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High-entropy alloy (HEA) coatings exhibit high hardness and high strength and have attracted wide attention. The improvement in the tribological performance, such as low friction coefficient and wear rate, is a longstanding challenge and is critical in the broad application of HEA coatings. In this study, a series of CrNbTiMoZr coatings was synthesized using the direct current magnetron sputtering by tuning substrate bias voltages. A continuous transformation in the structure from the amorphous phase to the face-centered cubic phase was observed in HEA carbide coatings. The residual stress and the hardness monotonously increased with the substrate bias voltage. The addition of carbon reduced the friction coefficient and the wear rate of HEA coatings. Consequently, we achieved a HEA carbide coating at −200 V combined with high hardness (17.4 GPa), low friction coefficient (0.3–0.4), and low wear rate (1.18 × 10−6 mm3·N−1·m−1). This study provides a new guidance for designing new HEA coatings with high strength and low wear.

CrNbSiTiZr high-entropy alloy films with different substrate bias voltages (from 0 V to–200 V) were fabricated on 304 stainless steel and Si substrates by radio-frequency magnetron sputtering. The microstructure, mechanical properties, tribological performance, and corrosion resistance were investigated in detail. Results show that all the as-fabricated films exhibit an amorphous phase. The columnar structure becomes featureless with the increase substrate bias due to re-sputtering effects and densification of the film. The film deposited at the bias of –50 V has a high residual compressive stress of –0.82 ± 0.04 GPa and a high hardness of 12.4 ± 0.3 GPa. The wear mechanism of the film is adhesive and slightly abrasive at low negative bias (0, –50, and –100 V), and that at high negative bias (–150 and –200 V) is abrasive. Polarization and electrochemical impedance spectrum measurements reveal that all films have a superior electrochemical corrosion resistance to the 304 stainless steel in 3.5 wt% NaCl solution, which indicates that the film can effectively protect substrate from corrosion. The values of Ecorr, icorr, and Rpo of the film deposited at the bias of –50 V are −283 mV, 0.0178 μA/cm2, and 2.084 × 106 Ω‧cm2, respectively.

Friction stir processing (FSP) was successfully performed on ultra-light dual-phase LZ91 Mg Li alloy, which provided a chance to study the microstructure and texture evolution of this alloy during severe plastic deformation. The results showed that LZ91 Mg Li alloy could be processed successfully with 200–400 rpm, 25 mm/min, and water cooling during FSP. No defects were observed on the surface and in the cross-section. The microstructure was strongly influenced by the material flow modes during FSP. Two greatly phase refinement regions were found in the stir zone where the α-Mg and β-Li phases were refined to submicron scale and homogeneously mixed. Maelstrom currents flow between two threads on the pin triggered this phase fragment. The high rotation rate of FSP leads to a remarkable recrystallization and grain growth due to the high heat input. The severe plastic deformation caused a phase transformation inside the refined α-Mg phase. The new phases enriched Li element exhibited a coherent relationship with the matrix. It shows that FSP promoted the short-term diffusion in refined α-Mg.

A rolled and recrystallized commercially pure Zr sheet was β-solution treated and then cooled at two rates, i.e. air cooling (AC) and furnace cooling (FC). Microstructures and textures of original and β-cooled specimens were characterized by use of electron channeling contrast imaging, electron backscatter diffraction and X-ray diffraction techniques. Results reveal a novel phenomenon, i.e. the concurrent inheritance of microstructure and texture in the FC specimen cooled at a very slow rate. In contrast, for the AC specimen with faster cooling, typical lamellar α phases are obtained with relatively scattered texture. Based on comparatively crystallographic and thermodynamic analyses, reasons accounting for microstructure and texture differences in both cases are discussed, highlighting the significant role played by the variant selection behavior. It is postulated that increasing cooling rates should be more feasible to change the transformed texture in Zr materials.

Two thermal-mechanical regimes were selected to investigate the recrystallization process of an as-extruded AA2099 alloy. Specimens were deformed to strains of 0.4, 0.7 and 0.9 at 520 °C and strain rates of 0.001 s −1 and 0.1 s −1 , respectively. Electron backscatter diffraction (EBSD) and electron channeling contrast (ECC) imaging were performed for all specimens to characterize their textures and microstructures. The texture evolution is reflected by variation of deviation angle between and extrusion directions, which appears to progressively approach ~35° ( //ED) due to lattice rotation in both regimes before e =0.7. The reconstruction maps indicate that the nucleation of recrystallization is related to strain incompatibility near grain boundaries. The textures of specimens deformed to strain of 0.9 exhibit significant difference between the two regimes, i.e the //ED fiber texture is comparatively weakened by recrystallization nuclei growth at the lower strain rate (0.001 s −1 ). ECC images for specimen deformed at 0.001 s −1 reveal significant differences in size and volume fraction of Al 3 Zr particles between recrystallized and unrecrystallized regions, suggesting remarkable influence of boundary migration on the thermal stability of Al 3 Zr particles.

