WC Ball Research Articles

Ti6Al4V alloy with diamond particle-reinforced Cu-based coatings: Microstructure and tribological performance

To enhance the surface wear resistance of the Ti6Al4V alloy, diamond particles-reinforced Cu-based composite coatings (D500/D1000/D2000 coating: 500/1000/2000 mesh diamond: Cu-based alloy powder = 1:30 (wt%)) were fabricated by vacuum cladding. Cu-based alloys with liquid phase temperatures lower than the phase transition temperature of Ti6Al4V alloys were employed as cladding materials to avoid performance deterioration of Ti6Al4V substrates. The microstructure, mechanical properties, and dry-sliding tribological properties of the Cu-based composite coatings have been investigated systematically. The Cu-based composite coatings are composed of the ductile intermetallic compounds Ti3Sn and SnTi2 as the metal matrix, the hard and brittle intermetallic compounds CuTi, CuTi2, Ti(Cu, Al)2 and CuSn3Ti5, in situ generated TiC and the directly introduced diamond particle as the reinforced phases. In addition, a TiC hard phase protective layer was formed around the diamond particles, which retained the original properties of the diamond. The hardness of diamond particles-reinforced Cu-based composite coatings is much higher than that of the Ti6Al4V. Among them, the D2000 coating possesses the highest microhardness. The average Vickers hardness (HV0.5) on the coating surface and nanoindentation hardness (H) on the coating cross-section (the middle part without diamond particles) of the D2000 coating are 1329.8 HV0.5 and 16.87 GPa), which are 4–5 times higher than that of the Ti6Al4V substrate (333 HV0.5 and 3.37 GPa). Nevertheless, the D2000 coating (wear rate of 50.75 ×10−5 mm3/Nm) demonstrates slightly inferior tribological performance compared to the D500 coating. The wear rate of the latter is approximately 13.37 × 10−5 mm3/Nm, which is only 1/5.6 of the substrate (75.67 ×10−5 mm3/Nm). The larger the diamond particle size, the more the diamond serves as a bearing capacity support point to prevent the hard WC ball from further ploughing into the composite coating, and the better the wear resistance of the coating. Notably, D500 coating with excellent wear resistance has the potential for application in various fields of the machinery industry, marine engineering, and aerospace.

Microstructural Evolution and Wear Resistance of Surface Alloyed AISI 316L Stainless Steel with Equi-atomic CoCrFeMnTi by Continuous Wave Diode Laser

In this investigation, a multicomponent alloyed surface was developed on AISI 316L stainless steel (AISI 316L SS) substrate by melting it with a fiber coupled diode laser having 3.6 mm beam diameter (using argon as shrouding gas) along with simultaneous melting of equiatomic pre-mixed elemental powders of cobalt (Co), chromium (Cr), iron (Fe), manganese (Mn) and titanium (Ti) (high entropy alloy). The process parameters used in the experiment were laser power (1800–2200 W) and scan speed (6 mm/sec to 8 mm/sec). Following laser surface alloying (LSA) a detailed microstructural characterization of the surface and evaluation of surface mechanical properties (micro/nano hardness, Young’s modulus and wear resistance) were undertaken. Due to LSA there is formation of near eutectic microstructure consisting of FCC and BCC phase mixtures along with the precipitates of Fe2Ti randomly distributed in the microstructure which was confirmed by X-ray diffraction (XRD) and electron back scattered diffraction (EBSD) analysis. There is an increase in microhardness in the processed zone from 180 VHN (of as received AISI 316L SS) to 309–650 VHN. In addition, there is an increase in Young’s modulus from 208 GPa for as received AISI 316L SS to 228–301 GPa for laser surface alloyed zone. The wear resistance (against WC ball in fretting wear mode) property of AISI 316L SS substrate after LSA was superior to the substrate. The wear mechanism was established.

