Al2O3 Counterpart Research Articles

Tribo-mechanical properties and biocompatibility of Ag-containing amorphous carbon films deposited onto Ti6Al4V

The addition of Ag to amorphous carbon (a-C) films is highly effective in tailoring the tribo-mechanical properties and biocompatibility. For biomedical applications, Ag-containing a-C (a-C:Ag) represents a promising film material for improving the biofunctional surface properties of Ti-based alloys. In a sputtering process, a-C:Ag films, with Ag contents up to 7.5 at.%, were deposited with a chemically graded TixCy interlayer onto Ti6Al4V. The tribo-mechanical and biocompatible properties of a-C:Ag were evaluated. The influence of the Ag content on these properties was analyzed and compared to those of uncoated Ti6Al4V.Raman spectroscopy reveals that the amount of incorporated Ag does not induce significant structural changes in the disordered network, only a reduced number of vacancies and sp3-coordinated C bonds within the sp2-dominant a-C network is assigned to the films with high Ag concentration. With increasing Ag content, stresses, hardness, and elastic modulus decrease from (2.02 ± 0.07) to (1.15 ± 0.03) GPa, from (17.4 ± 1.5) to (13.4 ± 0.9) GPa, and from (171.8 ± 8.1) to (138.5 ± 5.8) GPa, respectively. In tribometer tests, the friction behavior against Al2O3 in lubricated condition with a simulated-body-fluid-based lubricant is not affected by the Ag concentration, but the Al2O3 counterpart wear is reduced for all a-C:Ag films compared to a-C. The friction against ultra-high-molecular-weight polyethylene (UHMWPE) decreases continuously with increasing Ag concentration and the counterpart wear is lower at higher Ag contents. Compared to a-C:Ag, Ti6Al4V demonstrates lower friction against UHMWPE and higher friction against Al2O3. The a-C:Ag films are not exposed to abrasion by Al2O3 or pronounced material transfer of UHMWPE. The hardness difference and chemical affinity between the friction partners are decisive for the tribological behavior of a-C:Ag. Compared to Ti6Al4V, the a-C:Ag films show antibacterial activity against Staphylococcus aureus, while the proliferation of osteoblast-like cells is reduced by Ag.

Effect of Aging Temperature on the Microstructure, Local Mechanical Properties, and Wear Behavior of a UNS S32750 Super Duplex Stainless Steel

In this paper, the effect of aging temperature on the microstructure, local mechanical properties and wear behavior of a UNS S32750 super duplex stainless steel is investigated. A massive preferential precipitation of σ phase and Cr2N is detected at the periphery of ferrite with an increase in their extent as aging temperature increases. Simultaneously, the δ phase decomposition is accentuated with temperature and reaches its maximum at 850 °C. This behavior results in an enhancement in hardness and Young’s modulus accompanied by a higher plasticity ratio. The wear resistance of the aged samples is investigated in terms of friction coefficients and wear rates against two counterparts. The wear performance follows σ phase presence, the higher σ phase extent, the higher the wear resistance. It is found that the change in wear mechanisms in the 850 °C aged samples from abrasive against AISI-304L counterpart to adhesive-oxidative against Al2O3 counterpart is responsible in the increase in wear resistance.