In order to manifest the influence of specific microstructural component on the development of severe localized corrosion in an AA2099 aluminum–lithium alloy, the corrosion behavior of the alloy subjected to solution heat treatment, cold working and artificial ageing was investigated. Immersion testing and potentiodynamic polarization were employed to introduce localized corrosion; scanning electron microscopy and transmission electron microscopy were used to characterize the alloy microstructure and corrosion morphology. It was found that the susceptibility of the alloy to severe localized corrosion was sensitive to thermomechanical treatments. Additionally, the state of alloying elements influenced the mechanism of localized corrosion propagation. Specifically, the alloy in T8 conditions showed higher susceptibility to severe localized corrosion than that in other conditions. During potentiodynamic polarization, the alloy in solution heat-treated and T3 conditions displayed crystallographic corrosion morphology while the alloy in T6 and T8 conditions exhibited selective attack of grain interiors and grain boundaries in local regions.

Specimens cut from a rolled tin bronze sheet were annealed at 400–800 °C for 1 h and evolution of their microstructures was then characterized in details by electron channeling contrast imaging and electron backscatter diffraction techniques. Particularly, statistics on special boundaries (SBs) with Σ ≤ 29 and network connectivity of random high angle boundaries (HABs) in the annealed specimens were examined to probe optimization potentials of grain boundary character distribution (GBCD) for this material. Results show that the deformed microstructure in the as-received material begins to be recrystallized when the annealing temperature increase to 500 °C and average grain sizes surge with further increasing temperatures. As a result of the recrystallization, a large number of annealing twins (with Σ3 misorientation) are produced, leading to remarkably increased fractions of SBs (fSBs). Thanks to preexisting dense low angle boundaries, the majority of SBs in the 500 °C specimen with only partial recrystallization are Σ3ic (incoherent) boundaries, which effectively disrupt connectivity of random HABs network. Although the fSBs can be further increased (up to 72.5%) in specimens with full recrystallization (at higher temperatures), the Σ3ic boundaries would be replaced to some extent by Σ3c (coherent) boundaries which do not contribute directly to optimizing the GBCD. This work should be able to provide clear suggestions on applying the concept of grain boundary engineering to tin bronze alloys.

In this work, the surface of a fully recrystallized Zr702 is treated by pulsed laser following which microstructural changes are investigated by use of electron backscatter diffraction and electron channeling contrast imaging techniques. The pulsed laser treatment results in three distinctly different microstructural features from the surface to the substrate: fine α plates with a few hundred nanometers in width (zone I), irregular-shaped grains with varied sizes (zone II), and essentially unchanged equiaxed grains (zone III). The α plates result from rapid phase transformation due to easy heat extraction of the pulsed laser with dense nanoscale twins inside those plates closer to the surface. The origin of the irregular-shaped grains is found to be related to insufficient recrystallization of antecedently formed α plates near the substrate. Hardness tests reveal highest value (∼356.7 HV) near the surface in zone I and the lowest value (∼165.2 HV) in zone II. Reasons accounting for the difference are discussed in terms of various microstructural characteristics induced by the pulsed laser surface treatment.

The deposition parameters of high-entropy alloy films significantly influence their performance due to effective control of their microstructure. Thus, these parameters have become a research hotspot. In this study, CrNbTiMoZr high-entropy alloy films of amorphous or nanocrystalline solid solution were synthesized by direct current magnetron sputtering on silicon wafers and 304 stainless steel under different substrate bias voltages. The films' microstructure and tribo-mechanical properties were studied in detail. Results showed that the microstructure of films transformed from columnar structure to featureless with increased substrate bias voltage. In the nanoindentation test, the film deposited at −150 V exhibited the highest hardness of 9.7 GPa. Nevertheless, the CrNbTiMoZr films displayed excellent tribological properties under low bias voltage. Overall, our findings can guide the design of other novel high-entropy alloy films.

Peeling is considered to be the main technical obstacle for coating applications. There are many factors that affect the peeling process of coatings. The interfacial properties of the coating and substrate play a crucial role in the peeling process. In this study, the work of adhesion (Wad), interface energy (γi), and electronic structure of diamond (001)–Si(001) and Si(001)–Ti (0001) interface models have been investigated using first-principles calculations. The results indicate that the diamond (001)–Si(001) interface exhibits larger Wad and smaller γi values when compared with the Si(001)–Ti (0001) interface. However, the Wad of diamond–diamond, Si–Si, and Ti–Ti is 15.92, 4.92, and 3.84 J/m2, respectively. When compared with the two interface models, the Wad of Ti–Ti is the smallest, indicating that it will be the first to undergo deformation during the shear process. In addition, analysis of the charge density difference and density of states revealed that the interfacial Ti–Si bond is a covalent–metallic bond, which is much weaker than the Si–C bond (covalent bond), and therefore, the Si(001)–Ti (0001) structure is more inclined to delaminate.

The structure and corrosion resistance of anodized AA2099-T83 Al-Cu-Li alloy after layered double hydroxides (LDH) sealing and hot water sealing (HWS) were studied using scanning electron microscopy (SEM), X-ray diffraction, electrochemical impedance spectroscopy (EIS) and neutral salt spray test (NSST). Particularly, the corrosion resistance of the LDH-based coating system with reduced anodic film thicknesses was compared with that of the normal HWS-based coating system. It was found that LDH could be formed over the surface and within the pores of the anodic film within 30 min. With other conditions the same, the LDH-sealed alloy passed 1000 h of NSST without evident localized corrosion, contrasting with the HWS alloy, which showed severe localized corrosion after NSST for 120 h. Further, when the anodic film thickness was reduced from 3.7 to 1.3 μm, the LDH-sealed alloy still showed much better corrosion resistance than the normal HWS alloy. This work clearly demonstrates that it is possible to obtain high corrosion resistance for the anodized AA2099-T83 Al-Cu-Li alloy at much reduced anodic film thickness.

