NiAlCr-X overlay coatings deposited by magnetron sputtering on IN100 and CMSX-4 superalloys and thereafter top-coated with 7YSZ thermal barrier coatings by EB-PVD were investigated with emphasis on ...the effects of superalloy type and Hf or Zr doping. The sputtered films in the “as coated” condition (after EB-PVD deposition) showed strong diffusion effects of different elements from the superalloys. The measured phase content of β and γ′ was in good agreement with calculated data obtained from experimental compositions normalized to a Ni-Al-Cr system following the guidelines of site preference of ternary alloying elements. Microstructure evolution and failure characteristics after furnace cyclic tests at 1100°C were investigated as well. The lifetime of the coatings is equivalent to standard MCrAlY TBCs systems and is compared to PtAl and NiCoCrAlY coatings from literature. The effects of microstructure and elements diffusing from the substrates into the bond coat (Ti, Co, Mo and Ta) in combination with the effect of Hf- or Zr-doping is presented and discussed.
•The prepared NiAlCr bond coats consist of a β – γ’ phase sent to furnace cyclic tests to evaluate the effects of Zr or Hf additions on the TBC lifetime.•Zr-additions to the NiAlCr bond coat lead to a better performance in the IN100 than in the CMSX-4, whereas Hf-additions show an opposite effect.•The TBC lifetimes of the NiAlCrZr/IN100 were similar to thicker NiCoCrAlY bond coats, while on CMSX-4 the NiAlCrHf was even better than PtAl or NiCoCrAlY systems.•Magnetron sputtering is a promising technique for deposition of chemically well-controlled, well adherent bond coats.
Bovine-Derived Hydroxyapatite (BHAp) is Ca-deficient natural hydroxyapatite with several ions substitutions that play a crucial role in its biomimetic behavior. Natural quantities of ions such as ...Mg2+ and CO32– increase the bioactivity and the biological performance of BHAp compared to stoichiometric hydroxyapatite (HAp). In this contribution, BHAp powder was obtained from two years old bovines and thermally sprayed by Atmospheric Plasma Spray (APS) and High-Velocity Oxygen Fuel (HVOF) on 304L stainless steel substrates. BHAp coatings morphology and structure were analyzed by scanning electron microscopy (SEM), Fourier Transformed Infra-Red (FTIR) spectroscopy and Rietveld refinements of the coatings grazing incident X-ray diffraction (GIXRD) patterns. The bioactivity of the coatings was evaluated following the modifications of its structure and surface morphology after immersion in simulated body fluid (SBF) during 3, 5 and 10 days, by SEM and GIXRD. The Ca, P and Mg concentration in SBF was also measured by inductively coupled plasma optical emission spectrometry (ICP-OPS). The obtained BHAp powder was highly crystalline and mainly a B-type HAp. The main differences between BHAp and HAp are CO32– and the Mg2+ contents, which lead to the formation of dolomite in the crystalline content (48.75 wt%) during HVOF spraying. APS coating did not exhibit any secondary phases in its crystalline content. The typical polyhedral grain apatite layer was evident after 3 days of immersion in SBF for both coatings. However, SEM micrographs of HVOF coatings show delamination after 5 days of immersion. Thus, the dolomite phase is detrimental for coating stability and bioactivity.
•BHAp deposited by HVOF leads to the formation of the dolomite phase.•BHAp APS coating does not show any secondary phases in its crystalline content.•BHAp APS coating shows the formation of apatite layer after 3 days in SBF.•BHAp HVOF coating shows the formation of apatite layer after 3 days in SBF.•Dolomite is detrimental for the BHAp coating stability during immersion in SBF.
For over five decades, ultra-high molecular weight polyethylene (UHMWPE) has been the standard material for total knee replacements (TKR). Zero wear of the UHMWPE would be ideal; however, due to the ...natural knee movements, wear damage to the UHMWPE articulating surface is inevitable. The generated wear debris results in joint mechanical instability, reduced joint mobility, increased pain, and implant loosening. Because of these issues, the research on the materials in TKRs has increased their survival rate for up to 20 years; however, in younger patients, the durability of the UHMWPE component decreases due to increased physical activity. Hence there is a constant need for highly wear-resistant tribological pairs for TKRs. Carbon-based materials have an excellent balance between lubricating and mechanical properties and have shown great promise in tribological applications. This study used self-lubricating cubic titanium carbide (c-TiC) and multiwalled carbon nanotubes (MWCNTs) to improve the UHMWPE wear resistance further. The combination of carbon-based materials decreased the material loss by about 41.7 % compared to the UHMWPE vs. bare steel ball tribological pair. The improvement, attributed to the c-TiC self-lubricating coating surface, is close to 5 %. Cold flow and burnishing were the predominant wear mechanisms observed in all the systems; more subtle wear processes were detected for the sliding couple with c-TiC self-lubricating coating. Meanwhile, polymer delamination and micrometer-sized debris formation were the main wear mechanisms in the UHMWPE-MWCNT vs. bare steel ball system. The adhesion work obtained from the electronic structure calculations shows a more significant interfacial interaction of the CNTs on the c-TiC surface. This interaction can be associated with the layer formation that protects the surface from wear and friction.
