Search

In this study we have analysed the indentation hardness and modulus of cathodic arc deposited CrTiAlN coatings as a function of the stoichiometric variables Ti/Cr, Al content and cation mix. The coatings have been prepared using a combinatorial cathode composition approach, leading up to 14 different stoichiometries produced in 5 batches. The coatings have been inspected by glow discharge optical emission spectroscopy, scanning electron microscopy, X-ray diffraction and nanoindentation techniques. The coatings develop crystalline structures compatible with solid solutions of face-centered cubic unit cells for all the compositions produced. Such unit cells exhibited a downwards lattice parameter dependency on the aluminum concentration of the coatings (from 0.417 nm down to 0.413 nm). The indentation hardness as a function of the Ti/Cr is compatible with other previous studies reported. The films hardnesses and moduli also increase as the aluminum concentration increases (21 GPa up to 34 GPa). Both indentation responses upon Ti/Cr and Al are attributed to solid solution strengthening. However in order to prove this statement, the indentation hardness and modulus were studied as a function of the mixing term of the cations, as this term is well representative of the solid solution compositional map. The observed results unambiguously evidence that the solid solution strengthening effect is confirmed on the basis of the dependency between the indentation hardness and the so called degree of mixing. This work has been funded by the Spanish Ministry of Science and Innovation of Spain through the project PGC2018-096855-A-C44. The authors also acknowledge the Centro para el Desarrollo Tecnológico e Industrial (CDTI) for the support of the excellence program CERVERA through the project CER2019-1003.

Maraging steels combine excellent mechanical properties at medium-high temperatures with good fracture toughness, but they usually require the aid of thermochemical treatments to enhance superficial properties such as resistance to abrasive wear and corrosion resistance. In particular, plasma nitriding, due to its duration and temperature, which are compatible with the age-hardening cycles of maraging steels, permits the realization of both processes simultaneously. In this work, simultaneous ageing and arc-activated plasma nitriding of maraging steel grade 300 were studied as a function of the working pressure of the gases (N2 and Ar) present in the vacuum reactor chamber. In addition, the influence of the operating pressure was established by analysing the capacity of the plasma to penetrate in 2.5 mm in diameter blind holes. In-depth chemical composition, hardness and micro-hardness profiles, X-Ray diffraction, roughness, tribological characterization and corrosion tests were carried out to compare maraging steel samples treated in one simultaneous plasma nitriding and ageing process and in two-step processes. Metallographic tests and nanoindentation measurements were performed to study how the plasma penetrates and diffuses into the blind holes and how the nitride case layer thickness formed at the inner surfaces of the holes changes as a function of the distance to the surface for various working pressures.

In this work, a successful sequential co-implantation treatment of Cr+ and N2 + ions into electrodeposited nickel plates is presented. The goal of this treatment is the simultaneous enhancement of the wear resistance, mechanical stability and corrosion-protection properties of the Ni surfaces. The ion-implanted surfaces have been characterized by glow-discharge optical-emission spectroscopy, X-ray diffraction, nano-hardness, roughness, nano-wear and potentio-dynamic corrosion tests. It has been observed that the implantation of Cr+ or N2 + alone is not sufficient to achieve simultaneously the enhancement of both the wear-resistance and the corrosion-protection properties. Conversely, the sequential implantation of Cr+ and N2 + at 140keV and fluencies of 3×1017 and 1.5×1017ions/cm2 respectively, permits the formation of a functional surface capable of reducing both the corrosion rate and the wear rates, with respect to those exhibited by the un-implanted Ni surfaces.This treatment can be used to protect the surfaces of micro-embossing/stamping dies based on electroformed Nickel, as an alternative to other coating strategies. Furthermore, the ion implantation assures the non-modification of the net-shape and surface finish of these types of dies, which is of crucial importance when they are used for high-precision micro-texturing/imprinting applications. © 2011 Elsevier B.V.

