Fabrication and characteristics of ta-C biomaterial coatings on Ti–6Al–4V using metal plasma immersion ion implantation and deposition

We have formed amorphous diamond (ta-C) coatings on Ti–6Al–4V substrates using a metal plasma immersion ion implantation and deposition (MEPIIID) technique, and characterized the mechanical properties and biological compatibility of the coating material. The hemocompatibility of the coating compared favorably with that of low temperature isotropic (LTI) carbon, with kinetic clotting time and hemolysis rate approximately the same as for LTI carbon, and platelet consumption about twice that of the latter. The mechanical properties were good, with a microhardness greater than that of the uncoated metal substrates, and high adhesion of >0.75 GPa (interface shear stress) as estimated from a thermal quench method. Glancing-angle X-ray diffraction measurements indicated the presence of a TiC transition layer, suggesting the formation of a Ti/TiC/ta-C multilayer structure, leading in turn to good film–substrate adhesion. We conclude that this kind of amorphous diamond coating could provide benefit as a biocompatible hard coating for Ti–6Al–4V substrate material.     

Deposition of TiSiN coatings by arc ion plating process

Titanium silicon nitride (TiSiN) thin films were deposited on tungsten cemented carbide tools by cathode arc ion plating (AIP) process using alloy TiSi targets. The effects of silicon addition and negative substrate bias on the development of the textures of films were studied systematically by varying the bias voltage from −20 to −200 V. The structural features of the films were investigated in detail using X-ray diffraction. The effect of the texture on such mechanical properties as hardness and adhesion of the films was also studied. A maximum hardness of 42 GPa was obtained at a DC substrate bias of −150 V. The characteristics of TiSiN thin films exhibited excellent adhesion of over 150 N. The cutting performance of end-mills and drillers was evaluated by milling and drilling of highly hardened material under high-speed cutting conditions. The results reveal that cutting tools with TiSiN coatings markedly outperformed those with TiN coatings, and the uncoated cutting tools. TiSiN coating increased the cutting lifetime to seven times that of the uncoated one.     

Interaction of beam and coated metals at high power continuous irradiation

The beam-matter interaction with various coating effects has received continued attention in the high power laser community. Previous works suggest that coatings promote target damage when compared to beaming on uncoated surface. Three types of paint coatings (acrylic urethane, silicone alkyd and stealth blend) and a water coat on metals (Al, Ti and STS) are irradiated with a CO₂ laser. Both strain and temperature measurements are provided for assessing the instantaneous response characteristics of each coating on different metals. A selective combination of surface coats with metals has been proven to be effective in either preventing or enhancing damage, both thermal and mechanical, associated with focused beaming on a target.     

The evaluation of the performance of two pyroelectric detectors with vertically aligned multi-walled carbon nanotube coatings

Two LiTaO₃ pyroelectric detectors coated with vertically aligned multi walled carbon nanotube (MWCNT) black coatings were assembled and evaluated using NPL’s detector characterisation facilities. The vertically-aligned nanotube array (VANTA) black coatings were grown on a silicon substrate and subsequently lifted off the silicon and bonded on the pyroelectric crystal substrates. Despite some drawbacks, this method was shown to provide a reliable way of coating delicate substrates such as pyroelectric crystals with VANTA coatings. The performance of the coated and uncoated detectors was evaluated and compared by coating only half of the active area of the test detectors, leaving the other half uncoated. The relative spectral responsivity of the VANTA-coated pyroelectric detectors was shown to be spectrally flat in the 0.8–14 μm wavelength range within the uncertainty of the measurements. The spatial uniformity of response of both detectors exhibited fine structure which was assigned either to the thickness of the VANTA coatings or to their bonding to the pyroelectric crystal. Both coated and uncoated detectors exhibited a super-linear response. This observation was expected in the case of the uncoated detectors, but was surprising in the case of the coated detectors and indicates that the thermal conductivity of vertically aligned multi-walled carbon nanotubes is high along their long axis. The spatial variations of the phase delay experienced by the signal propagating through the VANTA coatings indicate that the thermal diffusivity of the coatings is not spatially uniform.     