Enhancement of mechanical and tribological properties on AISI D3 steel surfaces coated with CrN/AlN multilayer systems deposited in various bilayer periods (
Λ) via magnetron sputtering has been ...studied in this work exhaustively. The coatings were characterized in terms of structural, chemical, morphological, mechanical and tribological properties by X-ray diffraction (XRD), electron dispersive spectrograph, atomic force microscopy, scanning and transmission electron microscopy, nanoindentation, pin-on-disc and scratch tests. The failure mode mechanisms were observed via optical microscopy. Results from X-ray diffraction analysis revealed that the crystal structure of CrN/AlN multilayer coatings has a NaCl-type lattice structure and hexagonal structure (wurtzite-type) for CrN and AlN, respectively, i.e., made was non-isostructural multilayers. An enhancement of both hardness and elastic modulus up to 28
GPa and 280
GPa, respectively, was observed as the bilayer periods (
Λ) in the coatings were decreased. The sample with a bilayer period (
Λ) of 60 nm and bilayer number
n
=
50 showed the lowest friction coefficient (∼0.18) and the highest critical load (43
N), corresponding to 2.2 and 1.6 times better than those values for the coating deposited with
n
=
1, respectively. The best behavior was obtained when the bilayer period (
Λ) is 60
nm (
n
=
50), giving the highest hardness 28
GPa and elastic modulus of 280
GPa, the lowest friction coefficient (∼0.18) and the highest critical load of 43
N. These results indicate an enhancement of mechanical, tribological and adhesion properties, comparing to the CrN/AlN multilayer systems with 1 bilayer at 28%, 21%, 40%, and 30%, respectively. This enhancement in hardness and toughness for multilayer coatings could be attributed to the different mechanisms for layer formation with nanometric thickness such as the Hall–Petch effect and the number of interfaces that act as obstacles for the crack deflection and dissipation of crack energy.
The effect of particle velocity on deposition efficiency and microstructure of copper powder on aluminum alloy substrates using Low Pressure Cold Spray (LPCS) is here reported. For this, experimental ...substrate-coating systems were fabricated varying powder feed rate, transverse speed, and air pressure keeping the compressed air, substrate temperature, and stand-off distance constant (600 °C, 100 °C, and 5 mm, respectively). From the combination of low feed rates and low transverse speed, deposition efficiency tends to increase. The maximum deposition efficiency of 34.8% was obtained for a feed rate of 0.2 g/s, 10 mm/s transverse speed, and 8 bar of air pressure.
The pressure and stand-off distance effect on coatings was studied measuring the particle velocity with and without substrate. For this, spraying conditions were varied between 5–8 bar and 5–15 mm, respectively. Experimental measurements were compared with results from computational fluid dynamics simulation to understand the effect of the spraying parameters on the complete powder size distribution. The highest deposition efficiencies (36–37.5%) were obtained at 7 bar air pressure for spray distances between 5 and 12.5 mm. Increasing the pressure to 8 bar led to a decrease in the deposition efficiency (6–11%). The tendency of deposition efficiency seems to match with the in-flight particle velocity influenced by the presence of a substrate, which serves as evidence of the bounce-off effect. The reduction of the particle velocity, along with the low transverse speed seems to remove less attached particles by erosion through the peening effect.
•Deposition efficiencies between 36 and 37.5% were obtained in Cu coatings at 7 bar.•In-flight particle velocity is correlated with bounce-off effects.•Reduction of particle velocity and DE seems to be associated with erosion and bow shock.•The highest particle velocity was correlated with the highest deposition efficiencies.•Experimental data tendency correlates with numerical calculations.
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•Poled-BNT are novel biomaterials with tunable in-vitro properties for bone repair.•Effect of surface polarity of BNT on apatite formation and cell viability.•Apatite growth and ...maturation are strongly influenced by surface polarity.
Poled (Bi0.5Na0.5)TiO3 ceramics were firstly evaluated in the present study for their potential application as a novel biomaterial for bone repair. The formation of bone-like apatite was only observed on polarized surfaces showing a clear influence of polarity on its growth and maturation process after bioactivity tests. A non-cytotoxic effect of (Bi0.5Na0.5)TiO3 ceramics on MC3T3-E1 cells was shown in the viability test. Cells spread along the surface showed slight differences in shape and size due to polarity. Bioactive and non-cytotoxic behavior exhibited by poled (Bi0.5Na0.5)TiO3 ceramics makes them a promising material with tunable in-vitro properties for biomedical applications.
An experimental approach based on design of experiments, process maps and the analysis of deposition first stages to improve the biocompatibility of High-Velocity Oxygen Fuel (HVOF) hydroxyapatite ...(HAp) coatings is here presented. A two-level design of three factors (23) was performed using the stand-off distance (SOD), the fuel‑oxygen ratio (F/O) and the powder feed rate (PFR). The effect of these experimental factors on the first stages of the coating formation was investigated to study the physical state of the particles before and after impacting the substrate. This study allowed the selection of the most suitable deposition parameter combinations to obtain HAp coatings with optimal crystallinity (>45%), Ca/P ratio (approx. 1.67), phase content (>95% of HAp), which guarantee the coatings mechanical stability and biocompatibility. The behavior of the coating within simulated body fluid (SBF) and cell culture (hFOB) was studied to analyze the apatite layer formation and the extracts cytotoxicity on human osteoblasts, respectively. The results show that the F/O ratio is the most influential factor on temperature and velocity on the in-flight particles and therefore on the coating properties. The SBF results confirmed the formation of an apatite layer after 14 days of immersion. Finally, the mitochondrial activity, measured by the MTS assay, and cell membrane integrity measured by LDH liberation assays, show that the coating released material does not induce toxicity on the exposed cells.
•Optimized parameters for deposition of high quality HAp coatings by HVOF are here reported.•DoE methodologies and statistical analysis allowed to understand HAp coating formation by HVOF.•The leaching products generated by the HAp coatings deposited by HVOF do not induce cytotoxicity.
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.
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