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Due to global environmental concerns related to climate change, the need to improve the service life of structures and infrastructures is imminently urgent. Structural elements typically suffer service life reductions, leading to poor environmental sustainability and high maintenance costs. Graphene oxide nanosheets (GONSs) effectively dispersed in a cement matrix can promote hydration, refine the microstructure and improve interfacial bonding, leading to enhanced building materials’ performance, including mechanical strength and transport properties. Cement-based nanocomposites engineered with GONSs were obtained using two commercial nanofillers, a GO water suspension and a free-flowing GO nanopowder, characterized by fully comparable morphology, size and aspect ratio and different oxidation degrees (i.e., oxygen-to-carbon molar ratio), 0.55 and 0.45, respectively. The dosage of the 2D-nanofiller ranged between 0.01% and 0.2% by weight of cement. The electrical and thermal properties were assessed through electrochemical impedance spectroscopy (EIS) and a heat flow meter, respectively. The results were discussed and linked to micrometric porosity investigated by micro-computed tomography (μ-CT) and transport properties as determined by initial surface absorption test (ISAT), boil-water saturation method (BWS) and chloride ion penetration test. Extra-low dosage mortars, especially those loaded with a lower oxidation degree (i.e., 0.45GO), showed decreased permeability and improved barrier to chloride ion transport combined with enhanced thermal and electrical conductivity with respect to that of the control samples.

Chromium deposits rank among the most widespread metal coatings for functional and decorative purposes. However, electrodeposition from Cr(VI) aqueous solution, which is the industrial process currently used to achieve thin chromium deposits, presents several environmental issues, urging the development of alternative solutions. In this study, which aims to compare the functional and aesthetical properties of decorative coatings, 800 nm thick chromium layers were deposited directly onto copper substrates by means of magnetron sputtering (MS) and direct current electrodeposition (ED). The obtained coatings were characterized regarding their thickness, morphology, color index, chemical composition, and corrosion resistance viewpoints. With respect to the electroplated samples, which constitute the benchmark, the magnetron sputtered ones appeared to be darker but showed a pleasing reflective appearance and superior thickness homogeneity, as well as the absence of voids and macrocracks, as evidenced by scanning electron microscopy (SEM) investigation. Regarding the anticorrosion performances of the chromium layers, electrochemical and standard salt spray test (NSS test) were carried out at room temperature in 3.5% NaCl solution, and evidenced similar, if not better, results for the magnetron sputtered coatings. On the whole, the data displayed here demonstrates the suitability of magnetron sputtering technology for use as an industrially feasible finishing technology for both aesthetic and mild-condition anticorrosion purposes.

The XRF analysis is the most widespread in the industry setting to determine the thickness of metallic coatings, thanks to its ease of use, robustness, and non-destructive nature. However, accurate measurement requires primary standards that are expensive, not always available, and must be periodically replaced due to a limited shelf-life. In this context, we propose a versatile and cost-effective way for measuring the thickness of metallic coatings. Our method relies on a calibration curve based upon self-produced standards made through electroplating process and measured by a cross-sectional microscopy observation, either by SEM or light microscope. Thickness distribution was sufficiently homogeneous to be consistent with certified standard specifications: 5% of thickness variation in the central portion of the coatings (1 cm2) could be achieved for cathode length starting from 5 cm. Moreover, thickness distribution can be quantitatively predicted, relying only on primary current simulations, almost on simple shaped objects. The self-produced standard fit the calibration curve with a R2 > 0.999. Comparing different XRF quantitative methods with Student's t-test, we demonstrated that the proposed protocol is as effective as certified standards-based methods in terms of accuracy but at significantly lower costs.

Low-temperature nitriding of austenitic stainless steels produces modified surface layers, consisting mainly of the S phase, which improve surface hardness and corrosion resistance. Because of the localized plastic deformations, owing to modified layer formation, and ion bombardment occurring during the process itself, this treatment produces also modifications of surface morphology and roughness, which can affect wettability and corrosion behavior. In this study the effects of plasma nitriding, performed using different treatment conditions, on the surface morphology and roughness, and thus on wettability and corrosion resistance, of AISI 202 specimens with different initial finishings (2D and polished finishing) were investigated. Different probe liquids, having both high (bi-distilled water and solution of 3.5% NaCl) and low (ethanol and rapeseed oil) surface tension, were employed for assessing the wetting behavior with the sessile drop method. The contact angle values for water increased markedly when nitriding was performed on polished samples, while this increase was smaller for 2D samples, and on selected specimens a hydrophobic behavior was observed. Very low contact angle values were registered using low surface tension liquids, suggesting an oleophilic behavior. Corrosion resistance in a 5% NaCl solution was assessed, and it depended on the characteristics of the nitrided specimens.

