Reciprocating wear behavior of 7075Al/SiC in comparison with 6061Al/Al2O3 composites

In the present study, the reciprocating wear behavior of 7075Al/SiC composites and 6061Al/Al₂O₃ composites that are prepared through liquid metallurgy route is analyzed to find out the effects of weight percentage of reinforcement and load at the fixed number of strokes on a reciprocating wear testing machine. The Metal Matrix Composite (MMC) pins are prepared with different weight percentages (10, 15 and 20%) of SiC and Al₂O₃ particles with size of 36 μm. Hardness of these composites increases with increase in wt.% of reinforcement. However, the impact strength decreases with increase in reinforcement content. The experimental result shows that the volume loss of MMC specimens is less than that of the matrix alloy. However, the volume loss is greater in 6061Al/Al₂O₃ composites when compared to 7075Al/SiC composites. The temperature rise near the contact surface of the MMC specimens increases with increase in wt.% of reinforcement and applied load. The coefficient of friction decreases with increase in load in both cases.     

Taguchi approach to influence of processing parameters onerosive wear behaviour of Al7034-T6 composites

Taguchi technique was used to predict the influence of processing parameters on the erosive wear behavior Al7034-T6 composite reinforced with SiC and Al₂O₃ particles in different mass fractions. These hybrid metal matrix composites (HMMCs) were fabricated by using a simple technique called stir casting technique. Scanning electron microscope (SEM) was used to study the surface morphology of the composite and its evolution according to processing time. The design of experiment (DOE) based on Taguchi's L₁₆ orthogonal array was used to identify various erosion trials. The most influencing parameter affecting the wear rate was identified. The results indicate that erosion wear rate of this hybrid composite is greatly influenced more by filler content and impact velocity respectively compared to other factors. This also shows the significant wear resistance with the increase in the filler contents of SiC and Al₂O₃ particles, respectively.     

Examination of wire electrical discharge machining of Al2O3p/6061Al composites

Alumina particle reinforced 6061 aluminum matrix composites (Al₂O₃p/6061Al) have excellent physical and chemical properties than those of a traditional metal; however, their poor machinability lead to worse surface quality and serious cutting tool wear. In this study, wire electrical discharge machining (WEDM) is adopted in machining Al₂O₃p/6061Al composite. In the experiments, machining parameters of pulse-on time were changed to explore their effects on machining performance, including the cutting speed, the width of slit and surface roughness. Moreover, the wire electrode is easily broken during the machining Al₂O₃p/6061Al composite, so this work comprehensively investigates into the locations of the broken wire and the reason of wire breaking.The experimental results indicate that the cutting speed (material removal rate), the surface roughness and the width of the slit of cutting test material significantly depend on volume fraction of reinforcement (Al₂O₃ particles). Furthermore, bands on the machined surface for cutting 20 vol.% Al₂O₃p/6061Al composite are easily formed, basically due to some embedded reinforcing Al₂O₃ particles on the surface of 6061 aluminum matrix, interrupt the machining process. Test results reveal that in machining Al₂O₃p/6061Al composites a very low wire tension, a high flushing rate and a high wire speed are required to prevent wire breakage; an appropriate servo voltage, a short pulse-on time, and a short pulse-off time, which are normally associated with a high cutting speed, have little effect on the surface roughness.     

High temperature tribological behaviors of aluminum matrix composites reinforced with solid lubricant particles

The AA6061−10wt.%B₄C mono composite, AA6061−10wt.%B₄C−Gr (Gr: graphite) hybrid composites containing 2.5, 5, and 7.5 wt.% Gr particles, and AA6061−10wt.%B₄C−MoS₂ hybrid composites containing 2.5, 5, and 7.5 wt.% MoS₂ particles were fabricated through stir casting. The dry sliding tribological behaviors of the mono composite and hybrid composites were studied as a function of temperature on high temperature pin-on-disc tribotester against EN 31 counterface. The wear rate and friction coefficient of the Gr-reinforced and MoS₂-reinforced hybrid composites decreased in the temperature range of 30−100 °C due to the combined lubrication offered by the wear protective layer and its solid lubricant phase. Scanning electron microscopy (SEM) observation of the worn pin surface revealed severe adhesion, delamination, and abrasion wear mechanisms at temperatures of 150, 200, and 250 °C, respectively. At 150 °C, transmission electron microscopy (TEM) observation of the hybrid composites revealed the formation of deformation bands due to severe plastic deformation and fine crystalline structure due to dynamic recrystallization.     

