Prediction of abrasive wear rate of in situ Cu–Al2O3 nanocomposite using artificial neural networks

In this work, artificial neural networks (ANNs) technique was used in the prediction of abrasive wear rate of Cu–Al₂O₃ nanocomposite materials. The abrasive wear rates obtained from series of wear tests were used in the formation of the data sets of the ANN. The inputs to the network are load, sliding speed, and alumina volume fraction. Correlation coefficients between the experimental data and outputs from the ANN confirmed the feasibility of the ANNs for effectively model and predict the abrasive wear rate. The comparison between the ANNs and the multi-variable regression analysis results showed that using ANNs technique is more effective than multi-variable regression analysis for the prediction of abrasive wear rate of Cu–Al₂O₃ nanocomposite materials. Optimization of the training process of the ANN using genetic algorithm (GA) is performed and the results are compared with the ANN trained without GA. Sensitivity analysis is also done to find the relative influence of factors on the wear rate. It is observed that load and alumina volume fraction effectively influence the wear rate.     

Influence of turning parameters on the machinability of homogenized Al–Cu/TiB2 in situ metal matrix composites

The increasing demand for high-strength and lightweight materials in automobile, defense, and aerospace applications necessitates the development of new composite materials and their machinability studies with wide spectrum. In this aspect, an attempt has been made to investigate the machinability characteristics of homogenized Al–Cu/TiB₂ in situ metal matrix composites. The effect of parameters, such as cutting speed, feed, and depth of cut, on performance measures, such as cutting force and surface roughness, were investigated during turning operations. As a secondary objective, the built-up edge (BUE) and chip formation are also examined. Experimental results show that better surface finish is obtained at higher cutting speed and low feed. BUE formation is observed only at low cutting speed. The chip breakability is improved due to the presence of reinforcement.     

In situ formation of Al–Al3Ni composites on commercially pure aluminium by friction stir processing

Possibility of the formation of Al–Al₃Ni composite layers on commercial pure aluminium plates by friction stir processing (FSP) has been studied. It is believed that the hot working nature of FSP can effectively promote the exothermic reaction between Al and added Ni powder to produce Al₃Ni intermetallic compounds in the aluminium matrix. In this study, the effects of the rotational and traverse speed of the tool as well as the number of FSP passes on the in situ formation of Al₃Ni in aluminum matrix were examined. Besides, the microstructure and microhardness of the fabricated surface layers were also studied. The results showed that the ratio of tool rotational speed to traverse speed (ω/υ) is the main controlling parameter of the heat generated during FSP and hence the reaction between aluminium and nickel. Increasing the number of FSP passes also promoted the reaction between Ni and Al and improved the distribution of Al₃Ni compounds, too. The composite layer achieved by six passes of FSP showed the highest hardness, which was almost twice of that of the base metal.     

Wear behavior of Cu–La2O3 composite with or without electrical current

A new type Cu–La₂O₃ composite was fabricated by internal oxidation method using powder metallurgy. Sliding wear behavior of the Cu–La₂O₃ composites was studied by using a pin-on-disk wear tester under dry sliding conditions with or without electrical current, rubbing against GCr15 type bearing steel disk at a constant sliding speed of 20 m/s. The influence of varying applied load and electrical current was investigated. The worn surfaces were examined using scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) to determine the wear mechanisms. The results showed the Cu–La₂O₃ composites had an electrical conductivity of 81.9% IACS (International Annealed Copper Standard, 100% IACS = 58 MS/m) and a hardness of HV105. The wear rate of the Cu–La₂O₃ composite pins increased with the increase in the electrical current at high sliding speed. The main wear mechanisms of the Cu–La₂O₃ composites were found to be adhesive wear, abrasive wear and arc erosion.     

Characterization of hole circularity in pulsed Nd:YAG laser micro-drilling of TiN–Al2O3 composites

In micro-manufacturing, circularity of a drilled hole at entry and exit are important attributes which greatly influence the quality of a drilled hole. This study investigates the effect of five parameters in the circularity of drilled holes in pulsed Nd:YAG laser micro-drilling process. The drilling operation has been carried out on titanium nitride–alumina (TiN–Al₂O₃) composite, an important electroconductive ceramics suitable for wear and heating applications. The effect of various process parameters like lamp current, pulse frequency, pulse width, air pressure, and focal length of Nd:YAG laser micro-drilling on hole circularity at entry and exit has been investigated through response-surface-methodology-based experimental study. The parametric combination for optimal hole circularity at entry and exit has also been evaluated.     

