T.P.D. Rajan

Processing of surface-treated boron carbide-reinforced aluminum matrix composites by liquid–metal stir-casting technique

Boron carbide is one of the potential neutron-shielding materials and its use can be maximized for structural shielding application by dispersing it into metal matrixes such as aluminum. Dispersion of B4C and its interfacial stability is a major issue during its processing. This investigation is on the synthesis of B4C-reinforced 6061 aluminum matrix composite by liquid–metal stir-casting technique under optimized conditions after solving the issues related to the processing, and evaluation of the structural, mechanical, and interfacial characteristics. During processing of composites, pretreatment of B4C particles is necessary to improve its dispersion. However, higher preheating temperatures above 300°C lead to particle agglomeration in the matrix due to the formation of B2O3 phase during preheating. B2O3 is formed due to the surface oxidation of B4C particles above 300°C and this glassy phase leads to particle sintering and lump formation. Incorporation of particles preheated at 250°C has shown uniform distribution of particles in the composite. Interfacial characterization of the composite and the extracted B4C particles from the matrix has shown the presence of interfacial reaction products such as AlB2, Al3BC, AlB12, and AlB10.

Liquid Metal Infiltration Processing of Metallic Composites: A Critical Review

Metal matrix composites (MMC) are one of the advanced materials widely used for aerospace, automotive, defense, and general engineering applications. MMC can be tailored to have superior properties such as enhanced high-temperature performance, high specific strength and stiffness, increased wear resistance, better thermal and mechanical fatigue, and creep resistance than those of unreinforced alloys. To fabricate such composites with ideal properties, the processing technique has to ensure high volume fraction of reinforcement incorporation, uniform distribution of the reinforcement, and acceptable adhesion between the matrix and the reinforcing phase without unwanted interfacial reactions which degrades the mechanical properties. A number of processing techniques such as stir casting/vortex method, powder metallurgy, infiltration, casting etc. have been developed to synthesize MMC employing a variety of alloy and the reinforcement’s combinations. Among these, infiltration process is widely used for making MMC with high volume fraction of reinforcements and offers many more advantages compared to other conventional manufacturing processes. The present paper critically reviews the various infiltration techniques used for making the MMC, their process parameters, characteristics, and selected studies carried out worldwide and by authors on the development of metal ceramic composites by squeeze infiltration process.

Enhancement in tribological behaviour of functionally graded SiC reinforced aluminium composites by centrifugal casting

Enhanced tribological and location-specific properties achieved in functionally graded metallic composites make them potential materials for futuristic engineering components. The present investigation aims on the processing of homogenous and functionally graded Al matrix composites reinforced with SiC particles of 23 µm average particle size by gravity and centrifugal casting techniques. The sizes of the primary aluminium and eutectic silicon phases are finer towards the outer periphery due to the higher solidification rate. Functionally graded Al–SiCp composite rings produced by centrifugal casting show higher concentration of SiCp towards outer periphery, followed by a gradient transition region and the particle depleted zone. Particle agglomerates formed due to partially wetted particles associated with voids and gas porosities segregate towards the inner periphery. The higher concentration of reinforcement particles near the outer periphery in FGM enhances the hardness and wear resistance in rotary and reciprocating wear studies. Centrifugal cast alloys show enhanced wear resistance than the gravity cast specimen due to fine grains of primary aluminium and eutectic silicon. The rotary and reciprocating wear test shows the adhesive and abrasive type wear mechanisms.

Squeeze Infiltration Processing of Functionally Graded Aluminum–SiC Metal Ceramic Composites

The objective of the present work is on fabrication of functionally graded SiC/Al composite by direct squeeze infiltration of 6061 aluminum alloy using graded SiC porous preform prepared by inorganic porogen technique. Graded SiC preform is synthesized by varying the concentration of inorganic salt mixture and using Al as the binder. The microstructure analysis indicates the graded distribution of SiC particle and the melt has infiltrated completely throughout the preform to form functionally graded materials. The influence of preform and mold temperature, liquid metal superheat, squeeze pressure, and its rate of application plays major role on solidification microstructures and properties of the composites. The macro porous graded SiC preforms and the composites were characterized using SEM, optical microscopy, and XRD. The major interfacial reaction product is MgAl2O4 spinel which helps in formation of good interface bonding.

Synthesis of Porous SiC Preform and Squeeze Infiltration Processing of Aluminium-SiC Metal Ceramic Composites

Metal-Ceramic Composites with high volume fraction of reinforcement find wide applications in the area of tribology and high temperature resistant components like piston, brake pads, heat shields etc. Most of these components can be made by infiltration processing of porous ceramic preforms. The present investigation is to synthesize porous ceramic preform based on SiC particles using inorganic salt as a pore forming agent and Squeeze infiltration is applied to fabricate the Al-SiC metal-ceramic composites. The direct squeeze infiltration of 6061 aluminum alloy on SiC preform is successfully carried out with the controlled process parameters of initial preform temperature, liquid metal superheat, squeeze pressure and its rate of application, and die temperature. The preform and composites are characterized using XRD, optical microscopy, electron microscopy, and hardness and compression strength. Porous ceramic preform with more than 50% porosity has been fabricated by sodium chloride as pore former. The infiltrated composite have shown uniform and complete infiltration of Aluminium alloy in between SiC particles and posses very high hardness of 147 BHN in as cast condition compared to 57 BHN for the 6061 Al alloy.