The present work reports the application of RF-magnetron sputtering technique to realize CsPbBr 3 70 nm thick films on glass substrate by means of a one-step procedure. The obtained films show highly uniform surface morphology and homogeneous thickness as evidenced by AFM and SEM investigations. XRD measurements demonstrate the presence of two phases: a dominant orthorhombic CsPbBr 3 and a subordinate CsPb 2 Br 5 . Finally, XPS data reveals surface bromine depletion respect to the stoichiometrical CsPbBr 3 composition, nevertheless photoluminescence spectroscopy results confirm the formation of a highly luminescent film. These preliminary results demonstrate that our approach could be of great relevance for easy fabrication of large area perovskite thin films. Future developments, based on this approach, may include the realization of multijunction solar cells and multicolor light emitting devices.

Low temperature plasma nitriding was performed on CrNi-based (AISI 316L), CrMn-based (AISI 202) and nickel-free (P558) austenitic stainless steels. For all the used steels modified surface layers consist mainly of S phase without the precipitation of large amounts of nitrides, and they show enhanced surface microhardness and corrosion resistance in NaCl acqueous solution. The different electrochemical corrosion testing techniques evidence that the increase of corrosion potential may be ascribed mainly to nitrogen addition, while regarding the increase of potential, at which localized corrosion phenomena occur, also alloy elements, and in particular Mo, play an important role.

The wear phenomenon in friction clutches involves a variation in the contact pairs characteristics, defining a decay of transmissible torque properties. For multidisk clutch packs installed in electro-actuated differentials, the friction torque evolution allows to define how wear decay can influence the dynamic of the vehicle where the differential is installed in. A tribological analysis of a molybdenum-coated clutch pack was made under typical working conditions in terms of temperature, normal load and sliding speed. Friction coefficient and wear rate trends were outlined to define material characteristics through block-on-ring tests. Metallurgic studies on the specimens used in tribologic tests validated the base material used in the samples. Results from experimental analyses were used as input for a numerical study regarding wear and pressure evolutions during clutch engagement. The application of Reye's theory and Archard's law on a FE model of the clutch led to the definition of an algorithm to estimate the friction torque generated by the clutch system and the its lifetime.

Magnetron sputtering is a useful tool for producing coatings on various substrates at low temperature. The use of an austenitic stainless steel target in a nitrogen-containing plasma mixture allows to obtain nanostructured coatings with the formation of the so-called S phase, supersaturated interstitial solid solution of nitrogen in the expanded and distorted austenite lattice, which shows improved hardness and higher corrosion resistance in comparison with the bulk alloy. In the present research, RF magnetron sputtering deposition of austenitic stainless steel coatings using an AISI 316L target in nitrogen-containing plasma gas was studied. The effect of the N2/Ar gas ratio and the deposition temperature on nitrogen content, phase composition and crystallite size is investigated by mean of XPS, XRD and electron microscopy analyses. The results show that the nitrogen content in the resulting deposit slightly depends on the N2/Ar ratio in the chamber during the deposition, reaching a maximum value of about 35% with a 30% N2/Ar gas composition mixture in the chamber. Data obtained on different substrates are presented and a preliminary evaluation of the corrosion resistance behaviour is also reported.

This work is focused on the realization of a new manufacturing process based on the introduction of TiO2 nanostructured coatings on the surface of red earthenware pottery for domestic use. The aim of the study is to improve the technical properties of the product made from lime and iron-rich clays used to produce traditional artistic Tuscan pottery (Italy). The identified strategy involves the application of nanoparticles onto the surface of ceramic substrates via a sol-gel based process; the initial porosity of the Earthenware promotes the insertion of inert nanoparticles in the outermost part of the ceramic material by simple immersion of bisqueware in the colloidal solutions of nanoparticles. Morphological investigation of the functionalized surfaces has been carried out by scanning electron microscope and atomic force microscopy, while the effectiveness of the treatment was checked by evaluating the water absorption capacity in compliance with the standard method AS-1012.21-1999. The obtained results show a reduction of surface porosity, which turns into a reduced water uptake respect to the traditional pottery, maintaining, at the same time, identical aesthetical characteristics.

