Wear Behavior of Nanostructured Al and Al�CB4C Nanocomposites Produced by Mechanical Milling and Hot Extrusion

Wear properties of a nanostructured matrix of Al prepared via mechanical milling and hot extrusion were investigated before and after incorporation of B₄C nanoparticles. The sample powders were milled for a period of 20 h to produce nanopowders. Mechanical milling was used to prepare nanocomposite samples by addition of 2 and 4 wt% of B₄C nanoparticles into the Al matrix. A pin-on-disk setup was used to evaluate the wear properties of the hot extruded samples under dry condition. The results revealed a lower friction coefficient and a lower wear rate for the nanostructured matrix of Al in contrast to a commercial coarse grained Al matrix. The same pattern was also observed in the nanocomposite samples with respect to the base matrix. Hardness values were used to discuss the observed results. Scanning electron microscopy (SEM) was used to analyze the worn surface and wear debris.     

Friction and Wear Properties of ZrO2�CAl2O3 Composite with Three Layered Structure Under Water Lubrication

Zirconia?CAlumina (ZrO₂?CAl₂O₃) composite with three layered structure was prepared, and its friction and wear properties under water lubrication were investigated. The results indicate that the layered composite exhibited better tribological properties comparing with ZrO₂?CAl₂O₃ mono-layered composite at same tested conditions. Good combination of toughness and strength as well as subsequently excellent friction and wear properties were mainly contributed to the residual stress of the layered composite, which caused by thermal mismatch of sintering between layers through special design of compositions and structure. Friction coefficient and wear rate of the layered composite decreased with increment of load and/or velocity. The change of tribological properties was also relative to wear mechanisms, micro-cutting, and abrasive wear were main mechanisms at lower load and/or lower velocity but fatigue wear caused by plastic deformation became dominant at higher load and/or higher velocity.     

Finite element simulation of high-speed machining of titanium alloy (Ti�C6Al�C4V) based on ductile failure model

A Johnson?CCook material model with an energy-based ductile failure criterion is developed in titanium alloy (Ti?C6Al?C4V) high-speed machining finite element analysis (FEA). Furthermore, a simulation procedure is proposed to simulate different high-speed cutting processes with the same failure parameter (i.e., density of failure energy). With this finite element (FE) model, a series of FEAs for titanium alloy in extremely high-speed machining (HSM) is carried out to compare with experimental results, including chip morphology and cutting force. In addition, the chip morphology and cutting force variation trends under different cutting conditions are also analyzed. Using this FE model, the ductile failure parameter is modified for one time, afterword, the same failure parameter is applied to other conditions with a key modification. The predicted chip morphologies and cutting forces show good agreement with experimental results, proving that this ductile failure criterion is appropriate for titanium alloy in extremely HSM. Moreover, a series of relatively low cutting speed experiments (within the range of HSM) were carried out to further validate the FE model. The predicted chip morphology and cutting forces agree well with the experimental results. Moreover, the plastic flow trend along an adiabatic shear band is also analyzed.     

Effect of Operating Conditions on Tribological Response of Al–Al Sliding Electrical Interface

Aluminum is widely used in electrical contacts due to its electrical properties and inexpensiveness when compared to copper. In this study, we investigate the influence of operating conditions like contact load (pressure), sliding speed, current, and surface roughness on the electrical and tribological behavior of the interface. The tests are conducted on a linear, pin-on-flat tribo-simulator specially designed to investigate electrical contacts under high contact pressures and high current densities. Control parameters include sliding speed, load, current, and surface roughness. The response of the interface is evaluated in the light of coefficient of friction, contact resistance, contact voltage, mass loss of pins, and interfacial temperature rise. As compared to sliding speed, load, and roughness, current is found to have the greatest influence on the various measured parameters. Under certain test conditions, the interface operates in a “voltage saturation” regime, wherein increase in current do not result in any increase in contact voltage. Within the voltage saturation regime the coefficient of friction tends to be lower, a result that is attributed to the higher temperatures associated with the higher voltage (and resulting material softening). Higher interfacial temperatures also appear to be responsible for the higher wear rates observed at higher current levels as well as lower coefficients of friction for smoother surfaces in the presence of current.     