Experimental study of frictional behaviour of powdered soaps for wire drawing

Better understanding of frictional behaviour of powdered soaps used in dry wire drawing can lead to improvements in wire quality and large savings in energy consumption. The latter is particularly significant given the colossal amounts of energy expended in wire drawing processes. However, there is currently a very limited understanding of the subject, including a lack of quantitative data on soap friction. This is at least in part likely to be due to complex tribological behaviour of the powdered soaps, which is very different from that of lubricating oils. This paper studies frictional behaviour of sodium and calcium powdered soaps, using a ball-on-disc tribometer (ETM rig) incorporating a powder ‘scoop’, and under contact conditions pertinent to die-wire contact in wire drawing. Tests employed a WC ball and C15E steel disc to mimic die and wire materials respectively. Results show that under high sliding conditions, friction coefficient with powered soaps is remarkably low, at 0.03 and 0.04 for sodium and calcium soaps respectively. Friction generally decreased with increasing contact pressure and sliding speed. Post-test analysis of ETM specimens showed the presence of thick soap layers on the rubbed surfaces. However, in ETM tests friction was observed to sharply increase leading to the onset of scuffing, soon after the supply of soap to the contact was interrupted, suggesting that any solid deposited layers are easily removed and cannot exclusively explain the low friction. The observed trends suggest that low soap friction may be due to the ability of the soaps to form low shear stress lubricating films at high contact temperatures which are associated with the harsh conditions of high-speed and high-pressure. The results provide new insights into the frictional behaviour of powdered soaps which can be used to optimise the wire drawing processes as well as a direct input to wire deformation models.

Titanium carbide (TiC) dispersed surface on titanium based alloy (Ti-13Nb-13Zr) by in-situ laser composite surfacing and its wear performance

Ti-13Nb-13Zr is a promising titanium-based alloy for bioimplant applications due to its low Young’s modulus (80 GPa). However, it undergoes mechanical and mechano-chemical degradation after long-term application in the human body. The present study concerns the development of TiC dispersed surface on Ti-13Nb-13Zr by preplacement of graphite and subsequent melting with a continuous wave (CW) fiber-coupled diode laser using varied power (1000 W to 1400 W) and scan speed (10 mm/s to 20 mm/s). Laser composite surfacing leads to the formation of dispersion of carbide (TiC) in the beta (β) matrix. There is an improvement in microhardness from 257 VHN (for as-received) to 360–519 VHN for laser composite surfaced Ti-13Nb-13Zr and varied with process parameters. There is an increase in nanohardness value from 3.6 GPa (for as-received Ti-13Nb-13Zr) to 5.14–9.224 GPa and increased in Young’s modulus from 100 MPa (for as-received Ti-13Nb-13Zr) to 103.22–120.85 MPa due to laser composite surfacing. A significant improvement in wear resistance (5.8 times) and a decrease in coefficient of friction (COF) (2.8 times) against the WC ball in fretting wear mode was noticed. The wear mechanism has been schematically presented and discussed in details.

Tribological Properties of the Fast Ceramic Conversion Treated Ti-6Al-2Sn-4Zr-2Mo Alloy with a Pre-Deposited Gold Layer

Ceramic conversion treatment (CCT) is an effective way to modify the surface of titanium alloys. However, this process normally needs more than a 100-h treatment at 600–700 °C to form a hard and wear-resistant titanium oxide layer. In this paper, we pre-deposited a thin gold layer on the surface of Ti-6Al-2Sn-4Zr-2Mo (Ti6242) samples before CCT to investigate if Au can speed up the treatment. Treatments at 640/670/700 °C were carried out for 10 or 120 h. After CCT, the surface roughness, surface morphology, microstructure, elemental composition, and phase constituents were characterized. Surface hardness and the nano-hardness depth distribution were measured. Finally, reciprocating sliding tribological tests were carried out to study the friction and wear of the surface layers. Thin gold layers accelerated the CCT significantly with a much thicker oxide layer. The friction of the untreated Ti6242 alloy against the WC ball was unsteady and high, but it was much lower and stable for the CCTed samples pre-deposited with Au because of the formation of titanium oxides and lubrication effect of the gold particles. The wear resistance of the CCTed Ti6242 alloy samples with gold was reinforced significantly. By pre-depositing a thin gold layer on the surface of Ti6242, the treatment time can be cut significantly, and CCT becomes more efficient.