Low temperature nitriding is known as a useful treatment to increase surface hardness and corrosion resistance of austenitic stainless steels, but little information is reported about its effect on surface wettability of the nitrided alloys. In this preliminary study the modifications of water wetting properties due to this treatment were investigated and they were related to the surface morphology and roughness changes. Samples of AISI 316L and AISI 202 austenitic stainless steels were nitrided using the glow-discharge technique, and modified surface layers consisting mainly of the so called S phase were produced. The treatments affected also the surface morphology and caused the formation of peculiar features, which were due to both ion bombardment during sputtering and nitriding, and local plastic deformations promoted by the high amount of solubilised nitrogen. As a consequence, roughness increased markedly on nitrided samples in comparison with untreated ones. Water wetting tests, performed with the sessile drop method, showed that the apparent contact angle values were higher on the nitrided samples in respect of the untreated ones, up to a hydrophobic behaviour. According to the Cassie–Baxter model, it may be supposed that the drops lie on solid and air pockets, formed thanks to the rougher surfaces. Additional tests suggest that this state is metastable: when the water drop was pushed on the nitrided surface, filling of almost all the cavities and valleys was obtained, and smaller contact angles were measured, also in respect of the untreated samples, suggesting that a state near to that hypothesised by Wenzel was achieved.

In this study the effects of low temperature plasma nitriding on the characteristics of different austenitic stainless steels, CrNi-based (AISI 304L and AISI 316L) and CrMn-based (AISI 202), were compared. Samples were nitrided at 400 and 430 °C, at 1000 Pa for 5 h, and their microstructure, phase composition, microhardness and corrosion resistance were evaluated. The characteristics of modified surface layers depended on both treatment parameters and alloy composition. For all the steels modified surface layers had a double layer microstructure. In the outer modified layer, mainly consisting of S phase, deformation (or shear) bands were observed in the grains, and nitrogen induced h.c.p. martensite, e′ N , formed. The tendency to form shear bands and e′ N was higher for AISI 202 samples, and decreased for AISI 304L and then for AISI 316L ones, influencing the modified layer thickness. When nitriding was performed at 430 °C, nitrides formed, and their amount was affected by steel composition. Nitriding treatments allowed to markedly increase surface microhardness and corrosion resistance, in comparison with the untreated alloys. When nitrides did not form, as for the 400-°C nitrided samples, the corrosion behaviour of the considered steels was comparable. Nitride precipitation affected corrosion resistance, increasing corrosion phenomena.

In the last years an increasing interest has been taken in AISI 200 series austenitic stainless steels for use in industrial applications. In these steels nickel is partly replaced by other austenite stabilising elements, like manganese and nitrogen. However, their chromium content is usually lower than that of the largely used Fe–Cr–Ni based AISI 300 series stainless steels, so that their corrosion resistance may be lower. For AISI 300 series steels low temperature nitriding treatments have been successfully employed to increase their corrosion resistance, due to the formation of modified surface layers consisting of the so called S phase. In this research, a low nickel AISI 202 austenitic stainless steel was subjected to glow-discharge nitriding treatments in the range 653–773 K, for 5 h, at 10 hPa, and the microstructural, mechanical and corrosion resistance characteristics of the nitrided samples were investigated and compared to those of the untreated steel. The treatments produce modified surface layers having a double layer structure. When the treatments are carried out at temperatures up to 673 K, the outer modified layer consists mainly of the S phase and a nitrogen induced h.c.p. martensite; in the inner modified layer a solid solution of nitrogen in γ-Fe is present. As the treatment temperature increases, also chromium and iron nitrides are observed in the outer modified layer, and their amount increases as the treatment temperature is higher. High surface hardness values (from 940 to 1750 HK 0.025 depending on treatment temperature) have been observed on the treated samples. Corrosion resistance tests, performed in 5% NaCl aerated solution with the potentiodynamic method, show that, with the used treatment parameters, glow-discharge nitriding at temperatures up to 703 K allows to increase significantly the corrosion resistance in respect of the untreated alloy, reducing the anodic current values up to about 5 orders of magnitude.

Glow-discharge nitriding treatments can modify the hardness and the corrosion resistance properties of austenitic stainless steels. The modified layer characteristics mainly depend on the treatment temperature. In the present paper the results relative to glow-discharge nitriding treatments carried out on AISI 316L austenitic stainless steel samples at temperatures ranging from 673 to 773 K are reported. Treated and untreated samples were characterized by means of microstructural and morphological analysis, surface microhardness measurements and corrosion tests in NaCl solutions. The electrochemical characterization was carried out by means of linear polarizations, free corrosion potential–time curves and prolonged crevice corrosion tests. Nitriding treatments performed at higher temperatures (>723 K) can largely increase the surface hardness of AISI 316L stainless steel samples, but decrease the corrosion resistance properties due to the CrN precipitation. Nevertheless nitriding treatments performed at lower temperatures (⩽723 K) avoid a large CrN precipitation and allow to produce modified layers essentially composed by a nitrogen super-saturated austenitic metastable phase (S-phase) that shows high hardness and very high pitting and crevice corrosion resistance; at the same polarization potentials the anodic current density values are reduced up to three orders of magnitude in comparison with untreated samples and no crevice corrosion event can be detected after 60 days of immersion in 10% NaCl solution at 328 K.