Effect of silicon content on wear resistance and corrosion behaviour of Al–Si eutectic alloy

Abstract

In the present study, Al–Si eutectic alloys produced at the Aluminium Institution were studied. The alloys were cast and forged into bars of 20 mm diameter. The results obtained were compared with a pure aluminium sample. Metallographic analysis, spectral analysis, SEM and energy dispersive spectroscopy analysis, pin on disk abrasive wear tests and mass loss tests were performed. Wear resistances of alloys with various silicon contents were tested under different loads and constant abrasive speed. SiC abrasive paper of 80 grit size was used. The dry sliding tests were carried out under loads of 10, 20 and 30 N and the testing was conducted under a constant sliding velocity of 36˙8 m min^–1 in a dry air atmosphere. Corrosion rates were determined in 0˙1M NaCl acid solutions. The corrosion tests were performed at 2, 4, 6 and 8 h. The wear and corrosion resistance of all the eutectic alloys increased with increasing silicon content in the matrix.     

Effects of electromagnetic stirring and rare earth compounds on the microstructure and mechanical properties of hypereutectic Al–Si alloys

In this paper, the effects of rare earth addition and electromagnetic stirring on the microstructure and the mechanical properties of hypereutectic Al–Si alloys have been reported. Hypereutectic Al–Si alloy was prepared using liquid metallurgy route and modified with the addition of cerium oxide. To control the structure, slurry of hypereutectic Al–Si alloy was subjected to electromagnetic stirring before pouring into the mould. It was observed that the addition of cerium oxide (0.2 wt.%) refined the primary silicon particles and modified the eutectic silicon particles. Further, the electromagnetic stirring of the hypereutectic Al–Si alloy reduced the average size of primary silicon particles, from 152?±?9 to 120?±?6 μm, and the length of β-intermetallic compounds decreased from 314?±?12 to 234?±?10 μm. Similarly, the application of electromagnetic stirring on cerium oxide-modified hypereutectic Al–Si alloy also reduced the average size of primary silicon particles from 98?±?5 to 76?±?4 μm and the average length of β-intermetallic compounds from 225?±?7 to 203?±?5 μm. Mechanical properties namely tensile strength, ductility and hardness of the alloys were improved with electromagnetic stirring and addition of cerium oxide appreciably.     

Chip morphology study in high speed drilling of Al�CSi alloy

Chip formation during drilling operation is greatly influenced by the cutting parameters such as cutting speed, feed rate, and drill geometry. However, not many studies have focused on the direct observation of the chip formation during high speed drilling. This paper investigates the effect of cutting speed and feed rate on the chip morphology during high speed drilling of aluminum?Csilicon alloys using carbide drill. Observation on the multiview characterization of the chips was carried out which includes free surface, back surface, and cross-section of top surface. Structure and shape alterations of the free and back surfaces were analyzed using a scanning electron microscope. Finally, different geometrical parameters of chip cross-section were measured in order to study the effect of cutting parameters on chip compression ratio and thrust force. It was found that increase in cutting speed significantly affects the chip morphology especially on the structure of free surface and cross-section of the chips. Results also showed that built-up edge on the rake face of tool played an important role on the formation of irregular pattern on the chip back surface.     

Effect of Plasma Nitriding Environment and Time on Plain Fatigue and Fretting Fatigue Behavior of Ti–6Al–4V

Plasma nitriding was performed on Ti–6Al–4V fatigue test samples at 520°C in two environments (nitrogen and nitrogen–hydrogen mixture in a ratio of 3:1) for two time periods (4 and 18 h). Plain fatigue and fretting fatigue tests were conducted on unnitrided and plasma nitrided samples. Plasma nitriding degraded lives under both plain fatigue and fretting fatigue loadings. The samples nitrided in nitrogen exhibited superior lives compared with the samples nitrided in the nitrogen–hydrogen mixture, possibly due to the relatively higher hardness (and presumably lower toughness) of the nitrided layer of the samples nitrided in the nitrogen–hydrogen mixture environment. For those samples nitrided in the nitrogen–hydrogen mixture, those nitrided for 18 h exhibited superior lives compared with those nitrided for 4 h. This trend was observed for samples nitrided in nitrogen gas at lower stress levels only; the converse was true at higher stress levels of 550 MPa and 700 MPa under plain fatigue loading. However, under fretting fatigue loading, the plasma nitriding time did not influence the lives significantly.     

