Editorial Board Members’ Collection Series: Improving Structural Integrity of Metals: From Bulk to Surface

Metals and alloys continue to play a crucial role in the design and construction of load-bearing structures and mechanical components. Ferrous and non-ferrous alloys find countless applications in various industrial sectors, such as that of automotives, aerospace, the marine sector, construction, and manufacturing. When it comes to guaranteeing the structural integrity and safety of critical parts, a variety of protection and strengthening mechanisms may be used both at the bulk level and the surface level. At the bulk level, it is possible to take advantage of the correlation between the microstructure and mechanical properties of the material [1]. The chemical composition and content of alloy elements can be controlled to form new alloys or to improve existing ones. Manufacturing processes and heat treatments can be used to tailor the microstructure to possess the desired combination of mechanical properties (e.g., strength, ductility, hardness, and fracture toughness). For example, this can be done by controlling the grain size and/or phase type and distribution. Further, innovative manufacturing techniques, such as additive manufacturing, allow for the fabrication of components with complex geometries and specific mechanical behaviors [2]. Aside from material properties, the subject of structural integrity is also relevant to a variety of topics related to analysis methods [3]. For complex structures, advanced reliability methods and Monte Carlo simulations prove to be efficient tools to assess the probability of failure, and for improving the safety of structures in service [4]. When structures are assembled by welding, the structure integrity is controlled by the fatigue behavior of the welded joints, where high stress concentrations and material inhomogeneities make fatigue cracks more likely to nucleate and grow [5]. Analyses techniques, often supported by finite element calculations, can be carried out by considering the nominal, structural, and local stress or strain, as well as the notch stress intensity factor or fracture mechanics [6]. For structures subjected to tens of millions of fatigue cycles, the structure behavior in the Very High Cycle Fatigue (VHCF) regime is also of interest [7]. In many service conditions, the surface may play a key role in determining the performance and life of a component. Phenomena occurring on metal surfaces, such as wear, wet corrosion, and high-temperature oxidation, may act in synergy with external or even residual stresses, such that a premature failure occurs [8]. Causes of failure, such as corrosion fatigue, stress corrosion cracking, and hydrogen embrittlement, are of major concern in many applications, and many efforts have been made to study their mechanisms in different environments, as well as to model and predict the component behavior. As a consequence, the modification of the topmost layers of metals and alloys, in order to change their characteristics, has become an important step in the manufacturing of industrial components, with the aim of extending their life. Surface engineering techniques allow us to improve surface hardness, hence wear and fatigue resistance, and corrosion resistance in many environments by means of coating processes [9], such as physical vapor deposition (PVD), chemical vapor deposition (CVD) and thermal spray, as well as diffusion processes [10], such as carburizing and nitriding. Surface engineering treatments, either as a single process or as a combination of different processes, can be tailored to achieve the most suitable characteristics for preserving the structural integrity of components. The purpose of this Special Issue is to gather articles presenting up-to-date methods and approaches for analyzing, preserving, and improving the structural integrity of metallic components; we also pay attention herein to the phenomena occurring at the bulk and surface level, while also considering the role of the manufacturing process as it correlates to the material microstructure, as well as advanced methods for reliability analysis. The outcomes of experimental, numerical, and theoretical approaches are also considered.