The vacuum plasma spray (VPS) technique is a useful tool for designing the characteristics of the coatings and, thus, the tribological properties of coated components. In the present paper, the wear properties of iron boride coatings produced by means of VPS technique on AISI 1040 steel samples were evaluated as a function of their microstructural characteristics. One coating type was obtained by using Fe 2 B pure powder, the other with differentiated FeB + α-Fe blends, with the FeB content increasing and α-Fe content decreasing from the matrix to the surface. Wear tests were performed by means of a tribometer in block-on-ring configuration, without lubricant and in air, by using 40- and 60-N coupling loads and 0.8- and 1.6-m s −1 sliding velocities. On Fe 2 B coated samples, wear is essentially oxidative until the failure of the coating, the fragments of which cause a third body abrasion. On the FeB + α-Fe coated samples the wear mechanism is mainly oxidative and the coating totally wears out without spalling as a consequence of its graded structure, which succeeds in both improving the adhesion of the coating to the substrate and reducing the residual stress at the coating–substrate interface.

The reactive plasma spraying (RPS) of titanium powders in a nitrogen containing plasma gas produces thick coatings characterised by microdispersed titanium nitride phases in a titanium matrix. To increase the cohesion between the coating particles and decrease the coating porosity, an air oxidation is proposed as a post-coating treatment, and its influence on the microstructure, sliding wear resistance and corrosion resistance of Ti–TiN RPS coatings obtained on carbon steel substrates is studied. The oxidising treatment, carried out at 973 K for 2 h, promotes both the growth of titanium oxide on the coating pore walls, allowing a partial pore sealing, and interdiffusion processes, which increase the coating internal cohesion. After the post-coating treatment the average microhardness of the coating increases from about 650 to 800 HK 0.2 . Wear tests, performed in dry sliding conditions, show that for the sprayed and oxidised samples the wear volumes are lower, particularly at low sliding velocities (0.4, 0.8 m s −1 ), in comparison with the as-sprayed samples. Moreover, corrosion resistance tests, carried out in 0.5 M NaCl and 0.1 M HCl deareated solutions, show that a reduction of the anodic current values is achieved for the sprayed and oxidised samples. This simple post-coating treatment is effective in improving the wear and corrosion protection of Ti–TiN RPS coatings on carbon steel substrates.

The influence of treatment pressure on the characteristics of the modified surface layers produced by low-temperature d.c. glow discharge nitriding on AISI 316L austenitic stainless steel samples is investigated. Glow discharge nitriding treatments were performed at 703 K for 5 h at working pressures in the range of 1.5–20 hPa. Morphology and microstructure of the untreated and nitrided samples were studied by means of microscopy techniques, energy dispersion spectroscopy and X-ray diffraction analysis; microhardness measurements and corrosion resistance tests were also performed. The nitriding treatments produce a hardened surface layer consisting mainly of the so-called S phase. The presence of nitrides and the thickness of the modified layer depend on the used treatment pressure. When treatments are performed at 2.5 hPa, a fairly large amount of nitrides is observed in the modified layer, while when the nitriding pressure is lower or higher than 2.5 hPa, the nitride amount decreases and the layer becomes thinner. When the treatments are performed at 10 or 20 hPa, only a very small amount of chromium nitride is present as small surface precipitates. Metallographic analysis shows that many slip lines are present both at the surface and in the cross-section of the modified layer, presumably due to high stresses occurring during the formation of the layer. X-ray diffraction analysis of the S phase shows that its diffraction peaks are shifted from those of a perfect f.c.c. lattice; the observed shifts may be explained assuming that the S phase has an f.c.c. structure with a high density of stacking faults. Corrosion resistance tests, performed in 5% NaCl aerated solution with the potentiodynamic method, show that with the used treatment parameters nitriding at a pressure of 10 hPa or higher allows to obtain a significant improvement of the corrosion resistance in respect of the untreated alloy, reducing the anodic currents up to about 4 orders of magnitude.

