B.V. Manoj Kumar

Processing of polysiloxane-derived porous ceramics: a review

Abstract Because of the unique combination of their attractive properties, porous ceramics are considered as candidate materials for several engineering applications. The production of porous ceramics from polysiloxane precursors offers advantages in terms of simple processing methodology, low processing cost, and easy control over porosity and other properties of the resultant ceramics. Therefore, considerable research has been conducted to produce various Si(O)C-based ceramics from polysiloxane precursors by employing different processing strategies. The complete potential of these materials can only be achieved when properties are tailored for a specific application, whereas the control over these properties is highly dependent on the processing route. This review deals with processing strategies of polysiloxane-derived porous ceramics. The essential features of processing strategies—replica, sacrificial template, direct foaming and reaction techniques—are explained and the available literature reports are thoroughly reviewed with particular regard to the critical issues that affect pore characteristics. A short note on the cross-linking methods of polysiloxanes is also provided. The potential of each processing strategy on porosity and strength of the resultant SiC or SiOC ceramics is outlined.

Friction Stir Processing Strategies for Uniform Distribution of Reinforcement in a Surface Composite

Friction stir processing (FSP) is an important technique for preparing surface composites. Fabricating defect-free surface composites with uniform particle distribution by FSP is a challenging task. In this study, silicon carbide particles reinforced AA5083 alloy surface composites was fabricated using different FSP strategies including variation in process parameters, dual-tool processing and tool offset overlapping. Material flow of the processed material with reinforcement particles demonstrated that the distribution of particles was influenced by the stirring action of the probe as well as the extrusion of the plasticized material due to the movement of the tool. Process parameters, particularly rotational speed, showed a dominant influence on the distribution of silicon carbide particles.

Tribochemistry in sliding wear of TiCN-Ni-based cermets

W/Nb/Ta/Hf) at varying loads of 5N, 20N, and 50N against bearingsteel. With these experiments, we attempted to answer some of the pertinent issues:(i) how does the type of secondary carbide (WC/NbC/TaC/HfC) influence friction andwear behavior, and is such influence dependent on load?; and (ii) how does thesecondary carbide addition affect the stability and composition of the tribochemicallayer under the selected sliding conditions? Our experimental results reveal that theadded secondary carbides influence chemical interactions between different oxides andsuch interactions dominate the friction and wear behavior. A higher coefficient offriction (COF) range, varying from 0.75 to 0.64 was recorded at 5N; whereas thereduced COF of 0.46–0.52 was observed at 20N or 50N. The volumetric wear ratedecreased with load and varied on the order of 10

Fretting Wear Behavior of Ti(CN)-Based Advanced Cermets

Advanced ceramics and cermets, due to their excellent mechanical properties (elastic modulus, hardness), are increasingly appreciated in the tribological applications such as wear parts, cutting tools etc. Particularly for machining applications, Ti(CN)-based cermets represent common and important cutting tool inserts and now second to that of the conventional hardmetal (WC-Co). This research concentrates on the fretting wear behavior of Ti(CN)-Ni cermets reinforced with WC as secondary carbides. The wear tests were carried out on Ti(C0.7N0.3)-x WC-Ni (x the varying carbide content) against bearing steel in the ambient conditions of temperature and humidity (50-55 % RH). Friction results indicate that significantly lower Coefficient of Friction (COF) can be achieved with Ti(CN)-based cermets as compared to conventional WC- Co materials. Detailed analysis of the tribological data was carried out to unravel the influence of secondary carbide on the wear performance of Ti(CN)-Ni cermets. Additionally, the morphology of the worn surfaces was investigated using SEM and Raman spectroscopy to understand the wear mechanism.

Sustained drug release from surface modified UHMWPE for acetabular cup lining in total hip implant

Despite sterilization and aseptic procedure, bacterial infection remains a key challenge in total hip arthroplasties. This fact emphasizes the urgent need for development of new implant systems, which should releases the drug in a controlled manner without sparing its mechanical and tribological properties. In this study, the lining material of the acetabular cup, in total hip implant, has been modified for sustained release of drugs, which should be available throughout the site of implantation to fight the post-operation bacterial infection. A modified solvent based etching and lypolization technique has been used to engineer a thin porous surface layer on ultra-high molecular weight polyethylene (UHMWPE) substrate, which is clinically used as acetabular-cup lining. Gentamicin loaded chitosan solution has been impregnated into modified surface, which suitably gets released over a long period. The main challenge was to keep the mechanical and tribological behavior of this lining material unaffected after the modification. Modified surface offers reduction in friction coefficient and wear rate, by 26% and 19%, respectively, in comparison to UHMWPE, which is encouraging towards the intended application. Hardness and elastic modulus decreases slightly, by 27% and 20%, respectively, possibly due to improper impregnation of chitosan inside porous surface. However, after drug release, the modified surface regains the mechanical and tribological behavior similar to unmodified UHMWPE. Surface modified UHMWPE have shown an impressive release profile for drug up to 26days and released >94.11% of the total drug content. In vitro antibacterial tests have proven that the modified surface of UHMWPE can effectively release the drug and fight against infection. This surface engineered acetabular cup lining is a promising candidate in the area of drug eluting implant, which can bring a significant advancement to the functionality of commercially used orthopedic implants by providing inherent capacity for fighting infections in-vivo.

Processing of alumina-based composites via conventional sintering and their characterization

ABSTRACT The present work relates to the processing of dense alumina-based composites, their microstructural characterization and study of mechanical properties. Alumina ceramic material and alumina-based composites with m-Zirconia and Ceria addition are sintered at 1600°C, 1650°C and 1700°C temperatures via conventional sintering. Solid-state diffusion during sintering led to volume diffusion in alumina, and volume and grain boundary diffusion in alumina composite. In the present sintering conditions alumina is found to be the least dense as improper solid-state diffusion resulted in porosity, whereas alumina–zirconia composite achieved the highest density of 97%. Scanning electron microscope (SEM) micrograph shows homogeneous distribution of fine zirconia particles inside the alumina matrix, filling the voids of the alumina skeletal structure. Zirconia connects to alumina particles, restricting its abnormal grain growth. It results in strong bonding and grain refinement. Alumina–zirconia composite exhibits the highest hardness and fracture toughness of 14.37 GPa and 4.6 MPa · m1/2 at 1700°C. Alumina suppresses the transformation of m-t zirconia, resulting in high toughness of alumina composites. Alumina–zirconia–ceria composite revealed the presence of porosity, which led to less densification and low mechanical properties.

Challenges in Fabrication of Surface Composites by Friction Stir Processing Route

Friction stir processing is a newer technique for fabrication of surface composites. Surface composite fabrication by friction stir processing is simpler and offer many advantages as compared to conventional techniques. However, there are many challenges in composite fabrication due to asymmetric material flow and formation of defects. Reinforcement strategies, process parameters and reinforcement properties are key factors in fabrication of surface composites. In this study a newer reinforcement strategy is utilized to fabricate surface composites by pre-mixing the reinforcement particles with base alloy powders. The pre-mixing of ceramic reinforcement particles with metallic base alloy powder enhances the material flow and favours the uniform distribution of reinforcement particles.