Application of response surface method on machining of Al–SiC nano-composites

The newly fabricated metal matrix nano-composite (MMNC) of Al 7075 reinforced with 1.5 wt% SiC nano-particles was prepared by a novel ultrasonic cavitation method. The high resolution scanning electron micrograph (SEM) and field emission scanning electron micrograph (FESEM) shows uniform distribution and good dispersion of the SiC nanoparticles within the aluminum metal matrix. Electrical discharge machining (EDM) was employed to machine MMNC with copper electrode by adopting face centered central composite design of response surface methodology. Analysis of variance was applied to investigate the influence of process parameters and their interactions. Further a mathematical model has been formulated in order to estimate the machining characteristics. It has been observed that pulse current was found to be the most important factor affecting all the three output parameters such as material removal rate (MRR), electrode wear rate (EWR) and surface roughness (SR). The optimum parameter of combination setting has been identified for the MMNC are voltage 50.00 V, pulse current 8.00 A, Pulse on time 8.00 μs and pulse off time 9.00 μs. Finally the parameters were optimized for maximizing MRR, minimizing EWR and SR using desirability function approach.     

Springback prediction of high-strength sheet metal under air bending forming and tool design based on GA�CBPNN

Based on orthogonal test for air bending of high-strength steel sheets, 125 values of sheet thickness (t), tool gap (c), punch radius (r), ratio of yield strength to Young??s modulus (?? _y /E), and punch displacement (e) are used to model the springback for air bending of high-strength sheet metal using the genetic algorithm (GA) and back propagation neural network (BPNN) approach, where the positive model and reverse model of springback prediction are established, respectively, with GA and BPNN. Adopting the ??object-positive model?Creverse model?? learning method, air bending springback law is studied with positive model and punch radius is predicted by reverse model. Manifested by the experiment for air bending forming of a workpiece used as crane boom, the prediction method proposed yields satisfactory effect in sheet metal air bending forming and punch design.     

Influence of milling on surface integrity of Ti6Al4V—study of the metallurgical characteristics: microstructure and microhardness

The quality of titanium alloy parts in the aeronautical field demands high reliability, which is largely related to surface integrity. Surface integrity is generally defined by three parameters: a geometric parameter, a mechanical parameter and a metallurgical parameter. The present article addresses the influence of milling on the metallurgical parameter for a surface milled in Ti6Al4V material, focusing in particular on the microstructure and microhardness. Observation of the machined surface from a macroscopic perspective highlight an orange peel phenomenon. This effect is the combined result of redeposition and crushing of the milled material. No plastically deformed layer or lengthening of the grains was observed under the milled surface. As far as microhardness is concerned, a slightly softened region was observed under the milled surface. A diffusion of vanadium from the β phase to the α phase was also noted, but with no change in microstructure.     

Grain wear of brazed polycrystalline CBN abrasive tools during constant-force grinding Ti�C6Al�C4V alloy

Constant-force grinding experiments of titanium alloy Ti?C6Al?C4V were carried out with brazed polycrystalline cubic boron nitride (PCBN) abrasive wheel heads. Stock removal and tool wear of PCBN abrasive tools were evaluated by comparison with that of monocrystalline CBN counterparts. Grain wear of the brazed PCBN abrasive tools were examined using optical microscopy and scanning electron microscopy. Fracture mechanism of the PCBN abrasive grains was discussed. The results show that the brazed abrasive tools with PCBN grains give larger stock removal by 25% and the longer service life by 30% than the tools with CBN grains. PCBN abrasive grains have the capability to maintain sharp cutting edges by means of the fracture behavior of microcrystalline CBN particles. In case of strong fixing of the PCBN grains in the Ag?CCu?CTi filler layer, the crack of PCBN abrasive grains are mainly dominated in the intergranular mode dependent upon the joining effects of AlN binder material among the adjacent microcrystalline CBN particles.     