Nitriding treatments of austenitic stainless steels can be performed only at relatively low temperatures in order to avoid a decrease of corrosion resistance due to chromium nitride formation. These conditions promote the formation of the so-called S phase, which shows high hardness and good corrosion resistance. In the present paper, the influence of the treatment temperature of glow-discharge nitriding process on the microstructural and mechanical characteristics of AISI 316L steel samples was evaluated. Glow-discharge nitriding treatments were performed at temperatures in the range 673–773 K for 5 h at 10 3 Pa. The modified surface layer of the nitrided samples consists mainly of the S phase and, according to metallographic technique analysis, it seems to be essentially a modification of the austenite matrix. All the nitrided sample types show a peculiar surface morphology due to both plasma etching during nitriding and the presence of slip steps and relieves at grain boundaries, the latter features presumably due to the formation of the nitrided layer. X-ray diffraction analysis shows that for the samples nitrided at temperatures up to 723 K, besides the S phase, small chromium nitride precipitates are present at the surface, while using higher treatment temperatures both chromium (CrN) and iron (γ'-Fe 4 N) nitrides precipitate along the grain boundaries and in the middle of the grains, and their amount increases as treatment temperature increases. High hardness values (from ∼1450 to ∼1550 HK 0.01 , depending on nitriding conditions) are observed in the modified layer with a steep decrease to matrix values. Preliminary corrosion resistance tests, carried out in 5% NaCl aerated solution with the potentiodynamic method, show that with the used treatment parameters a substantial improvement of corrosion resistance can be achieved when glow-discharge nitriding treatments are performed at temperatures in the range 703–723 K.

Thermal oxidising treatment is an easy and environmental friendly technique that can be used to harden the surface of titanium alloys, and hence improve the poor tribological properties of these materials. The aim of the present research was to evaluate the tribological behaviour of thermally oxidised titanium alloy samples as both counterparts. With this purpose, Ti–6Al–4V alloy disks were treated in an air circulating furnace at 1173 K for 2 h at 105 Pa, and then quenched using compressed air, in order to remove the poorly adherent part of the oxide scale. The modified surface layer shows decreasing hardness values, from ∼970 HK0.025 to matrix values; the case depth of the hardened layer is ∼35 μm. Wear tests, carried out on both untreated and oxidised samples in block-on-ring configuration, in dry sliding conditions, with sliding velocity in the range 0.4–1.6 m s−1, 50 N coupling load and 3000 m sliding distance, show that the thermal oxidation treatment is able to substantially improve the wear resistance of Ti–6Al–4V samples, reducing the wear volumes from about 4 to 6 times in respect of the untreated alloy. Moreover, further wear tests (sliding velocity: 0.8 m s−1; coupling load: 50 N; sliding distance: 1700 m), performed on untreated, glow-discharge nitrided and thermally oxidised samples, point out that, with the used test conditions, a marked improvement of the wear resistance is obtained for the oxidised samples in respect of both untreated and nitrided ones.

The poor tribological properties of titanium and titanium alloys can be improved by using diffusion treatments, which take advantage of the high reactivity of titanium with respect of carbon, nitrogen or oxygen to produce high hardness surface layers well bonded to the tough matrix. The present paper reports a comparison of the effects of glow-discharge and furnace processes, performed using air as treatment atmosphere, on the microstructure and mechanical properties of Ti-6Al-4V alloy samples. Both treatment types, performed at 973 and 1173 K for 0.5, 2 and 4 h, produce modified surface layers, consisting of an outer compound layer and an inner diffusion layer. The compound layer consists mainly of TiO2, small amounts of TiNxOy and, in the 1173-K treated samples, small amounts of Al2O3 concentrated at the outer part of the scale. In the diffusion layer, a solid solution of interstitial atoms in α-Ti is present; moreover, at the compound layer–diffusion layer interface a peculiar microstructure, consisting of oxygen-rich Ti3Al phase and α-Ti solid solution, is observed on samples treated at 1173 K. A higher efficiency in surface hardening is shown by the glow-discharge treatment in respect of the furnace process: by using the same treatment temperature and time, glow-discharge treated samples have thicker hardened layers with higher hardness values than the furnace treated ones, and this effect is more marked for 973-K treated samples, while it is reduced for 1173-K treated samples. Moreover, the a, c lattice parameters of the α-Ti solid solution, evaluated by means of the Rietveld method from X-ray diffraction patterns, are also influenced by the treatment type.

The lubricated rolling–sliding wear of an untreated and ion nitrided Ti–6Al–4V alloy has been investigated. All the tests were carried out under boundary lubrication using commercial SAE 14-W oil. The results show that nitriding improved wear resistance of the Ti–6Al–4V alloy. In particular the material nitrided for 24 h displayed the best wear resistance because the compound layer was effectively sustained by the hardened diffusion layer at the contact loads here investigated. Friction coefficient, on the other hand, was found to be higher in the nitrided materials, although the λ -factors were similar in all the tribological couplings. This was attributed to the lower wettability of the lubricant versus the nitrided layer than the passivated surface of the untreated alloy.