Dry Sliding Wear Behavior of a Novel 6351 Al-(Al4SiC4 + SiC) Hybrid Composite

In this research study, the dry sliding wear behaviors of 6351 Al alloy and its composites with single and hybrid reinforcements (ex situ SiC and in situ Al₄SiC₄) were investigated at low sliding speed (1 ms^?1) against a hardened EN 31 disk at different loads. In general, the wear mechanism involved adhesion (coupled with subsurface cracking) and microcutting-abrasion at lower loads. With higher loads, abrasive wear involving microcutting and microplowing along with adherent oxide formation was observed. At higher loads, the abrasive wear mechanism caused rapid wear loss initially up to a certain sliding distance beyond which, by virtue of frictional heat generation and associated temperature rise, an adherent oxide layer was developed at the pin surface, which drastically reduced the wear loss. Moreover, the overall wear rates of all the composites (either single or hybrid reinforcement) were found to be lower than that of the 6351 Al alloy at all applied loads. The ex situ SiC particles were found to resist abrasive wear; while, in situ Al₄SiC₄ particles offered resistance to adhesive wear. Accordingly, the 6351 Al-(SiC + Al₄SiC₄) hybrid composite exhibited the best wear resistance among all composites.     

Effect of thermal-cooling cycle treatment on thermal expansion behavior of particulate reinforced aluminum matrix composites

Two micron SiC particles with angular and spherical shape and the sub-micron Al2O3 particles with spherical shape were introduced to reinforce 6061 aluminium by squeeze casting technology.Microstructures and effect of thermal-cooling cycle treatment(TCCT) on the thermal expansion behaviors of three composites were investigated.The results show that the composites are free of porosity and SiC/Al2O3 particles are distributed uniformly.Inflections at about 300 °C are observed in coefficient of thermal expansion(CTE) versus temperature curves of two SiCp/Al composites,and this characteristic is not affected by TCCT.The TCCT has significant effect on thermal expansion behavior of SiCp/Al composites and CTE of them after 3 cycles is lower than that of 1 or 5 cycles.However,no inflection is observed in Al2O3p/Al composite,while TCCT has effect on CTE of Al2O3p/Al composite.These results should be due to different relaxation behavior of internal stress in three composites.     

Sand Abrasive Wear Behavior of Hot Forged Al 6061-TiO2 Composites

Nickel-coated TiO₂ particulate reinforced Al6061 matrix composites developed using the vortex technique were hot forged at a temperature of 500 °C. A constant deformation ratio of 6:1 was adopted. Hot forged Al6061 alloy and Al6061-TiO₂ composites were then subjected to heat treatment by solutionizing at a temperature of 530 °C for duration of 2 h followed by ice quenching. Both natural and artificial aging at 175 °C were performed on the quenched samples from 2 to 8 h duration in steps of 2. Microstructure, microhardness, and dry sand abrasive wear behavior of both matrix alloy and developed composites in both as-forged and heat-treated conditions have been evaluated. Worn surface studies have been carried out using scanning electron microscope. Results have revealed that nickel-coated TiO₂ particles are uniformly distributed through out the matrix alloy. Microhardness of Al6061-TiO₂ composites increases with increase in percentage of reinforcement. Heat-treated forged alloy and its composites possesses higher hardness when compared with the forged composites. Forged Al6061-TiO₂ composites exhibited lower abrasive wear loss when compared with the forged matrix alloy. Heat treatment has a profound effect on the abrasive wear resistance of both as-forged Al6061 alloy and Al6061-TiO₂ composites.     

Superior Tribological Properties of Particulate Aluminum Matrix Nano Composites

Aluminum is the best metal for producing metal matrix composites which are known as one of the most useful and high-tech composites in our world. Combining aluminum and nano Al₂O₃ particles will yield a material with high mechanical properties. Characterization of tribological properties revealed that the presence of nano particles significantly increased wear resistance of the composite. In case of unreinforced Al alloy, the depth of penetration is governed by the hardness of the specimen surface and applied load. But, in case of Al matrix composite, the depth of penetration of the harder asperities of hardened steel disk is primarily governed by the protruded hard ceramic reinforcement. The hard Al₂O₃ particles act as a protrusion over the matrix, carries a major portion of the applied load and protect the abrasives from penetration into the specimen surface.     

