Micro-structural Analysis and Densification Behavior of Al–ZrB<Subscript>2</Subscript> Powder Metallurgy Composite During Upsetting

The performance of the product components in application greatly depends on the morphological parameters and inherent capabilities of the material. In the present study, Al–ZrB₂ composite is made out of powder metallurgy route. Incremental weight% (0, 2, 4 and 6 wt%) of ZrB₂ were added into Al matrix to produce different composites. Composites were prepared by cold axial compaction followed by pressureless sintering at 550 °C for 1 h in controlled atmosphere (Ar gas). Hardness increased with the amount of ZrB₂ in the composite. To enhance the properties further, composites were deformed at 25, 400 and 500 °C respectively. The size, shape and orientation of the grains in the deformed composites were analyzed and correlated with the mechanical properties. The mechanical adhesion of ZrB₂ particle with the Al matrix was examined in different composites during different temperature conditions of deformation process. The fracture strain of the composites decreased with increase of ZrB₂ in the composite.     

Synthesis and Characterization of Al–Al/(SiO<Subscript>2</Subscript>)<Subscript>np</Subscript> Composite by Powder-in-Tube Method

In this study, a macro-nanocomposite of Al–Al/(SiO₂)_np was synthesized using powder-in-tube method. Pure aluminum cylinders were cast and then machined to prepare tubes. Nanocomposite powders of Al/(SiO₂)_np were prepared by mixing 1 and 2 wt% SiO₂ nano-particle with aluminum. Then macro-nanocomposites were prepared by compaction of the nanocomposites inside the tubes. The effects of reinforcement weight fraction, volume fraction of nanocomposite in the macro-nanocomposites and hot extrusion on the microstructure and mechanical properties were investigated. Scanning electron microscope (SEM) and optical microscope (OM) were used for microstructural examinations. Mechanical properties were investigated using tensile and compression tests at room temperature. The results revealed that when 25 vol% of the powder-in-tube composite was the nanocomposite reinforced with 2 wt% of nano-particle, the tensile strength was increased by 10.8%. Tensile strength was improved by up to 24% when 64 vol% of nanocomposite reinforced with 1 wt% of nano-particle was employed. Additionally, significant increase in compressive strength was achieved. This is noteworthy that coupling of a pure aluminum sheath with the nanocomposite enhanced the strength with limited loss of ductility. Micrographs showed integrated composites in which the interface between the sheath and the core had no defects.     

Characterization of Vacuum Plasma Sprayed Reinforced Hydroxyapatite Coatings on Ti–6Al–4V alloy

Two reinforced hydroxyapatite (HA) coatings with an intermediate layer of zirconia were deposited on Ti–6Al–4V by vacuum plasma spray (VPS) technique. In first coating, HA was reinforced with 10 wt % Al₂O₃ whereas in second coating, HA was reinforced with 10 wt % ZrO₂. The objective of this study was to investigate the microstructure, phase formation and mechanical properties like hardness and bond strength of as-sprayed coatings and the coatings after post coating heat treatment at 700 °C for 1 h. The characterization of the coatings was performed by using SEM/EDAX, XRD, porosity, crystallinity and roughness measurement. The coatings were also evaluated for mechanical properties like hardness and tensile bond strength. It was observed that after post coating heat treatment, crystallinity increased and porosity decreased which indicated recrystallization of amorphous phases of as-sprayed coatings. Heat treatment resulted into improvement in cross-sectional hardness, however sharp decrease in bond strength was observed.     

Multi-objective Optimization of Electrodeposition of Ni–Al<Subscript>2</Subscript>O<Subscript>3</Subscript> Nano Composite Coating on Al6061 Substrate

Response surface methodology based Grey relation analysis has been used to optimize the coating parameters of composite coating on aluminium based alloys. This approach gives the best combination of coating parameters to get maximum coating thickness, adhesive strength, microhardness, and minimum wear rate. For each response, the effect of coating parameters at different levels have been discussed. From Grey relation grade, the optimum parameters for better composite coating performance are found to be: temperature, 34 °C; current density, 1 A/dm²; and percentage of particle loading, 1.2 g/L. At 95% significance level, the Current density shows statistical significance on overall composite coating performance.     