Post-oxidising treatments can be performed to improve the corrosion resistance of nitrided steel components. The glow-discharge process appears particularly attractive, since it allows to carry out both nitriding and post-oxidising treatments in a single technological operation, simply varying the treatment atmosphere and the working conditions. In the present paper the effects of using air as the treatment atmosphere of glow-discharge post-oxidising treatment have been evaluated. Nitriding treatments were performed at 773 K for 5 h, and post-oxidising treatments were carried out at 623 and 773 K for 1 h. The nitriding and nitriding+post-oxidising treatments produce modified surface layers consisting of an outer compound layer and an inner diffusion layer. When the post-oxidising treatments are performed, the compound layer consists of an oxide layer on the top of the nitride layer. With a 623 K post-oxidising treatment the oxide layer consists mainly of magnetite, Fe 3 O 4 , while when post-oxidising is carried out at 773 K it consists essentially of hematite, Fe 2 O 3 . In the inner nitride layer iron (γ′-Fe 4 N, e-Fe 2–3 N) and chromium (CrN) nitrides are present. In all the treated samples high hardness values are obtained in the modified layers. The hardness profiles of the post-oxidised samples are only slightly affected by the 773 K post-oxidising treatment. The corrosion resistance of the treated samples was tested and the results show that the nitriding+623 K post-oxidising treatment is able to significantly improve the corrosion resistance of the untreated and treated AISI H11 samples.

The corrosion properties of TiN layers obtained by glow discharge on Ti–6Al–4V samples were investigated by polarisation curves, cyclic voltammetry and loss weight tests, in different HCl solutions. The results were compared with those obtained on the untreated alloy tested in the same conditions. The corrosion resistance of nitrided samples depends on the quality of the film and increases as the thickness increases. At potential lower than 1000 mV (SSE) nitrided samples show passive behaviour even in concentrated HCl solution (4M). If the potential is higher than a threshold, which depends on the acid concentration, it is observed a high anodic current related to the TiN oxidation. This enhanced oxide growth promotes cracking of the oxide layer and the exposure of fresh TiN surface.

The surface hardening of sintered stainless steel components is a major goal, in order to extend the applications of these materials. The aim of the present study was to evaluate the influence of the treatment atmosphere on the microstructure and mechanical properties of AISI 316L austenitic and AISI 410 martensitic sintered stainless steels by performing glow-discharge nitriding and nitrocarburizing treatments. The treatments, performed at 773 K for 8 h, produced modified surface layers. The use of a nitrocarburizing atmosphere is able to promote the formation of e carbonitride [Fe2−3(N, C)], especially on AISI 410 martensitic samples. The microhardness profiles of the treated samples show high hardness values in the modified layers and a steep decrease to matrix values. The AISI 316L samples have thinner hardened layers and lower hardness values, in comparison with AISI 410 ones. Thinner hardened layers with a steeper decrease to matrix values are obtained using a nitrocarburizing atmosphere, if compared with those of nitrided samples. On the modified layers of both the nitrided and nitrocarburized AISI 316L samples the metastable S phase is detected. The X-ray diffraction analysis has shown that its lattice parameter values, evaluated by fitting it with a face centred tetragonal lattice, are influenced by the treatment atmosphere and that the amount of this phase increases when a nitrocarburizing atmosphere is used.

The tribocorrosion behavior of plasma nitrided Ti–6Al–4V alloy is investigated in a 0.9 M NaCl solution at room temperature by means of a sliding wear tribometer, utilizing alumina balls as the counterface material. Tests were performed at open circuit potential and under anodic polarization and the electrochemical parameters, namely anodic current, potential and galvanic current were continuously monitored. The plasma nitriding treatments were performed at two different temperatures, 973 K and 1173 K, and the resulting microstructures and phases were characterized. At 973 K a thin TiN–Ti 2 N layer was formed while at the higher temperature this compound layer was thicker and an inner hardened sublayer was present. In the absence of such an inner layer the sliding of the alumina pins promoted the nucleation and growth of microcracks in the nitride layer, leading to quick failure of the coating. The samples treated at higher temperature showed a more uniform wear process of the nitride layer, without crack formation, and even after its removal, the hardened sublayer did not suffer from the typical delamination wear of untreated Ti–6Al–4V. The damaging or removal of the protective passive film due to rubbing leads to the formation of a galvanic couple between the anodic wear track and the outside surface. The fraction of electrochemically removed material with respect to the total wear volume was approximately 0.2 for the untreated alloy and 0.5 for the nitride layer.