A comparative study on microstructural evolution and surface properties of graphene/CNT reinforced Al6061−SiC hybrid surface composite fabricated via friction stir processing

A comparative study on the surface properties of Al−SiC−multi walled carbon nanotubes (CNT) and Al−SiC−graphene nanoplatelets (GNP) hybrid composites fabricated via friction stir processing (FSP) was documented. Microstructural characterization reveals a more homogeneous dispersion of GNPs in the Al matrix as compared to CNTs. Dislocation blockade by SiC and GNP particles along with the defect-free interface between the matrix and reinforcements is also observed. Nanoindentation study reveals a remarkable ∼207% and ∼27% increment in surface nano-hardness of Al−SiC−GNP and Al−SiC−CNT hybrid composite compared to as-received Al6061 alloy, respectively. On the other hand, the microhardness values of Al−SiC−GNP and Al−SiC−CNT are increased by ∼36% and ∼17% relative to as-received Al6061 alloy, respectively. Tribological assessment reveals ∼56% decrease in the specific wear rate of Al−SiC−GNP hybrid composite, whereas it is increased by ∼122% in Al−SiC−CNT composite. The higher strength of Al−SiC−GNP composite is attributed to the mechanical exfoliation of GNPs to few layered graphene (FLG) in the presence of SiC. Also, various mechanisms such as thermal mismatch, grain refinement, and Orowan looping contribute significantly towards the strengthening of composites. Moreover, the formation of tribolayer by the squeezed-out GNP on the surface is responsible for the improved tribological performance of the composites. Raman spectroscopy and various other characterization methods corroborate the results.     

Effect of SiC particles on microstructure and mechanical property of friction stir processed AA6061-T4

Friction stir processing of AA6061-T4 alloy with SiC particles was successfully carried out.SiC particles were uniformly dispersed into an AA6061-T4 matrix.Also SiC particles promoted the grain refinement of the AA6061-T4 matrix by FSP.The mean grain size of the stir zone (SZ) with the SiC particles was obviously smaller than that of the stir zone without the SiC particles.The microhardness of the SZ with the SiC particles reached about HV80 due to the grain refinement and the distribution of the SiC particles.     

Preparation, microstructure and properties of molybdenum alloys reinforced by in-situ Al2O3 particles

The conventional molybdenum alloys, lacking of hard particles enhancing wear property, have relative poor wear resistance though they are widely used in wear parts. To resolve the above question, Mo alloys reinforced by in-situ Al₂O₃ particles are developed using powder metallurgy method. The in-situ α-Al₂O₃ particles in molybdenum matrix are obtained by the decomposition of aluminum nitrate after liquid-solid incorporation of MoO₂ and Al(NO₃)₃ aqueous solution. The α-Al₂O₃ particles well bonded with molybdenum distribute evenly in matrix of Mo alloys, which refine grains of alloys and increase hardness of alloys. The absolute density of alloy increases firstly and then decreases with the increase of Al₂O₃ content, while the relative density rises continuously. The friction coefficient of alloy, fluctuating around 0.5, is slightly influenced by Al₂O₃. However, the wear resistance of alloy obviously affected by the Al₂O₃ particles rises remarkably with the increasing of Al₂O₃ content. The Al₂O₃ particles can efficiently resist micro-cutting to protect molybdenum matrix, and therefore enhances the wear resistance of Mo alloy.     

High Wear-Resistant Aluminum Matrix Composite Layer Fabricated by MIG Welding with Lateral B<Subscript>4</Subscript>C Powder Injection

In this work, a low-cost technique combining MIG welding and lateral powder injection was developed to fabricate B₄C particles-reinforced aluminum matrix composite (AMC) layer on a T6 heat-treated 7075 aluminum alloy (AA7075-T6) substrate. The AMC layer was 6-7 mm thick and well bonded to the substrate. The B₄C particles were dispersed throughout the AMC layer with an average content of approximately 7 vol.%. No significant reaction products existed either at the particle–matrix interface or in the Al-matrix. In pin-on-disk dry sliding wear tests against Al₂O₃ grinding wheels, the AMC layer exhibited excellent wear resistance with volume wear rate approximately 1/10-3/10 that of the quenched AISI 1045 steel and only approximately 2-7% that of the AA7075-T6 alloy under the same wear conditions. A small addition of ceramic particles can greatly improve wear resistance, suggesting that this technique has good prospects for a wide variety of applications.     