Mechanically tailored surface of titanium based alloy (Ti6Al4V) by laser surface treatment

In this study, laser surface treatment (LST) of Ti6Al4V carried out by melting within a narrow regime of optimum process parameters for the formation of a surface with improved wear and tribo-corrosion resistance is presented. The effect of applied power and shrouding gas on the microstructure, phase, surface hardness, residual stress, dry wear (against tungsten carbide, WC) and tribocorrosion resistance (against ZrO2 in Hank's solution) is established. LST in argon atmosphere leads to the formation of a composite structure consisting of acicular α’ martensite and α. LST in nitrogen atmosphere causes the formation of titanium nitride (TiN and Ti2N) dispersed in α matrix. Due to LST, there is an increase in surface microhardness both under argon (435–630 VHN) and nitrogen atmosphere (839–1327 VHN) when compared to untreated Ti6Al4V (278 VHN). There is a marginal decrease in wear rate (against WC ball) due to laser surface melting (5.17–5.81 × 10−3 mm3/Nm) under argon and a substantial decrease in wear rate when melting was conducted under nitrogen atmosphere (1.91–4.94 × 10−3 mm3/Nm) as compared to Ti6Al4V (5.93 × 10−3 mm3/Nm). The mechanism of wear is established. On the other hand, the tribo-corrosion rate is found to decrease for laser surface melting (3.5–4.8 × 10−3 mm3/Nm) and nitriding (1.3–3.2 × 10−3 mm3/Nm) as compared to Ti6Al4V (5.7 × 10−3 mm3/Nm). Bioactivity in terms of calcium phosphate deposition followed by dipping in Hank's solution was found to increase due to both melting and nitriding, though nitriding offered a marginally higher bioactivity than only melting.

Impact of ball milling on the cubic Sb2O3 into orthorhombic Sb2O3 and SbO2 materials – Structural and other characterization studies

The present investigation adds new information about the cubic Sb2O3 and orthorhombic Sb2O3 and SbO2 phases to the scientific society. In this work, the Sb2O3 (commercial) powder was ball-milled in a tungsten carbide (WC) jar using WC balls with different diameters at 300 ​rpm for several time intervals (1, 3, 5, 10, 20, and 30 ​min and 1, 2, 5, 10, 20, and 30 ​h) and reported their findings of structural, thermal, optical, and morphology. Interestingly, the ball-milled powder undergoes phase transformation from cubic Sb2O3 into orthorhombic Sb2O3 and SbO2 in a short duration (3–30 ​min) of ball milling. While the 0, 1, and 3 ​min ball milled samples preserve the cubic Sb2O3 structure, the 5 ​min ball milled sample exhibits a nearly single-phase orthorhombic Sb2O3 structure. Mixed phases of orthorhombic Sb2O3 and SbO2 phases are seen for the 10–20 ​min ball milled samples. For a 30 ​min ball milled sample, an orthorhombic SbO2 phase is observed. Furthermore, the 1, 3, 5, 10, 20, and 30 ​h ball milled samples retain the orthorhombic SbO2 phase. Maximum weight loss of 34.4 ​% is noted for the commercial Sb2O3 powder, whereas the 1 and 3 ​min of ball-milled samples reveal the weight loss of 9.3 and 4.7 ​%, respectively. The other ball-milled samples exhibit both weight loss and weight gain in the thermogravimetric analysis (TGA) curves. The Raman features of ball-milled orthorhombic SbO2 are quite different from those of other types of antimony-based oxides. Bar/bundle-shaped and spherical-shaped with agglomerated particles are seen for the commercial Sb2O3 phase and ball-milled (1 and 30 ​h) SbO2 phase samples.

Impact of the Amount of the Gold Layer on the Tribological Performance of the Ceramic Conversion Treated CP-Titanium

Titanium alloys are characterised by poor tribological properties, and a ceramic TiO2 layer formed on the surface can greatly improve its performance. By pre-depositing a gold layer on the titanium surface, the gold particles promoted the outward diffusion of titanium in the ceramic conversion treatment to react with the inward-coming oxygen to form a compact titanium dioxide layer. The surface morphology, microstructure, and phase constituents were characterised by SEM/EDX and XRD. The adhesion of the oxide layers was assessed by a scratch test. The distribution of gold particles in the oxide layer enhanced the surface hardness and reduced the friction and wear against a WC (tungsten carbide) ball in the reciprocal tribological test. The ceramic conversion process was accelerated efficiently at 620–660 °C, and the more gold pre-deposited, the thicker the oxide layer.Graphical

Effect of mechanical ball milling on the electrical and powder bed properties of gas-atomized Ti–48Al–2Cr–2Nb and elucidation of the smoke mechanism in the powder bed fusion electron beam melting process