Studies on electroless nickel boride coating on boron carbide particles

Abstract Ni–B alloy deposits were successfully formed over alkali surface treated boron carbide by electroless technique and the effects of processing parameters such as reduction bath pH, temperature and post-heat treatment were investigated. Microstructural studies show remarkable changes in structural morphology from mesh-like structure to platelet type Ni–B coating. The main Ni–B phases observed were NiB, Ni2B, Ni3B and Ni4B3. An effective Ni–B alloy coating with better surface characteristics was formed at pH 8 under 75°C reaction bath temperature in the presence of bath stabiliser. The post-heat treatment of Ni–B coated particles under varying bath reaction temperatures at 400°C showed remarkable Ni–B phase transformation from metastable NiB and Ni2B to stable crystalline Ni3B phase. The NiB coated particle shows lower particle–matrix interfacial reaction, better wettability and enhanced dispersion in aluminium composites compared to uncoated particles.

Design and Processing of Bimetallic Aluminum Alloys by Sequential Casting Technique

Sequential casting is a facile and fairly new technique to produce functionally graded materials (FGMs) and components by controlled mold filling process. In the present investigation, functionally graded bimetallic aluminum alloys are produced by sequential gravity casting using A390–A319 and A390–A6061 alloy combinations. The control in pouring time between two melts has shown a significant effect on the quality and nature of interface bonding. The microstructure reveals good interface miscibility achieved through diffusion bonding between the alloys. A higher hardness of 160 BHN in the A390 region is obtained in both sequential cast systems, and a minimum value of 105 and 91 BHN is observed in the A319 and A6061 regions, respectively. The tensile and compression strength for A390–A319 are 337 and 490 MPa, whereas for A390–A6061, they are 364 and 401 MPa, respectively, which are significantly higher compared with the standard values of the base alloys, which confirms strong interface bonding. The A390 region shows higher wear resistance compared with other regions of the sequential cast system. The process described in this study is a potential and efficient approach to create good bonding between two different aluminum alloys to develop advanced functional and structural materials.

Optimization of Drilling Process on Al-SiC Composite using Grey Relation Analysis

This study reveals the multi objective optimization of machining parameters in drilling of SiC reinforced with aluminium metal matrix composites through grey relational analysis. The composite is prepared with varying volume fraction of the reinforcement by liquid metal stir casting technique. Uniform distribution of SiC particle in the matrix is witnessed through microscopy study and observed that the hardness and strength on different composite. The drilling experiments were performed with coated carbide tool with different point angle such as 90o, 120o and 140o. Cutting speed, feed, point angle and volume fraction are considered as input parameters and the performance characteristics such as surface roughness and thrust force are observed as output response in this study. The significant contributions of these factors are determined using Analysis of Variance (ANOVA). The optimized process parameters have been validated by the confirmation test. The experimental result shows that point angle influences more on output performance followed by feed and cutting speed.

Processing and Characterization of Hypoeutectic Functionally Graded Aluminum – SiC Metal Matrix Composites

The present study describes the processing and characterization of hypoeutectic A319 functionally graded Aluminium metal matrix composite (FGMMC) reinforced with 10 weight percentage SiCp particles of 23 μm size. FGMMC’s are processed by liquid stir casting method followed by vertical centrifugal casting. Metallographic analysis of FGMMC casting reveals the influence of the centrifugal force on the gradation of various phases in the matrix and an increasing gradient distribution of SiC reinforcements gradually from inner towards the outer periphery forming different zones. Tensile and the compressive tests show that the variation in properties are structure sensitive and is confirmed by the dry wear tests. The study clearly depicts the gradient nature in the structure and mechanical properties of the FGM castings produced by centrifugal casting method.

Development of Al 319-Micro Silica Metallic Composite by Squeeze Infiltration Technique

The objective of present investigation is to synthesize porous micro silica based ceramic preform with varying composition of particles using burn out technique and processing of Al-Micro silica metal-ceramic composites by squeeze infiltration method. Direct squeeze infiltration of 319 aluminum alloy on micro silica preform is successfully carried out with the controlled process parameters of initial preform temperature, liquid metal superheat, squeeze pressure and its rate of application, and die temperature. The preform and composites are characterized using optical microscopy, electron microscopy, hardness and compression strength testing. Porous ceramic preform with more than 70% porosity has been fabricated by PEG as pore former. The infiltrated composite have shown uniform and complete infiltration of aluminum alloy in between micro silica particles.