Slight Delamination Research Articles

High-Pressure-Assisted Large-Area (>2400 mm2) Sintered-Silver Substrate Bonding for SiC Power Module Packaging.

The emergence of new semiconductor devices puts forward higher requirements for packaging technology. Sintered silver technology has gradually developed into critical packaging technology in silicon carbide power module packaging due to its good heat dissipation performance and reliability. However, high sintering drive requirements, low sintering densification, and high thermal-mechanical stresses limit the application of sintered silver technology for large-area bonding. In this study, the high-pressure-assisted (≥10 MPa) large-area sintered-silver interconnection process between a substrate and baseplate was discussed. C-scan acoustic microscopy, warpage testing, and microanalysis were used to analyze the effects of drying methods, sintering pressure, and holding time on the sintered joints, and thermal fatigue reliability tests were conducted on large-area sintered silver joints. The results demonstrated that the quality of large-area sintered joints obtained via open-face convective drying is higher than that via close-face convective drying. Combining the performance of sintered joints and productivity, the recommended process condition is determined as follows: open-face convective drying, sintering temperature of 250 °C, sintering pressure of 15 MPa, and holding time of 5 min. Large-area sintered joints have outstanding reliability, with slight delamination of the sintered layer at the corners and no cracking after 1000 cycles of temperature cycling.

Effect of Ti on the microstructure and wear behavior of a selective laser melted Al-Cu-Mg-Si alloy

The elimination of hot cracking and enhancement of wear resistance have important practical significance for wide application of high-strength Al–Cu–Mg–Si series aluminum alloys fabricated by selective laser melting (SLM). In the present work, Ti was introduced to refine the microstructure of the selective laser melted Al–Cu–Mg–Si alloy, whose effect on the densification, microstructure evolution and wear resistance was explored in detail. After adding 0.6 wt % Ti, the microstructure transformed from coarse columnar grains to a fine duplex microstructure consisting of equiaxed and columnar grains, while microhardness of the SLM processed Al–Cu–Mg–Si alloy was increased from 148.9 ± 1.5 HV to 159.3 ± 1.7 HV, respectively. The wear behavior was evaluated on a ball-on-flat tribometer by sliding against 100Cr6 steel at room temperature. With the addition of Ti, the wear rate of SLM processed Al–Cu–Mg–Si was decreased by 49.6% for the applied load of 10 N. The refined heterogeneous microstructure helps to achieve strength-ductility synergy of the Al–Cu–Mg–Si–Ti alloy, which provides superior resistance to indentation behavior and initiation of cracks. The wear mechanism of the Al–Cu–Mg–Si alloy under the applied load of 10 N is abrasive wear and delamination wear, which for the Al–Cu–Mg–Si–Ti alloy is abrasive wear with slight delamination wear.

Subsurface deformation and wear behavior of 15% SiCp/2009Al aluminum matrix composite under cryogenic sliding

Subsurface deformation and wear behavior of 15% SiCp/2009Al aluminum alloy matrix composites induced by sliding wear at room and cryogenic temperature were investigated in the present work. An external cryogenic device was designed to produce a steady cryogenic environment in the course of experiments. Microstructure evolution in the subsurface layer and wear mechanism on the worn surface were analyzed by various characterization methods. The results showed that sliding at cryogenic temperature caused greater plastic deformation in the subsurface layer than that at room temperature. This can be attributed to the increased plasticity of aluminum alloy matrix and increased brittleness of SiC particles at cryogenic temperature, which can reduce the block effect of SiC particles on the deformation of aluminum alloy matrix. Wear rate of the composite material was significantly reduced after cryogenic sliding, whose decrement was much higher under higher applied load. Worn surface presented a lower surface roughness and higher surface evenness after sliding at cryogenic temperature. Wear mechanism was found to be transformed from severe oxidative, adhesive and delamination wear at room temperature, to slight delamination wear and cracking feature under cryogenic sliding. Deformation layer after cryogenic sliding played a role of nanocrystalline work-hardening layer, as the work-hardening rate and dislocation density were increased at cryogenic temperature. This is responsible for suppressing the generation of cracks and correspondingly improving the wear performance of material. This work also offers a new strategy for designing high surface-performance aluminum matrix composites via the method of self-adaptively forming nano hardening layer in cryogenic temperature environment.