Effect of the nanostructuring of a Cu substrate on the fracture of heat-resistant Si-Al-N coatings during uniaxial tension

The effect of the nanostructuring of the surface layers in a Cu substrate on the microstructure, mechanical properties, and fracture mechanisms of heat-resistant Si-Al-N coatings during uniaxial tension is studied. The nanostructuring of a substrate is performed by the following two methods: bombardment by Zr⁺ ion beams and ultrasonic impact treatment. Depending on the state of the substrate, different spallation mechanisms are found to operate in the Si-Al-N coatings during mechanical loading. The maximum shear strength of the coating/substrate interface is shown to be achieved due to ion bombardment of the substrate.     

不同基底石墨烯涂层的层间滑移减磨性能研究

石墨烯薄膜作为一种二维材料,是提高微/纳机电系统(MEMS/NEMS)摩擦力学性能的优异润滑剂.为了探究基底材料和石墨烯层数对其减磨性能的影响,本文通过在不同基底制备了不同层数的石墨烯涂层,利用原子力显微镜(AFM)实验和分子动力学(MD)仿真结合的方法,研究了石墨烯层数对减磨效应的影响.并且通过建立不同层数石墨烯涂层的摩擦性能分析模型,探究出石墨烯层间滑移是产生减磨的主要因素.结果表明:在不同载荷下,石墨烯涂层对硅基底和铜基底均有优异的减磨效果,摩擦力随着石墨烯层数的增加逐渐降低,当石墨烯层数大于10层时,达到最优99.3%的减磨效果.通过仿真分析发现,随着层数增加,石墨烯与基底的干摩擦转变为石墨烯的层间摩擦,并产生层间剪切滑移,石墨烯层间滑移是导致多层石墨烯优异减磨性能的主要因素.     

Formation of Al2O3 coatings on NiTi alloy by micro-arc oxidation method

Rough and porous Al₂O₃ coatings containing Ca and P were prepared on Ti–50.8 at.% Ni alloy by micro-arc oxidation (MAO) technique. The microstructure, elemental and phase composition of the coatings were investigated by scanning electron microscopy (SEM), energy dispersive X-ray spectrometer (EDS) and thin-film X-ray diffraction (TF-XRD). The thickness of the coatings was measured by eddy current coating thickness gauge. The corrosion resistance and the nickel release of the coated and uncoated samples were examined by potentiodynamic polarization tests and immersion tests in Hank’s solution, respectively. The results show that the coatings are mainly composed of γ-Al₂O₃ crystal phase. The Ni content of the coatings is about 3.5 at.%, which is greatly lower than that of NiTi substrate. With increasing treatment time, both thickness and roughness of the coatings increase. The corrosion resistance of the coated samples is about two orders of magnitude higher than that of the uncoated NiTi alloy. The concentration of Ni released from coated NiTi samples is much lower than that of uncoated NiTi sample. It can be reduced in the factor of one-seventh compared with the uncoated NiTi sample after 3 weeks immersion in Hank’s solution.     

Microstructure development and properties of the AlCuFe quasicrystalline coating on near-α titanium alloy

A protective quasicrystalline AlFeCu coating was deposited on TIMETAL 834 substrate by nonreactive magnetron sputtering in order to improve resistance of the alloy to oxidation. Microstructure characterisation of the substrate and the coating was performed by analytical scanning- and transmission electron microscopy as well as X-ray diffractometry. Depending on annealing temperature and time, the deposited coating (2.7 μm thick) has a different microstructure. The coating in Specimen 1 (annealed 600 °C/4 h in vacuum) consisted of two zones: outer, composed of Al₅Fe₂ and Al₂Cu₃ phases and inner, in which only quasicrystalline ψ phase was present. The coating in Specimen 2 (annealed 600 °C/4 h + 700 °C/2 h in vacuum) was fully quasicrystalline and consisted of icosahedral ψ phase.Both coatings exhibit higher microhardness than the substrate material. It was established that the applied surface treatment essentially improves oxidation resistance of the alloy tested at 750 °C during 250 h in static air. Sample weight gain was 60% lower than in the case of uncoated sample. Oxide scale spallation occurred for uncoated alloy while the coated one did not show any spallation. It was found that the very brittle scale formed during oxidation on the uncoated alloy was consisting of TiO₂, while that on the coated one consisted mainly of α-Al₂O₃.     