Mechanism of material removal during tribological behaviour of aluminium matrix (Al–Zn–Mg–Cu) composites

In the present study an attempt is made to synthesise Al–Zn–Mg–Cu alloy–SiC particle reinforced composite using liquid metallurgy route and to characterize the composites in terms of microstructure and sliding wear. It is to be noted that seizure pressure is enhanced by 37.5% due to the addition of 10 wt% of SiC particles in aluminium alloy. The wear mechanism is dictated by the formation and stability of oxide layer, mechanically mixed layer (MML) and subsurface deformation and cracking. There is also mutual transfer of pin surface and counter surface materials. The critical load at which MML gets removed is also examined. These phenomenon are represented schematically in this paper and the wear mechanism is explained.     

Influence of graphite content on the dry sliding and oil impregnated sliding wear behavior of Al 2024–graphite composites produced by in situ powder metallurgy method

The influence of graphite content on the dry sliding and oil impregnated sliding wear characteristics of sintered aluminum 2024 alloy–graphite (Al/Gr) composite materials has been assessed using a pin-on-disc wear test. The composites with 5–20 wt.% flake graphite particles were processed by in situ powder metallurgy technique. For comparison, compacts of the base alloy were made under the same consolidation processing applied for Al/Gr composites. The hardness of the sintered materials was measured using Brinell hardness tester and their bending strength was measured by three-point bending tests. Scanning electron microscopy (SEM) was used to analyze the debris, wear surfaces and fracture surfaces of samples. It was found that an increase in graphite content reduced the coefficient of friction for both dry and oil impregnated sliding, but this effect was more pronounced in dry sliding. Hardness and fracture toughness of composites decreased with increasing graphite content. In dry sliding, a marked transition from mild to severe wear was identified for the base alloy and composites. The transition load increased with graphite content due to the increased amount of released graphite detected on the wear surfaces. The wear rates for both dry and oil impregnated sliding were dependent upon graphite content in the alloy. In both cases, Al/Gr composites containing 5 wt.% graphite exhibited superior wear properties over the base alloy, whereas at higher graphite addition levels a complete reversal in the wear behavior was observed. The wear rate of the oil impregnated Al/Gr composites containing 10 wt.% or more graphite particles were higher than that of the base alloy. These observations were rationalized in terms of the graphite content in the Al/Gr composites which resulted in the variations of the mechanical properties together with formation and retention of the solid lubricating film on the dry and/or oil impregnated sliding surfaces.     

Mechanical and tribological properties of NiCr–Al2O3 composites at elevated temperatures

The effect of Al₂O₃ content on the mechanical and tribological properties of Ni–Cr alloy was investigated from room temperature to 1000 °C. The results indicated that NiCr–40 wt% Al₂O₃ composite exhibited good wear resistance and its compressive strength remained 540 MPa even at 1000 °C. The values obtained for flexural strength and fracture toughness at room temperature were 771 MPa, 15.2 MPa m^1/2, respectively. Between 800 °C and 1000 °C, the adhesive and plastic oxide layer on the worn surface of the composite was claimed to be responsible for low friction coefficient and wear rate.     

Wear development on wiper Al2O3–TiC mixed ceramic tools in hard machining of high strength steel

This paper explores the wear mechanisms occurring for the mixed ceramic inserts against 60 HRC alloy steel (equivalent to AISI 5140 or DIN 41Cr4) specimens in dry and hard finish turning operations. Several machining wear tests were performed under varying feed rate, constant cutting speed of 100 m/min and small depth of cut of 0.2 mm. Light optical microscopy (LOM), scanning electron microscopy (SEM) and back-scattering electron (BSE) technique were employed to observe morphological features of worn surfaces produced by various wear mechanisms. In addition, the elemental compositions of wear products were evaluated by energy-dispersive X-ray (EDX) micro-analysis, called sometimes energy-dispersive X-ray spectroscopy (EDS). As a result, both microscopic and microstructural aspects of ceramic tool wear were considered. In general, wear mechanisms identified in the machining tests involve abrasion, fracture, plastic flow and transferred layers, BUE and tribochemical effects. Specific wear symptoms appeared depending on the mechanical and thermal conditions generated in the wear zones. In particular, two types of material transfer with different morphologies occurring at the rake–chip interface are distinguished.     

The influence of Cu addition on precipitation in Fe–Cr–Ni–Al–(Cu) model alloys

Precipitation in Fe–Cr–Ni–Al–(Cu) model alloys was investigated after ageing for 0.25, 3, 10 and 100 h at 798 K. Characterization of nanoscale precipitates was performed using three-dimensional atom probe microscopy and transmission electron microscopy. The precipitates are found to be enriched in Ni and Al (Cu) and depleted in Fe and Cr. After 0.25 h of ageing the number density of precipitates is ∼8×10²⁴ m⁻³, their volume fraction is about 15.5% and they are near-spherical with an average diameter of about 2–3 nm. During further ageing the precipitates in the both alloys grow, but the coarsening behaviour is different for both alloys. The precipitates of the Cu-free alloy grow much faster compared with the Cu-containing alloy and their density decreases. Precipitates in Cu-free alloy change to plate shaped even after 10 h of ageing, whereas those of Cu-containing alloy remain spherical up to 10 h of ageing. The influence of Cu addition on precipitation in these model alloys is discussed with respect to the different coarsening mechanisms.     

