Hard coatings are continuously improved due to the industrial needs and urgency to reduce the environmental impact of manufacturing processes. For these reasons, scientists seek hard coatings ...resistant to high mechanical and thermal loads under extreme working conditions (i.e., dry machining), which is why Hf and other rare earth metals have been added to the metastable c-AlxTi(1-x)N nitrides. In the present investigation, Hf-doped c-Al0.64Ti0.36N was deposited in a 2- & 3-axis rotation system using a semi-industrial coater. For this purpose Hf-pins were fixed in Al/Ti targets that produced coatings with ~0.2 at. % Hf-contents homogeneously dispersed. Hf effect on the crystalline state and microstructure, mechanical properties, high-temperature resistance, and the tribological performance of the coating in an Ar-jet at 900 °C were analyzed. It was found that the Hf-doped Al0.64Ti0.36N 5.07 μm thick-layer was mainly cubic fcc + traces of the hcp phases and displayed higher mean hardness (36 GPa) and E-module (416 GPa) than the coating without Hf (h = 32 GPa and E = 402 Pa). The Hf-containing nitride oxidizes dynamically during the high-temperature tribology testing and produces t-Ti2O3 & o-Al2TiO5 after short exposure periods (2.5–5 min), which strongly affected the CoF, before evolving to thermodynamically stable α-Al2O3 & anatase TiO2 between 10 & 30 min in the Ar-flow, thus resulting in the relative stability of the CoF. The mechanical evaluation of the oxidized coatings indicates that a specific oxide thickness must be reached to avoid catastrophic system damage at high normal loads.
•Hf-doped c-Al0.66Ti0.34N coating was deposited in a semi-industrial PVD coater.•0.2 at. % Hf is enough to improve hardness and E-module of arc PVD c-Al0.66Ti0.34N.•t-Ti2O3 & o-Al2TiO5 are built (<5 min) and evolve to α-Al2O3 & a-TiO2 (>30 min) in an Ar-jet at 900 °C.•Fragile unstable oxides are affecting the high-temperature tribology of c-Al0.638Ti0.36Hf0.002N coatings.•The oxides generated at 900 °C modify the stiffness of the coating-substrate system.
Diamond-like carbon (DLC) coatings have excellent mechanical and tribological properties, as well as good wear and corrosion resistance. They are well established in medical, metalworking and ...automotive applications. However, further improvements are needed and substrate pre-treatment plays an important role in supporting and enforcing the adhesion and service performance of the DLC coatings. In this work, the synergetic effect of low-pressure arc plasma-assisted-nitriding (PAN) treatment of M2 steel and plasma-enhanced chemical vapor deposition (PECVD) on the DLC coatings adhesion was analyzed. Adhesion strength of a nitriding + DLC duplex coating system was compared to the performance of DLC-coatings applied on non-nitrided M2 steel substrates. The nitrided layer was analyzed by optical microscopy, electronic microscopy, X-ray microanalysis, X-ray diffraction, Vickers microhardness and atomic force microscopy. DLC coatings were analyzed using Raman spectroscopy revealing that DLC a-C:H type was obtained. The adhesion properties were analyzed by scratch testing supported by optical microscopy and scanning electron microscope, showing results with an improvement of the DLC's adhesion on the nitrided surfaces.
•The combined process (PAN and PECVD) increased the DLC's coating adhesion to a M2 steel surface.•A DLC with 20 at.% hydrogen and 40–60% sp3 was obtained corresponding to type a-C:H.•Roughness from nitrided is an important factor in DLC's adhesion on M2 steel surface.
•Proposed electroless plating for producing metal matrix composite powder.•Prepared Ni matrix composite powder with a high fraction of Al2O3 nanoparticles.•Demonstrated the processability of the ...Ni/Al2O3 powder by selective laser melting.