This work reports on the growth and properties of Cathodic Arc Physical Vapor Deposition of low friction-coefficient CrCN coatings, as deposited on the basis of complementary carbon/nitrogen gradient concentrations through the film thickness. The coatings developed in this study exhibited friction coefficients ranging from 0.2 to 0.6, against 100Cr6 bearing steel, depending on the preparation conditions. Gradient CrCN films with COF of 0.35 and comparable mechanical strength to that of CrN were achieved. The adhesion rate of metallic elements such as Fe during the sliding process of CrCN coated tools on AISI316L steels were monitored using a pin-on-disc experimental set-up. The results demonstrated a low tendency of the gradient CrCN deposited films to pick up material from the AISI316L steels surfaces, in contrast to that found when using standard CrN cathodic arc PVD films.

The use of ion implantation as a surface treatment technology has been dominated by its applications to prevent wear and oxidation in metal alloys, although some early works already pointed out that ion implantation could also be effective as a surface treatment for other materials, including polymers. Further research has shown that low-dose implantation of energetic light ions could be very effective for improving properties such as hardness and wear resistance in many different polymers. Cross linking of polymeric chains due to ionization energy provided by the stopping process is the main mechanism to explain the changes in mechanical properties. According to this model the lighter the ion is, the stronger is the effect: hydrogen and helium ions would be the ideal options to be employed in the treatment of polymers. This paper presents the results obtained by helium implantation in ultra high molecular weight polyethylene (UHMWPE). He+ ions were at 90 and doses between 5 × 1015 and 2 × 1016 ions/cm2. Nitrogen was also implanted in separate samples, under the same conditions, as a reference. Universal Hardness was measured using micro indenter at a maximum load of 2 mN. The results clearly show a higher increase in hardness and surface elastic modulus for samples implanted with helium, in comparison to those implanted with nitrogen or unimplanted. The effect also increases with the dose, although it saturates at 1 × 1016 ions/cm2.

CrN multilayer coatings are possible replacements for hard chromium because of their good mechanical and chemical properties. This paper focuses on X-ray photoelectron spectroscopy (XPS) to study the mechanism of electrochemical stripping of multilayered Cr-N based coatings. The samples were produced by electron beam (e-beam) physical vapour deposition (PVD), on mirror polished M2 steel. Multilayers constituted three separate layers of CrN with intermediate interlayers of Cr (0.1 μm). The total coating thickness was in the range 4.5-5.5 μm. Under galvanostatic conditions, anodic oxidation of CrN leads to replacement of nitrogen in the CrN coating by oxygen, forming oxy-nitrides on the samples surface. Contrary to findings described by some authors, we have not detected Cr6+ in this research. © 2006 Elsevier B.V. All rights reserved.

Diamond-like carbon (DLC) coatings have found great applicability in the automotive industry because of their low friction coefficient and high wear resistance. Nevertheless, their tribological performance can be greatly reduced on soft substrates such as titanium alloys. The hard DLC coating cannot usually follow elastic and plastic deformation of the substrate without failing. In order to overcome this property mismatch between hard coating and soft substrate, triode plasma nitriding was applied as a pre-treatment to improve the mechanical properties of the Ti6Al4V alloy and further enhance the load support for the DLC coating. DLC and multilayered TiN/DLC, CrN/DLC CrAlN/DLC coatings were deposited onto “standard” and plasma nitrided Ti6Al4V substrates. Triode plasma nitriding increased the load-bearing capacity of the coating/substrate system, as higher critical adhesion loads were recorded for DLC coatings on plasma nitrided Ti6Al4V substrates. This treatment also reduced the wear rate of the DLC coating/substrate. Further load support and lower wear rates were achieved by using TiN, CrN and CrAlN as intermediate layers on plasma nitrided Ti6Al4V substrates.