Smoke is unexpected powder-splashing caused by electrostatic force and is one of the main problems hindering the process stability and applicability of the powder bed fusion electron beam (PBF-EB) technology. In this study, mechanical stimulation was suggested to suppress smoke of gas-atomized (GA) Ti–48Al–2Cr–2Nb powder using Al2O3 and WC ball milling. The deformation mechanism of the GA powder depending on the ball milling media was discussed based on the developed particle morphology distribution map and contact mechanics simulation. It was revealed that the rapid decrement of flowability and packing density after WC ball milling owing to the formation of angular fragments by the brittle fracture. The variation of surface and electrical properties by mechanical stimulation was investigated via XPS, TEM, Impedance analysis. The electrical resistivity of the ball-milled powders gradually decreased with increasing milling duration, despite the increased oxide film thickness, and the capacitive response disappeared in Al-60 and WC-30 via metal–insulator transition. This could be due to the accumulation of strain and defects on the oxide film via mechanical stimulation. The smoke mechanism of ball-milled powders was discussed based on the percolation theory. In the smoke experiment, smoke was more suppressed for WC-10 and WC-20 than that for Al-40 and Al-50, respectively, despite the longer charge dissipation time. This could be due to the high probability of contact with conductive particles. For the Al-60 and WC-30 powders, smoke was further restricted by the formation of a percolation cluster with metal-like electrical conductivity. We believe that this study will contribute to a better understanding of the smoke mechanism and process optimization of the PBF-EB.

Uticaj mehaničke aktivacije na smešu SrTiO3 i Fe2O3 kao aditiva

The authors investigated the influence of mechanical activation on the structure of SrTiO3 mixture with 6 wt.% Fe2O3. Powders were mechanically activated in a planetary ball mill with WC balls in time intervals from 0 to 120 minutes. XRD method was used for the identification of phase structure, while SEM and PSA were employed for monitoring of changes in morphology and particle size distribution. Structural changes were followed by Raman spectroscopy, and band gap values were calculated as well. The purpose of mechanical activation is lowering the temperature and time of sintering in the process of obtaining the final product.

Influence of High-Pressure Torsion Processing on the Tribological Properties of Aluminum Metal Matrix Composites

The motivation for the current study was to improve the wear and frictional properties of Al, Al-Al2O3, and SiC MMCs through HPT processing. The wear test using a tungsten carbide (WC) ball was carried out for different PM and HPT-processed Al and MMC samples. The effect of the sample processing methods on the wear rate, friction, and wear surface morphology was thoroughly investigated. The high hardness after Al grain refinement and reinforcement fragmentation through the HPT processing of the samples increased the wear resistance by 16-81% over that of the PM samples. The average coefficient values and variation ranges were reduced after HPT processing. The Al and Al MMC processing methods affected the wear mechanism and surface morphologies, as proven by the microscopic observations and analyses of the worn surfaces of the samples and WC balls.

Surface degradation behavior of aluminium cenosphere composite foam developed by powder metallurgy route

The present study concerns understanding the effect of cenosphere content (5 vol% to 50 vol%.) on surface degradation behavior (by wear and corrosion) of aluminum cenosphere composite foam. Composite foam was developed by compaction of pre-mixed aluminum and cenosphere (varying from 5 vol % to 50 vol %) powders at a compaction pressure of 250 MPa, by two-step sintering. The density of the composite foam was found to decrease from 2.7 g/cm3 (as received aluminum) to 2.02–2.44 g/cm3 (aluminum cenosphere composite) and decreased with increase in cenosphere percentage. Detailed study of wear resistance against WC ball under fretting wear mode showed that the wear resistance of the foam increased with increase in cenosphere content up to 30 vol % following which it deceased. The mechanism of wear revealed that the mode of wear is due to the combined effect of adhesive and abrasive wear. A detailed study of corrosion resistance in a 3.56 wt % NaCl solution showed that the corrosion rate of foam increased up to 30 vol % of cenosphere following which it decreased. The EIS measurements and post corrosion microstructural observation confirmed that the interface between aluminum and cenosphere was the potential site for initiation of corrosion.

