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.     

Effect of ball milling the hybrid reinforcements on the microstructure and mechanical properties of Mg-(Ti + n-Al2O3) composites

In this study, composites containing pure magnesium and hybrid reinforcements (5.6 wt.% titanium (Ti) particulates and 2.5 wt.% nanoscale alumina (n-Al₂O₃) particles) were synthesized using the disintegrated melt deposition technique followed by hot extrusion. The hybrid reinforcement addition into the Mg matrix was carried out in two ways: (i) by direct addition of the reinforcements into the Mg-matrix, Mg-(5.6Ti + 2.5n-Al₂O₃) and (ii) by pre-synthesizing the composite reinforcement by ball milling and its subsequent addition into the Mg-matrix, Mg-(5.6Ti + 2.5n-Al₂O₃)_BM. Microstructural characterization revealed significant grain refinement due to reinforcement addition. The evaluation of mechanical properties indicated a significant improvement in microhardness, tensile and compressive properties of the composites when compared to monolithic magnesium. For the Mg-(5.6Ti + 2.5n-Al₂O₃) composite, wherein the reinforcements were directly added into the matrix, the improvement in strength properties occurred at the expense of ductility. For the Mg-(5.6Ti + 2.5n-Al₂O₃)_BM composites with pre-synthesized ball-milled reinforcements, the increase in strength properties was accompanied by an increase/retention of ductility. The observed difference in behaviour of the composites is primarily attributed to the morphology and distribution of the reinforcements obtained due to the ball-milling process, thereby resulting in composites with enhanced toughness.     

Co-electrodeposition and characterization of Cu-Si3N4 composite coatings

Smooth copper coatings containing well-distributed silicon nitride particles were obtained by co-electrodeposition in acidic sulfate bath. The cathodic current density did not show significant influence on incorporated particle volume fraction, whereas the increase of particle concentration in the bath led to its decrease. The increase of stirring rate increased the amount of embedded particles. The microhardness of the composite layers was higher than that of pure copper deposits obtained under the same conditions due to dispersion-strengthening and copper matrix grain refinement and increased with the increase of incorporated particle volume fraction. The microhardness of composites also increased with the increase of current density due to copper matrix grain refining. The composite coatings presented higher strength but lower ductility than pure copper layers. Pure copper and composite coatings showed the same corrosion resistance in 0.5 wt.% H₂SO₄ solution at room temperature.     

Microstructure and wear studies of laser clad Al-Si/SiC(p) composite coatings

Coatings of a composite material consisting of an Al-Si matrix reinforced with SiC particles were produced by laser cladding on UNS A03560 cast Al-alloy substrates from mixtures of powders of Al-12 wt.% Si alloy and SiC. The influence of the processing parameters on the microstructure and abrasive wear resistance of the coatings was studied. For an interaction time of 0.08 s and a power density of 330 MW/m², corresponding to a specific energy of 26 MJ/m², the interaction between SiC and liquid Al is limited and the reinforcement particles remain essentially undissolved. The coating's microstructure is formed of SiC particles dispersed in a matrix consisting of primary α-Al dendrites and interdendritic α-Al + Si eutectic. For interaction times of 0.3 and 0.45 s and a power density of 193 MW/m², corresponding to specific energies of 58 and 87 MJ/m², SiC reacts with molten Al and partially dissolves. The resulting microstructure consists of undissolved SiC particles, found mainly at the bottom of the clad tracks, where the maximum temperature reached during processing is lower, and Al₄SiC₄ and Si particles dispersed in a matrix of α-Al + Si eutectic. The coatings prepared with higher specific energy (58 MJ/m²) present a hardness of 250 V and an abrasive wear rate in three-body abrasion tests with SiC as abrasive of 1.7 × 10^− 4 mm³/m, while those produced with 26 MJ/m² present a hardness of 120 V and a wear rate of 0.43 × 10^− 4 mm³/m. These results show that Al₄SiC₄ and Si increase the hardness of the material by dispersion hardening but do not contribute to its abrasive wear resistance, because they are softer than the abrasive particles, and confirm that the parameters used to prepare Al-Si-SiC composite coatings by laser cladding must be selected so that only minimal reactions occur between SiC and molten Al.     