Synthesis and Characterization of Al–Mg–SiO<Subscript>2</Subscript> Particulate Composite Using Amorphous SiO<Subscript>2</Subscript> from Rice Husk Ash

This paper discusses the effect of the dispersion of amorphous nano size (35–55 nm) SiO₂ particles in Al–Mg (5%) alloy. Amorphous SiO₂ (>95% SiO₂) extracted from rice husk was added to the Al–Mg (5%) alloy in the proportion of 5 wt% of the Al–Mg alloy. The work aims to study the evolution of different phases like MgAl₂O₄, Mg₂Si, and MgO in Al–Mg–SiO₂ composite using amorphous nano SiO₂. Experimental results of the synthesized composite show presence of MgAl₂O₄ (Spinel structure) and other phases like MgO and Mg₂Si which impart hardness of 126.82 HV_10g to the composite. The Al–Mg (5%) SiO₂ composite microstructure appeared as a typical lamellar structure. The XRD and energy dispersive spectroscopy analysis display the presence of Mg₂Si formed along the grain boundary.     

Structure–Property Correlation of Al–SiC–Al<Subscript>2</Subscript>O<Subscript>3</Subscript> Composites: Influence of Processing Temperatures

This paper deals with the change in the mechanical behaviour of aluminium alloy 6061 with different weight percentage of Silicon Carbide (SiC) and Alumina (Al₂O₃) ceramic powders and change in processing temperature. The crucial properties of this aluminium alloy are relatively light in weight, better corrosion resistance, wear resistance and have low production cost. These properties make them pleasant for different applications such as aerospace, defense, automotive sectors. The purpose of designing Metal Matrix Composite is to figure the desired qualities of metals and ceramics. The fabrication of the MMC was done by stir casting process. The tensile test, hardness test and impact test were performed on these composite samples to study the mechanical behaviour. The result shows that there is a significant increase in tensile strength for the samples that are processed at the temperature of 750 °C with a higher weight fraction of SiC. Also, the samples made at 850 °C exhibit better hardness and impact strength with increased content of alumina. The internal microstructure of the composites was analyzed by scanning electron microscope.     

Evaluation of Microstructural Features of HVOF Sprayed Ni–20Al Coatings

The present study evaluates the microstructural features of high velocity oxy-fuel (HVOF) sprayed Ni–20Al coatings with liquefied petroleum gas (LPG) as fuel. The Ni–20Al coatings are commonly used for bond coat applications and as high temperature oxidation resistant coating. The quality of the deposited coating has been evaluated in terms of porosity, oxide content, surface roughness, micro-hardness, composition and morphology (surface and cross-sectional). The results indicate that, it is possible to develop dense Ni–20Al coatings with low oxide and porosity content along with high surface roughness using HVOF technology. Importantly, HVOF sprayed Ni–20Al coatings show better quality as compared to air plasma spray and can be used as an alternative to VPS in terms of quality to cost ratio for bond coat applications.     

Deposition,Characterization and Evaluation of Monolayer and Multilayer Ni,Ni–P and Ni–P–Nano ZnO<Subscript>p</Subscript> Coatings

Ni, Ni–P and Ni–P–ZnO_p monolayer films along with multilayer coatings containing different arrangements of these layers were produced on steel substrates by electrodeposition and electroless deposition techniques. Co-deposition of ZnO nano-particles, as well as morphology, cross-section, microstructure and microhardness of coatings were investigated. Corrosion behaviors of monolayer coatings were studied by potentiodynamic polarization and electrochemical impedance spectroscopy techniques, and the results were compared to multilayer films. Results revealed that, Ni–P–1.5 vol% ZnO_p monolayer film obtained from a bath with 4 g L^?1 of these particles had the highest hardness between all samples. Further addition of nano-particles to the bath lead to the formation of discontinuous films. Most of the multilayer coatings with different arrangements exhibited higher corrosion resistance as compared to monolayer films. Corrosion current density of three-layer Ni–P–ZnO_p/Ni/Ni–P coating, considered as the most corrosion resistant film, was about 538 times lower than monolayer Ni–P coating.     