Factors determining the flowability and spreading quality of gas-atomized Ti-48Al-2Cr-2Nb powders in powder bed fusion additive manufacturing

A high-quality powder bed is necessary for obtaining high-quality products using powder bed fusion-based additive manufacturing. In this study, mechanical ball milling was suggested to improve the flowability and spreadability of gas-atomized (GA) Ti–48Al–2Cr–2Nb powder in the powder bed fusion additive manufacturing process. The deformation mechanism of the GA powder significantly differed depending on the ball milling media. Surface grinding mainly occurred during Al 2 O 3 ball milling, while the pulverization was dominant in WC ball milling because of the higher impact force. The flowability of the GA powder under dynamic conditions was improved after Al 2 O 3 and WC ball milling owing to the decreased cohesive force. The high cohesive force in the GA powder under dynamic conditions was attributed to the electrostatic force caused by charge accumulation on the oxide film. The packing density of GA powder was increased after WC ball milling despite the formation of numerous irregular particles owing to the synergetic effect of rapid energy dissipation, minimized wall effect, and void filling effect. Furthermore, the spreadability of the GA powder was improved by ball milling because of the decrease in the cohesive force. Therefore, it was demonstrated that the flowability and spreadability of the GA powder can be improved via ball milling because of changes in particle size, shape, and surface properties. • Flowability of GA powder under the dynamic condition was improved after ball milling owing to the decreased cohesion force. • High cohesive force in GA powder was mainly attributed to the electrostatic force caused by charge accumulation on the oxide film. • Spreadability of GA powder was improved after ball milling due to the decreased cohesion force.

Titanium boride and titanium silicide phase formation by high power diode laser alloying of B4C and SiC particles with Ti: Microstructure, hardness and wear studies

In this work a novel multiphase titanium metal matrix composite (TMMC) coating was developed by high power diode laser assisted alloying of Cp-Ti with the preplaced Boropak powder consisting of B4C and SiC ceramic particles. The XRD, optical microscopy, scanning electron microscopy, EDAX, microhardness and wear testing techniques were employed to investigate structural phase, hardness and wear properties of the alloyed coating. Under the influence of multipass laser alloying, the B4C and SiC ceramic particles decompose to yield boron, silicon and carbon species that react with molten titanium to form TiB2, TiB, TiC and Ti5Si3 phases in the laser alloyed coating. In addition, the un-melted B4C and SiC ceramic particles are dispersed in the titanium matrix. Microstructure of the alloyed coating consists of dendrites and coralline-like structure. The tips of the coralline-like structure are in the range of 150–500 nm. The ceramic multiphase TiB2, TiB, TiC and Ti5Si3 formation resulted in average microhardness around 800–2200 HV0.2 at different regions of the TMMC coating cross section. To correlate the phase formation and microstructural features, surface temperature evolved at the interaction area during laser surface alloying was estimated by a simple equation. Activation energy for the laser melted track was calculated using the Arhennius equation. The linear reciprocating wear test performed on laser alloyed coating against WC ball showed wear rate value of 1.623 х 10−4 mm3/N.m which is 6 times lower compared to the untreated titanium.

Effect of Cryogenic Treatment on the Microstructure Modification of SKH51 Steel

This research aimed to investigate the microstructure modification mechanism used to improve the hardness and wear resistance of SKH51 steel. The cryogenic treatment (CT), including both shallow cryogenic treatment (SCT) and deep cryogenic treatment (DCT), was used to modify the microstructure of SKH51 steel in this research. The effect of short and long holding time (12 and 36 h) in CT was studied. The microstructures were evaluated by using a light optical microscopy (LOM) and a scanning electron microscopy (SEM). The phase identifications of the matrix, carbides, and a-parameter of the matrix were analyzed by using X-ray diffraction (XRD). The M6C and MC carbides size, aspect ratio, and distribution were analyzed using digimizer image analysis software on the SEM micrographs. Micro-Vickers were employed to evaluate the hardness of the targeted samples. Wear tests were performed by using a 6 mm diameter WC ball as the indenter and 5-N-constant load with a ball-on-disk wear tester. The results suggested that the increase of the secondary carbide was caused by the contraction and expansion phenomena of the matrix’s lattice, forcing the carbon atom out and acting as the carbide nucleation. The influence of holding time in the SCT and DCT regions was different. For the SCT, increasing the holding time increased the volume’s fraction of MC carbide. Conversely, the M6C carbide size grew with increasing holding time in the DCT region, while no significant increase in the number of MC carbide was observed. The cryogenic treatment was found to increase the volume fraction of the MC carbide by up to 10% compared to the conventional heat treatment (CHT) condition in the SCT region (both 12 and 36 h) and DCT with 12 h holding time. Due to the microstructure modification, it was found that the cryogenic treatment can improve material hardness and lead to an increase in the wear resistance of SKH51 by up to 70% compared to the CHT treated material. This was due to the increase in the compressive residual stress, precipitation of the MC, and growth of the M6C primary carbide.