The objective of this work is to investigate the feasibility to use electroless plating as a feedstock powder production method for additive manufacturing of metal matrix composites (MMCs). MMCs are of importance because of their improved properties compared with existing metallic alloys for additive manufacturing. However, the current powder processing methods (e.g., high-energy ball milling) are difficult to incorporate a high fraction of nanoparticles with a homogeneous dispersion. Electroless plating is proposed to produce MMC powder in this work. Ni/Al2O3 composite powder with a high fraction of Al2O3 nanoparticles was successfully produced using a Ni electroless plating bath containing Al2O3 nanopowder. X-ray diffraction analysis was performed on the prepared powders, showing both Ni and Al2O3 phases as designed. Scanning electron microscopy (SEM) characterization showed the Ni and Al2O3 phases were uniformly distributed in the powder. The Ni/Al2O3 powder was then laser melted into tracks to investigate the effects of process parameters using a commercial selective laser melting (SLM) system. SEM showed stable tracks were achieved under a wide range of process parameters. Both Ni and Al2O3 phases were identified in the melted tracks, possessing a hierarchical micro/nano-structure. The SLM behavior demonstrated the feasibility of electroless plating for producing MMC feedstock powder.
Cold Spraying of high strength materials, i.e., Inconel 718 is still challenging due to the limited deformability of the material restricting the quality of deposits. Thus, process parameters must be ...tuned for reaching higher particle impact velocities and temperatures to allow for maximum amounts of well-bonded particle-substrate and particle-particle interfaces. In the present study, Inconel 718 powder was cold sprayed under varied process gas temperatures for a systematic study of the influence on the quality of thick deposits. In addition, one set of samples of each batch was exposed to post heat treatment procedures by hot isostatic pressing, thermal soft annealing, and aging for attaining hard bulk material properties. Deposits microstructure, porosity, electrical conductivity, hardness, and residual stress were analyzed in as-sprayed and as-heat treated conditions. Results are discussed in terms of the “coating quality parameter”, defined as the ratio between particle impact velocity and critical velocity. As-sprayed deposits exhibit microstructures with highly deformed particles and well bonded internal interfaces. X-ray diffraction reveals that powder and deposits present a γ-solid-solution phase, allowing to assume conventional softening behavior for estimating critical conditions for bonding. Increasing the process gas temperature leads to lower coating porosity and higher electrical conductivity. Deposits showed similarly high microhardness and compressive residual stresses, both caused by work hardening during cold spraying. Subsequent heat treatments improved the quality of internal interfaces, mostly for deposits with high values of “coating quality parameters”. By distinguishing influences on several coating properties, these results contribute to gain basic knowledge for successful manufacturing of Inconel 718 thick deposits by cold spraying, particularly concerning needed coating quality parameters for adjusting desired properties.
•High quality IN718 thick deposits were successfully produced by cold spray.•Deposit properties show a correlation with the estimated “coating quality parameters”.•Process gas temperatures were selected to maximize the deposit properties.•Enhanced thick deposit properties were achieved by heat treatment.
An experimental-numerical methodology for failure analysis of the c-Al0.66Ti0.34N/Interface/M2 steel coating system is proposed here. This c-Al0.66Ti0.34N coating was deposited by the arc-PVD ...technique. The values of the elastic modulus, the fracture energy release rate and the nano-hardness of the coating were obtained by nanoindentation. Normal and shear stress limits of the interface, as well as the adhesive and cohesive critical loads, were measured with the scratch test method. A finite element analysis, using the experimental mechanical properties, was carried out to understand the relationship between the irreversible work vs. depth curve and the mechanical failure evolution of the coating-substrate system, associating the pop-in with nucleation, crack growth and cracking pattern. Extended finite element method (XFEM) was applied for modeling of the mechanical behavior of the coating; the cohesive zones approach was applied for modeling the interface and the Ramberg-Osgood law for modeling the substrate. This approach proposes an experimental-numerical methodology for failure analysis of hard coatings (monolithic body) allowing to calculate fracture energy of the coating material and to model cracking patterns caused by contact mechanics. This work is the first step to answer questions about multi-scale approaches for multi-functional multi-layer coatings to push their enhancements and further applications.
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•Experimental-numerical XFEM + CZM approach for understanding the hard coatings failure•The irreversible work vs. depth curve is related to the cracking mechanism.•Elastoplastic deformation energy translate into crack nucleation and opening.•Correlation between the irreversible work and the modeled cracking patterns is attain.•The XFEM + CZM methodology is validated through the morphology of ring cracks.
