Characterization of microshrinkage casting defects of Al–Si alloys by X-ray computed tomography and metallography

The statistical pore size characterization by metallography in the framework of Extreme Value Statistics (EVS) is presented and applied to different sets of cast AlSi7Mg specimens. Specimen production by separate casting or by extraction from automotive cast parts is found to result in different SDAS and porosity (i.e. pore morphology and size) but did not influence the fatigue strength. The application of two equivalent pore size definitions (i.e. maximum Feret diameter and (Area)1/2) combined with the EVS approach is discussed in terms of predicted critical pore sizes and observed fatigue strengths. The role of casting pore morphology on stress concentration is investigated using the X-ray computed tomography and the finite element method

Directing Surface Functions by Inducing Ordered and Irregular Morphologies at Single and Two-Tiered Length Scales

Surface topography outlines material's interaction with its immediate environment. Herein, a series of cost-effective and scalable treatments are used to obtain single-scale and two-tiered surfaces with ordered/disordered arrangements of micro and nano features. The applied treatments induced a wide variety of surface features regarding length scale and arrangement. The individual and synergistic contributions of roughness length scale, regularity, and hierarchy are analyzed on surface functionalities. The performance of further functionalized and lubricant-infused surfaces is evaluated regarding their interaction with wetting media, as well as tribological and electrochemical resistance. The hierarchical surfaces show improved wear and corrosion resistance. The prominence of the surface features’ length scale and orderedness varies based on the loading conditions and test environments. Wettability is mainly directed by micro-scale features. Tribology is largely led by the ability of the surfaces in forming a stable low-surface-energy liquid interface. Electrochemical activity is primarily influenced by the synergic barrier effect of the nano-features and the infused lubricant regardless of their arrangement. The results indicate that combining the distinctive and complementary role of micro and nano features can offer the possibility of obtaining versatile multifunctional surfaces with tunable performances based on the expected in-service conditions

Effect of phosphating time on protection properties of hurealite coating: Differences between ground and shot peened HSLA steel surface

Shot peening is a standard surface treatment primarily used for enhancement of fatigue properties of metallic materials. However, its influence on surface properties is so radical, that subsequent techniques of surface treatment used on the shot peened surface need to be reconsidered in order to minimize the possible negative side effects of shot peening. In this case, the differences between hurealite formation on the ground and shot peened surfaces of modern high strength low alloy (HSLA) steel were evaluated by morphological and electrochemical corrosion observations and measurements. The surface morphologies of the formed coatings were observed by the scanning electron microscopy (SEM) and analysed by energy-dispersive X-ray analysis (EDX). The corrosion resistance of the HSLA steel with hurealite coating was evaluated using electrochemical impedance spectroscopy (EIS) by the analysis of Nyquist plots obtained in 0.1 M NaCl solution after various phosphating times on both types of pre-treated surfaces (ground and shot peened). The results showed that used technique of shot peening negatively influenced the phosphating process by prolonging the phosphating process in order to reach the coating with maximal protection properties in tested medium. Moreover, shot peened surface caused significantly enlarged size of the hurealite crystals and greater thickness of the coating compared to the surface pre-treated by grinding on the tested HSLA steel at the expense of a lower compactness and corrosion protection