Effect of microarc oxidation coating on fatigue performance of Ti-Al-Zr alloy

Ceramic coatings of different thickness were fabricated on Ti6Al2Zr1Mo1V alloy by microarc oxidation (MAO), and the effect of the coating on fatigue life was evaluated by 810 Material Test System. The microstructure, phase and chemical composition of the coatings were determined by SEM, XRD and EDS techniques. The coating mainly consists of rutile and a small amount of anatase TiO₂. With oxidation time ranging from 10 to 30 min, the coating thickness increases from 13 to 25 μm, while the interface between coating and substrate becomes more zigzag, characterized by increasing overgrowth regions of coating into substrate. Under the same cyclic stress of 750 MPa, the fatigue life decreases from 2.08 × 10⁶ cycles for uncoated specimen to about 3 × 10⁴ cycles for microarc oxidized specimen. Under the cyclic stress, the thicker the coating, the more cracks initiate in the overgrowth regions of coating into substrate near the interface, which are considered as the notch sites of stress concentration to induce the crack initiation, also is the key factor to cause the facture.     

Microstructure, mechanical properties, and oxidation resistance of nanocomposite Ti-Si-N coatings

Ti-Si-N coatings with different silicon contents (0-12 at.%) were deposited onto Si(1 0 0) wafer, AISI M42 high speed steel, and stainless steel plate, respectively. These coatings were characterized and analyzed by using a variety of analytical techniques, such as XRD, AES, SEM, XPS, nanoindentation measurements, Rockwell C-type indentation tester, and scratch tester. The results revealed that the hardness was strongly correlated to the amount of silicon addition into a growing TiN film. The maximum hardness of 47.1 GPa was achieved as the Si content was 8.6 at.%. In the mechanical and oxidation resistance measurements, the Ti-Si-N coatings showed three distinct behaviors. (i) The coatings with Si contents of no more than 8.6 at.% performed good adhesion strength quality onto the HSS substrates. (ii) The fracture toughness of the coatings decreased with the increase in Si content. (iii) The Ti-Si-N coating with 8.6 at.% Si showed the excellent oxidation resistance behavior. The cutting performance under using coolant conditions was also evaluated by a conventional drilling machine. The drills with Ti-Si-N coatings performed much better than the drills with TiN coating and the uncoated drills.     

Influence of annealing treatment on the microstructure and mechanical performance of cold sprayed 304 stainless steel coating

In this study, 304 stainless steel coatings were deposited on interstitial-free steel substrate by cold spraying method. The effect of annealing treatment on microstructure, microhardness, ultimate tensile strength and fracture performance of the coatings were studied. The results showed that annealing treatment had made a dominant contribution to heal up the incomplete interfaces between the deposited particles. Both of the microstructure and the mechanical properties have been obviously optimized by annealing treatment. In addition, the coating microhardness decreased from 345 HV_0.2 for the as-sprayed coating to 201 HV_0.2 for the annealed coating. The coating ultimate tensile strength increased from 65 MPa for the as-sprayed coating to 357 MPa for the annealed coating, which resulted from the increase of the metallurgically bonded areas in the coating induced by annealing treatment. Fracture morphology of the coatings also revealed that annealing treatment changed the fracture character of the cold sprayed 304 stainless steel coating from brittle type to plastic type.     

Preparation of biomedical Ag incorporated hydroxyapatite/titania coatings on Ti6Al4V alloy by plasma electrolytic oxidation

Nano-Ag incorporated hydroxyapatite/titania(HA/TiO2) coatings were deposited on Ti6Al4V substrates by the plasma electrolytic oxidation process. Compared with the substrate, the deposited coatings display attractive mechanical and biomedical properties. First, the coatings have stronger wear resistance and corrosion resistance. Second, they show a strong antibacterial ability. The mean vitality of the P. gingivalis on the coating surfaces is reduced to about 21%.Third, the coatings have good biocompatibility. The mean viability of the fibroblast cells on the coating surface is increased to about 130%. With these attractive properties, Ag incorporated HA/TiO2 coatings may be useful in the biomedical field.     