Microstructure and wear performance of Al5083/CeO2/SiC mono and hybrid surface composites fabricated by friction stir processing

Friction stir processing (FSP) was utilized to produce surface composites by incorporating nano-sized cerium oxide (CeO₂) and silicon carbide (SiC) particles individually and in combined form into the Al5083 alloy matrix. The study signified the role of these reinforcements on microstructure and wear behavior of the resultant surface composite layers. The wear characteristics of the resultant mono and hybrid surface composite layers were investigated using a pin-on-disc wear tester at room temperature. The microstructural observations of FSPed regions and the worn out surfaces were performed by optical and scanning electron microscopy. Considerable grain refinement and uniform distribution of reinforcement particles were achieved inside the nugget zone. All the composite samples showed higher hardness and wear resistance compared to the base metal. Among the composite samples, the hybrid composite (Al5083/CeO₂/SiC) revealed the highest wear resistance and the lowest friction coefficient, whereas the Al5083/SiC composite exhibited the highest hardness, i.e., 1.5 times as hard as that of the Al5083 base metal. The enhancement in wear behavior of the hybrid composites was attributed to the solid lubrication effect provided by CeO₂ particles. The predominant wear mechanism was identified as severe adhesive in non-composite samples, which changed to abrasive wear and delamination in the presence of reinforcing particles.     

6061铝合金表面激光熔覆稀土CeO_2+Ni60组织及摩擦磨损性能

为提高铝合金的表面性能,利用激光熔覆技术在6061铝合金表面制备了添加稀土Ce O2的Ni60熔覆层,并通过金相显微镜、SEM、显微维氏硬度计和摩擦磨损试验机等设备研究了CeO2对Ni60熔覆层组织结构、硬度及摩擦磨损性能的影响.结果表明,加入2%的Ce O2可有效地减少熔覆层中的裂纹、孔洞和夹杂物,促进晶粒细化,提高熔覆层的组织均匀性、表面硬度及耐磨损性能;在相同磨粒磨损条件下,CeO2+Ni60熔覆层的耐磨性是铝合金的7.1倍,是Ni60熔覆层的1.6倍;Ni60熔覆层可以显著降低铝合金表面摩擦系数,而添加稀土CeO2能提高Ni60熔覆层的摩擦系数稳定性,从而改善Ce O2+Ni60熔覆层的耐磨性能.     

Effect of Reinforcement Coating on the Oxidation Behavior of AA6061/SiC/20p Composite

The oxidation behavior of SiO₂-active coatings on SiC reinforcement particles of an aluminium-matrix composite, AA6061/SiC/20p, was studied. In order to improve the processing behavior of the composites the SiC particles were coated prior to composite manufacture by a casting procedure, using the sol–gel technique. The oxidation resistance of the composites was analyzed to determine the influence of the manufacturing varibles. Gravimetric tests were used to evaluate the oxidation kinetics at 500°C. The nature of the corrosion products before and after accelerated testing was analyzed by Scanning-Electron Microscopy (SEM), EDX and low-angle X-ray Diffraction (XRD), to determine the influence of the oxidation environment on microstructural changes. Corrosion damage to the AA6061/SiC/20p composite was dependent on the manufacturing process and increased with the manufacturing temperature. Three corrosion products were detected –Al₂O₃, MgO and MgAl₂O₄. The corrosion resistance decreased slightly when the SiO₂ coating was used, and the matrix/SiC interfaces acted as preferential nucleation sites, but the intensity of the oxidation process was low. The use of active coatings on reinforcement particles is justified by the improvement in their wettability by molten aluminum, in spite of some slight loss of oxidation resistance     

Cold spray of SiC and Al<Subscript>2</Subscript>O<Subscript>3</Subscript> with soft metal incorporation: A technical contribution

Al + SiC, Al + Al₂O₃ composites as well as pure Al, SiC, and Al₂O₃ coatings were prepared on Si substrates by the cold gas dynamic spray process (CGDS or cold spray). The powder composition of metal (Al) and ceramic (SiC, Al₂O₃) was varied into 1:1 and 10:1 wt.%, respectively. The propellant gas was air heated up to 330 °C and the gas pressure was fixed at 0.7 MPa. SiC and Al₂O₃ have been successfully sprayed producing coatings with more than 50 μm in thickness with the incorporation of Al as a binder. Also, hard ceramic particles showed peening effects on the coating surfaces. In the case of pure Al metal coating, there was no crater formation on hard Si substrates. However, when Al mixed with SiC and Al₂O₃, craters were observed and their quantities and sizes depended on the composition, aggregation and size of raw materials.     