Alternative metallic matrices for WC-based HVOF coatings

Thermal spray coatings based on WC-CoCr are widely employed to protect industrial components against wear and corrosion. Although they provide good technical performances, it is necessary to replace Co-based hardmetal compositions to protect human health as well as for economic reasons. Alternative hardmetal formulations with little or no Cobalt were deposited by High Velocity Oxygen-Fuel (HVOF) spraying using agglomerated and sintered feedstock powders. They consist of WC as hard phase, but metallic matrices include iron- and nickel-based alloys (WC-NiMoCrFeCo, WC-FeNiCrMoCu, WC-FeCrAl). The characterization is focused on microstructure, mechanical and tribological properties (sliding and abrasive wear behaviour) and corrosion resistance in 3.5% NaCl. Very low porosity, limited carbides' dissolution in the matrix, deposition efficiency ≥50%, and hardness values (≈1200 HV) comparable to conventional WC-CoCr mean that the studied coatings are viable for industrial applications. Both WC-NiMoCrFeCo and WC-FeNiCrMoCu coatings show intrinsically high sliding wear resistance (specific wear rates between 10−8 and 10−7 mm3/(N∙m) in a ball-on-disc test against Al2O3 counterpart), but they are less resistant to high-stress abrasion by coarse particles (wear rates ≈10−3 mm3/(N∙m)). Their performances are anyway comparable to those of reference WC-CoCr samples. Additionally, WC-NiMoCrFeCo coatings show even better corrosion resistance in a 3.5% NaCl aqueous solution (ICorr ~ 10−6 A/cm2). WC-FeCrAl coatings exhibit slightly poorer performances than the other samples: the formation of Al-based oxide inclusions during spraying cause higher wear losses, whilst the FeCrAl matrix has limited corrosion resistance.

Impact of Gate Dielectric Material on Basic Parameters of MO(I)SHEMT Devices

In this work, the behavior of MISHEMT devices with different gate materials is analyzed. Two-gate insulator materials (Al2O3 and SiN) were analyzed through the transfer characteristic, threshold voltage, hysteresis and transconductance. Although devices with SiN insulator present smaller hysteresis, better DIBL and it is nearest to a normally off devices, the leakage current showed to be much higher than for the Al2O3 counterpart. Besides the double conduction that occurs in SiN devices results in an anomalous behavior of transconductance and consequently an unexpected behavior of threshold voltage with temperature.

Improving metal-ceramic systems subjected to sliding contact by reinforcing the metallic counterpart with ceramic particles

The study of sliding wear is important as it occurs in many industrial mechanical systems. In metal-ceramic sliding wear, reinforcing the metallic counterpart with ceramic particles transforms the system from a pure metal-ceramic interaction to one that contains both metal-ceramic and ceramic-ceramic interactions, which may improve the wear performance of both materials involved. This study shows that incorporating NbC particles into a bearing stainless steel reduces its wear rate against SiC, WC and Al2O3 counterparts but its wear rate remained unchanged against ZrO2. For the ceramic counterparts, SiC and WC also experienced reduced wear while Al2O3 showed negligible wear across all tests. ZrO2, on the other hand, experienced a very high level of wear when the stainless steel contained 5 vol% NbC but the wear rate gradually decreased as the volume fraction of NbC increased to 15 vol%. Higher NbC volume fractions are thus expected to yield further improvement.

Electron-Transport Characteristics through Aluminum Oxide (100) and (012) in a Metal-Insulator-Metal Junction System: Density Functional Theory-Nonequilibrium Green Function Approach.

Al2O3 is commonly used in modern electronic devices because of its good mechanical properties and excellent electrical insulating property. Although fundamental understanding of the electron transport in Al2O3 is essential for its use in electronic device applications, a thorough investigation for the electron-transport mechanism has not been conducted on the structures of Al2O3, especially in nanometer-scale electronic device settings. In this work, electron transport via Al2O3 for two crystallographic facets, (100) and (012), in a metal–insulator–metal junction configuration is investigated using a density functional theory-based nonequilibrium Green function method. First, it is confirmed that the transmission function, T(E), decreases as a function of energy in (E – EF) < 0 regime, which is an intuitively expected trend. On the other hand, in the (E – EF) > 0 regime, Al2O3(100) and Al2O3(012) show their own characteristic behaviors of T(E), presenting that major peaks are shifted toward lower energy levels under a finite bias voltage. Second, the overall conductance decay rates under zero bias are similar regardless of the crystallographic orientation, so that the contact interface seemingly has only a minor contribution to the overall conductance. A noteworthy feature at the finite bias condition is that the electrical current drastically increases as a function of bias potential (>0.7 V) in Al2O3(012)-based junction compared with the Al2O3(100) counterpart. It is elucidated that such a difference is due to the well-developed eigenchannels for electron transport in the Al2O3(012)-based junction. Therefore, it is evidently demonstrated that at finite bias condition, the contact interface plays a key role in determining insulating properties of Al2O3–Pt junctions.

