investigated. Results showed that the microstructure of TiBx coatings transformed from dense to fibre columnar grain with the increase in T.S. distance, whilst the hardness decreased from 20.9 GPa to 9.4 GPa. The Rockwell-C indentation adhesion strength grade was also improved from HF6 to HF1. An adhesion evaluation factor G, which is related to the mechanical properties and the microstructure of TiBx coating, is proposed based on the test results. The adhesion strength increased with G, which corresponded well with the results of indentation test. The high-speed rubbing test with a sliding speed of 300 m/s was performed to check the Al-adhesion resistance of the TiBx coating against Al–hBN seal coating.

Nanoscale Multi-Layer Thin Film Fabricated by Cathodic Arc Evaporation (CAE) Method

In the present study, TiN and CrN single-layer and TiN/CrN nanoscale multi-layer thin films have been deposited on 420C stainless steel (SS) substrate using a cathodic arc evaporation (CAE) method. The nanoindentation test showed that hardness of TiN/CrN nanoscale multi-layer thin film was 30 GPa that is harder than TiN (HTiN = 23 GPa) and CrN (HCrN = 19 GPa). Ball-on-disk tribometer and Rockwell-C indentation methods showed respectively better sliding wear performance for TiN/CrN nanoscale multi-layer coating and better adhesion strength for CrN single-layer coating in comparison to all samples. Finally it was found that the TiN/CrN nanoscale multi-layer thin film can be used for tribological applications on 420C SS where high hardness and wear resistance and low friction coefficients are essential.

Growth kinetics of Fe2B layers formed on the AISI 4150 steel by different approaches

In the present work, the AISI 4150 steel has been pack-borided in the temperature range of 1123-1273 K for a treatmenttime of 2 to 8 h. The mixture of powders containing 20% B4C, 10% KBF4 and 70% SiC has been used for producing a singleboride layer (Fe2B) at the surface of AISI 4150 steel. The presence of Fe2B phase has been confirmed by XRD analysis.The SEM observations have been done to investigate the morphology of boride layers and measure their thicknesses.The cohesion of boride layers has been evaluated by using the Daimler-Benz Rockwell-C indentation technique.The borided sample at 1173 K for 8 h has shown a best cohesion of boride layer to the substrate in comparison to the sampletreated at 1173 K during 2 h. Kinetically, different approaches have been used to estimate the boron diffusion coefficients inthe Fe2B layers and to predict the value of Fe2B layer thickness obtained at 1253 K for a treatment time of 2.5 h. Theestimated values of activation energies for boron diffusion in AISI 4150 steel have been in the range of 193.45 to 199.74 kJmol-1. These values of activation energies have been depended on the diffusion models used. In addition, a good agreementhas been observed between the experimental value of Fe2B layer thickness obtained at 1253 K for 2.5 h with the predictedvalues from these different diffusion models.

Hard Cr2O3 coatings on SS316L substrates prepared by reactive magnetron sputtering technique: a potential candidate for orthopedic implants.

316L stainless steel (SS) implants suffer from tribological and biocompatibility problems which limit their service lifetime. In order to improve the surface properties of 316L SS for orthopedic implant applications, hard chromium oxide coatings were applied on 316L SS substrates using a reactive magnetron sputtering technique. The morphological, structural, and phase compositional analyses were conducted on the deposited coatings by scanning electron microscopy, X-ray diffraction, Raman spectroscopy, and X-ray photoelectron spectroscopy. The Rockwell-C indentation tests were performed on the coated substrates to qualitatively evaluate the adhesion of coatings on the steel substrates. The surface characteristics of coatings were measured by using an optical profilometer. The mechanical properties of coatings were reported by measuring the Hardness and Young's modulus. The corrosion resistance of coated and uncoated SS substrates was compared using potentiodynamic polarization tests. An inductively coupled plasma optical emission spectrometry (ICP-OES) was employed to analyze the biocompatibility of the samples by measuring the amount of toxic Cr ions released after the immersion test. The results show that the coatings are adherent and composed of a single Cr2O3 phase with a hardness of 25 to 29GPa. The corrosion resistance of the SS has been improved by applying a chromium oxide coating. The coated SS samples have also demonstrated better wear resistance and lower friction coefficient compared to bare SS samples under a reciprocating sliding condition in saline solution. The biocompatibility of the SS has been enhanced by the Cr2O3 coating as much less Cr ions were released after immersion tests. These results indicate that the hard Cr2O3 coatings can be considered as a candidate for extending the lifetime of SS implants.