Diamond-like carbon films (DLC) with different silicon contents combined with W interlayer are deposited by plasma-assisted reactive magnetron sputtering. The structures and high-temperature tribological properties of the films are investigated. The results reveal that the pure DLC film is worn out at 400 °C because of graphitization, while the Si-DLC film with Si content of 4.56 at.% keeps low friction coefficient (0.2–0.05) at high temperature up to 500 °C. The 14.56 at.% Si-DLC film failed at 500 °C induced by the formation of SiO2. The improved high-temperature tribological performance of the 4.56 at.% Si-DLC film is attributed to the tribochemistry of W interlayer at 500 °C which formed a film composed of tungsten oxides and carbide.

The hot rolling microstructures and textures were strongly influenced by the prior heat treatments. Various prior heat treatments were utilized to investigate the effects of precipitates on microstructure and β-fiber texture after hot rolling. For the microstructure, the extent of planar slips strongly affects the hot rolling microstructure. Shear events of δ′ particles resulted in massive shear bands, which were the consequence of extensive planar slips. T1 platelets and T2 rods would homogenize the dislocation slips, resulting in a homogenous microstructure. The abnormal microstructure in overaged specimens was ascribed to successive work softening in the precipitation free zones (PFZs). With respect to hot rolling texture, the kind of precipitates in the matrix affected the intensities and locations of the β-fiber tube in Euler space, especially in the section between Copper and S orientation.

The erosion behavior of a QAl9-4 alloy as a ship propeller material was investigated. The effects of the solution, the impact angles and the sand content were considered. The test results demonstrate that the mass loss of the alloy in 3.5 wt% NaCl solution is 1.35 times that in tap water, due to the corrosive effect of Cl−. The mass loss of the alloy increases as the impact angle increases up to ~ 30° and consequently decreases as the impact angle increases. Also, this feature is typical for the ductile metal behavior. At the impact angle of 0°, this feature is associated with the predominant erosion mechanisms, such as shallow plowing and surface fatigue; at 30°, this feature is micro-cutting, deep plowing and surface fatigue; and at 45°, it becomes indentation accompanied by extruded lips. The mass loss and surface roughness of the alloy increase as the sand content increases under the testing conditions.

The anodizing behavior of iron-containing intermetallic particles in AA2099 aluminum-lithium alloy and their effect on structure and corrosion resistance of the anodic film were investigated using electrochemical measurements and scanning electron microscopy. High-copper-containing Al-Fe-Mn-Cu particles (HCCPs) dissolved preferentially through dealloying at ∼ 0 V (vs. saturated calomel electrode) in a tartaric-sulfuric acid solution, at 22, 37 and 42◦C, leading to formation of copper-rich nanoparticle of 50–200 nm diameters. They dissolved completely under normal anodizing conditions, resulting in cavity defects of micrometer dimensions in the anodic film and sunken regions in the alloy substrate immediately beneath the dissolved HCCPs. Immersion testing of the anodized alloy in 3.5% NaCl solution for 24 h indicated that localized corrosion of the anodized alloy predominantly developed at the site containing dissolved HCCPs at the film/alloy interface. It is suggested that HCCPs play a critical role in controlling the corrosion resistance of the anodic film formed on AA2099 aluminum-lithium alloy.

The micro-scale abrasive wear behavior of TiZrNbTa (TZNT) alloy in Hank’s solution and distilled water was studied using the TE66 machine. The effect of load and sliding distance was considered. The results of experiments show that the wear volume of the TZNT alloy is increased with increasing distance because of the greater damage, but the wear volume is not present the same regularity as the increase of load due to the effect of several factors. Only three-body abrasive wear is present at the lower load, while the mixed wear mechanism includes three-body and two-body abrasive wears at the higher load. Through observation, the wear appears under the same sliding distance at various simulated body fluids. The wear appearance is related to the wear mechanism. For wastage map, under the conditions of this paper, the majority of the area is medium wastage, the rest is low wastage, and there is no high wastage. The wastage map is related to the wear volume of the alloy under different conditions.

Localized corrosion in an AA2099-T83 aluminum–lithium alloy has been correlated with localized plastic deformation (LPD) introduced by cold working. The high population density of dislocations in the slip bands associated with LPD promoted preferential precipitation of needle-shaped T1 (Al2CuLi) phase during artificial aging. Consequently, preferential attack of the electrochemically active T1 phase in corrosive environment resulted in selective corrosion of the bands, leading to the development of the characteristic morphology of narrow, parallel volume of corrosion. Copyright © 2015 John Wiley & Sons, Ltd.

The corrosion behavior of intermetallic particles and their role in the process of localized corrosion in AA2099-T83 aluminum–lithium alloy has been investigated. It was found that both high- and low-copper containing Al–Fe–Mn–Cu-(Li) particles could result in superficial pits on the alloy, and the high level of lithium in the high-copper-containing particles rendered them electrochemically more active than the low-copper-containing particles. Additionally, severe localized corrosion was found not to be directly related to the distribution of constituent particles in the alloy. The findings are not only relevant to the understanding of corrosion mechanism but also beneficial to the evaluation of thermomechanical treatments of the alloy.