Ni nanocatalysts supported on mesoporous Al2O3-CeO2 for CO2 methanation at low temperature.

The selectivity and activity of a nickel catalyst for the hydrogenation of carbon dioxide to form methane at low temperatures could be enhanced by mesoporous Al2O3–CeO2 synthesized through a one-pot sol–gel method. The performances of the as-prepared Ni/Al2O3–CeO2 catalysts exceeded those of their single Al2O3 counterpart giving a conversion of 78% carbon dioxide with 100% selectivity for methane during 100 h testing, without any deactivation, at the low temperature of 320 °C. The influence of CeO2 doping on the structure of the catalysts, the interactions between the mesoporous support and nickel species, and the reduction behaviors of Ni2+ ions were investigated in detail. In this work, the addition of CeO2 to the composites increased the oxygen vacancies and active metallic nickel sites, and also decreased the size of the nickel particles, thus improving the low temperature catalytic activity and selectivity significantly.

Tribological Properties of Mo2N Films at Elevated Temperature

Mo2N films were synthesized using the reactive magnetron sputtering system in a mixture of argon and nitrogen, and the tribological properties were investigated at different testing temperatures against an Al2O3 counterpart. The relative intensity ratio (RIR) method was used to calculate the weight fraction of the tribo-film (MoO3) on the wear tracks of the films. The results showed that the average friction coefficient first increased from 0.30 at 25 °C to 0.53 at 200 °C, and then decreased to 0.29 at 550 °C, while the wear rate decreased from 2.1 × 10−6 mm3/Nmm at 25 °C to 5.3 × 10−7 mm3/Nmm at 200 °C and then increased to 3.1 × 10−5 mm3/Nmm at 550 °C. The weight fraction of tribo-film was mainly attributed to changes in the average friction coefficient and the wear rate. Besides this, the relative humidity also influenced the tribological properties at 25–200 °C.

Spark Plasma Sintering and tribological behavior of Ti3SiC2–Ti5Si3–TiC composites

Herein, we study the effect of TiC content on the tribological behavior of four Ti3SiC2/Ti5Si3/TiC composites, prepared through Spark Plasma Sintering. The tribological properties were investigated under dry sliding, against Al2O3 counterpart at room temperature, under different normal loads and sliding speeds. Vickers indentation results showed that the composites preserve some damage tolerance properties. Scanning Electron Microscopy (SEM) and Raman spectroscopy results showed that the low wear stage is associated with the formation of a lubricious tribofilm consisting of a mixture of Ti6O11 Magnéli-phase and graphitic carbon. On the other hand, the tribo-oxidation products of the free TiC composite were identified as a mixture of TiO2 and SiO2 oxides. The composite reinforced up to 25 wt % TiC showed no transition from the low to the high wear rate as a function of normal loads. The influence of processing variables on microstructure development and wear mechanisms of the composites is discussed.

Tribocorrosion Behavior of SAF 2205 Duplex Stainless Steel in Artificial Seawater

Tribocorrosion behaviors of SAF 2205 duplex stainless steel sliding against an Al2O3 counterpart were investigated in artificial seawater. The tribocorrosion mechanisms and synergistic actions between corrosion and wear were analyzed in this work. The results indicated that a higher load was beneficial for the formation of the σ intermetallic phase and strain hardening; thus, the hardness increased first, and then the pure mechanical wear resistance of SAF 2205 was improved by the hardening effect. The wear mechanisms of SAF 2205 were dominated by abrasive wear under lower loads and by abrasive wear and plastic deformation under higher loads. Furthermore, galvanic corrosion was established between the σ intermetallic phase/ferritic/austenitic and passive film (cathode)/fresh surface, which caused corrosion-accelerated wear. Thus, the total damage to SAF 2205 during tribocorrosion in artificial seawater was determined by the mechanical wear and synergetic effects between corrosion and wear. Therefore, improving hardness was an effective way to increase the tribocorrosion properties of metal materials, such as SAF 2205 and 316L.