Structure and Wear Resistance of Plasma-Sprayed NiCrBSiC–TiCrC Composite Powder Coatings

Powder Metallurgy and Metal Ceramics - The NTC20 and NTC40 composite powders were produced by conglomeration from the NiCrBSiC self-fluxing alloy with additions of 20 and 40 wt.% TiCrC,...     

Synthesis of new metal-matrix Al–Al<Subscript>2</Subscript>O<Subscript>3</Subscript>–graphene composite materials

The mechanism of formation of ceramic microparticles (alumina) and graphene in a molten aluminum matrix is studied as a function of the morphology and type of precursor particles, the temperature, and the gas atmosphere. The influence of the composition of an aluminum composite material (as a function of the concentration and size of reinforcing particles) on its mechanical and corrosion properties, melting temperature, and thermal conductivity is investigated. Hybrid metallic Al–Al₂O₃–graphene composite materials with up to 10 wt % alumina microparticles and 0.2 wt % graphene films, which are uniformly distributed over the metal volume and are fully wetted with aluminum, are synthesized during the chemical interaction of a salt solution containing yttria and boron carbide with molten aluminum in air. Simultaneous introduction of alumina and graphene into an aluminum matrix makes it possible to produce hybrid metallic composite materials having a unique combination of the following properties: their thermal conductivity is higher than that of aluminum, their hardness and strength are increased by two times, their relative elongation during tension is increased threefold, and their corrosion resistance is higher than that of initial aluminum by a factor of 2.5–4. We are the first to synthesize an in situ hybrid Al–Al₂O₃–graphene composite material having a unique combination of some characteristics. This material can be recommended as a promising material for a wide circle of electrical applications, including ultrathin wires, and as a structural material for the aerospace industry, the car industry, and the shipbuilding industry.     

Reaction Kinetics at the Fiber/Matrix Interface of SiC<Subscript>f</Subscript>/Ti–15–3 Composites

In the current research work, spark plasma consolidated beta-titanium alloy Ti–15V–3Cr–3Al–3Sn composites reinforced with SiC fibers (Sigma SM1240) were subjected to high temperatures (1173, 1223 and 1273 K) for different time periods (2.7, 11, 25 and 44 h) to investigate the kinetics of the chemical reactions at the fiber/matrix interface. Through microstructural studies and room temperature tensile tests, we have attempted to study the effect of the formed brittle reaction zone on the final mechanical properties of the composite. We have observed that, prior to the SiC fiber, the protective carbon coating reacts with the matrix and results in the formation of a reaction zone (predominantly TiC) at the fiber/matrix interface. The reaction zone propagates into the matrix with increase in time at the expense of the carbon coating, and finally ends with the onset of titanium silicide reaction. The reaction kinetics at the fiber/matrix interface was predominantly controlled by diffusion of carbon through the reaction zone and the activation energy for the same was calculated to be 149 kJ/mol. It was clear from the tensile test results that the mechanical properties of the composites do not earnestly decrease until the commencement of titanium silicide reaction.     