HISTOLOGICAL CHANGES IN EXPERIMENTAL KERATITIS IN RABBITS AGAINST THE BACKGROUND OF STEM CELL ADMINISTRATION

The article highlights the results of histological research of experimental keratitis in rabbits after administration of allogeneic mesenchymal stem cells. These research results provide an opportunity for further study of the effect of allogeneic mesenchymal stem cells on clinical cases of keratitis in animals.
 A decrease in the function of the eye or its biological activity at the tissue level leads to the development of a serious eye disease - keratitis. The causes of keratitis are acute and chronic inflammatory processes in the parenchyma of the eye, ionizing radiation, degenerative changes, surgical operations, and others. Clinical manifestations of keratitis vary from redness to destructive damage of eye tissues. The use of complex stimulating therapy often smoothes the clinical picture of keratitis and for a short time stops inflammatory processes in the eye, which can later lead to a latent state of the eye. All this indicates that it is necessary to investigate the use of stem cells in eye diseases in animals.
 Our histological studies have shown that the regeneration of eye tissues with injected allogeneic mesenchymal stem cells is more effective means of treating keratitis than the traditional method of treatment (daily instillation of gentaline 0.4% and cypronorm 4-6 times a day). Specifically, stem cells act as a regulator of proliferation in damaged tissues, activate the synthesis of anti-inflammatory mediators and strengthen their own antioxidant properties.
 It was established that with the help of allogeneic mesenchymal stem cells, the differentiation of epithelial cells in the layers of the eye and a slight delamination of collagen fibrils were noted already on the 7th day, and on the 14th day the epithelial layer approached normal and there was no inflammatory infiltration of the cornea. Also, on the 30th day of the experiment, almost complete restoration of the structures of the damaged tissue of the eye and the end of the inflammatory process had already taken place. That is, histological studies show that allogeneic mesenchymal stem cells not only restore the function of damaged tissue structures, but also affect the intensity of the inflammatory process, which significantly reduces the time of eye tissue repair at the level of cells and tissues. The obtained data using stem cells can be used for new modern effective methods of treatment of eye pathologies.

Fretting wear properties and microstructure evolution in micro-arc oxidation bioceramic coating pretreated using laser remelting

To improve fretting wear resistance, bio-ceramic coatings were successfully fabricated on TC6 alloy substrates using a combination of laser remelting (LRM) and micro-arc oxidation (MAO). The surface morphology, composition, and residual stress distribution of the coatings were characterized using scanning electron microscopy, energy-dispersive spectroscopy, X-ray diffraction, ultra-deep field three-dimensional microscopy, and X-ray stress analysis. The influence of LRM pretreatment on the fretting wear behaviour of MAO bioceramic coatings was investigated. The LRM pre-treatment did not change the phase composition of the MAO coatings, which were all composed of Al2TiO5, rutile TiO2, and anatase TiO2 phases. However, increasing the content of the rutile TiO2 phase from 68 to 89% improved the uniformity and density of the coatings and decreased the porosity by 2.8%. The fretting wear test results showed that the LRM pretreated MAO coating exhibited the best performance against fretting wear in a simulated body fluid environment. In this case, the fretting wear mechanism was attributed to slight delamination and fatigue wear.