Properties of HVOF-sprayed TiC-FeCrAl coatings

As an alternative to WC-CoCr and Cr3C2-NiCr coatings for wear and corrosion protection, a TiC – 25 vol% (Fe-20 wt%Cr-5 wt%Al) powder, free from hazardous and/or supply-critical elements (Ni, Co, W), was produced by high-energy ball-milling and processed by High Velocity Oxygen-Fuel (HVOF) spraying, obtaining dense (<1 vol% porosity), hard (HIT > 12 GPa) layers with reasonably good deposition efficiency of ≈ 54%.Tribological testing revealed that the TiC-FeCrAl coatings are particularly promising for sliding contacts, as their ball-on-disc wear rates against an Al2O3 counterpart were lower than those of an HVOF-sprayed Cr3C2-NiCr reference, both at room temperature and at 400 °C, although they could not match the performance of WC-CoCr. At room temperature, brittle fracture along oxidized lamellar boundaries caused localized spallation, releasing debris in the contact region, but, in the incubation period before spallation cracks could propagate, remarkably low friction (≈0.27) was recorded. At 400 °C, spallation was largely suppressed by thermal softening, whilst coarser abrasive grooving became the dominant wear mechanism.TiC-FeCrAl coatings appeared less suited to high-stress abrasion, since extensive brittle fracture resulted in higher wear rates than HVOF-sprayed Cr3C2-NiCr, and to (acidic) corrosive environments. Electrochemical polarisation tests in 0.1 M HCl indeed revealed limited corrosion resistance of the FeCrAl matrix.

Friction and wear properties of MoAlB against Al2O3 and 100Cr6 steel counterparts

The present work investigates, for the first time, the dry sliding friction and wear behaviour of fully dense, predominantly single-phase MoAlB ceramics against alumina (Al2O3) and 100Cr6 steel counterparts. Against Al2O3, the friction coefficient (μ) increased with increasing load and the wear was highly dependent on the load applied. A transition from mild wear under 1 N and 4 N to severe wear at 10 N occurred. Scanning electron microscopy revealed that abrasion is the dominant wear mechanism. Against steel, μ decreased with increasing load and the wear rates were low, under all applied loads. The morphologies of the worn surfaces against steel were characterized by the appearance of a rippled layers. Atomic force microscopy and Raman spectroscopy were used to propose a possible formation mechanism of such patterns. X-ray photoelectron spectroscopy revealed the rippled surfaces to be composed of Fe2O3 and a mixture of MoOx.

Microstructural effect on the tribo-corrosion behaviors of magnetron sputtered CrSiN coatings

Minimization of corrosion loss or corrosion-related loss is highly desirable for enhancing the tribo-corrosion resistance of physical vapor deposition (PVD) hard coatings. Various tribo-corrosion tests against Al2O3 counterparts combined with microscopic examinations, were used to study the tribo-corrosion behaviors of three typical kinds of magnetron sputtered CrSiN coatings. The dense and columnar coating exhibited superior tribo-corrosion resistance, with a lowest specific tribo-corrosion rate of 6 × 10−16 m3/N m and a lowest friction coefficient of ~0.14, where the dominant mechanism was considered as a layer-by-layer mechanical removal and the chemical corrosion was inappreciable. The porous and columnar coating failed for its poor intrinsic corrosion resistance. For the almost column-free coating, brittle fracture leaded to an increase of the corrosion component in the material wear, despite that the coating had the best intrinsic corrosion resistance. The comparison studies demonstrated that the dominant factors of the tribo-corrosion resistance are more complicated than purely mechanical wear or purely chemical corrosion; high compactness, effectively crack-controlled wear, and the dynamic equilibrium of depassivation-repassivation surfaces on the worn are indispensable for the highly tribo-corrosion resistant PVD hard coatings.