The high oxygen affinity of titanium can be used to improve the surface hardness and wear resistance of titanium and titanium alloy components by means of thermal treatments. In the present paper a comparison of the effects of glow-discharge and furnace processes, carried out using air as treatment atmosphere, on the microstructure and mechanical properties of commercially pure titanium samples is reported. Both treatment types, performed at 973 and 1173 K for 0.5, 2 and 4 h, produce modified surface layers: the outer layer (compound layer) consists essentially of TiO2 and small amounts of TiNxOy, while the inner layer (diffusion layer) consists of α-Ti crystals rich in interstitial atoms. The plasma treatment is shown to be more efficient in hardening titanium surface layers than the furnace process: by using the same treatment temperature and time, plasma treated samples have a thicker hardened layer, with higher hardness values than the furnace treated ones. A crystallographic characterisation of the α-Ti solid solution has also been performed and the a, c lattice parameters have been evaluated. Plasma treated samples show larger lattice parameters and c/a values than the furnace treated samples, suggesting a higher concentration of interstitial atoms due to the plasma treatment.

The glow-discharge nitriding process is particularly suitable to harden the surface of sintered stainless steels components, owing to the high porosity levels of these materials. On wrought austenitic stainless steels this treatment produces a metastable phase, known as supersaturated austenite or S phase, which has shown high hardness values and good corrosion resistance. In the present paper the influence of glow-discharge nitriding process on the microstructural and mechanical properties of AISI 316L austenitic sintered stainless steel has been evaluated and it is compared with the results obtained with ion-nitrided martensitic (AISI 410) and ferritic (AISI 430L) sintered stainless steels. The ion-nitriding treatment, performed at 773 K for 4 and 8 h, produces modified surface layers. The microhardness profiles show high hardness values in the modified layers and a steep decrease to matrix values, thinner hardened layers and lower hardness values are observed on AISI 316L samples, in comparison with AISI 410 and AISI 430L samples. The S phase is detected on the modified layers of the ion-nitrided AISI 316L samples. The crystallographic characterisation has shown that a face centred tetragonal lattice as base for this phase fits well the diffraction spectra, in respect of the ‘traditional’ face centred cubic lattice usually adopted, since the lattice shows a strong distortion, in spite of this, the d -spacing values calculated with a f.c.t. base show a good agreement with literature data, when the used f.c.c. indexing is modified for the f.c.t. lattice.

Reactive plasma spraying of titanium in a nitrogen-containing plasma gas allows the formation of hard titanium composite coatings reinforced by in situ formed titanium nitrides (TiN and Ti2N). In the present study, the formation of titanium nitrides during the reactive spraying of titanium was studied by means of two different analysis techniques: X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The diffusion and solidification sequence predicted by the Ti-N phase diagram was consistent with the experimental results. The nitrogen retained in the coating was found mainly as titanium nitrides and not as interstitial nitrogen in the titanium lattice. It is hypothesised that the formation and direct solidification of TiN occurs during the flight of the sprayed particles. The presence of solid TiN constrains the thermal contraction of titanium splats upon solidification. The observed cell distortion of the residual α-Ti is thus attributed to tensile stresses arising from the solidification process.

The low hardness and the poor tribologic characteristics of titanium can be positively modified by means of reactive plasma spraying. The present study describes experimental results concerning reactive low pressure plasma spraying of pure titanium powders in an Ar/N 2 plasma gas in order to obtain thick titanium composite coatings with a high percentage of hard titanium nitrides (TiN and Ti 2 N). As measured by means of X-ray diffraction, the volume fraction of nitrides in the coating with increases increasing nitrogen content in the plasma gas mixture and with increased spraying distance. The nitrogen content of the coating shows a linear relationship with the microhardness of the coating. By varying the Ar/N 2 plasma gas ratio, adherent hard composite coatings, up to Knoop 1200 hardness and with low porosity are obtained. Such characteristics make them particularly suitable in all those technological applications where good corrosion resistance of titanium and high tribologic properties are required.

The contemporary glow-discharge oxidising and nitriding treatment has shown to produce modified surface layers with enhanced hardness properties, in comparison with the conventional ion-nitriding process. The aim of the present study was to evaluate the tribological properties of ion-oxinitrided samples and to compare their wear behaviour with the one of furnace oxinitrided and ion-nitrided samples. At low coupling loads (50 N) the wear volumes of the treated samples result small and comparable for all the tested velocities. On the other hand, when high coupling loads are used (100 N), the wear of the ion-nitrided samples is higher than that of the oxinitrided ones, this effect becoming more remarkable as sliding velocity increases; moreover, the ion-oxinitriding treatment allows to achieve lower wear volumes than the ones obtained by means of the furnace oxinitriding process.