Microstructural and mechanical properties of Al-Mg/Al2O3 nanocomposite prepared by mechanical alloying

The effect of milling time on the microstructure and mechanical properties of Al and Al-10 wt.% Mg matrix nanocomposites reinforced with 5 wt.% Al₂O₃ during mechanical alloying was investigated. Steady-state situation was occurred in Al-10Mg/5Al₂O₃ nanocomposite after 20 h, due to solution of Mg into Al matrix, while the situation was not observed in Al/5Al₂O₃ nanocomposite at the same time. For the binary Al-Mg matrix, after 10 h, the predominant phase was an Al-Mg solid solution with an average crystallite size 34 nm. Up to 10 h, the lattice strain increased to about 0.4 and 0.66% for Al and Al-Mg matrix, respectively. The increasing of lattice parameter due to dissolution of Mg atom into Al lattice during milling was significant. By milling for 10 h the dramatic increase in microhardness (155 HV) for Al-Mg matrix nanocomposite was caused by grain refinement and solid solution formation. From 10 to 20 h, slower rate of increasing in microhardness may be attributed to the completion of alloying process, and dynamic and static recovery of powders.     

Abrasive Wear of In Situ AlB2/Al-4Cu Composite Material Produced by Squeeze Casting Method

The wear behavior of a weight fraction of particles with up to 30 wt.% in situ AlB₂ flakes reinforced in Al-4Cu matrix alloy composites and fabricated by a squeeze casting method was investigated in a pin-on-disk abrasion test instrument against different SiC abrasives at room conditions. Wear tests were performed under the load of 10 N against SiC abrasive papers of 80, 100, and 120 mesh grits. The effects of sliding speed, AlB₂ flake content, and abrasive grit sizes on the abrasive wear properties of the matrix alloy and composites have been evaluated. The main wear mechanisms were identified using an optical microscope. The results showed that in situ AlB₂ flake reinforcement improved the abrasion resistance against all the abrasives used, and the abrasive wear resistance decreased with an increase in the sliding speed and the abrasive grit size. The wear resistances of the composites were considerably bigger than those of the matrix alloy and increased with increases in in situ AlB₂ flake contents.     

Fabrication and characterization of Al356/SiCp semisolid composites by injecting SiCp containing composite powders

Al356/5 vol.% SiC_p cast composites were fabricated by the injection of reinforcement particles into the melt in three different forms, i.e. as untreated SiC_p, milled particulate Al-SiC_p composite powder, and milled Al-SiC_p-Mg composite powder. The resultant composite slurries were then cast in the semisolid temperature range of the alloy, upon which the effects of the type of injected powder on the distribution and incorporation of the reinforcement particles, along with the hardness of the cast composites, were investigated. Injection of milled composite powders resulted in considerable improvement in SiC_p wetting as well as the incorporation and distribution of SiC_p in the Al356 matrix alloy. Al356/5 vol.% SiC_p composite with well dispersed reinforcement particles of less than 3 μm average diameter was successfully produced by injecting Al-SiC_p-Mg composite powder into the melt. The best microstructural characteristics in terms of the reinforcement incorporation and distribution, and the highest hardness value of the cast composites, were achieved when magnesium was added through the injected composite powder and not directly into the melt.     

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.     

Physical,Mechanical, and Tribological Attributes of Stir-Cast AZ91/SiCp Composite

In the present investigation, composites with silicon carbide particle （SiCp） as reinforcement and AZ91 magnesium alloy as matrix have been synthesized using liquid metal stir-casting technique with optimized processing conditions. The composites with good particle distribution in the matrix, and better grain refinement and good interfacial bonding between the matrix and reinforcement have been obtained. The effect of SiCp content on the physical, mechanical, and tribological properties of Mg-based metal matrix composite （MMC） is studied with respect to particle distribution, grain refinement, and particle/matrix interfacial reactions. The electrical conductivity, coefficient of thermal expansion, microas well as macro-hardness, tensile and compressive properties, and the fracture behavior of the composites along with dry sliding wear of the composites have been evaluated and compared with the base alloy.     