Tribological behavior of WC-Co HVAF-sprayed composite coatings modified by nano-sized TiC addition

The method of improving the properties of WC-Co thermally sprayed coatings by addition of nanostructured reinforcement for mechanical strengthening was explored in this research. Nanostructured WC-Co coatings were characterized by higher hardness than commercial counterparts, but wear tests in the literature have shown contrasting results, whereas bimodal coatings, where nanostructured components are mixed with conventional, micrometer-sized WC grains, exhibited enhanced abrasive and friction wear resistance, in comparison to coatings obtained exclusively from nano-sized powders. A mixed effect of matrix reinforcement by nanoparticles and strong fixing of the micron-sized WC grains was proposed as a possible reason for the enhanced wear resistance of bimodal coatings.A conventional, agglomerated and sintered WC-Co (83-17) feedstock powder was therefore blended with nano-sized TiC (40–100 nm) particles to obtain multimodal coatings containing a nanostructured reinforcement. The amount of TiC added into the powder mixture was in the range of 1–7 wt%. Powder mixtures were deposited onto carbon steel substrate using a High Velocity Air Fuel (HVAF) process. The dry sliding tribological behavior of the coatings was evaluated via ball-on-disk tests against Al2O3 counterparts. The tests were performed at room temperature as well as at 400 °C, with a sliding speed of 0.1 m/s, a sliding distance of 5000 m and a normal force of 10 N. The wear rates of the coatings and of the Al2O3 counterparts were measured separately, and friction coefficients were recorded during each test. The influence of TiC nano-particles on the sliding wear mechanisms was discussed in this work, based on an analysis of wear scars and wear debris through SEM + EDX and micro-Raman spectroscopy.

The effect of ceramic tribo-elements on friction and wear of smooth steel surfaces

The pin-on-disc dry sliding friction and wear experiments have been made on 42CrMo4 steel in contact with Si3N4, SiC, WC, Al2O3, and ZrO2 ceramic balls. The tests were carried out at sliding speeds of 0.16 m/s, 0.24 m/s, and 0.32 m/s. During the tests, the friction force was monitored as a function of time. Discs and balls wear was measured after the tests using a white light interferometer Talysurf CCI Lite and Altisurf 520 optical profilometer with a CL1 confocal probe. To decrease variations in the experimental results, during the tests, wear debris was continuously removed from the disc surfaces. It was found out that with Al2O3 counterpart the wear volume of the steel discs was the largest. However, the largest wear volume of the balls was observed for Si3N4 ceramic balls.

High Wear Resistance of Magnetron Sputtered Cr80Si20N Nanocomposite Coatings: Almost Independent of Hardness

Hardness has been popularly considered as an essential factor defining the wear resistance of hard coatings. Here, we report magnetron sputtered Cr80Si20N nanocomposite coatings, of widely varied packing densities, that exhibited identical specific wear rates, while the hardness changed over a wide range (from ~12 to ~36 GPa). All the Cr80Si20N coatings were free of extended and uninterrupted columnar boundaries, and retained low specific wear rates in the ball-on-plate sliding tests against Al2O3 counterpart with a normal load of 5 N (less than 3.0 × 10−16 m3/N m under ambient condition and less than 2.0 × 10−15 m3/N m under 3.5 wt% NaCl solution, respectively). Post examination reveals extensive interruption or termination of cracks in the wear tracks of the under-dense coatings, indicative of extrinsic toughening mechanisms by effective relief of local contact stress. Our results suggest that a critical role of toughening rather than hardening, played in enhancing the wear resistance of hard coatings, and thus would pave a way to develop highly wear-resistant coatings with a low hardness.

Response of a molybdenum alloy to plasma nitriding

A molybdenum alloy (TZM: 0.50 wt% titanium, 0.08 wt% zirconium and 0.02 wt% carbon with balanced molybdenum) was used to investigate its response to plasma nitriding in terms of layer formation and hardening at temperatures between 500 and 760 °C using various times. A thin hard nitride case plus a shallow diffusion zone was formed after plasma nitriding. The thickness of nitride layer increased with the treatment temperature and time. The nitrided surface of molybdenum alloy had a low coefficient of friction against the Al2O3 counterpart ball at ambient atmosphere and elevated temperatures, and the wear resistance of the surface was greatly improved. Molybdenum had a tendency to react with nitrogen to form a mixed nitride phases at the tested temperature range, and the TZM alloy had an activation energy of 330 kJ/mol.

