Afsaneh Dorri Moghadam

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.

Beyond Wenzel and Cassie–Baxter: Second-Order Effects on the Wetting of Rough Surfaces

The Wenzel and Cassie-Baxter models are almost exclusively used to explain the contact angle dependence of the structure of rough and patterned solid surfaces. However, these two classical models do not always accurately predict the wetting properties of surfaces since they fail to capture the effect of many interactions occurring during wetting, including, for example, the effect of the disjoining pressure and of crystal microstructure, grains, and defects. We call such effects the second-order effects and present here a model showing how the disjoining pressure isotherm can affect wettability due to the formation of thin liquid films. We measure water contact angles on pairs of metallic surfaces with nominally the same Wenzel roughness obtained by abrasion and by chemical etching. These two methods of surface roughening result in different rough surface structure, thus leading to different values of the contact angle, which cannot be captured by the Wenzel- and Cassie-type models. The chemical and physical changes that occur on the stainless steel and aluminum alloy surfaces as a result of intergranular corrosion, along with selective intermetallic dissolution, lead to a surface roughness generated on the nano- and microscales.

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.