A 10 1 ¯ 1 twin relationship between α plates was repeatedly reported in β-quenched Zr alloys in literature. In this paper, however, we demonstrate that the special twin relationship between α plates should be correctly identified as one of five common Burgers misorientations. The shared plane between two α plates with such a Burgers misorientation is determined to be 10 1 ¯ 1.06 . Such a clarification helps to reach more accurate understanding of boundary characteristics of β-quenched microstructure in Zr alloys.

A Cu–25Cr alloy prepared by vacuum induction melting method was treated by the high current pulsed electron beam (HCPEB) with pulse numbers ranging from 1 to 100. Surface morphologies and microstructures of the alloy before and after the treatment were investigated by scanning electron microscopy and X-ray diffraction. The results show that significant surface modification can be induced by HCPEB with the pulse number reaching 10. Craters with typical morphologies on the Cu–25Cr alloy surface are formed due to the dynamic thermal field induced by the HCPEB. Micro-cracks, as a unique feature, are well revealed in the irradiated Cu–25Cr specimens and attributed to quasi-static thermal stresses accumulated along the specimen surface. The amount of cracks is found to increase with the pulse number and a preference of these cracks to Cr phases rather than Cu phases is also noted. Another characteristic produced by the HCPEB is the fine Cr spheroids, which are determined to be due to occurrence of liquid phase separation in the Cu–25Cr alloy. In addition, an examination on surface roughness of all specimens reveals that more pulses will produce a roughened surface, as a result of compromising the above features.

In this study, friction stir processing (FSP) has been used to fabricate aluminum alloy 7075 based surface hybrid composite with a mixture of SiC and MoS2 reinforcement particles. The surface hybrid composite layer has been successfully fabricated at different content ratio of SiC and MoS2 particles by one-pass FSP. The SiC and MoS2 particles were distributed almost homogeneously over the nugget zone. The average Vickers hardness at nugget zone increased to about 190 at 100% SiC, and it decreased with increasing the MoS2 content ratio in reinforcement. The wear weight loss of the surface hybrid composite depended on the applied load and the relative content ratio of SiC and MoS2 particles. The surface hybrid composite of 75% SiC and 25% MoS2 showed superior wear resistance among all tested samples. The wear failure was attributed to the combination of the combination of abrasive wear and delamination.

The electrochemical corrosion behaviour of biomedical Ti–25Nb–3Mo–3Zr-2Sn (TLM) alloy was investigated in various simulated body fluids at 37±0·5°C utilising potentiodynamic polarisation and current–time curves. The Ti–6Al–4V (TC4) alloy was also investigated to make a comparison. The different simulated body fluids comprised of 0·9%NaCl saline, Hank’s and Ringer’s solution were employed. The effect of heat treatment on the electrochemical behaviour of the TLM alloy was also considered. It was discovered that all the test specimens were passivated once immersed into the simulated body fluids. It was also found that the TLM alloy has poorer corrosion resistance in Hank’s solution, due to the chemical composition of the Hank’s. After different heat treated, the TLM alloy had different phases and microstructure, and the corrosion behaviour of the TLM alloy was different. In this study, after the heat treatment of 760°C/1 h/AC+550°C/6 h/AC, the TLM alloy had better corrosion resistance. Owing to the c...

The micro-scale abrasion behaviors of surgical implant materials have often been reported in the literature. However, little work has been reported on the micro-scale abrasive wear behavior of Ti–25Nb–3Mo–3Zr–2Sn (TLM) titanium alloy in simulated body fluids, especially with respect to friction pairs. Therefore, a TE66 Micro-Scale Abrasion Tester was used to study the micro-scale abrasive wear behavior of the TLM alloy. This study covers the friction coefficient and wear loss of the TLM alloy induced by various friction pairs. Different friction pairs comprised of ZrO2, Si3N4 and Al2O3 ceramic balls with 25.4 mm diameters were employed. The micro-scale abrasive wear mechanisms and synergistic effect between corrosion and micro-abrasion of the TLM alloy were investigated under various wear-corrosion conditions employing an abrasive, comprised of SiC (3.5 ± 0.5 μm), in two test solutions, Hanks' solution and distilled water. Before the test, the specimens were heat treated at 760 °C/1.0/AC + 550 °C/6.0/AC. It was discovered that the friction coefficient values of the TLM alloy are larger than those in distilled water regardless of friction pairs used, because of the corrosive Hanks' solution. It was also found that the value of the friction coefficient was volatile at the beginning of wear testing, and it became more stable with further experiments. Because the ceramic balls have different properties, especially with respect to the Vickers hardness (Hv), the wear loss of the TLM alloy increased as the ball hardness increased. In addition, the wear loss of the TLM alloy in Hanks' solution was greater than that in distilled water, and this was due to the synergistic effect of micro-abrasion and corrosion, and this micro-abrasion played a leading role in the wear process. The micro-scale abrasive wear mechanism of the TLM alloy gradually changed from two-body to mixed abrasion and then to three-body abrasion as the Vickers hardness of the balls increased.