Tribological properties of NiCr–Al2O3 cermet-based composites with addition of multiple-lubricants at elevated temperatures

The tribological properties of NiCr-40 wt% Al₂O₃ (NC40A) cermet-based composites containing SrSO₄ and other lubricant (graphite, MoS₂ and Ag) against alumina ball were evaluated to identify their self-lubrication mechanisms from room temperature to 800 °C. The composites demonstrated distinct improvements in effectively reducing friction and wear, as compared to NC40A cermet. The best results were observed for NC40A–10SrSO₄–10Ag composite, which exhibited satisfactory reproducibility of friction coefficient over a wide temperature range (200–800 °C) through high temperature cyclic friction tests due to the formation of synergistic lubricating films SrAl₄O₇, NiCr₂O₄ and Ag on the contact surface.     

A comparative study on the wear properties of coarse-grained Al6061 alloy and nanostructured Al6061–Al2O3 composites

Wear behavior of nanostructured Al6061 alloy and Al6061–Al₂O₃ nanocomposites produced by milling and hot consolidation were investigated. The samples were characterized by hardness test, pin-on-disk wear test, X-ray diffraction (XRD), and scanning electron microscopy (SEM). Nanocomposites containing 3 vol% Al₂O₃ showed a maximum hardness of 235 HV and optimum wear rate of 4×10⁻³ mg/m. Increasing the amount of Al₂O₃ up to 5 vol% resulted in decrease in hardness values (∼112 HV) and a sharp rise in wear rate (∼18×10⁻³ mg/m).     

Tribological Properties and Wear Mechanisms of NiCr–Al2O3–SrSO4–Ag Self-Lubricating Composites at Elevated Temperatures

NiCr–Al₂O₃–SrSO₄–Ag self-lubricating composites were prepared by powder metallurgy method and the tribological properties of composites were evaluated by a ball-on-disk tribometer against alumina ball at wide temperature range from the room temperature to 1,000 °C in air. The linear coefficient of thermal expansion was evaluated for investigation of thermal stability of composites. The tribo-chemical reaction films formed on the rubbing surfaces and their effects on the tribological properties of composites at different temperatures were addressed according to the surface characterization by SEM, XRD, and XPS. The results show that the NiCr–Al₂O₃ composite with addition of 10 wt% SrSO₄ and 10 wt% Ag exhibits satisfying friction and wear properties over the entire temperature range from room temperature to 1,000 °C. The composition of the tribo-layers on the worn surfaces of the composites is varied at different temperatures. The synergistic lubricating effect of SrAl₄O₇, Ag, and NiCr₂O₄ lubricating films formed on worn surfaces were identified to reduce the friction coefficient and wear rate from room temperature to 800 °C. Meanwhile, at 1,000 °C, the SrCrO₄ and NiAl₂O₄ was formed on the worn surfaces during sliding process, combining with the NiCr₂O₄, Al₂O₃, Cr₂O₃, Ag, and Ag₂O, which play an important role in the formation of a continuous lubricating film on the sliding surface.     

Influence of Test Conditions on the Lubricated Friction and Wear Behaviour of Al–25Zn–3Cu Alloy

The friction and wear properties of Al–25Zn–3Cu alloy were investigated over a range of oil flow rate, pressure and sliding speed using a pin-on-disc machine, after examining its microstructure and mechanical properties. The results obtained were compared with those of a conventional-bearing material (SAE 65 bronze). It was observed that the microstructure of the Al–25Zn–3Cu alloy consisted of aluminium-rich α, eutectoid α + η and θ phases, while the microstructure of the SAE 65 bronze revealed copper-rich α, and eutectoid α + δ phases. It was found that the friction coefficient, temperature and wear volume of both the alloys decreased sharply with increasing oil flow rate and attained almost constant levels beyond a certain range of oil flow rate. It was also found that the friction coefficient and the wear volume of the alloys decreased with increasing pressure, but was observed to be almost independent of the sliding speed. The Al–25Zn–3Cu alloy exhibited higher wear resistance as compared to that of the bronze under all the test conditions. Smearing type of adhesion appeared to be the most effective wear mechanism for the Al–25Zn–3Cu alloy, while abrasion dominated one for the SAE 65 bronze.     