Improved critical current density property in ex situ processed MgB2 tapes using filling powders with metallic particle addition

MgB2 powders milled with low-melting-point metallic particles, Bi and In, and Fe-sheathed tapes using those milled powders were sintered at various temperatures. With increasing the amount of those additives, the wear of WC jar and balls during milling process is promoted. Compared with In addition, Bi addition clearly causes the formation of some amorphous or poor crystalline phase in the as-milled state. Concerning the sintered tape samples, the optimal sintering temperature (Tsin), at which best performance in transport critical current density (Jc) at 4.2 K in 10 T is obtained, is 680 °C for the tapes using the milled powders with In addition. This temperature is lower than that by 30 °C for the tapes without additives. Furthermore, In addition promotes the reaction at the interface between the MgB2 core and the Fe sheath. In contrast, Bi addition appreciably causes neither reduction of the optimal Tsin nor the promoted reaction at the interface. Although both additives hardly bring about critical temperature (Tc) reduction, only Bi addition can improve the transport Jc property. This Jc enhancement is mainly attributed to improved grain connectivity. In addition itself can be effective for grain connectivity improvement as well. However, reduced upper critical and irreversibility fields (Hc2 and Hirr) brought about by the addition degrade the Jc property.

Wear and mechanical properties of Al chips and Al chips composites recycled by high-pressure torsion

Pure Al chip, Al chip-20% Al 2 O 3 , and Al chip-20% SiC samples were recycled using high-pressure torsion (HPT). Influence of the HPT processing on the feasibility of the consolidation, the microstructure evolution, the hardness, and the wear properties of pure Al chip, Al chip-20% Al 2 O 3 , and Al chip-20% SiC samples were investigated and compared with those of the as-received Al and HPTed Al solid samples. The HPT processing successfully produces approximately fully dense ultrafine-grained (UFG) microstructure Al and Al composite samples with relative densities ranged from 99.7 to 98.3%. The HPT processing of the Al chip and Al chip composites samples effectively refine and fragmented the Al matrix and reinforcement particles, and so the hardness increases. The increase of the hardness enhances the wear resistance and frictional properties of the Al after recycling the Al chip and Al chip composites via HPT processing. The enhancement of the hardness and so the wear resistance affects the wear mechanism of the different samples. Worn surface morphology and analysis of the wear samples and WC ball and so support the wear and friction results.

Fretting wear behaviour and frictional force mapping of Al2O3 based thermal barrier coatings

Efficiency and structural stability of gas-turbine engines were acheived with compliant thermal barrier coatings (TBCs) on structural components. In TBCs, top ceramic coatings encountered with other structural parts in a relative motion (amplitude of 100–500 μm and frequency of 1–5 Hz) was leading to failure, namely fretting wear. So, a high hardness material, Al2O3 based ceramic matrix composite (CMC) coatings were utilized to improve the tribological properties of the engineered surface. At this juncture, fretting wear behaviour of atmospheric plasma sprayed Al2O3–3 and 8 mol% Y2O3 stabilized ZrO2 (3YSZ and 8YSZ)‑carbon nanotube (CNT) based CMC coatings were investigated. The fretting wear rate of Al2O3 based CMC coatings against WC ball was observed as 0.97–1.87 × 10−6 mm3N−1 m−1. The least in wear resistance of Al2O3-CNT (1.87 × 10−6 mm3N−1 m−1) among the composite coating is attributed to low hardness and high Hertzian contact pressure (1.65 GPa) on the coatings. Among the composite coatings, Al2O3-3YSZ and Al2O3-8YSZ-CNT showed an improved wear resistance (~40.1% and ~34.5%, respectively) with wear rate of 0.97 × 10−6 mm3N−1 m−1 and 1.06 × 10−6 mm3N−1 m−1, respectively. It is attributed to improved mechanical properties, altered surface by reciprocating motion and the presence of wear debris, which reduces the wear rate by acting as a third body. So, there is an overestimation of wear rate (4.1–6.6 times) compared to that of experimentally calculated wear rate. Further, the Al2O3-YSZ-CNT composite showed fatigue crack on the fretting wear surface due to low plasticity index (62.0–109.3 MPa) of the coating. Also, the gradual change of running-in regime to the steady-state regime is achieved in the CNT reinforced composite coatings due to high resistance by the coatings which possess commendable mechanical properties. The frictional force mapping during the reciprocating motion confirms the rapid and gradual transition of two different regimes in the composite coatings.

