Tribological characteristics of microtextured surfaces under mixed and hydrodynamic lubrication

Improving energy utilization is becoming increasingly important given the impact that energy resource management can have on the environmental, economic, and security, for example, surface damage due to friction and resulting part repairs and replacement has cost US industries a reportedly US $280 billion/year. Reducing friction and wear losses in mechanical systems is an effective approach to improve energy efficiency. Engineering the surface of contacting components with designed micro-sized texture is a potential method of improving the tribological performance, specifically friction and wear reduction. Surface texturing also referred to as surface structuring is the process of applying a specific roughness onto a surface in order to change its properties. Ultrashort pulse lasers offer many new possibilities to tailor surface textures and control their properties in a way that cannot be matched by other techniques. Textures with features on multiple scales can be applied, starting in the nanometer range and extending up to the millimeter range. The technology furthermore can be applied on any material and can be used for texturing 3D curved surfaces. The creation of specific patterned surface microstructures can be achieved in many ways, for example abrasive blasting, reactive-ion etching, and ultrasonic machining. However, laser technology offers the most control and precision over the produced geometry. Also, laser ablation does not use chemical reagents or produce significant waste. Ultrashort pulse laser texturing enables many new applications of engineered surfaces, where specific surface textures can be used to influence the functional properties, e.g., the wetting, tribological, or optical properties. Such surfaces are also referred to as functional surfaces. Recent work in the field of surface modification and texturing has shown that, artificially created micro textures significantly reduce friction and wear of lubricated surfaces. Micro-scale artificial textures in friction paring contacts acts as lubricant reservoirs and wear particle receptacles to boost hydrodynamic pressure, which influences the lubrication regimes wear resistance, fatigue strength, coefficient of friction, lubrication, wear rate and corrosion resistance of the machined parts. These surface textures are in the form of protrusions (positive asperities) or cavities (negative asperities) of known size and geometry. The benefits of such surface textures include lower friction torque, higher load capacity and lower operating temperatures; However, it still depends on the pattern or shape of the texture on the surface of material under certain sliding condition. This research advances the understanding and potential application of surface texture technology to enhance tribological performance while introducing a micro-texturing technique that is effective and easily adaptable to an industrial manufacturing setting.