We report the mechanical characterization by multiscale indentation of particle reinforced dense Ni/Al2O3 metal matrix nanocomposites (MMNC) obtained by high-kinetic processing (HKP) of ball milling ...of the powders with a systematic variation of alumina nanoparticles fractions (from 1 to 20 vol. %) and spark plasma sintering (SPS). The morphology and particle size distribution of powder were evaluated as a function of milling time up to 10 h. Samples from the 10 h milled powders were densified by SPS. The mechanical properties of the sintered samples were obtained by micro and nanoindentation using diamond tips of Vickers and Berkovich geometry, respectively. The combination of HKP and SPS allowed a homogeneous dispersion of Al2O3 nanoparticles in the nickel matrix and effective reinforcing effects, which is the case of Ni/10 vol. % Al2O3 and Ni/15 vol. % Al2O3 samples. The highest hardness (4.68 ± 0.37 GPa) was obtained for Ni/15 vol. % Al2O3 MMNC, which is almost twice that of pure nickel (2.45 ± 0.22 GPa) processed at the same conditions. The highest elastic modulus (346 ± 30 GPa) was obtained for the Ni/10 vol. % Al2O3 sample. The analysis of the load-depth curves confirmed the reinforcing of the MMNCs as a function of the alumina particle content. Discussion of the possible reinforcing mechanisms is also included. The Ni/Al2O3 MMNC sintered specimens exhibit outstanding mechanical property results, which make them candidates for various high-temperature applications.
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•Homogeneous dispersion of Al2O3 nanoparticles in dense Ni-matrix SPSed MMNCs.•HV Hardness increases with Al2O3-content (max. of 4.68 GPa at Ni/15 vol. % Al2O3).•Elastic modulus increases with Al2O3-content (max. of 346 GPa at Ni/10 vol. % Al2O3).•Nanoindentation results confirm reinforcing effects of Al2O3-nanoparticles in MMNCs.•A critical volume between 10 and 15 vol. % Al2O3 reinforcing particles was identified.
The development of homogeneous, dense, and smooth hard coatings is a challenging task, and that is why the high power impulse magnetron sputtering (HiPIMS) method has been proposed to tailor and ...control the microstructure through the modification of the duty cycle. HiPIMS offers extensive possibilities to obtain good quality films with fine and dense morphology. In this work, the synthesis of CrxN coatings by HiPIMS with the variation of duty cycle (τ = 2.7% and 12%), substrate bias voltages (Vb = −150 and − 250 V), and gas ratio (fN2/Ar = 0.2 and 0.4) was evaluated. The influence of these processing conditions on the chemical composition, microstructure, and adhesion of HiPIMS CrxN was investigated. A significant increment of the deposition rate and the chromium content in the CrxN coatings is observed at τ = 12%; meanwhile, at τ = 2.7%, films showed high nitrogen content. The crystalline phases like α-Cr + h-Cr2N, h-Cr2N, and h-Cr2N + c-CrN were identified in the as-deposited films. The Cr-rich coatings presented faceted columns with cauliflower-like surface morphology, while the growth of the h-Cr2N phase caused a grain size refinement and a denser microstructure. The surface morphology of the h-Cr2N coatings changed from pyramidal to stacked pyramids with the reduction of the duty cycle. The transformation of the h-Cr2N to c-CrN leads to highly dense columnar microstructures with a fine granular morphology and a smooth surface. The duty cycle strategies can be applied to develop a particular microstructure with specific chemical composition and crystallographic phases, resulting in an alternative method to produce graded or multilayer systems. The duty cycle reduction increases the interfacial adhesion strength of the coatings.
•Duty cycle modifies composition, phases, microstructure, and morphology.•Higher duty cycle enhances target current and coating deposition rates.•Duty cycle strategy is a good option to deposit graded or multilayer systems.