Microstructure and properties of Fe–Al intermetallic coatings on the low carbon steel synthesized by mechanical alloying

Fe–Al coating was obtained on low carbon steel substrates using mechanical alloying and subsequent heat treatment. Light optical microscopy and a scanning electron microscope equipped with energy dispersive spectroscopy were used to conduct the microstructure characterization. Mechanical properties of the coatings were evaluated by microhardness measurements and wear tests. The corrosion behavior was determined by potentiodynamic polarization measurements in 3.5 % NaCl solution. The results of the mechanical and corrosion tests showed that the hardness and wear resistance of the coatings decreased with increasing the milling time, while increase in the milling time resulted in a significant increase in the thickness, porosity level, and corrosion resistance.     

Analysis on microfinger with grooved patterns and its application in electric�Cthermal microgripper

The properties of a microfinger with groove patterns etched on its surface were discussed in this paper. An analytical model of the deflection was built up to study the effect of the groove size on the bending stiffness and the deflection of the grooved finger. The calculation of the analytical model is consistent with the simulation and experimental results. When the grooves depth is 0.5???m, the spring constant of grooved microfinger is 22.8%, smaller than that of flat finger without grooved patterns. The spring constant of the finger decreases with the increasing of the depth of the grooves. A stable novel microelectric?Cthermal gripper is introduced based on the grooved finger. It consists of four sub-cantilever beams positioned at the diagonal lines of a square frame in the end of the main cantilever structure suspended from the silicon substrate, which guarantees an effective contact by the four-point contact area on the top surface to grab components of importance. The thermal-expansion-induced deflection makes the fingers moving vertically from an ??open?? position to a working one. The grooved finger helps to decrease the bending stiffness of the finger and increase the deflection and the initial gap. The simple fabrication process has a feasibility of compatible and mass production.     

Fretting wear of mechanically alloyed AlFe and AlFeMn alloys

A double mechanical alloying process (dMA) was employed to fabricate AlFe and AlFeMn alloys containing finely distributed intermetallic compounds and inert dispersoids (Al₄C₃ and Al₂O₃). The tribological properties of the produced alloys were investigated under fretting conditions. It was shown that the fretting behaviour strongly depends on contact conditions which are mainly determined by displacement and normal load, and the wear resistance of Al alloys can be improved by dispersion of large amount of intermetallics and inert dispersoids. Compared with current and competitive wear resistant Al alloys, the dMA AlFeMn alloy shows attractive wear and friction properties. The results indicate that Al alloys fabricated by dMA are promising for wear-resistance applications.     

Effects of sintering aids and solid lubricants on tribological behaviours of CMC/Al2O3 pair at 650°C

Ten kinds of self-lubricating composites with different amounts of sintering aids and solid lubricants in Al₂O₃ matrix were fabricated by hot-pressed sintering. Their friction and wear behaviours in unlubricated sliding against Al₂O₃ were tested by using a pin-on-disk wear tester at 650°C. It was shown that the amount of sintering aids strongly affected friction coefficient and wear rate of the Al₂O₃–20Ag20CaF₂ composite, the appropriate amount of sintering aids was 10 wt% for beneficial effect on the reduction of wear at 650°C. Also it was shown that the addition of equal quantities of Ag and CaF₂ in Al₂O₃ matrix can promote the formation of the well-covered lubricating film, and effectively reduce the friction and wear. The composite with 40 wt% of lubricants (20 wt% Ag, 20 wt% CaF₂) presented an optimum tribological behavior at 650°C (friction coefficient μ is about 0.3, wear rates are about 4 x 10^-6 mm³/N,m and 5 x 10^-7 mm³/N,m for the disk and pin, respectively). This revised version was published online in August 2006 with corrections to the Cover Date.     