Plasma nitriding of different substrates such as Ti6Al4V and AISI M2 steel was achieved by means of D.C. glow discharges assisted by thermionic emission (triode configuration). The higher ionisation levels achieved using a D.C. triode configuration reduced the treatment time and nitriding temperature required to obtain hard and reasonably deep nitrided cases in the Ti6Al4V alloy. For this alloy, surface hardness values of 560–600 HV 0.05 and nitrided layer depths of 30–40 μm were achieved at 700 °C. Up to this nitriding temperature, hardening seemed to be mainly accomplished by incorporation of nitrogen in the α-Ti phase, as the formation of a titanium nitride layer on the surface could not be detected by SEM. For the AISI M2 steel, hard (1379–1524 HV 0.05 ) nitrided layers of 100–150 μm were obtained at 480–500 °C for 240 min, depending on total pressure, gas composition and substrate bias. For the highest nitrogen concentration and lowest bias voltage, no compound layer was formed. The triode plasma nitriding process allowed a significant reduction in processing time for both M2 steel and Ti6Al4V alloy in comparison to conventional D.C. diode plasma nitriding.

Cr–N benefits from good oxidation and corrosion resistance, which has, until recently, caused difficulties in removing the coating without damage to substrates. Consequently, the industrial use of Cr–N coatings, particularly on expensive tools, has been limited. As a new commercially viable wet-stripping process has been developed that causes little or negligible damage to steel substrates, it is appropriate to investigate the effect of coating thickness and structure on the stripping rate of different Cr–N films. In this work, Cr–N coatings deposited by magnetron sputtering, arc and electron beam evaporation, having different thicknesses, was wet-stripped. The stripping rate was evaluated by statistical analyses for each deposition method and thickness. The stripping rate for the various deposition methods was correlated to the coating phases, structure, morphology, and surface roughness, which varied depending on the deposition process. For all deposition methods, the stripping rate was constant at a given as-deposited coating thickness. Regardless of the deposition method, the stripping rate for all different as-deposited thicknesses was statistically similar within the same deposition process, indicating that the stripping rate was independent of the coating thickness. Moreover, the stripping rate was not influenced by changes in the coating structure with increased thickness, which occurred in arc and electron beam Cr–N coatings. For coatings having similar as-deposited thicknesses, the highest stripping rate was obtained in magnetron sputtered Cr–N (∼ 4.4 μm h − 1 ), followed by electron beam and arc Cr–N coatings, which displayed similar stripping rates (∼ 3.3 μm h − 1 ). The highest stripping rate recorded for magnetron Cr–N coatings could not be explained by changes in coating structure/morphology and surface roughness. The differences in the stripping were attributed to the amount of CrN phase present in the coatings.

This work reports a comparative investigation on tribological performance enhancement induced by nitrogen Plasma Immersion Ion Implantation (PI3) and conventional Nitrogen Ion Implantation (I2) on Ti and Al based alloys. The study has been carried out on the basis of the surface modification produced by both treatment techniques, in terms of the implanted nitrogen in-depth profiles, and its effect on surface hardening and wear resistance increase of the treated samples. Under the experimental conditions described, PI3 Ti-based alloys treated samples evidenced slightly better tribological performance than those subjected to I2 treatments. In the case of Al alloys, however, PI3 caused strong detrimental modification on the treated samples as revealed in the increase by a factor 100 of its surface roughness. Consequently, different criteria should be deemed in order to establish the adequacy of one or other technique, not only taking into account set up costs but also considering specific applications.

This work reports on the preparation and characterization of hard (Ti,Si)N nanocomposite coatings as a function of composition and ion bombardment during growth. The energy delivered to the growing film was changed using both bias voltage change and solenoid coils placed between the targets and the substrate holder. The stoichiometry of the films was investigated by Rutherford backscattering spectrometry (RBS). With reduced energy delivered to the growing film and low deposition temperatures, the coatings developed an fcc Ti1xSixNy phase (a=0.416 nm in a sample with 18 at.% of Si) where some Si atoms are probably occupying Ti positions in the TiN1x matrix, and can be identified as a metastable phase. With higher levels of ion irradiation, an fcc TiN phase with higher lattice parameters was developed, and a significant increase in hardness was obtained. The enhancement in species mobility at the film surface is enough to ensure an effective phase segregation, leading to the formation of an nc-TiN/a-Si3N4 nanocomposite. In spite of the development of some degree of residual stresses, the overall results confirm the potential benefits of ion bombardment during film growth. The fact that these high compressive stresses can be released through thermal annealing in vacuum, keeping the coating hardness values of about 45 GPa even after thermal treatments at 900 8C, is an example of these benefits. D 2004 Elsevier B.V. All rights reserved.