Research on tribological behavior of graphene with in-situ MgO nanoparticles reinforced AZ91 alloy composite

Magnesium-coated graphene (GNPs) was successfully prepared by a novel organic chemical reduction method with significantly improved wettability and dispersion. The GNPs were uniformly distributed in the matrix, while a finer and more dispersed strengthening phase β-Mg17Al12 was precipitated around it. Moreover, MgO nanoparticles were formed by in-situ reaction on the surface of GNPs, forming nano-scale contact and tight interfacial bonding with the substrate, thereby significantly improving the wear resistance of the composites. The wear mechanism has also changed from severe delamination and abrasive wear to mixed wear of slight delamination, adhesion, and oxidation. The increase in wear resistance is attributed to the combined effect of the lubrication and load transfer of GNPs, the enhanced effect of fine precipitates on the mechanical properties of the matrix, and the synergistic effect of in situ generated MgO nanoparticles against deformation.

AZ91 alloy nanocomposites reinforced with Mg-coated graphene: Phases distribution, interfacial microstructure, and property analysis

A new organic chemical reduction method was successfully used to synthesize magnesium-coated graphene (GNPs), and xGNPs/AZ91 nanocomposites with different contents were fabricated by vacuum hot-pressing sintering. The microstructure of the composite was mainly composed of the matrix (α-Mg) and the precipitated phase (β-Mg17Al12) with different morphologies such as rods, spindles, and granules. The coarse irregular β phases precipitated along the grain boundaries, while fine rod-like β phases were distributed inside the crystal grains. With the increase of GNPs content, the grain and structure are significantly refined under the action of two mechanisms of increasing the nucleation rate and hindering the growth of grains. The average grain size of the 2.5-wt% GNPs/AZ91 composite dropped from 40.78 µm to 25.39 µm, a reduction of 37.7%. In addition, the orientation relationship (OR) between β-Mg17Al12 and α-Mg was shown as [—3 —1 —1]β-Mg17Al12)∥[1 —1 0 —1]α-Mg. Further, finer β phases were further precipitated in the grain boundaries and matrix. Moreover, the β precipitated phase and the GNP, as well as the GNP and magnesium-matrix formed a nano-scale contact interface and a diffusion bonding interface, thereby greatly enhancing the interface bonding strength between GNP and the matrix. Compared with AZ91 alloy, the grain refinement and load transfer caused by GNPs increased the microhardness of the composite by 17.6% and the friction coefficient was decreased by 37.4%. The significant improvement in the wear resistance of the composites was due to the effect of the lubricating layer formed by GNPs on the wear surface, which changed from severe delamination wear to slight delamination and abrasive wear behavior.

Dry sliding wear of microalloyed Er-containing Al–10Sn–4Si–1Cu alloy

With the rapid development of the machinery industry, bearing materials with better tribological properties are demanded. Al alloys containing Erbium (Er) and Zirconium (Zr) have better comprehensive performance, whose tribological properties have hardly been reported before. In this work, dry sliding wear tests were performed on the Al–Sn and Al–Sn–Er–Zr alloys in two different annealing states to study the effect of trace Er, Zr on the tribological properties of the Al–Sn alloys. The Al–Sn–Er–Zr alloys showed better wear resistance than the Al–Sn alloys, which was mainly due to the higher hardness and strength of the Al–Sn–Er–Zr alloys. The wear losses of the alloys annealed at 375 °C for 100 h at the load of 70 N were significantly lower than those of the alloys annealed at 300 °C for 4 h. The wear coefficient K of the alloys annealed at 375 °C for 100 h decreased with the increasing load. The Al–Sn–Er–Zr alloys showed smoother worn surfaces than the Al–Sn alloys. With the load increasing, the wear mechanism changed from abrasive wear, mild adhesive wear and slight delamination wear to severe adhesive wear and delamination wear. The wear scars of different samples under the same load were similar, indicating that the addition of trace Er, Zr and annealing process did not change the wear mechanism. All samples experienced cracks and voids in the tribolayers. And oxygen accumulated in these defects. Most wear debris were lamellar, which was related to the adhesive wear and consist with the delamination theory.