Experimental and theoretical analysis of friction stir welding of Al–Cu joints

This paper presents a study of friction stir welding of aluminium and copper using experimental work and theoretical modelling. The 5083-H116 aluminium alloy and pure copper were successfully friction-stir-welded by offsetting the pin to the aluminium side and controlling the FSW parameters. A theoretical analysis is presented along with key findings. The process temperatures are predicted analytically using the inverse heat transfer method and correlated with experimental measurements. The temperature distribution in the immediate surroundings of the weld zone is investigated together with the microstructures and mechanical properties of the joint. This was supported by a finite element analysis using COMSOL Multiphysics. In this study, two rotational speeds were used and a range of offsets was applied to the pin. The microstructure analysis of the joints was undertaken. This revealed some particles of Cu inclusion in the nugget zone. The energy dispersive spectroscopy showed a higher diffusion rate of aluminium towards the interface while copper maintained a straight base line.     

Mechanical and tribological properties of Cr–Nb double-glow plasma coatings deposited on Ti–Al alloy

Double-glow plasma (DGP) coatings are recommended for metallic components to mitigate the damage induced by complex working conditions in previous studies. In this paper, Nb-rich (Cr–Nb₄) and Cr-rich (Cr₄–Nb) -alloyed layers were formed onto the Ti–Al substrate via a DGP process to enhance its wear resistance. Scratch and Nano-indentation tests were used to evaluate the mechanical properties of the coatings. The tribological behaviour of the coatings were investigated using a pin-on-disc tribometer by rubbing against the GCr15 ball. Results from surface analysis techniques showed that the coatings mainly comprised Cr, Nb and Cr₂–Nb phases, and were well bonded to the substrate. The hardness of the Cr–Nb₄ coating was 11.61GPa and the Cr₄–Nb coating was 9.66 GPa which all higher than that of the uncoated Ti–Al which was 5.65 GPa. However, the critical load of the Cr₄–Nb coating ~21.64 was higher than that of the Cr–Nb₄ coating ~17.6. And the specific wear rate of Cr–Nb₄ coating, Cr₄–Nb coating and uncoated Ti–Al were 3.54 × 10^?4, 0.01 × 10^?4 and 1.53 × 10^?4mm³ N^?1 m^?1_, respectively. The low-wear mechanism of the coatings is discussed in detail in this paper.     

Parameter optimization and mechanism of laser–arc hybrid welding of dissimilar Al alloy and stainless steel

Laser–cold metal transfer arc hybrid welding of 6061 Al alloy and AISI304 stainless steel (304SS) was carried out. Bead morphologies and intermetallic compound (IMC) layer characterizations of the joints were studied in detail. The optimal parameter range for accepted bead appearances (OPRBA) without surface and interface defects was obtained, and the growth mechanism of the IMC layer was summarized. The results showed that the nonuniformity in the thickness and shape along the fusion zone/304SS interface from the top surface to the bottom increases with increasing heat input and is more sensitive to laser power because the interface temperature is dominated by a high-temperature laser keyhole throughout the molten pool. As the welding parameters are within the OPRBA and the heat input is within the range of 80–110 J/mm, the joints are stronger than 130 MPa and the corresponding IMC layer thickness is at the range of 3–6.5 μm. The kinetic analysis showed that a controlling interface temperature no more than 1,120 °C may limit the growth of the IMC layer.     

Chemical characterization and nanomechanical properties of antiwear films fabricated from ZDDP on a near hypereutectic Al–Si alloy

X-ray absorption near edge structure (XANES) spectroscopy was used to monitor the products formed during the breakdown of the engine additive ZDDP during its action as a protective tribochemical agent. This investigation examines the film formed under various physical conditions on a near hypereutectic Al–Si alloy. For the first time, tribochemical films (tribofilms) formed on a high silicon weight content alloy, with virtually no ferrous component have been studied. Phosphorus K- and L-edge spectroscopies show that under typical engine operating conditions, the tribofilms have similar chemical composition over a range of different test conditions. X-ray photoelectron emission microscopy (X-PEEM) reveals that the polyphosphate glasses formed vary in chain length within localized regions. The mechanical properties of the substrate and the tribofilms were acquired using a Triboscope^® from Hysitron Inc. The elastic moduli can be extracted from the indentation curves and show that the tribofilms mechanical properties are similar to those of the tribofilms which form on steel under similar conditions.