Microstructure, adhesion and tribological properties of CrN/CrTiAlSiN/WCrTiAlN multilayer coatings deposited on nitrocarburized AISI 4140 steel

In this study, the CrN/CrTiAlSiN/WCrAlTiN multilayer coatings have been deposited on polished AISI 4140 steel substrates (named only-coating specimens) and plasma nitrocarburized specimens (named duplex specimens) by cathodic multi-arc evaporation. The microstructure and composition of the specimens were studied using X-ray diffraction (XRD), scanning electron microscopy (SEM) with Energy dispersive X-ray analysis (EDX), and transmission electron microscope (TEM) techniques. The micro-hardness and nano-hardness were measured by Vickers hardness tester and nanoindentation, respectively. The adhesion and tribological behavior were evaluated using the Rockwell-C indentation and micro-tribometer, respectively. The results showed that plasma nitrocarburizing gives rise to a modified layer due to diffusion of nitrogen/carbon, leading to surface hardness, H, of 13.0 GPa, compared to H = 6.8 GPa for the untreated steel. Notably, it shows that the super-hardness (H = 47.9 GPa) multilayer coating consists of a bottom CrN layer, a middle CrTiAlSiN layer, and an outmost superlattice WCrTiAlN layer. The nitrocarburizing pretreatment considerably improves adhesion strength of the duplex specimen compared with the only-coating one. The improved mechanical and tribological properties of the duplex specimen are mainly related to the gradient in the hardness profile of the diffusion nitrocarburized layer.

Characterization and boriding kinetics of AISI T1 steel

The AISI T1 steel was hardened by the solid boriding process in the temperature range 1123–1273 K for a time duration of 2 to 8 h. A kinetic model, based on the integral method, was applied to the growth of a single boride layer (Fe2B) at the surface of AISI T1 steel. This diffusion model has been validated experimentally by considering two additional boriding conditions. A numerical solution was then obtained after solving the set of differential algebraic equations in order to compare the experimental thicknesses of Fe2B layers with the predicted values. The activation energy for boron diffusion in AISI T1 steel was estimated as 212.76 kJ mol−1and a comparison was made with other values available in the literature. The formed boride layers with a saw-tooth morphology were examined by scanning electron microscopy (SEM). X-ray diffraction confirmed that the borided layer was composed of only Fe2B. The Daimler-Benz Rockwell-C indentation technique was employed to assess the cohesion of Fe2B layers on AISI T1 steel. In addition, the pin-on-disc and wear scratch tests were carried out for investigating the wear behaviour of borided AISI T1 steel.

Effects of functionally graded TiN layer and deposition temperature on the structure and surface properties of TiCN coating deposited on plasma nitrided H13 steel by PACVD method

The poor adhesion of nitride coatings to steel substrates is one of the main challenges for industrial applications. In this study, plasma nitriding process and TiN functional intermediate layer were used in order to increase the adhesion of TiCN coating to the hot worked steel H13 substrate and also to improve its mechanical properties. The functionally graded nanostructured TiCN coating was deposited using pulsed-DC plasma-assisted chemical vapor deposition (PACVD) method. The coatings microstructural and mechanical properties were investigated using X-ray diffraction (XRD), scanning electron microscopy (SEM), optical microscopy (OM), Rockwell-C indentation, micro hardness and ball-on-disk tests. The results showed that peaks of TiN and TiCN phases existed in the XRD pattern and the size of their crystallites is about 7 nm. Carbon and nitrogen contents in the TiCN coating gradually increased from the substrate to its surface. The functional coating prepared at 475 °C had higher adhesion to the substrate in comparison with those deposited at 450 and 500 °C. The high adhesion led to reduction of radial and peripheral cracks within the coating. Decrease in the friction coefficient and lost volume during ball-on-disk tests indicated that the wear resistance of the functional coating deposited at 475 °C was 78% higher than that of the other coatings.