Corrosion-wear behavior of a biocompatible magnesium matrix composite in simulated body fluid

Magnesium matrix composites are a new generation of biocompatible implant materials, but they will inevitably undergo simultaneous wear and corrosion in the human body. In this study, hydroxyapatite (Ca10(PO4)6(OH)2, HA) is used in a magnesium matrix composite to study its effects on the corrosion–wear behavior. Two samples (a magnesium alloy composed of Mg, Zn, and Zr (ZK60) alloy and ZK60/10HA composite) were fabricated using the powder metallurgy (PM) process. Their corrosion–wear behavior was investigated using the sliding wear test in a simulated body fluid (SBF). At all the sliding velocities tested, the corrosion-wear resistance of ZK60/10HA was superior to ZK60. At a sliding velocity of 942.5 mm/min, ZK60/10HA demonstrated a 42% improvement in corrosion–wear resistance compared to ZK60. For ZK60, the main wear mechanism under dry conditions was abrasion, while the wear mechanisms in the SBF were abrasion and corrosion. For ZK60/10HA, the wear mechanisms under dry conditions were abrasion and delamination, while in SBF they were mainly abrasion and corrosion, accompanied by slight delamination. The results indicated that HA particles can be used as an effective corrosion–wear inhibitor in biocompatible magnesium matrix composites.

High-mass-proportion TiCp/Ti6Al4V titanium matrix composites prepared by directed energy deposition

Titanium matrix composites (TMC) have potential applications in the aerospace industry because of their excellent performance. The comprehensive performance of TMC mainly depends on the matrix, reinforcement and interface characteristics. Hence, this study discussed the knowledge of microstructure-property relationships in detail. Crack-free high-mass-proportion TiCp/Ti6Al4Vcomposites were successfully prepared by directed energy deposition (DED). As the TiCp mass fraction increasing from 0 to 50%, the quantity of primary TiC and unmelted TiC (UMT) increased. Meanwhile, the refined α-Ti in the composites had a relatively weak texture. In addition, the interface between primary TiC and α-Ti was a semi-coherent interface, exhibiting a 112-0 α-Ti // [110]TiC, 1-100 α-Ti // 1-11 TiC orientation relationship, which facilitated the heterogeneous nucleation of Ti and improved bonding of primary TiC with the matrix. With the increase in microhardness taking the form of a cubic function, the wear mechanism was found to transform from abrasive wear to slight delamination wear. Due to the fact that both UMT and primary TiC bonded well with Ti64 matrix, they shared partial friction to protect matrix from severe abrasion, resulting in an excellent wear resistance of composites. Moreover, the thermal conductivity of 50% TiCp/Ti6Al4V was 9.063 W∙m-1∙K-1, which was nearly 26.5% higher than that of Ti6Al4V. Owing to the premature cracking of brittle UMT and dendritic TiC, the tensile strength and elongation of the composite with 50% TiCp were 515.5 MPa and 1.83%, which decreased by 45.8% and 78.8%, respectively. Adding a high proportion of TiCp can significantly improve the hardness and wear resistance of TMC, whereas it is detrimental to the tensile performance of TMC. The study have significant implications for the design of novel TMC, particularly for the aerospace industrial applications.

Anisotropic Dry Sliding Friction and Wear Properties of a Novel Stainless Steel/ZA8 Alloy Interpenetrating Phase Composite Produced by Squeeze Casting

Novel interpenetrating phase composites (IPCs) were produced by infiltrating ZA8 alloy into sintered 304 stainless steel fiber preforms through squeeze casting. Microstructural characteristics and dry sliding wear behavior of the IPCs at room and elevated temperatures under different applied loads were investigated. The results indicate that the microstructures and wear behavior of the IPCs exhibit anisotropy. The IPCs have better wear resistance properties and lower friction coefficients in the longitudinal direction compared to the radial direction. Compared with the unreinforced alloy, the composites exhibit lower friction coefficients at both room and elevated temperatures, and the wear rate of the IPC is higher at room temperature and significantly lower at 120 °C. The friction coefficients and wear rates of the IPCs first decrease and then increase with increasing fiber fraction. The IPC with 35.98 vol% has the best wear resistance. For the IPCs, a higher applied load leads to a higher friction coefficient and wear rate. The predominant wear mechanisms for the ZA8 alloy are delamination wear, which becomes more severe with increasing applied load at room temperature, and plastic deformation and adhesive wear at 120 °C, and the IPCs show predominant abrasive (ploughing) wear and slight delamination wear. Abrasive wear becomes more severe for a too high fiber fraction at both temperatures.