Electroless ternary Ni-W-P alloys containing micron size Al2O3 particles

In the present investigation electroless ternary NiWP-Al₂O₃ composite coatings were prepared using an electroless nickel bath. Second phase alumina particles (1 µm) were used to codeposit in the NiWP matrix. Nanocrystalline ternary NiWP alloys and composite coatings were obtained using an alkaline citrate based bath which was operated at pH 9 and temperature at 88 ± 2 °C. Mild steel was used as a substrate material and deposition was carried out for about 4 h to get a coating thickness of 25 ± 3 µm. Metallographic cross-sections were prepared to find out the coating thickness and also the uniform distribution of the aluminum oxide particles in NiWP matrix. Surface analysis carried out on both the coatings using scanning electron microscope (SEM) showed that particle incorporation in ternary NiWP matrix has increased the nodularity of composite coatings compared to fine nodular NiWP deposits. Elemental analysis of energy dispersive X-ray (EDX) results showed that codeposited P and W elements in plain NiWP deposit were 13 and 1.2 wt.%, respectively. There was a decrease in P content from 13 to 10 wt.% with a marginal variation in the incorporated W (1.01 wt.%) due to the codeposition of aluminum oxide particles in NiWP matrix. X-ray diffraction (XRD) studies carried out on as-plated deposits showed that both the deposits are X-ray amorphous with a grain size of around 3 nm. Phase transformation studies carried out on both the coatings showed that composite coatings exhibited better thermal stability compared to plain NiWP deposits. From the XRD studies it was found that metastable phases such as NiP and Ni₅P₂ present in the composite coatings heat treated at major exothermic peak temperature. Annealed composite coatings at various temperatures revealed higher microhardness values compared to plain NiWP deposits.     

Electrodeposition of sol-enhanced nanostructured Ni-TiO2 composite coatings

A novel electroplating method has been developed to produce nanocrystalline metal-matrix nano-structured composite coatings. A small amount of transparent TiO₂ sol was added into the traditional electroplating Ni solution, leading to the formation of nanocrystalline Ni-TiO₂ composite coatings. These coatings have a smooth surface. The Ni nodules changed from traditional pyramid-like shape to spherical shape. The grain size of Ni was also significantly reduced to the level of 50 nm. It was found that the amorphous anatase TiO₂ nano-particles (∼ 10 nm) were highly dispersed in the coating matrix. The microhardness was significantly increased from 320 HV₁₀₀ of the traditional Ni coating to 430 HV₁₀₀ of the novel composite coating with 3.26 wt.% TiO₂. Correspondingly, the wear resistance of the composite coating was improved by ∼ 50%.     

Pin-on-disk wear behavior in a like-on-like configuration in a biological environment of high carbon cast and low carbon forged Co–29Cr–6Mo alloys

In order to examine the effects of carbides and microstructures on the wear behavior of a biomedical Co–Cr–Mo alloy in Hanks solution, the wear behavior of a forged Co–Cr–Mo alloy without addition of Ni and C (hereafter designated the forged CoCr alloy) and a high carbon cast CoCr alloy (hereafter designated the cast CoCr alloy) sliding against themselves have been investigated using a pin-on-disk type wear testing machine. The wear loss of the forged CoCr alloy was found to be much smaller than that of the cast CoCr alloy. Carbide precipitation in the coarse-grained structure of the cast CoCr alloy would account for the higher abrasive wear loss. The forged CoCr alloy, with no carbide and a refined grain size, which is more prone to strain-induced martensitic transformation, would exhibit excellent like-on-like wear resistance, mostly against surface fatigue wear, compared to the carbide-hardened cast CoCr alloy.     

Selective Laser Melting of in-situ TiC/Ti5Si3 composites with novel reinforcement architecture and elevated performance

A novel Selective Laser Melting (SLM) process was applied to prepare bulk-form TiC/Ti₅Si₃ in-situ composites starting from Ti/SiC powder system. The influence of the applied laser energy density on densification, microstructure, and mechanical performance of SLM-processed composite parts was studied. It showed that the uniformly dispersed TiC reinforcing phase having a unique network distribution and a submicron-scale dendritic morphology was formed as a laser energy density of 0.4 kJ/m was properly settled. The 96.9% dense SLM-processed TiC/Ti₅Si₃ composites had a high microhardness of 980.3HV_0.2, showing more than a 3-fold increase upon that of the unreinforced Ti part. The dry sliding wear tests revealed that the TiC/Ti₅Si₃ composites possessed a considerably low friction coefficient of 0.2 and a reduced wear rate of 1.42 × 10^− 4 mm³/Nm. The scanning electron microscope (SEM) characterization of the worn surface morphology indicated that the high wear resistance was due to the formation of adherent and strain-hardened tribolayer. The densification rate, microhardness, and wear performance generally decreased at a higher laser energy density of 0.8 kJ/m, due to the formation of thermal cracks and the significant coarsening of TiC dendritic reinforcing phase.     