Kinetics of boron diffusion and characterization of Fe2B layers on AISI 9840 steel

In this work, the AISI 9840 steel was subjected to the powder-pack boriding in the temperature range of 1123–1273 K for various times ranging from 2 to 8 h. A kinetic model based on the principle of mass conservation at the growing interface was used to estimate the boron diffusion coefficients through the Fe2B layers. The pack-borided samples were experimentally characterized by different techniques such as: Scaning electron microscopy, XRD analysis, Microhardness Vickers testing. The Daimler-Benz Rockwell-C indentation technique was used to assess the adhesion quality of boride coatings on AISI 9840 steel. Finally, the scratch and pin-on-disc tests for wear resistance were respectively performed using an LG Motion Ltd and a CSM tribometer under dry sliding conditions. The boron activation energy for the AISI 9840 steel was estimated as 193.08 kJ /mol by applying the present model. To confirm and extend the validity of the diffusion model, the experimental values of Fe2B layers thicknesses obtained for other boriding conditions were compared with the predicted values.

Pack-boriding of AISI P20 steel: estimation of boron diffusion coefficients in the Fe<SUB align="right">2B layers and tribological behaviour

In the present study, the AISI P20 steel was pack-borided in the temperature range of 1,123-1,223 K for treatments times between 2 and 8 h. A new kinetic model based on the integral method was used to estimate the boron diffusion coefficients in the Fe2B layers. As a result, the activation energy for boron diffusion in the AISI P20 steel was estimated as 194.3 kJ mol−1. This value of energy was compared with the literature results. Furthermore, to validate experimentally the present model, two additional boriding conditions were used. The morphology of cross-sections of borided samples was examined by scanning electron microscopy. The formation of a single boride layer was confirmed by x-ray diffraction analysis. The Daimler-Benz Rockwell-C indentation technique was used to evaluate the cohesion of boride layers on the surface of AISI P20 steel. Finally, the scratch and pin-on-disc tests for wear resistance were carried out by means of a LG Motion Ltd and a CSM tribometer respectively under dry sliding conditions.

The influence of plasma nitriding on microstructure and properties of CrN and CrNiN coatings on Ti6Al4V by magnetron sputtering

In this paper, the CrN and CrNiN coatings were deposited on the non-nitrided and nitrided Ti6Al4V alloys with the method of closed-field unbalanced magnetron sputter ion plating (CFUBMSIP). The influence of plasma nitriding treatment on microstructure, mechanical and tribological properties of Physical Vapor Deposition (PVD) films was evacuated by means of SEM (EDS), XRD, Rockwell-C indentation testing, nanoindentation testing, and ball-on disc tribotesting. With the addition of Ni, the preferred orientation changes to CrN (200) and the grain is refined. The indentation tests indicated that the duplex treated samples exhibited the best combined properties. The nanoindentation testing results showed that the hardness of the coatings increased, the plastic deformation reduced and they had higher H3/E2 values than PVD coatings with the plasma nitriding before PVD treatment due to the increase of substrate's load bear capacity after plasma nitriding process. The friction and wear tests demonstrated that the tribological performance of the PVD coatings improved after plasma nitriding which is attributed to the enhanced the mechanical compatibility between the hard PVD coating and soft substrate and the resistance of CrN coating is better than that of CrNiN coating because of the transfer layer (constituted of TiN and Ti2N) deposited by nitriding.