The roles of stress in the thermal shock failure of YSZ TBCs before and after laser remelting

In order to reveal the roles of stress in the thermal shock failure of thermal barrier coatings (TBCs), yttria-stabilised zirconia (YSZ) TBCs were prepared via atmospheric plasma spraying and then remelted by a laser remelting process. Subsequently, thermal cycling tests of the as-sprayed YSZ TBCs and remelted YSZ TBCs were carried out at 1100 °C. The thermal shock failure mechanism of the two TBCs was investigated comparatively from the perspective of stress, i.e., phase transformation stress of ceramic coating, growth stress and thermal mismatch stress generated by thermally grown oxide (TGO). The results showed that, compared with the as-sprayed YSZ TBCs, there was no m-ZrO2 in the remelted YSZ TBCs, which avoided the ceramic coating phase transformation stress produced by the transformation between m-ZrO2 and t-ZrO2 during thermal cycling. Therefore, the thermal shock failure mode of the as-sprayed YSZ TBCs was severe buckling driving delamination, while that of the remelted YSZ TBCs was slight edge delamination. In addition, the TGO growth stress and the thermal mismatch stress between the TGO and the bonding coating were reduced by the laser remelting treatment, leading to the spallation tendency of YSZ TBCs was decreased. Consequently, the remelted YSZ TBCs exhibited superior thermal shock resistance to the as-sprayed YSZ TBCs. Therefore, the phase transformation stress, growth stress and thermal mismatch stress determined the thermal shock failure mode and thermal shock life of these two YSZ TBCs.

Investigations on microstructure, mechanical properties and tribological behavior of in-situ Mg2Si particles reinforced AZ91 composites

In this work, AZ91 matrix composites reinforced with in-situ Mg2Si particles were prepared by liquid metallurgy method, and the effect of Mg2Si phase on the microstructure, mechanical properties and tribological behavior was investigated. The experimental results showed that with the increase of Si concentration, the volume fractions and size of Mg2Si phase were enhanced gradually, and the morphology of Mg2Si changed from Chinese script shape to coarse dendritic shape. As the Mg2Si phase increased, the grain size of composites was refined by 50%, from 215 μm to 108 μm. In addition, both Brinell hardness and yield strength of Mg2Si/AZ91 composites were improved significantly due to the grain refinement strengthening and load transfer effect. The wear loss of composites was reduced greatly with increasing Mg2Si phase amount, and as the Mg2Si addition was 11.5 vol%, it was decreased by 32%, indicating in-situ formed Mg2Si could significantly improve the wear resistance of AZ91 alloy. Microstructure analysis on worn surface revealed that the composites exhibited smaller value in the width and depth of the grooves, and could resist more plastic deformation and wear damage due to the improved hardness and strength. During the sliding wear process, the wear mechanism of Mg2Si/AZ91 composites was dominated by abrasive wear, slight plastic deformation and delamination, but it was much less than that of AZ91 alloy.

Effect of hybrid ratio on friction and wear behavior of AZ91D matrix nanocomposites under oil lubricated conditions

Abstract Friction and wear behavior of AZ91D and its nanocomposites reinforced by different contents of hybrid multi-walled CNTs and nano-SiC particulates under oil lubrication was investigated using a MRS-10P four-ball tribometer. Friction coefficients and wear rates were measured within a load range of 200–1000 N at a spindle rotary speed of 380 r/min. Worn surface morphologies, phase and element compositions were studied by scanning electron microscope (SEM), X-ray diffraction (XRD) and energy dispersive spectroscopy (EDS), respectively. The mechanism of synergistic effect of CNTs and SiC nanoparticles was discussed. The results indicate that the AZ91D nanocomposites show better wear resistance properties and different wear mechanisms compared with AZ91D. The AZ91D nanocomposites reinforced with 0.5% CNTs and 0.5% nano-SiC have the best tribological capacity. The wear mechanisms for the Mg-based hybrid nanocomposites appear to be a mix-up of micro-ploughing, micro-cutting, slight adhesive wear and delamination.