To predict the evolutions of turning forces, temperatures and tool wears, finite element method (FEM) models for micro-turning by using cubic and spherical single-grain ceramic tools have been established. Single-grain ceramic tools with different grain sizes and shapes have been investigated. Initial and boundary conditions of numerical simulations have been adopted and the coefficients of archard models for different grain sizes have been obtained by reciprocating friction tests. The results are summarized as follows. Wear depths of spherical ceramic tools with size 1 μm are bigger than those caused by cube ceramic tools with the same conditions. The predicted maximum turning forces for globular single-grain tools are bigger than those of cube single-grain tool. Also, turning forces of three directions for cube single-grain ceramic tools with size 10 μm are significantly higher than those of single-grain ceramic tools with 1 μm. Wear depths increase sharply with the increase of single-grain ceramic tool sizes, and wear depths of cube single-grain ceramic tools with size 10 μm are bigger than those of 1 μm cube single-grain tool with the same turning condition. The obtained results would provide the fundamental and practical guidelines of single-grain ceramic tools choice for the hard micro-turning.

Turning speed, depth of cut, and feed rate are only considered for the traditional turning tool life model of nano ceramic tool. But installation and geometry parameters of the tool and the material characteristics for manufactured materials have not been taken into account for ordinary tool life model. Three-dimensional numerical simulations of turning process using nano ceramic tool have been researched by finite element method (FEM) and archard wear model in the research. The influences of tool shapes, tool rake angle and manufactured metal properties on the contact stresses, sliding speeds, and the temperature have been discussed. A new type of tool life model for nano ceramic tool has been established which include turning speed, depth of cut, the feed amount and other factors. The influences of tool shape, tool rake angle and manufactured metal properties, as well as other turning parameters on tool wear life have been studied deeply. Turning experiments have been done. The preliminary tool life prediction model and evaluation system based on the finite element simulation for nano ceramic tool turning hard steel have been constructed. The model can provide fundamental and practical guidelines of the hard turning.

Hierarchical γ-AlOOH with siamesed straw-sheaf morphology was synthesized by a simple template-free hydrothermal route. The obtained hierarchical γ-AlOOH structure was assembled by nanowire and exhibited large Brunauer–Emmett–Teller (BET) surface area of 163 m2/g and pore volume of 0.30 cm3/g. The adsorption efficiency of the samples with Congo red (CR) was studied by UV–vis spectroscopy. The sheaflike hierarchical γ-AlOOH shows an extremely high Congo red (CR) removal efficiency from waste water showing almost complete removal within 10 min. The maximal adsorption reaches 99 mg/g.

In this work, we report on synergistic effect of chloride ion and albumin on the corrosion of pure magnesium through corrosion tests. We show that the adsorption of albumin mainly affects the anodic polarization behavior of pure magnesium in NaCl solution. Low concentration of albumin enhances the reaction reactivity of pure magnesium and the initial evolvement of hydrogen at the initial immersion time. Addition of 1 g/L albumin provides limited corrosion control for pure magnesium in NaCl solution. In comparison with low concentration albumin, addition of 10 g/L albumin can effectively inhibit the further dissolution of pure magnesium in test solutions with NaCl concentration of 0.2–0.8 wt.%, but this effect lowers gradually with increasing the concentration of chloride ion.

Fluorinated diamond-like carbon (DLC) films have good biocompatibility and bloodcompatibility. When they are used in cardiac valve prosthesis, the wear resistance has to be investigated in more detail. In this paper, the tribological behavior of fluorinated DLC films under different loads and sliding speeds in bull serum albumin (BSA) solutions were investigated by ball-on-disc friction tests. The results show that the proteins in BSA solutions promoted the DLC film adhesion failure because of the increased friction coefficients and accelerated corrosion rate. The fluorine doping can lower the corrosion rate of DLC film, thereby improving the adhesion stability and wear resistance of DLC in BSA solutions.

Impacts of four amino acids, viz. lauroyl glutamine, lauroyl glycine, lauroyl alanine, and oleoyl glycine, on biodegradability, oxidation stability, and corrosiveness of HVI 350 mineral lubricating oil were studied. The biodegradabilities of neat lubricating oil and its formulations with the amino acids were evaluated on a biodegradation tester and the microbial characters in the biodegradation sewage observed through a microscope. Furthermore, the oxidation stability and corrosiveness of neat oil and the formulated oils were determined on an oxidation tester and a copper strip corrosion tester, respectively. The results indicated that the amino acids markedly enhanced biodegradability of unreadily biodegradable mineral lubricating oil by promoting microbe production in the biodegradation processes, thus accelerating biodegradation of mineral lubricating oil. On the other hand, the amino acids to some extent retarded oxidation of mineral lubricating oil by inhibiting increases of acidity, viscosity and in...

PurposeThe purpose of this paper is to understand the impacts of oleoyl glycine on biodegradation, friction and wear performances of a mineral lubricating oil.Design/methodology/approachThe biodegradabilities of a neat oil and its formulations with oleoyl glycine were evaluated on a biodegradation tester and the microbial characters in the biodegradation sewage observed through a microscope. Also, the friction and wear performances of neat oil and the formulated oil were determined on a four‐ball tribometer. The morphologies and tribochemical features of the worn surfaces were analyzed by scanning electron microscopy and X‐ray photoelectron spectroscopy.FindingsOleoyl glycine markedly enhanced biodegradation of unreadily biodegradable mineral oil and effectively improved its anti‐wear and friction‐reducing abilities. The enhancement of biodegradability of the mineral oil was preliminarily ascribed to the increment of microbial populations in the biodegradation processes, while the improvement of anti‐wear and friction‐reducing abilities was mainly attributed to the formation of a boundary adsorption film of oleoyl glycine on the friction surfaces.Originality/valueOleoyl glycine is a biodegradable and low eco‐toxic compound. The authors' work has shown that oleoyl glycine is effective in improving biodegradability and tribological performances of mineral lubricants. Enhancing biodegradability of petroleum‐based lubricants by additives is a new attempt. The paper has significance for improving ecological and tribological performances of mineral lubricants, even for developing petroleum‐based biodegradable lubricants.