Microstructure, billet surface quality and tensile property of (Al2O3 + Al3Zr)p/Al composites in situ synthesized with electromagnetic field

The aluminum matrix composites reinforced by Al₂O₃ and Al₃Zr particulates were fabricated via in situ chemical reaction between Al-15 wt.% Zr(CO₃)₂ systems. In the process of in situ reaction, a low frequency electromagnetic field (EMF) is employed to improve the conditions of reaction between reactants powder and melt. The optimized electromagnetic density of low frequency EMF is 0.025 T. During the direct chill casting process of composites melt, the custom-designed electromagnetic fields are introduced to control the microstructures and improve the billet surface quality. XRD analysis shows that Al₂O₃ and Al₃Zr reinforcement phases have been obtained. The Lorenz force improves the kinetic condition and accelerates the nucleation of endogenetic particulates. Microstructure analysis by SEM indicates that the average size of particulates and grain size of matrix are refined to 0.5-1 μm and 20-40 μm, respectively. The surface quality of round billet is greatly improved by the high frequency EMF. The results of tensile properties test show that the tensile strength of composites in situ fabricated with EMF is 254.6 MPa, which is increased by about 104 MPa and 69.4% compared with those of composites in situ fabricated without EMF.     

Fabrication of A356 composite reinforced with micro and nano Al2O3 particles by a developed compocasting method and study of its properties

Aluminum/alumina composites are used in automotive and aerospace industries due to their low density and good mechanical strength. In this study, compocasting was used to fabricate aluminum-matrix composite reinforced with micro and nano-alumina particles. Different weight fractions of micro (3, 5 and 7.5 wt.%) and nano (1, 2, 3 and 4 wt.%) alumina particles were injected by argon gas into the semi-solid state A356 aluminum alloy and stirred by a mechanical stirrer with different speeds of 200, 300 and 450 rpm. The microstructure of the composite samples was investigated by Optical and Scanning Electron Microscopy. Also, density and hardness variation of micro and nano composites were measured. The microstructure study results revealed that application of compocasting process led to a transformation of a dendritic to a nondendritic structure of the matrix alloy. The SEM micrographs revealed that Al₂O₃ nano particles were surrounded by silicon eutectic and inclined to move toward inter-dendritic regions. They were dispersed uniformly in the matrix when 1, 2 and 3 wt.% nano Al₂O₃ or 3 and 5 wt.% micro Al₂O₃ was added, while, further increase in Al₂O₃ (4 wt.% nano Al₂O₃ and 7.5 wt.% micro Al₂O₃) led to agglomeration. The density measurements showed that the amount of porosity in the composites increased with increasing weight fraction and speed of stirring and decreasing particle size. The hardness results indicated that the hardness of the composites increased with decreasing size and increasing weight fraction of particles.     

Microstructure and mechanical properties of Mg-Al-Mn-Ca alloy sheet produced by twin roll casting and sequential warm rolling

Microstructural evolution and mechanical properties of twin roll cast (TRC) Mg-3.3 wt.%Al-0.8 wt.%Mn-0.2 wt.%Ca (AM31 + 0.2Ca) alloy strip during warm rolling and subsequent annealing were investigated in this paper. The as-TRC alloy strip shows columnar dendrites in surface and equiaxed dendrites in center regions, as well as finely dispersed primary Al₈Mn₅ particles on interdendritic boundaries which result in the beneficial effect on microstructural refinement of strip casting. The warm rolled sheets show intensively deformed band or shear band structures, as well as finely and homogeneously dispersed Al-Mn particles. No evident dynamic recrystallization (DRX) takes place during warm rolling process, which is more likely attributed to the finely dispersed particle and high solid solution of Al and Mn atoms in α-Mg matrix. After annealing at 350 °C for 1 h, the warm rolled TRC sheets show fine equiaxed grains around 7.8 μm in average size. It has been shown that the present TRC alloy sheet has superior tensile strength and comparative elongation compared to commercial ingot cast (IC) one, suggesting the possibility of the development of wrought magnesium alloy sheets by twin roll strip casting processing. The microstructural evolution during warm rolling and subsequent annealing as well as the resulting tensile properties were analyzed and discussed.     