Fabrication and Tribological Behavior of Stir Cast Mg/B4C Metal Matrix Composites

Magnesium-based metal matrix composites (MMMCs) have emerged as good alternative material to conventional materials due to their promising advanced properties. In the present work, magnesium-based metal matrix composites (MMMCs) reinforced with B4C particles were successfully fabricated by cost-effective conventional stir casting technique. MMMCs with an average particle size of 63 µm and different weight percent (wt pct) of B4C between 3 and 12 were fabricated. Wear tests were carried out using a pin-on-disk against a steel disk under dry sliding condition at loads that varied between 1 and 5 kg at fixed sliding velocity of 1 m/s. The wear data clearly showed that wear resistance of cast composites is better than that of unreinforced magnesium, which is attributed to dispersion hardening caused by carbide particles. An increase in wt pct of B4C showed the wear resistance and hardness to increase significantly. The wear rate and coefficient of friction increased with an increase in applied load. The SEM and EDS analysis of the worn surfaces delineated the dominant wear mechanisms to be abrasion, adhesion, and oxidation under the different sliding conditions. At lower loads, the wear mechanism transformed from severe abrasive wear in pure magnesium (Mg) to mild abrasion, slight delamination, and oxidation in the Mg/12 wt pct B4C fabricated composite. At higher loads, severe abrasion, adhesion, delamination, and oxidation were found to be the major wear mechanisms in pure Mg, whereas in the Mg/12 wt pct B4C fabricated composites the corresponding mechanisms were mild abrasion, mild adhesion, slight delamination, and oxidation.

Photoluminescence of Mg2Si films fabricated by magnetron sputtering

To understand the photoluminescence mechanisms and optimize the design of Mg2Si-based light-emitting devices, Mg2Si films were fabricated on silicon (111) and glass substrates by magnetron sputtering technique, and the influences of different substrates on the photoelectric properties of Mg2Si films were investigated systematically. The crystal structure, cross-sectional morphology, composition ratios and temperature-dependent photoluminescence (PL) of the Mg2Si films were examined using X-ray diffraction (XRD), Scanning electron microscope (SEM), energy dispersive X-ray spectroscopy (EDS) and PL measurement system, respectively. XRD results indicate that the Mg2Si film on Si (111) displays polycrystalline structure, whereas Mg2Si film on glass substrate is of like-monocrystalline structure.SEM results show that Mg2Si film on glass substrate is very compact with a typical dense columnar structure, and the film on Si substrate represents slight delamination phenomenon. EDS results suggest that the stoichiometry of Mg and Si is approximately 2:1. Photoluminescence (PL) of Mg2Si films was observed for the first time. The PL emission wavelengths of Mg2Si are almost independence on temperature in the range of 77–300K. The PL intensity decreases gradually with increasing temperature. The PL intensity of Mg2Si films on glass substrate is much larger than that of Mg2Si film on Si (111) substrate. The activation energy of 18meV is determined from the quenching of major luminescence peak(1342nm) as a function of temperature in the Mg2Si film grown on Si (111) substrate, which is much smaller than that deduced in the sample grown on glass substrate (about 25meV). The small activation energy can be attributed to the additional nonradiative centers originated from relatively poor crystal quality.The physical mechanism responsible for the measured ∼1342nm and other three longer wavelengths emissions may be respectively result from strong Mgi donor level to valence band transitions and other defect-related radiative recombination occurred in the Mg2Si films.