Factors influencing the ballistic impact resistance of elastomer-coated metal substrates

An experimental study was carried out of various factors affecting the ballistic penetration resistance of elastomer/steel bilayers. For blunt penetrators, the contribution of the coating to performance is optimized using the hardest substrates, front surface placement of the elastomer, and (when normalizing by added weight) thin, ca. 2–3?mm, coatings. These results, none of which are predicted by existing models, evince the marked coupling of coating and substrate in the impact response of the bilayer. We also show that nanoparticle fillers have a modest effect on ballistic performance of polyurea coatings, changing the penetration velocity by a few percent or less. This contrasts with the linear dynamic mechanical behavior, which shows much more significant increases in energy absorption due to nano-reinforcement.     

Interface adhesion properties of functional coatings on titanium alloy formed by microarc oxidation method

Three functional coatings (namely Al-C, Si-P-Al and P-F-Al coating) were fabricated by microarc oxidation method on Ti6Al4V alloy in different aqueous solutions. The microstructure, phase and chemical composition of coatings were investigated using scanning electron microscope, X-ray diffraction and energy dispersive spectroscopy. The interface adhesion failure mode of the coating is revealed by shear, tensile and thermal shock methods. The coatings exhibit high adhesion strength by the quantitative shearing test, registering as 110, 70, and 40 MPa for Al-C, Si-P-Al and P-F-Al coating, respectively. The tensile test of the coated samples shows that microarc oxidation treatment does not significantly deteriorate mechanical properties of substrate titanium alloy. The observations of the coating failure after subjected to the identical tensile elongation of 3.0% are well in agreement with those results of the shear test. The thermal cycle test indicates that all the coatings have good anti-thermal shocking properties.     

Development of copper coatings on ceramic powder by electroless technique

Electroless (EL) coating technique is one of the elegant ways of coating by controlling the temperature and pH of the coating bath in which there is no usage of electric current. EL nano-copper coating on ceramic particles of micron size is not reported. In this investigation, ceramic powders of ∼100 μm size have been coated with copper by EL technique in the pH and temperature ranges of 12-13.5 and 60-85 °C, respectively. The optimization of EL copper bath has been evaluated through the combination of process parameters like pH and temperature. The optimized value of pH is found to be 12.5 and temperature as 75 °C. The coated and uncoated powders have been subjected to microstructural studies by scanning electron microscope (SEM) and the phases present have been analyzed by X-ray diffraction. An attempt has been made to understand the bonding mechanism of coating. The adherence with the substrate is attributed to the chemical and mechanical bonding at the interface. A model has been suggested for the mechanical bonding effect at the interface.     

Study of luminescent defects in hafnia thin films made with different deposition techniques

Hafnia thin films for high-power optical coatings have been characterized by photoluminescence pumped by 4.66 eV photons and photothermal deflection measurements. These data are compared to the statistical laser damage behavior in order to find correlations between destructive and non-destructive characterizations. Thin films have been produced at two thicknesses and using different thin-film deposition techniques typically employed for optical coating fabrication: EBD (HfO₂ target), EBD (Hf target), RLVIP and DIBS. The photoluminescence spectra show significant differences depending on the deposition techniques and thicknesses. EBD films show significant luminescence but the luminescence of ion-assisted films could not be distinguished from the uncoated substrate. All EBD coating spectra could be described by a linear combination of four bands. Further, XRD measurements show that the 255-nm-thick films had a relatively high crystallinity: EBD films contained the monoclinic phase and the ion-assisted films contained oriented nanocrystals of orthorhombic hafnia. The presence of orthorhombic phases indicates high compressive strain quenching the photoluminescence of these samples.     

Numerical simulation of temperature distribution and TiC growth kinetics for high power laser clad TiC/NiCrBSiC composite coatings

A three dimensional model was proposed to simulate high power laser clad TiC/NiCrBSiC composite coatings on Ti6Al4V alloys. The temperature distribution, temperature curves on different nodes, three dimensional shape and size of TiC melting region, molten pool and heat affected zone (HAZ) of the substrate were obtained. To have a clear physical insight into the phase transformation and microstructure evolution in the coatings during laser cladding process, a theoretical kinetic analysis was performed to elucidate the nucleation, growth velocity, and size of TiC particles on the basis of simulated temperature curves of the molten pool. A good quality TiC/NiCrBSiC composite coating with low dilution rate and excellent metallurgical bond was fabricated under optimal processing parameters using powder mixture of TiC and NiCrBSiC as clad material and cuboid of Ti6Al4V alloys as substrate. To validate the reliability of the proposed model, the theoretical results were compared with the microstructure of the coatings. It shows that these theoretical results are in excellent agreement with the experiment cases.     