Solution-processed ternary alloy aluminum yttrium oxide dielectric for high performance indium zinc oxide thin-film transistors

In this study, we evaluated the structural, chemical, and electrical properties of ternary alloy aluminum yttrium oxide (Al2-xYxO3) films prepared by employing a low-cost spin-cast technique. Al2-xYxO3 films annealed at 400 °C were found to possess smooth and excellent insulating characteristics compared to their binary Al2O3 or Y2O3 film counterparts. This superior performance of the Al2-xYxO3 films as a gate insulator can be explained based on structure stabilization from the cation alloying mixing effect. The amorphous indium zinc oxide (a-IZO) thin-film transistor (TFT) with the ternary alloy Al0.45Y1.55O3 film exhibited a high mobility of 52.9 cm2/V, a low subthreshold gate swing of 0.19 V/decade, a threshold voltage of −0.51 V, a high ION/OFF ratio of 4 × 106, and good hysteresis-free stability, suggesting that the solution-based Al0.45Y1.55O3 dielectric film is an attractive candidate as a gate dielectric for high-performance and low-cost a-IZO TFTs.

High temperature wear performance of HVOF-sprayed Cr3C2-WC-NiCoCrMo and Cr3C2-NiCr hardmetal coatings

A novel Cr3C2-WC-NiCoCrMo and commercial Cr3C2-NiCr thermal spray-grade powders with particle size of −45+15μm were prepared by an agglomeration and sintering process. Cr3C2-WC-NiCoCrMo and Cr3C2-NiCr coatings were deposited by high velocity oxygen fuel (HVOF) spraying. The fundamental properties of both coatings were evaluated and friction wear test against Al2O3 counterbodies of both coatings at high temperatures (450°C, 550°C, 650°C) were carried out ball-on-disk high temperature tribometer. All specimens were characterized by optical microscopy, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy with energy dispersive spectroscopy (SEM/EDS) and 3D non-contact surface mapping profiler. The results have shown that the Cr3C2-WC-NiCoCrMo coating exhibited lower porosity, higher micro-hardness compared to the Cr3C2-NiCr coating. The Cr3C2-WC-NiCoCrMo coating also exhibited better wear resistance and higher friction coefficient compared to the Cr3C2-NiCr coating when sliding against the Al2O3 counterpart. Wear rates of both coatings increased with raising temperature. Both coatings experienced abrasive wear; hard phase particles (WC and Cr3C2) with different sizes, distributed in the matrix phase, will effectively improve the resistance against wear at high temperatures.

Hard and wear resistant VB2 coatings deposited by pulsed DC magnetron sputtering

Vanadium boride (VB2) coatings have been less concerned, although they have advantages of super-hardness as well as self-lubrication. In this study, VB2 coatings were deposited by pulsed DC magnetron sputtering, and the effect of deposition parameters on the microstructure, mechanical and tribological properties of coatings were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), nano- and micro-indentation, and ball-on-disk tribometer. Under the growth condition with high adatom mobility, the coatings exhibited complete (001) orientation and dense texture. A nanocomposite structure that nanocolumns were separated by a secondary phase was especially observed in the coating deposited at 773 K. Both hardness and intrinsic stress of the coatings were improved substantially by increasing the substrate bias or the pulse frequency. The coating deposited at −30 V and 250 kHz, had the hardness of ∼43.6 GPa and the compressive stress of ∼2.0 GPa. Under the load of 2 N, the friction coefficients were ∼0.7 against Al2O3 counterpart, and the wear rates were in the range of 7 × 10−16–8 × 10−16 m3/N m. Under the load of 5 N, the coatings with low intrinsic stress showed better wear resistance, with the wear rate of 10−16 m3/N m.