Alumina matrix composites containing 5 and 10 wt% of ZrO 2 were sintered under 100 MPa pressure by spark plasma sintering process. Alumina powder with an average particle size of 600 nm and yttria-stabilized zirconia with 16 at% of Y 2 O 3 and with a particle size of 40 nm were used as starting materials. The influence of ZrO 2 content and sintering temperature on microstructures and mechanical properties of the composites were investigated. All samples could be fully densified at a temperature lower than 1400 °C. The microstructure analysis indicated that the alumina grains had no significant growth (alumina size controlled in submicron level 0.66–0.79 μm), indicating that the zirconia particles provided a hindering effect on the grain growth of alumina. Vickers hardness and fracture toughness of composites increased with increasing ZrO 2 content, and the samples containing 10 wt% of ZrO 2 had the highest Vickers hardness of 18 GPa (5 kg load) and fracture toughness of 5.1 MPa m 1/2 .

Tribology of bio-implants is a major limiting issue in materials selection of the appropriate implant for the appropriate patient activity level [1]. For example, for wear of replacement hip joints, wear caused by the sliding action of the bearing surface of the femoral head against the counterface occurs in synovial fluid. Hence, the major challenge of materials scientists in replacement of such materials is to optimize the wear resistance, minimize any potential tribo-corrosion interaction and adverse biocompatibility effects caused by such interactions and reduce wherever possible any adsorption of wear debris into the surrounding tissue. In Tribology, and in Aqueous Corrosion, various mapping methodologies[1-7] have been developed to characterize the various interactions. The wear map developed by Lim and Ashby [2] classifies the wear regimes at ambient conditions in terms of applied load and velocity, illustrating significant temperature rises and attendant corrosion reactions as a function of the tribological variables. The Pourbaix diagram[8] considers various transitions in terms of potential and pH, therefore presenting corrosion regimes as a function of the driving force of the electrochemical reaction and the hydrogen ion concentration. In tribo-corrosion, there is an extensive recent literature combing the concepts of both approaches to construct tribo-corrosion maps [2-8]. Despite such work, there has been very little work carried out until very recently[9] on the construction of tribo-corrosion maps for application to bio-tribo-corrosion environments. This is despite the fact that such maps may have significant application in optimizing materials for specific patient activity/mass combinations, all of which are important in selection of the most appropriate material combination in total replacement joint procedures. In studies of wear of candidate hip joint materials, it has been observed that particle concentration of wear debris can have an adverse effect on loosening of the joint, leading to osteolysis and potential revision of the replacement joint material [10]. In such cases, it is important to identify the effects of wear debris on the tribo-corrosion mechanism [12]. Assessing the effects of such particle concentrations with load is also of significance as it will indicate what dependency, if any, particle concentration has at various body masses as defined by variation of applied load. Hence, in this paper, the effect of applied load and abrasive concentration were assessed at a range of applied loads for Ti rotating against an inert Zirconia ball, in which abrasive particles of SiC were entrained in Hanks solution. The results were used to construct micro-abrasion-corrosion maps for application to biological environments. The significance of the bio-tribo-corrosion map in identifying mechanisms of wastage and the extent of synergy between the tribological and corrosion processes is addressed in this paper.

The preparation of ultrafine-grained alumina ceramics by the fast sintering technique Self-propagating High-temperature Synthesis plus Quick Pressing (SHS-QP) method and spark plasma sintering (SPS) technique was reported. The effects of different heating rates (SHS-QP-1600 °C/min, SPS-200 °C/min) on the preparation of ultrafine structure were compared. The densification and grain growth as a function of sintering time and temperature were discussed. Within a short sintering time (

The in vitro degradation behaviour of Mg–Ca alloy was studied in the presence of albumin by in-situ observation, hydrogen evolution method and various electrochemical techniques. The corrosion and hydrogen evolution rates decreased and the formation of filiform corrosion induced by Cl � was also significantly inhibited due to the adsorption of albumin molecule. Moreover, the higher the concentration of albumin, the higher is the inhibitive effect. The EIS results further show that addition of albumin enhanced the charge transfer resistance and film resistance at the open-circuit potential. The synergistic effect of the negatively charged adsorbed albumin molecule and OH � has been discussed.

A novel Ni-P-SiC composite coating was prepared by electroless plating in order to improve the corrosion capacity and wear resistance of AZ91D magnesium alloy. The influence of pH values on deposition rates and properties of the coatings was studied. The microstructure and phase structure of the Ni-P-SiC coatings were analyzed by scanning electron microscopy (SEM) and X-ray diffractometry (XRD). The corrosion and wear resistance performances of the coatings were also investigated through electrochemical technique and pin-on-disk tribometer, respectively. The results indicate that the composite coating is composed of Ni, P and SiC. It exhibits an amorphous structure and good adhesion to the substrate. The coatings have higher open circuit potential than that of the substrate. The composite coating obtained at pH value of 5.2 possesses optimal integrated properties, which shows similar corrosion resistance and ascendant wear resistance properties to the substrate.