In this contribution, we report on the structural and the tribological characterisation of low-energy nitrogen-ion-implanted Vanadium Titanium (V5Ti) alloys as a function of the annealing temperature during the bombardment process. The surface of the alloys was bombarded with N 2 + ions accelerated at 1.2 keV in a vacuum chamber equipped with a Kaufman-type ion source. The temperature during the low-energy ion implantation were 480, 500, and 575 °C. In this temperature range, the penetration depth reached by the implanted ions is not only exclusively ballistic (i.e., kinetic energy dependent), but diffusion effects also play a decisive role. The structural changes can be drawn as the formation of a nitrogen diffusion layer containing a blend of pristine bcc V5Ti and a solid nitrogen solution having an expanded bcc phase. It has been found that the temperature favours the increase of both, the thickness of the diffusion layer and the relative nitrogen content in the solid solution. We have investigated the microhardness, friction and wear coefficients of the implanted V5Ti surfaces as a function of the annealing temperature. The reported results indicate that both hardness and wear resistance against mechanical abrasion increase as the temperature during the bombardment increases. This increment of the hardness and wear resistance could be directly correlated to the amount of the expanded phase exhibited by the V5Ti surfaces, as observed by X-ray diffraction. The hardness and wear resistance modification upon annealing temperature are discussed in terms of the plastic deformation undergone by the expanded bcc phase to release the accumulated lattice stresses.

The stoichiometry, structure and mechanical properties of ion beam sputtered TiC x N y thin films have been studied as a function of the assistance conditions. Tuning the ratio between the current density of assisting N 2 + ions and the target sputtering rate allows us to achieve films with stoichiometries in the range of 0.6> x >0.25, keeping x + y ≈1. The surface topography is also sensitive to the assisting conditions where the RMS roughness is an increasing parameter as the ion beam bombardment increases. In terms of the Ar + ion beam assistance, the films undergo a significant amorphisation and a steep increase in lattice strain as the current density and energy of the impinging ions are increased. The observed changes are discussed in terms of the energy transfer of the bombarding Ar + ions to the layers below the surface of the growing films, leading to vacancies and defects and to a sharp decrease in film crystallinity.

The nano-hardness (HV) of TiCxNy (x+y≈1) thin films has been investigated by nano-indentation as a function of the ion beam assistance for different contact depths and annealing temperatures. The hardness at low indentation depths (i.e. 10 nm) is observed to decrease abruptly from 55 down to 26 GPa when the carbon content in the films decreases from x≈0.2 to x≈0.05 (∼TiN). On the contrary, hardness measured at penetration depths of 40 nm is observed to decrease very slightly. After annealing in UHV the hardness of the coatings becomes independent of the penetration depths. Moreover, the values of the hardness of the annealed coatings are similar to the values measured for the untreated coatings at high penetration depths. All this suggests that, the surface of the films are hardened significantly, and that this hardening can be reduced not only by annealing but also by increasing the ion beam bombardment during the growth process. The mechanism of the film hardening has been addressed in terms of the content of lattice defects and its dependence on the ion bombardment.

Amorphous carbon nitride thin films were prepared in a dual ion beam sputtering (DIBS) system. The N/C atomic concentration ratio ranged between 0.3 and 0.5 as determined by quantitative X-ray photoelectron spectroscopy (XPS) of the surface. Fourier Transform Infrared spectroscopy (FT–IR), XPS and X-ray Absorption Spectroscopy (XAS) were used to obtain information about the different types of bonding present in the films. The hardness and the Young's modulus of the samples were determined by nanoindentation measurements. The hardness varied in the range 15–30 GPa with Young's modulus between 170 and 250 GPa. In order to explain the measured hardness, some of the films are considered as heterogeneous, in good agreement with the XPS, FT–IR and XAS data.