Structural and tribological properties of CrTiAlN coatings on Mg alloy by closed-field unbalanced magnetron sputtering ion plating

In this paper, a series of multi-layer hard coating system of CrTiAlN has been prepared by closed-field unbalanced magnetron sputtering ion plating (CFUBMSIP) technique in a gas mixture of Ar + N₂. The coatings were deposited onto AZ31 Mg alloy substrates. During deposition step, technological temperature and metallic atom concentration of coatings were controlled by adjusting the currents of different metal magnetron targets. The nitrogen level was varied by using the feedback control of plasma optical emission monitor (OEM). The structural, mechanical and tribological properties of coatings were characterized by means of X-ray photoelectron spectrometry, high-resolution transmission electron microscope, field emission scanning electron microscope (FESEM), micro-hardness tester, and scratch and ball-on-disc tester. The experimental results show that the N atomic concentration increases and the oxide on the top of coatings decreases; furthermore the modulation period and the friction coefficient decrease with the N₂ level increasing. The outstanding mechanical property can be acquired at medium N₂ level, and the CrTiAlN coatings on AZ31 Mg alloy substrates outperform the uncoated M42 high speed steel (HSS) and the uncoated 316 stainless steel (SS).     

Mechanical spectroscopy of decagonal Al–Cu–Fe–Cr quasicrystalline coatings

Mechanical spectroscopy measurements were performed on decagonal quasicrystalline Al–Cu–Fe–Cr coatings of three different thicknesses deposited on a mild steel substrate. The mechanical loss spectra indicate that the internal friction is mostly caused by the quasicrystalline coating and that the contributions of both the steel substrate and the interface are small. The shear modulus measured in torsion increases with temperature, while the Young’s modulus measured in flexion behaves normally. This shear modulus anomaly is interpreted as being due to solid friction between cracked segments of the quasicrystalline coating. This phenomenon also explains the broad athermal maximum found to occur in isochronal internal friction measurements. A quantitative model successfully reproducing the observed behaviour has been developed. Finally, the reversible high-temperature exponential background was interpreted as being due to the onset of the brittle-to-ductile transition in the quasicrystalline coating. The measured activation enthalpy is similar to the value that was deduced from compression tests performed at high temperatures on icosahedral Al–Cu–Fe bulk material.     

The influence of semiconducting properties of passive films on the cavitation erosion resistance of a NbN nanoceramic coating

To alleviate the cavitation damage of metallic engineering components in hydrodynamic systems operating in marine environments, a NbN nanoceramic coating was synthesized on to a Ti-6Al-4V substrate via a double cathode glow discharge technique. The microstructure of the coating consisted of a ~13 μm thick deposition layer of a hexagonal δ′-NbN phase and a diffusion layer ~2 μm in thickness composed of face-centered cubic (fcc) B1-NaCl–structured (Ti,Nb)N. The NbN coating not only exhibited higher values of H/E and H²/E than those measured from NbN coatings deposited by other techniques, but also possessed good adhesion to the substrate. The cavitation erosion resistance of the NbN coating in a 3.5 wt% NaCl solution was investigated using an ultrasonic cavitation-induced apparatus combined with a range of electrochemical test methods. Potentiodynamic polarization measurements demonstrated that the NbN coated specimens demonstrated both a higher corrosion potential (E_corr) and lower corrosion current density (i_corr) than the uncoated substrate. Mott-Schottky analysis, combined with the point defect model (PDM), revealed that, for a given cavitation time, the donor density (N_D) of the passive film on the NbN coating was reduced by 1 ~ 2 orders of magnitude relative to the uncoated Ti-6Al-4V, and the diffusivity of the point defects (D₀) in the passive film grown on the NbN coating was nearly one order of magnitude lower than that on the uncoated substrate. In order to better understand the experimental observations obtained from Mott-Schottky analysis and double-charge layer capacitance measurements, first-principles density-functional theory was employed to calculate the energy of vacancy formation and the adsorption energy for chloride ions for the passive films present on both the NbN coating and bare Ti-6Al-4V.