Electrochemical Characteristics of Anion-Redox Type Cathode Materials with High Specific Capacity

1. IntroductionIn recent years, high energy-density lithium-ion batteries have been used for power sources such as hybrid and electric vehicles and for home energy storage systems. However, with increasing performance of equipment, energy storage devices with higher energy density than conventional lithium-ion batteries are required. Co-doped Li2O (CDL), which utilizes the redox reaction of oxygen for charge compensation, has been investigated as such a material. In this material, Co plays a role in improving the electrochemical activity of oxygen; CDL has a high specific capacity of about 450 mAh g-1, but there is a problem of the active material decomposition when overcharged. In this work, Me-Li2O-MOX (Me: transition metal, M: Al and Si) was investigated to suppress the degradation reaction of active materials by simultaneously dissolving oxides such as Al2O3 without 3d orbitals and transition metal oxides with 3d orbitals in Li2O.2. experimentalα and β-Li5AlO4(α and β-LA) were synthesized by a sol-gel method. Co-substituted α and β-Li5AlO4 (α and β-CSLA) were prepared via mechanical alloying of LiCoO2 (LCO) with α- and β-LA, respectively, in a 1:1 molar ratio as follows. The precursor mixture was sealed in a tungsten carbide (WC) pod with WC balls in an Ar-filled glove box (Pure box, Yamato Co., Ltd., Osaka, Japan), and then planetary ball milling (Premium Line P-7, Fritsch) was conducted at 300 rpm for 36 h to pulverize the oxides. The local structures of the obtained materials were measured by X-ray absorption spectroscopy (XAS) at SR center in Ritsumeikan University. The electrochemical characteristics were evaluated by charge–discharge cycling tests. The active material (α- or β-CSLA) was mixed with acetylene black (AB, Denka black, Denka Co., Ltd., Tokyo, Japan) and polyvinylidene difluoride (PVDF, #1100, Kureha Co., Ltd., Tokyo, Japan) in a 70:20:10 ratio by weight to form a paste, which was then applied to an Al foil using a doctor blade casting method and dried under vacuum at 60 °C for 12 h to obtain a working electrode. The working electrode, a Li metal sheet (the counter electrode), the electrolyte, and a polyolefin film separator (ND525, Asahi Kasei Co., Ltd) were assembled in a demountable coin-type cell (Hosen Corp., Osaka, Japan).3. Results and DiscussionXAS measurements were performed to investigate the local structure of α and β-CSLA. We found a new bonding state of O, which was not observed in LiCoO2 and Li5AlO4 as raw materials. This is likely to be derived from the Co3+-O at tetrahedral coordination formed by Co-substitution to Li5AlO4 during the mechanical alloying. The pre-edge peak attributed to Co3+-O at the hexagonal coordination in the Co K-edge XANES spectra of α and β-CSLA suggests that α and β-CSLA contain unreacted LiCoO2.The charge-discharge curves of α and β-CSLA are shown in Figure 1. This shows that α and β-CSLA exhibit specific capacities of 200 and 250 mAh g-1 in the first cycle, respectively; the higher discharge capacities of β-CSLA by about 25% compared to α-CSLA may be due to the substitution of more Co in β-CSLA compared to α-CSLA. Figure 1

Mechanical and High-Temperature Tribological Properties of Cr3C2-NiCr/TiN Duplex Coating

Preparation of duplex coating is an innovative way to improve components surface in terms of mechanical and tribological properties by the combination of high velocity oxy-fuel (HVOF) and physical vapor deposition (PVD) technologies. The present work focused on the construction, mechanical properties and high temperature tribological behaviors of the duplex coating consisting of a thick HVOF Cr3C2-NiCr interlayer and a thin PVD TiN top layer, as well as compared it with the Cr3C2-NiCr coating and the single TiN film. The results showed that the Cr3C2-NiCr/TiN duplex coating exhibited higher hardness, elastic modulus, H/E and H3/E2 ratios and superior load-bearing capacity than the single TiN film. The introduction of Cr3C2-NiCr intermediate layer did not affect the microstructure of TiN film but significantly improved the adhesion strength between TiN film and substrate, as well as the wear resistance sliding against WC ball at different temperatures. In addition, the friction and wear mechanism of the Cr3C2-NiCr coating, TiN film and Cr3C2-NiCr/TiN duplex coating was revealed by investigating the friction-induced morphological and structural evolutions of the sliding surface at elevated temperature.