Wear analysis of Cu–Al coating on Ti–6Al–4V substrate under fretting condition

Fretting behavior of Cu–Al coating on Ti–6Al–4V substrate was investigated with and without fatigue load. Soft and rough Cu–Al coating resulted in abrasive wear and a large amount of debris remained at the contact surface, which caused an increase in tangential force during the fretting test under gross slip condition. Fretting in the partial slip condition also showed the wear of coating. To characterize wear, dissipated energies during fretting were calculated from fretting loops and wear volumes were obtained from worn surface profiles. Energy approach of wear analysis showed a linear relationship between wear volume and accumulated dissipated energy. This relationship was independent of fatigue loading condition and extended from partial slip to gross slip regimes. As an alternate but simple approach for wear analysis, accumulated relative displacement range was correlated with the wear volume. This also resulted in a linear relationship as in the case of accumulated dissipated energy suggesting that the accumulated relative displacement range can be used as an alternative parameter for dissipated energy to characterize the wear. When the maximum wear depth was equal to the thickness of Cu–Al coating, harder Ti–6Al–4V substrate inhibited further increase in wear depth. Only when a considerable energy was supplied through a large value of the applied displacement, wear in the substrate material could occur beyond the thickness of coating.     

Tribological behaviour of alternate hypereutectic Al–Si alloys with different antiwear additives

Abstract

Two alternate hypereutectic Al–Si alloys, varying in composition and processing route, were investigated alongside their commercial equivalents, with two different lubricant antiwear chemistries. A reciprocating sliding wear test was used with a steel nitrided piston ring on substrate configuration. The conditions (average load and speed) replicated those seen in a fired gasoline engine. The oil containing zinc dialky dithiophosphate (ZDDP) antiwear gave the best antiwear protection, determined from the lower specific wear rate and friction coefficient with all alloy types. A zinc–phosphorus–sulphur based protective film was found in the wear track. The poor performance of a zinc free active phosphate ester (ashless antiwear additive) was thought to be due to no phosphorus based film forming. The presence of a calcium based film, originating from the detergent, suggests that it had a higher film forming affinity in the competitive surface interactions. The commercially termed Alusil (A390, Al–18·5Si alloy) is currently used as cylinder material in various gasoline engines. This reference material had a different microstructure to that produced by rheo-die casting. The high shear rate during the rheo-die casting process produced a finer microstructure with smaller but more numerous primary and secondary silicon particles. The increased surface area was envisaged to increase the wear resistance and evenly distribute the applied load. However, the reference Alusil gave considerably better wear performance with all oil types tested. The wear track microstructures showed material loss, void formation with fracture, fragmentation and sinking of the primary silicon particles into the aluminium matrix. The damage was controlled to an extent by use of the ZDDP oil with an organic friction modifier. An uneven wear pattern termed stick slip was occasionally observed. It was found not to be dependent on substrate alloy or oil type. The only differences were greater fluctuation in friction coefficient during the running-in period, higher overall wear track hardness and striated lines on a considerable number of fractured primary silicon particles.     

Al2O3—Cu基复合材料的制备

用内氧化技术制备了弥散硬化Ａｌ２Ｏ３－Ｃｕ基复合材料，研究了其显微组织特性。结果表明，该技术简单，易行，复合材料中的Ａｌ２Ｏ３粒子数量随基体中铝含量的增加而增加。     

Investigations of flank wear, cutting force, and surface roughness in the machining of Al-6061�CTiB2 in situ metal matrix composites produced by flux-assisted synthesis

This paper presents the results of an experimental investigation on the machinability of in situ Al-6061?CTiB₂ metal matrix composite (MMC) prepared by flux-assisted synthesis. These composites were characterized by scanning electron microscopy, X-ray diffraction, and micro-hardness analysis. The influence of reinforcement ratio of 0, 3, 6, and 9?wt.% of TiB₂ on machinability was examined. The effect of machinability parameters such as cutting speed, feed rate, and depth of cut on flank wear, cutting force and surface roughness were analyzed during turning operations. From the test results, we observe that higher TiB₂ reinforcement ratio produces higher tool wear, surface roughness and minimizes the cutting forces. When machining the in situ MMC with high speed causes rapid tool wear due to generation of high temperature in the machining interface. The rate of flank wear, cutting force, and surface roughness are high when machining with a higher depth of cut. An increase in feed rate increases the flank wear, cutting force and surface roughness.     

Wear of SiC-reinforced Al-matrix composites in the temperature range 20–200°C

The influence of temperature on wear resistance was studied in a 2618 Al alloy reinforced with 15 vol% SiC particulates and the corresponding unreinforced alloy in the temperature range 20–200 °C. A transition from mild to severe wear (shown by an increase of two orders of magnitude in the wear rates) was observed in both materials beyond a critical temperature. The addition of the SiC particulates improved the wear resistance by a factor of two in the mild wear region, and the transition temperature, which was around 50 °C higher in the composite. This higher transition temperature was due to the retention of the mechanical properties in the composite at elevated temperature. Heat treatments (either natural or artificial aging) did not modify substantially the wear resistance of either the composite or the unreinforced alloy.