The erosion-corrosion behaviour of QSn6 alloy used as propellers in marine environment was evaluated by erosion-corrosion experiments with/without cathodic protection, electrochemical tests and scanning electron microscope (SEM) observations. The analysis was focused on the effect of flow velocity. The dynamic polarization curves showed that the corrosion rate of the QSn6 alloy increased as the flow velocity increased, due to the protective surface film removal at higher velocities. The lowest corrosion current densities of 1.26 × 10−4 A cm−2 was obtained at the flow velocity of 7 m s−1. Because of the higher particle kinetic energies at higher flow velocity, the mass loss rate of the QSn6 alloy increased as the flow velocity increased. The mass loss rate with cathodic protection was lower than that without cathodic protection under the same conditions. Also, the lowest mass loss rate of 0.7 g m−2 h−1 was acquired at the flow velocity of 7 m s−1 with cathodic protection. However, the increase rate of corrosion rate and mass loss were decreased with increasing the flow velocity. Through observation the SEM morphologies of the worn surfaces, the main wear mechanism was ploughing with/without cathodic protection. The removal rates of the QSn6 alloy increased as the flow velocity increased in both pure erosion and erosion-corrosion, whereas the erosion and corrosion intensified each other. At the flow velocity of 7 m s−1, the synergy rate (ΔW) exceeded by 5 times the erosion rate (Wwear). Through establishment and observation the erosion-corrosion mechanism map, the erosion-corrosion was the dominant regime in the study due to the contribution of erosion on the mass loss rate exceeded the corrosion contribution. The QSn6 alloy with cathodic protection is feasible as propellers, there are higher security at lower flow velocity, such as the flow velocity of 7 m s−1 in the paper.

Small amount of lauroyl glutamine was incorporated into HVI 350 mineral lubricating oil and the biodegradabilities of neat oil and the formulated oil in soils were evaluated. Thereafter, the biodegradation rate equations for the two lubricating oils were simulated based on the exponential model. The results indicated that lauroyl glutamine effectively promoted biodegradation of HVI 350 mineral lubricating oil. Under given test conditions, the exponential model well fitted the biodegradation of lubricating oils in soils. The biodegradation rate equation for HVI 350 mineral lubricating oil can be described as ln(St/S0) = –0.0155t, while that for the oil formulated with lauroyl glutamine as ln(St/S0) = –0.0235t. The biodegradation half-lives of neat oil and the formulated oils were 44.72 days and 29.50 days, respectively.

Spherical LaAlO 3 nanoparticles in a reverse microemulsion consisting of solution (water phase), Tween-80 and Span-80 (surfactant), n -butanol (cosurfactant, and cyclohexane (oil phase) were prepared. Precursor powders and calcined powders were characterized by differential thermal analysis (DTA), thermogravimetry analysis (TG), X-ray diffraction (XRD) and transmission electron microscopy (TEM). A pure perovskite LaAlO 3 formed when the precursor hydroxides calcined at 800 °C for 2 h. The particle size was about 50 nm and the shape of the monodisperse particles is spherical. The reverse microemulsion process can dramatically lower the crystallization temperature of LaAlO 3 about 700 °C than the classical solid-state reaction method.

Microstructures and microwave dielectric properties of 0.5Ba(Mg1/3Nb2/3)O3-0.5Ba(Ni1/3Nb2/3)O3 ceramics with x wt% CuO−x wt% MnO2 additions (x=0.25–1) prepared by conventional solid-state route were investigated. It is found that low level-doping of CuO-MnO2 can significantly improve the density of the specimens and their microwave dielectric properties. The relative density of 0.5Ba(Mg1/3Nb2/3)O3-0.5Ba(Ni1/3Nb2/3)O3 ceramics can be increased by 95% sintering at 1 330 °C due to the liquid phase effect. The second phase is not observed in ceramics with CuO-MnO2 addition. The parameter er increases with increasing sintering temperature, and Qf is effectively promoted by CuO-MnO2 addition. Higher CuO-MnO2 content would make τf value more positive. Meanwhile, er value of 30.5, Qf value of 63 200 GHz and τf value of 0.5 ppm/°C were obtained for 0.5Ba(Mg1/3Nb2/3)O3-0.5Ba(Ni1/3Nb2/3)O3 ceramics with 0.5 wt% CuO-0.5 wt% MnO2 addition sintered at 1 330 °C for 4 h.

Nanocrystalline Ba(Mg1/3Nb2/3)O3 (BMN) powders were successfully synthesized through a modified combustion synthesis method by using Ba(NO3)2, Mg(NO3)3·6H2O and Nb2O5 as starting materials. Gel precursor and calcined powders were characterized by thermogravimetric (TG), differential scanning calorimetry (DSC), X-ray powder diffraction (XRD) and transmission electron microscopy (TEM). The results demonstrate that pure perovskite Ba(Mg1/3Nb2/3)O3 powder formed at 800 °C for 2 h. And the crystallite size was about 40 nm. The specimen sintered at 1550 °C for 12 h shows 96.3% of the theoretical density and gave the excellent microwave dielectric properties: ɛr = 31.3 and Qf = 71,800 GHz.