Development of new magnesium based alloys and their nanocomposites

In the present study, 1 and 2 wt.% of aluminum were successfully incorporated into magnesium based AZ31 alloy to develop new AZ41 and AZ51 alloys using the technique of disintegrated melt deposition. AZ41-Al₂O₃ and AZ51-Al₂O₃ nanocomposites were also successfully synthesized through the simultaneous addition of aluminum (1 and 2 wt.%, respectively) and 1.5 vol.% nano-sized alumina into AZ31 magnesium following same route. Alloy and composite samples were then subsequently hot extruded at 400 °C and characterized. Microstructural characterization studies revealed equiaxed grain structure, reasonably uniform distribution of particulate and intermetallics in the matrix and minimal porosity. Physical properties characterization revealed that addition of both aluminum and nano-sized alumina reduced the coefficient of thermal expansion of monolithic AZ31. The presence of both Al and nano-sized Al₂O₃ particles also assisted in improving overall mechanical properties including microhardness, engineering and specific tensile strengths, ductility and work of fracture. The results suggest that these alloys and nanocomposites have significant potential in diverse engineering applications when compared to magnesium AZ31 alloy.     

Ti-coated SiC particle reinforced sintered Fe-Cu-Sn alloy

Ti-coated SiC particles were developed to improve the wear resistance of Fe-Cu-Sn alloy metal matrices designed for diamond tools. The phase structure of the Ti-coated SiC particles was investigated by X-ray diffraction. Ti coating on SiC was composed of Ti₅Si₃, TiC, and Ti. Excellent interfacial bonding between SiC and the matrix was realized. The SiC/iron alloy composites, prepared by hot pressing at 820 °C, were studied by wear and bending strength tests, and scanning electron microscope. For the composites reinforced by uncoated SiC particles, the wear resistance was improved, but the bending strength decreased. The composites with Ti-coated SiC particles outperformed the composites with uncoated SiC particles in both wear resistance and bending strength tests.     

Influence of yttrium on microstructure and mechanical properties of as-cast Mg-5Li-3Al-2Zn alloy

The influence of Y on microstructure and mechanical properties of as-cast Mg-5Li-3Al-2Zn alloy was investigated. The results show that the phase compositions of Mg-5Li-3Al-2Zn consist of α-Mg and AlLi phases. Adding Y to the alloy results in the formation of Al₂Y compound and facilitates grain refinement. The addition of 0.8 wt.% Y produces the smallest grain size. The tensile tests performed at room temperature show that the additions of Y can improve the mechanical properties of the alloy; the tensile strength and ductility reach peak values when the Y additions are 0.8 wt.% and 1.2 wt.%, respectively. The mechanisms of improvement are related to grain refinement and compound strengthening effects.     

Microstructure and mechanical behavior of a Ti-24Nb-4Zr-8Sn alloy processed by warm swaging and warm rolling

A combination processing technique of warm swaging and warm rolling is proposed to refine grains and improve the mechanical properties of a multifunctional β-type Ti-24Nb-4Zr-8Sn (wt.%) alloy. The results show that a highly swirled marble-like microstructure can be easily produced by warm swaging at an initial temperature of 573 K, whereas it has little effect on the nonlinear elastic deformation compared with the hot forged alloy with an equiaxed microstructure. Although the swirled microstructure has the limitation of an inhomogeneous distribution, swaging has the great advantage of refining the initial subgrains produced by hot forging with little loss of ductility. The following warm rolling at an initial temperature of 673 K results in a uniform microstructure comprising β phase with a size less than ∼200 nm and the precipitation of nanosized α phase. Therefore, significant grain refinement was achieved through the formation and refinement of the subgrains. The ultrafine grained alloy exhibits large scale nonlinear deformation behavior with a recoverable strain of up to ∼3.4% in combination with a high strength of ∼1150 MPa, a low elastic modulus of ∼56 GPa and good ductility of ∼8%. Such an improvement in mechanical properties indicate great potential for biomedical applications.