The effect of pre-oxidation treatments at various oxygen partial pressures (pO2) on the microstructure of ReneN5/(Ni,Pt)Al/7YSZ thermal barrier coatings systems and the number of furnace cycles at ...1100 °C up to top coat spallation is here presented. (Ni,Pt) Al bond coats deposited on ReneN5 superalloy were pre-oxidized under different pO2 before top coat deposition. After pre-oxidation, a 7YSZ ceramic top coat was deposited on the samples using the electron beam physical vapor deposition. The pre-oxidized specimens in the range of 1 × 10−19 ≤ pO2 ≥ 1 × 10−1 atm showed a higher number of furnace cycles compared to those either pre-oxidized at pO2 = 2.1 × 10−1 atm and without pre-oxidation. The thermally grown oxide (TGO) scale after top coat deposition of pre-oxidized samples in the range of 1 × 10−19 ≤ pO2 ≥ 1 × 10−1 atm showed the lowest thickness and thus slow growth kinetics. Moreover, a microstructural analysis by scanning electron microscopy revealed the formation of a mixed zone within the TGO of non-pre-oxidized samples, whereas for all pre-oxidized conditions a dense continuous Al2O3 scale was observed. Upon furnace cyclic exposure, phase transformations from B2 to L10 and L12 were identified by electron backscattering diffraction in all bond coats, which are most likely a feature associated with high heating/cooling rates under furnace cyclic tests.
•Furnace cyclic testing data of pre-oxidized ReneN5/(Ni,Pt)Al/7YSZ TBC's are reported.•Pre-oxidation at low PO2 of ReneN5/(Ni,Pt)Al/7YSZ leads to high number of thermal cycles.•Pre-oxidation of ReneN5/(Ni,Pt)Al/7YSZ prevents a mixed zone formation within the Al2O3 scale.•Rapid cooling in furnace cyclic test caused B2 to L10 and L12 phase transformations in/(Ni,Pt)Al.
In the present work, the structural, magnetic, and theoretical analysis of the Fe–Si alloy prepared by melting and heat-treated was performed. The ordered FeSi simple cubic (sc) phase was obtained by ...melting and heat treatment processes as determined by X-ray diffraction. The presence of the superstructure peak in the (312) crystalline direction confirms the high structural order reached. Using Mössbauer spectrometry (MS), a paramagnetic behavior with quadrupole splitting of SQ = 0.53 ± 0.02 mm/s was obtained. Although MS indicates paramagnetic behavior, vibrating sample magnetometry (VSM) showed ferromagnetic behavior with a coercive field of 25 Oe, associated with a small amount of Fe3Si segregations detected by scanning electron microscopy/energy dispersive spectrometry (SEM/EDS). Using density functional theory (DFT), the crystalline structures for the simple cubic (sc) Fe
50
Si
50
, face-centered cubic (fcc) Fe
3
Si, and body-centered cubic (bcc) Fe
3
Si crystalline structures were simulated. Electron total density values were calculated to perform energetic comparisons with magnetic behavior. The electronic structures and magnetic properties of the Fe–Si alloys in different stoichiometric configurations were calculated by CASTEP, which employed first principles DFT. The density of states (DOS) and band structures were calculated together with magnetic properties. The results showed that the high value of the polarization spin for the fcc and bcc structures is due to the contribution of the high amount of Fe atoms above the Si atoms, which is reflected in an increase in the magnetic moment and that their presence could explain the ferromagnetic behavior observed by VSM.
Mechanical and tribological properties of titanium nitride, zirconium nitride, and (TiN/ZrN)n multilayers were studied to examine the potential of Kelvin probe force microscopy (KPFM) to identify ...wear mechanisms. Crystalline structure, chemical composition, residual stress, and the mechanical properties showed that the coatings are iso-structural polycrystalline multilayers, with a reduction of grain size, crystallite size, and compressive stress; however, hardness increased with increase in the number of the bilayers. Pin-on-disc test was used for tribological evaluation, and wear tracks were analyzed using field-emission scanning electron microscopy/energy dispersed spectroscopy (FE-SEM/EDS) and KPFM. The increase in mechanical properties generated predominantly abrasive wear mechanisms. Abrasive and adhesive wear mechanisms differentiated by KPFM demonstrated that fragile wear mechanisms presented differences in capacitance and surface potential and that the method is sensitive when the adhered material presents differences in chemical composition. We have demonstrated KPFM to be a promising technique to study tribo-oxidation processes, providing experimental evidence to understand the wear mechanisms at nanometric scales.
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