The Effect of Al<Subscript>2</Subscript>O<Subscript>3</Subscript>–TiB<Subscript>2</Subscript>/Fe Complex Reinforcement on Wear and Mechanical Properties of Al-Matrix Composites

In this study, the effect of Al₂O₃–TiB₂/Fe complex ceramic–metal reinforcement (CCMR) on wear and mechanical properties of Al-(Al₂O₃–TiB₂/Fe) composites were investigated. For this purpose, Al₂O₃–TiB₂/Fe CCMR was synthesized by mechanochemical process. The produced reinforcement powders were added to Al matrix, milled for 10 h and then hot extruded. The results showed that the metallic component (Fe rich phase) in this reinforcement acted as a pin, sticking the ceramic parts (Al₂O₃–TiB₂) to Al matrix. The best volume percentage of CCMR in Al matrix was recognized to be about 2.5 %. This composite showed a combination of wear resistance (0.005 mg/m), strength (500 MPa) and ductility (of about 6 %).     

Micro Structural Investigation On Friction Stir Welded Al–4.5Cu–5TiB<Subscript>2</Subscript> Composite

Aluminium matrix composites are widely used in defence and aerospace applications. Welding them is very difficult and is an outstanding issue in a cost effective way. Friction stir welding is a solid state welding technique which is circumventing those barriers and is applied successfully to many such materials recently. In the present work, Al–4.5Cu alloy with TiB₂ reinforcement as in situ which was synthesized by stir casting method was welded by friction stir welding. Threaded pin was used as the friction stir tool profile. One of the joints was found to have tunnel defect in the stir zone due to improper material flow. The microstructural investigation through XRD and SEM revealed that the nugget zone had numerous small particles and refined fine grains which were distributed uniformly and hardness at the welded zone was found to be higher than that of the base material.     

Mechanical and Wear Properties of Al–Al<Subscript>2</Subscript>O<Subscript>3</Subscript> Metal Matrix Composites Fabricated by the Combined Effect of Stir and Squeeze Casting Method

The effects of nano particles on double shear strength and tribological properties of A356 alloy reinforced with Al₂O₃ nano particles of size 30 nm were investigated. The percentage inclusions of Al₂O₃ were varied from 0.5 to 1.5 wt%. The particles were added with stirring at 400 rpm and squeeze casting at 750 °C and pressure of 600 MPa in a squeeze casting machine. Comparison of the performance of as cast samples of A356/Al₂O₃ nano composite was conducted. The tribological properties of the samples were also investigated by pin-on-disk tests at 10, 30 and 50 N load, sliding speed 0.534 m/s and sliding distance 1100 m in dry condition. SEM images of microstructure analysis of the composite, Al₂O₃ (0.5 and 1 %) particles were well dispersed in the A356 alloy matrix. Partial agglomeration was observed in metal matrix composite with higher (1.5 %) Al₂O₃ particle contents. The nano dispersed composites containing 0.5 and 1 wt% of Al₂O₃ nano particles exhibited the highest double shear strength, lesser wear loss and coefficient of friction.     

Deformation Behavior of Inclusion System CaO–Al<Subscript>2</Subscript>O<Subscript>3</Subscript>–SiO<Subscript>2</Subscript> with Different Compositions During Hot Rolling Processes

The present study was aimed at exploring the influence of compositions on the deformation behavior of inclusion system CaO–Al₂O₃–SiO₂, during hot rolling processes. The plastic deformations of four inclusions with different compositions, at different rolling temperatures (800, 850, 900, 982 and 1100 °C), were simulated using a finite element model. The equivalent plastic strain distributions and the shapes of the inclusions after rolling were obtained via the model. The influences of rolling temperature, flow stresses of inclusions and matrix, reduction, etc., on the void length and the deformation degree of inclusions were analyzed. The critical temperatures of the four inclusions during hot rolling were different. No voids occurred above the critical temperature. Voids only occurred along the length direction, but not the width and thickness directions, below the critical temperature. Low rolling temperatures led to long void length and small deformation of inclusions. The inclusion with high SiO₂ content had a high critical temperature and a high risk of void formation. Results generated by the experiment on deformation behaviors of inclusions with different SiO₂ content, were in good agreement with the simulated results.