Corrosion Resistance of Copper Coatings Deposited by Cold Spraying

In the article, a study of corrosion resistance of copper and copper-based cermet (Cu+Al₂O₃ and Cu+SiC) coatings deposited onto aluminum alloy substrate using the low-pressure cold spraying method is presented. The samples were subjected to two different corrosion tests at room temperature: (1) Kesternich test and (2) a cyclic salt spray test. The selected tests were allowed to simulate service conditions typical for urban, industrial and marine environment. Examination of corroded samples included analysis changes on the coating surface and in the microstructure. The physicochemical tests were carried out using x-ray diffraction to define corrosion products. Moreover, microhardness and electrical conductivity measurements were conducted to estimate mechanical and physical properties of the coatings after corrosion tests. XRD analysis clearly showed that regardless of corrosion conditions, for all samples cuprite (Cu₂O) was the main product. However, in the case of Cu+Al₂O₃ cermet coating, chlorine- and sulfate-containing phases such as Cu₂Cl(OH)₃ (paracetamite) and Cu₃(SO₄)(OH)₄ (antlerite) were also recorded. This observation gives better understanding of the lowest microstructure changes observed for Cu+Al₂O₃ coating after the corrosion tests. This is also a justification for the lowest decrease in electrical conductivity registered after the corrosion tests for this coating.     

Wear characteristics of Al−Si−Mg−(Cu)/Al2O3 composites fabricated by thermit reaction

Al₂O₃ particles could be formed by a thermit reaction in an Al-12Si-4Mg-1.5Cu/Al₂O₃ composite due to thein-situ reaction between Al-12Si-4Mg-(1.5Cu) molten metal and SiO₂ particles in preform, which took place at 1173 K for 24 hours, resulting in the decomposition of SiO₂ particles and the formation of Al₂O₃ particles simultaneously. The mechanically mixed layers (MMLs) consisting of α-Fe and Fe oxides existed on the subsurface layers beneath the worn surface in composites or mother alloys, which improved the wear resistance. The characteristics of wear resistance and hardening of an Al-12Si-4Mg-1.5Cu/Al₂O₃ composite are superior to those of the Al-12Si-4Mg/Al₂O₃ composite and Al-12Si-4Mg-1.5Cu alloy.     

Abrasive wear behavior of Ni-P coated Si3N4 reinforced Al6061 composites

Ni-P coated Si₃N₄ reinforced Al6061 composites were fabricated by vortex method. Percentage of reinforcement was varied from 6 wt.% to 10 wt.% in steps of 2. Cast matrix alloy and developed composites were hot forged at a temperature of 500 °C using a 300T hydraulic hammer. Both as cast and hot forged matrix alloy and its composites were subjected to microstructure studies, grain size analysis, microhardness and abrasive wear tests. Microstructure studies reveal uniform distribution of silicon nitride particles with good bond between matrix and reinforcement in both as cast and hot forged condition. It is observed that, increased content of reinforcement in both as cast and hot forged composites do result in significant grain refinement. However, when compared with as cast matrix alloy and its composites hot forged alloy and its composites exhibits higher extent of grain refinement. Both as cast and hot forged composites exhibit improved microhardness and abrasive wear resistance when compared with the unreinforced alloys under identical test conditions. Abraded worn surfaces were examined using scanning electron microscopy (SEM) for possible wear mechanisms. Increased abrasive particle size and load has resulted in larger extent of grooving leading to increased abrasive wear loss for both the matrix alloy and developed composites.     

Sintering and sliding wear studies of B4C-SiC composites

Dense boron carbide (B₄C) – silicon carbide (SiC) composites were obtained by spark plasma sintering technique at 1800°C with 3 wt% and 6 wt% aluminium oxide (Al₂O₃) additives. Addition of sintering additives results in formation of aluminium silicate (Al₂SiO₅) liquid phase which accelerates sintering kinetics and helps in obtaining high density ~ 99%. Microstructures reveal uniformly distributed SiC particles in B₄C matrix. Increase in alumina from 3 wt% to 6 wt% results in decrease in hardness from 35.1 ± 0.8 to 33.7 ± 0.9 GPa, and increase in fracture toughness from 5.9 ± 0.4 to 6.5 ± 0.4 MPam^0.5. Using a ball-on-disk tribo tester under dry unlubricated conditions at 5, 10 or 15 N load, influence of alumina content on friction and wear properties of B₄C-SiC composites was investigated against SiC counterbody with a linear speed of 0.08 m/s for 60 min. The coefficient of friction (COF) increased from 0.25 to 0.65 with load, and the influence of alumina on frictional behaviour appeared to be negligible. With increase in load, wear volume of the composites increased from 7.5 × 10⁻² mm³ to 16.1 × 10⁻² mm³ for B₄C-10 wt% SiC - 3 wt% Al₂O₃ and from 4.7 × 10⁻² mm³ to 14.8 × 10⁻² mm³ for B₄C-10 wt% SiC - 6 wt% Al₂O₃ composites. Microcracking, abrasion and pull-outs contributed as major wear mechanisms of composites in selected wear conditions. The relation between wear behaviour and mechanical properties of sintered composites is discussed.