Combined glow discharge oxidising and nitriding treatments allow the production on Ti–6Al–4V of modified surface layers with enhanced hardness properties compared with a traditional ion nitriding process. The treatment atmosphere has a marked influence on the properties of these hardened layers: as the oxygen concentration increases, thicker diffusion layers, characterised by greater hardness values and smoother gradients, are obtained. In the present paper the effects of treatment atmosphere and duration on the glow discharge oxynitriding of Ti–6Al–4V specimens are evaluated, by performing tests at 1173 K with oxygen concentration varied in the range 0–21 vol.-% and for treatment durations in the range 0·5–8 h. The modified layers produced consist of an outer compound layer and an inner diffusion layer. The compound layer consists of nitrides, oxides, and oxynitrides of titanium and, in some cases, of alloy element oxides too. With increasing oxygen concentration and/or time, the compound layer d...

Yttria-stabilized zirconia coatings were deposited by atmosphere- and temperature-controlled spraying (ATCS) on IN 100 superalloy substrates for thermal engine applications. The whole deposition process was performed in an Ar atmosphere, adopting a new liquid Ar device that cooled the samples during the spraying down to 60°C. Coatings prepared by ATCS were well adherent with a dense, microcracked microstructure. However, as found previously, as-sprayed zirconia coatings were understoichiometric and highly disordered; the presence of excess oxygen vacancies and high defect density led to an increased stability of the tetragonal (t) and cubic (c) polymorphs with respect to the monoclinic (m) one. Under such conditions a low temperature annealing was sufficient to cause remarkable phase changes. It was found that under the most effective cooling conditions the coating was made of a mixture of t- and c-phases, the m-phase being totally absent. The crystal structure and thermal stability of the present zirconia polymorphs were studied by X-ray diffraction full-pattern analysis, differential scanning calorimetry and thermogravimetric analysis.

Thick two-layered thermal barrier coatings made of Ni-Co-Cr-Al-Y and yttria-partially stabilized zirconia were plasma sprayed at controlled deposition temperature onto stainless steel substrates. During the spraying of the top coat, the deposition temperature was kept as constant as possible using a front air or liquid-argon-cooling system. The correlation between process parameters and microstructure was investigated by scanning electron microscopy and X-ray diffraction (XRD) analysis. The application of a new procedure for XRD data processing, based on the Rietveld method, made it possible to obtain good accuracy in the phase determination and quantitative evaluation of zirconia polymorphs. Moreover, the crystallite size and microstrain were refined simultaneously to phase percentages. Also the preferred orientation in the coating could be taken into account, adding useful information and increasing the reliability of all the other results. The influence on the coating microstructure of changing the deposition temperature and environment is also discussed.

The drift of positrons under the action of an electric field in Kapton has been observed by using a variable-energy positron beam and the Doppler broadening technique. Even if the maximum applied field (2 MV/cm) is so high that the electrostatic work for a displacement of less than 0.15 nm is larger than the thermal energy, the experimental data can be fit by the diffusion model with a field-independent mobility. The best-fit value of the mobility (ca. 1×10−3 cm2 V−1 s−1) is extremely low in comparison with other dielectrics. The results are discussed with regards to the interaction of positrons with the molecular field.

This paper compares two methods for determining the composition of Ti/TiN coatings deposited by reactive plasma spraying. The coatings were obtained by spraying titanium powder in a low-pressure N2/Ar atmosphere. The resulting film has a variable nitrogen content in the form of titanium nitrides, depending on gas partial pressure, total pressure, sample-source distance, and other parameters. The composition of the film was determined using X-ray diffraction and X-ray photoelectron spectroscopy. The two techniques provide similar results and either can be used for the compositional characterization of these coatings.

This work reports on the structural and mechanical properties of Ni-C films, deposited on silicon substrates by RF magnetron sputtering of a plasma-sprayed Ni-C target. X-ray diffraction was used to determine the phase structure, while the atomic composition and the chemical states were given by X-ray photoelectron and Auger electron spectroscopies. The internal stress, Young's modulus, hardness and scratch resistance were investigated, as a function of the RF electric power. The microstructure and the mechanical properties were found to be governed by the kinetic energy transferred to the growing film. In low energy conditions, the Ni-C films behaved mechanically as diamond-like carbons, and the microstructure coincided with that of an amorphous C-fcc Ni composite. Inversely, in high energy growth conditions, the films were composed of dispersed Ni3C small crystallites in an amorphous Ni-C mixture. Such a microstructure was characterized by low mechanical properties.

A systematic study on phase formation and stabilisation in the Ba-Cu-C-O system in the temperature range 20-500°C, under various atmospheres, by traditional thermal analysis techniques, high temperature X-ray diffraction and high resolution electron microscopy, has permitted to identify and characterise the formation kinetics of a new copper containing phase isomorphic to γ-BaCO3.