The chapter explores the rheological and thermophysical properties of lubricants, emphasizing their structure, classification, and performance under various conditions. Conventional lubricants are examined alongside the nanoparticle-enhanced formulations, with focus on their fabrication, lubrication mechanisms, and tribological applications. The concept of superlubricity and boundary-induced anomalies in disperse systems is highlighted as emerging phenomena in lubrication science. Experimental determination of rheological parameters is discussed through capillary and rotational rheometry, shear flow studies, and advanced techniques such as capillary breakup extensional rheology. Thermophysical properties, including viscosity, thermal conductivity, and temperature-dependent behaviors, are presented with insights from photothermal, photopyroelectric, and machine learning-based methods, particularly for hybrid ferro-lubricants. Performance evaluation techniques cover friction, wear, wettability, and tribochemical and physiochemical analyses, providing comparative perspectives with the conventional fuels. The chapter also integrates rheological modeling approaches, including lubrication theory, direct numerical simulations, and the viscoelastic Reynolds equation, to describe thin film lubrication, shear-thinning, and non-Newtonian behaviors via the Carreau–Yasuda model. Through this comprehensive overview, the chapter bridges experimental methods, theoretical modeling, and emerging nanotechnological strategies to advance the design and application of high-performance lubricants.

The TiNi and ZnO powders were mixed at a 1:1 ratio and mechanically milled for 30 and 60 h, respectively. The XRD analysis of the milled powder revealed a predominantly single broad peak after 30 and 60 h. Raman analysis also revealed a broad peak indicative of the short-range order or lack of crystallinity due to MM. TEM images showed the lattice fringes with a decreased number of diffraction rings due to the partial formation of amorphous particles complementing the XRD and Raman results. Thermal analysis showed an exothermic peak at 543 °C, while no exothermic peak has emerged in the 60 h milled ZnO-TiNi powder.

Incorporating TiAl alloys in engine applications offers benefits including reduced fuel consumption and improved efficiency. However, understanding the wear behaviour of these materials is an important consideration due to their use in harsh environments involving movable parts. This study investigated the wear behaviour and mechanisms of Ti–48Al–2Nb–0.3Si-1Sn (TiAl–S1) together with Ti–48Al–2Nb–0.3Si (TiAl–S0) as a reference alloy against an alumina ball. Scanning electron microscopy (SEM) analysis showed that the addition of Sn refined the lamellar structure from 216 $\mu \mathrm{m}$ to 130 $\mu \mathrm{m}$ and promoted more uniform deformation. SEM observations also indicated that abrasive wear is the dominant mechanism in the TiAl alloys. The TiAl–S1 exhibited lower hardness, resulting in deformation of wear debris and promoting third body acting as a lubricant. SEM-EDS revealed that the tribo-layer and wear debris originated from the TiAl materials rather than the counterpart alumina material. Both alloys demonstrated noble wear resistance, with a wear rate of 7.542 × 10⁻⁶ mm³/Nm for TiAl–S1 and 6.729 × 10⁻⁶ mm³/Nm for TiAl–S0. Even though both TiAl alloys experienced abrasive wear mechanisms, the addition of Sn emerges as a promising alloying strategy, for enhancing ductility without significantly increasing material loss.