Wear and Mechanical Behaviour of Hypo-Eutectic Al-7%Si-0.5%Mg Alloy (A357) Reinforced with Al<sub>2</sub>O<sub>3</sub> Particles

In this study, A357 (Al-7%Si-0.5%Mg) alloy/Al2O3 composites with various volume fractions (4%, 8%, 10%) were prepared by using permanent mould casting. In addition, A357 alloys were cast for comparison purposes. The alloys and composites were given a T6 heat treatment process (solution treatment and artificial ageing), Also microstructure, hardness and tensile properties of these composites were evaluated and compared. In addition, tribological properties of these composites were evaluated using a Pin-on-Disc apparatus at a constant sliding velocity of 1m/s and pressure of 0.35 MPa. The microstructure of the composites shows homogenous distribution of Al2O3 plate-like particles in the Al matrix except in the A357/10%Al2O3 composite. The wear and mechanical properties of composites improve with increasing the volume fraction of Al2O3 upto 8% and then decreases. Particularly, mechanical properties of the A357/10%Al2O3 composite are lower than the alloy indicating that the critical volume fraction of Al2O3 reinforcement in the A357 alloy is 8%. Wear morphology studies show that abrasive and delamination wear are extensive in the alloy whereas the slight delamination wear with some abrasive grooves are found in the composites.

Structural changes on vermiculite treated with methanol and ethanol and subsequent microwave irradiation

Present work reports the alcohol treatment and subsequent irradiation with microwave of commercial vermiculites. Alcohol treatment resulted in slight delamination of the layers and the color of the samples changed into brilliant golden and no expansibility was observed (k≤1.3). Samples treated with alcohol and subsequently irradiated with microwaves expanded; the greater expansibility (k=8 for 1h) was provided by the most complex sample and treated with methanol. The structural changes were studied by using X-ray diffraction (XRD), thermogravimetric analysis (TG and DTA), infrared spectroscopy and carbon analysis. The results of these analysis indicated dehydration-hydration and order–disorder which would be related to the entry of alcohol into the vermiculites and the loss of water content. The changes occurred in a similar way to the temperature and vacuum, and were less pronounced for the purest vermiculite. The crystallite size and lattice strain values which reflect changes in crystallinity and structural order varied slightly regardless of treatment and time. Alcohol treatment and subsequent microwave irradiation may be the procedure for obtaining purest vermiculite from less pure sample.

Friction and wear behavior of nanoeutectic Fe1.87C0.13 under air and vacuum conditions

In this paper, the tribological behavior of nanoeutectic Fe1.87C0.13 alloy and its coarse-grained-eutectic counterpart under air and vacuum was investigated. The results showed that the wear rate of both alloys was lower in air than in vacuum, and their friction coefficient was related to applied load and testing atmosphere. The nanoeutectic Fe1.87C0.13 alloy exhibited lower wear rate than the coarse grained counterpart in both environments. The wear rate of both alloys increased but the friction coefficient decreased with increasing applied load under both air and vacuum. The dominant wear mechanisms were adhesion wear in vacuum but oxidation wear along with slight delamination in air.

Dry sliding wear behavior of ES-processed AZ31B magnesium alloy

The friction and wear properties of AZ31B magnesium alloy fabricated by a new severe plastic deformation called extrusion-shear (shorted for ES) have been investigated in dry sliding condition. Dry sliding tests for AZ31B magnesium alloy processed by direct extrusion have been performed and compared with that of the alloy prepared by ES process. The results show that the wear resistance of AZ31B alloy was improved by Extrusion-Shear process, compared with direct extrusion. This was mainly attributed to the grain size refinement in Extrusion-Shear process. The main wear mechanisms of both alloys are abrasion slight deformation, oxidation delamination and melting under different frequencies. The effective stresses for the surface region during wear process have been calculated by using FE (Finite Element) method. The simulation results indicates that a higher effective stress is accumulated in the direct extrusion alloy than in the ES alloy, which may cause a larger volumetric wear rate of AZ31B magnesium alloy.