Emad Omrani

Mechanical, physical and tribological characterization of nano-cellulose fibers reinforced bio-epoxy composites: An attempt to fabricate and scale the 'Green' composite.

The development of bio-based composites is essential in order to protect the environment while enhancing energy efficiencies. In the present investigation, the plant-derived cellulose nano-fibers (CNFs)/bio-based epoxy composites were manufactured using the Liquid Composite Molding (LCM) process. More specifically, the CNFs with and without chemical modification were utilized in the composites. The curing kinetics of the prepared composites was studied using both the isothermal and dynamic Differential Scanning Calorimetry (DSC) methods. The microstructure as well as the mechanical and tribological properties were investigated on the cured composites in order to understand the structure-property correlations of the composites. The results indicated that the manufactured composites showed improved mechanical and tribological properties when compared to the pure epoxy samples. Furthermore, the chemically modified CNFs reinforced composites outperformed the untreated composites. The surface modification of the fibers improved the curing of the resin by reducing the activation energy, and led to an improvement in the mechanical properties. The CNFs/bio-based epoxy composites form uniform tribo-layer during sliding which minimizes the direct contact between surfaces, thus reducing both the friction and wear of the composites.

Tribology of Metal Matrix Composites

Metal matrix composites (MMCs) are an important class of engineering materials that are increasingly replacing a number of conventional materials in the automotive, aerospace, marine, and sports industries due to their lightweight and superior mechanical properties. In MMCs, nonmetallic materials are embedded into the metals or the alloys as reinforcements to obtain a novel material with attractive engineering properties, such as improved ultimate tensile strength, ductility, toughness, and tribological behavior. In this chapter, an attempt has been made to summarize the tribological performance of various MMCs as a function of several relevant parameters. These parameters include material parameters (size, shape, volume fraction, and type of the reinforcements), mechanical parameters (normal load and sliding speed), and physical parameters (temperature and the environment). In general, it was shown that the wear resistance and friction coefficient of MMCs are improved by increasing the volume fraction of the reinforcements. As the normal load and sliding speed increase, the wear rate of the composites increases and the friction coefficient of the composites decreases. The wear rate and friction coefficient decrease with increasing temperature up to a critical temperature, and thereafter both wear rate and friction coefficient increase with increasing temperature. The nano-composites showed best friction and wear performance when compared to micro-composites.

New Emerging Self-lubricating Metal Matrix Composites for Tribological Applications

Self-lubricating metal matrix composites (SLMMCs) are an important category of engineering materials that are increasingly replacing a number of conventional materials in the automotive, aerospace, and marine industries due to superior tribological properties. Implementing self-lubricating composites into different operating systems is a solution to reduce the use of external toxic petroleum-based lubricants at sliding contacts in a way to help the environment and to reduce energy dissipation in industrial components for strategies toward energy efficiency and sustainability. In SLMMCs, solid lubricant materials including carbonous materials, molybdenum disulfide (MoS2), and hexagonal boron nitride (h-BN) are embedded into the metal matrices as reinforcements to manufacture a novel material with an attractive self-lubricating properties. Due to their lubricious nature, these solid lubricant materials have attracted researchers to synthesize lightweight self-lubricating metal matrix composites with superior tribological properties. This chapter focuses on the recent development in tribological behavior of self-lubricating metal matrix (aluminum, copper, magnesium, and nickel) composites. It is important to note that the tribological parameters, such as normal load, sliding speed, and temperature vary on a wide range and also the counterface materials differ in different experimental tests, comparing the results of tribological behavior of different self-lubricating composites is extremely difficult. In this chapter, attempts have been made to summarize the tribological performance of various SLMMCs as a function of several tribological parameters. These parameters include material parameters (size, shape, volume fraction, and type of the reinforcements), mechanical parameters (normal load and sliding speed), and physical parameters (temperature and environment). The mechanisms involved for the improved mechanical and tribological performances are discussed.

Effect of In-situ Processing Parameters on the Mechanical and Tribological Properties of Self-Lubricating Hybrid Aluminum Nanocomposites

In the present investigation, aluminum/TiB2/Al2O3 metal matrix composite was fabricated using the liquid metallurgy route. The transmission electron microscopy study was conducted in order to investigate the microstructure of the in-situ processed composites. X-ray diffraction analysis of the composite was performed to investigate the various phases present in the composite. Dry sliding tests were conducted using pin-on-disk tribometer in order to understand the self-lubricating behavior of developed composite. The microstructural characteristics revealed formation of in-situ phases and uniform dispersion of the reinforcement phases throughout the composite. The developed hybrid self-lubricating nanocomposites showed superior mechanical and tribological properties. The superior tribological properties of hybrid composite are attributed to the formation and synergetic effect of TiB2 and Al2O3 particles in the composites. The Al2O3 hard ceramic particles act as the obstacles to the movement of dislocation and thus enhance the mechanical properties. The oxidation of TiB2 on the surface forms H3BO3 and TiO2 tribolayer resulting in superior tribological properties.

Fundamentals of Solid Lubricants

Solid lubricants technology is a flourish field that deserves the attention of the designer of machines and devices that will operate in ordinary as well as in extreme environments. This chapter describes solid lubrication processes, the mechanisms by which solid lubricants function, the properties of solid lubricants, and the materials involved in solid lubrication and techniques for their application. Reliability of solid lubrication and wear life of solid-film lubricants are being improved by designing machine elements specifically to employ solid lubricants and by careful matching of the solid lubricant with the substrate bearing material. Solid lubricants are applied either as surface coatings or as fillers in self-lubricating composites. Tribological (friction and wear) contacts with solid lubricant coatings typically result in transfer of a thin layer of material from the surface of the coating to the counterface, commonly known as a transfer film or tribofilm. The wear surfaces can exhibit different chemistry, microstructure, and crystallographic texture from those of the bulk coating due to surface chemical reactions with the surrounding environment. As a result, solid lubricant coatings that give extremely low friction and long wear life in one environment can fail to do so in a different environment. Most solid lubricants exhibit non-Amontonian friction behavior with friction coefficients decreasing with increasing contact stress. The main mechanism responsible for low friction is typically governed by interfacial sliding between the worn coating and the transfer film. Strategies are discussed for the design of novel coating architectures to adapt to varying environments.

Self-Lubricating Polymer Composites

Friction and wear during sliding or rolling of solid surfaces are universal phenomena, and they reflect the tendencies of energy to dissipate material to deteriorate. In general, solid surfaces in relative motion require lubrication, which dramatically reduces the extent of friction and wear. The situation when no external lubrication is required is called self-lubrication. Self-lubricating polymer composite materials are two-phase system that contain soft second-phase particles in the polymer matrix. The soft phase exposed to the surface during sliding. So the properties of both the hard matrix and the soft second-phase particles, as well as the shape and size of the particles, control the processes of deformation and flow of the soft phase. This chapter details polymer matrix structures, self-lubricating polymer composites, mechanisms of polymer composite lubrication, transfer film mechanisms, factor affecting polymer composites on friction, and wear and application of polymer composites.