The mechanical characteristics of the macro-arc oxidation (MAO) coating on Mg alloy AZ91 were examined by means of nano scratch tester. The corrosion and erosion corrosion behavior of AZ91 with and without MAO coating were investigated by using potentiodynamic electrochemical technique and micro-abrasion tribometer in simulated body fluids, respectively. The influence of HCO 3 − ions on the erosion corrosion was discussed. The results show that the coating and its substrate are in a pronounced bond. The MAO coating increases 1–2 orders of magnitude of the corrosion resistance of AZ91 alloy. HCO 3 − ions enhance the corrosion rates of the AZ91 alloys more significantly than the alloys with MAO coating. However, there exists an obvious passivation process of AZ91 without coating in the HCO 3 − solutions. Moreover, an MgCO 3 film formed in HCO 3 − containing solutions leads to an enhancement in micro-wear resistance. MAO coating deteriorates the erosion corrosion resistance of AZ91 alloy due to the formation of oxidation debris resulted from the broken MAO coating.

Effect of preparation methods on microstructures and microwave dielectric properties of Ba(Mg1/3Nb2/3)O3 ceramics was investigated. Ba(Mg1/3Nb2/3)O3(BMN) ceramics were prepared by the conventional mixed oxides method and the molten salt synthesis method. It was shown that the single-phase of BMN was obtained at 900 °C in the molten salt synthesis method. No single-phase BMN was obtained in the conventional mixed oxides method, although the calcining temperature was increased up to 1400 °C. BMN powders prepared by the molten salt synthesis method had better sinterability than that prepared by the conventional mixed oxides method. Because of the very different nature of the powders, different microstructures were observed. The molten salt synthesis method ceramics have a higher B-site ordering parameter (S) and larger grain size than that of the conventional mixed oxides ceramics at same sintering temperature. The variation of Qf, e r and τ f were also explained based on the difference in microstructures.

This review provided some recent progress of the research on corrosion mechanisms of magnesium and its alloys and a basis for follow-on research. Galvanic corrosion, pitting corrosion, intergranular corrosion (IGC), filiform corrosion, crevice corrosion, stress corrosion cracking (SCC), and corrosion fatigue (CF) were discussed. The influence of metallurgical factors such as alloying elements, microstructure and secondary phases, processing factors such as heat treatment and weld, and environmental factors including temperature, relative humidity, solution pH values and concentration on corrosion were discussed. In particular, a mechanism of pitting corrosion caused by AIMn particles was proposed. The corrosion properties of AZ91D weld material were investigated.

The fretting wear behavior of the AZ91D and AM60B magnesium alloys are investigated using a reciprocating fretting wear machine under dry conditions with different numbers of cycles, different normal loads, slip amplitudes and frequencies. The worn surfaces and wear debris were examined using scanning electron microscopy and optical microscopy in order to understand the predominant wear mechanisms of two magnesium alloys. The results indicate that the AZ91D alloy displays a lower friction coefficient and lower wear quantity than the AM60B alloy. The AZ91D shows a higher capability than AM60B in resisting crack nucleation and propagation. Both AZ91D and AM60B show similar friction and wear characteristics. The wear quantity increases with increasing normal load, but decreases with increasing frequency. The friction coefficient also decreases as the normal load is increased. Fretting frequency had little effect on the friction coefficient. In a long term, the fatigue wear and abrasive wear were the predominant wear mechanisms for AM60B and delamination wear, adhesive wear and abrasive wear for AZ91D.

The tribological characteristics of a magnesium alloy, AZ91D, were investigated in a sliding lubricating system using various N-containing compounds as lubricating additives on a Timken type tester against a bearing steel (AISI52100) ring. Results indicated that a significant improvement in the tribological performance exists using N-containing compounds as additives. The characteristics of anti-wear, anti friction and load-carrying capacity increased with an increase in the number of amidogen groups in amine molecules. Antiwear and antifriction characteristics were also observed with an increase in the length of the carbon chain in amide compounds. The amide showed a much better performance than the amine in terms of the tribological characteristics of the magnesium alloy. Electromicroscopy revealed that mild abrasive wear was a predominant wear mechanism of the magnesium alloy using an amine (or amide) additive; while the dominant wear mechanism was severe abrasive wear with severe material deformation using only base oil. Analysis showed the formation of a boundary film on the magnesium alloy. XPS analysis suggested the occurrence of tribo-chemical reactions between Mg and N-containing compounds with the formation of a chemically stable complex of magnesium and amine (or amide), as well as the formation of friction polymer.

The friction reduction and antiwear properties of a range of nitrogen- and sulfur-containing organic borates as oil additives in mineral oil were assessed using a Timken tester with a bearing steel ring against an AZ91D magnesium alloy block. X-ray photoelectron spectrometry and scanning electron microscopy were employed to examine the boundary film formed on the surface of the magnesium alloy block. The results show that the borate additives were effective at reducing the wear of magnesium. The acting mechanism of borate, which acted as additive in the magnesium-on-steel tribological system, was proposed. Copyright © 2006 John Wiley & Sons, Ltd.

Effects of four borates with different chemical structure on the tribological properties of magnesium alloy in sliding contact with bearing steel were investigated under boundary lubrication using a Timken type tester. It was shown that the borate without active element is not effective at reducing the friction and wear of magnesium alloy, and the borates containing nitrogen, sulfur and chlorine are effective at improving the tribological properties of magnesium alloy. Different active elements have different action characteristics at improving the tribological properties of magnesium alloy. The rubbed surfaces were investigated using Scanning Electron Microscopy (SEM) and X-ray Photoelectron Spectroscopy (XPS), the wear mechanisms were also proposed.