We present a brief review of the microstructures and mechanical properties of selected metallic alloys processed by additive manufacturing (AM). Three different alloys, covering a large range of technology readiness levels, are selected to illustrate particular microstructural features developed by AM and clarify the engineering paradigm relating process–microstructure–property. With Ti-6Al-4V the emphasis is placed on the formation of metallurgical defects and microstructures induced by AM and their role on mechanical properties. The effects of the large in-built dislocation density, surface roughness and build atmosphere on mechanical and damage properties are discussed using steels. The impact of rapid solidification inherent to AM on phase selection is highlighted for high-entropy alloys. Using property maps, published mechanical properties of additive manufactured alloys are graphically summarized and compared to conventionally processed counterparts.

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The austenitic stainless steel 316L was additively manufactured using Selective Laser Melting (SLM). The corrosion characteristics of the additively manufactured (3D printed) specimens were investigated by both potentiodynamic and potentiostatic techniques. The production parameters were deliberately varied during SLM, to produce 316L specimens fabricated by different laser scan speed (in the range of 860-1160 mm/s) and laser power (in the range of 165-285 W). The fabrication parameters were found to influence the porosity of the resulting specimens. The pitting potentials, metastable pitting rates and repassivation potentials of the 3D printed specimens are presented herein as a function of the laser scan speed and laser power, and also discussed in the context of specimen porosity. The corrosion characteristics of the 3D printed 316L were also compared with wrought 316L, revealing higher pitting potentials and lower rates of metastable pitting for most SLM 316L specimens, the related concepts of which are discussed herein. Stainless steels are a critically important class of alloy in several industries.1 The corrosion resistance of stainless steel (SS) is attributed to the presence of alloyed chromium (> ∼11 wt%), enabling the formation of a chromium oxide (Cr 2 O 3 ) based passive film upon the metal surface.1-3 The addition of elements such as nickel, nitrogen, molybdenum, carbon, aluminum, copper, sulfur and selenium can modify the corrosion resistance, strength, ductility, machinability, and the phases present (and their stability) in stainless steels.1-3 The types of stainless steel are most conveniently categorized according to their microstructure, classified as: austenitic, martensitic, ferritic and austenoferritic (duplex). Such structures are realized by specific alloying additions and metallurgical processing.1-4 Additive manufacturing has recently been explored as a means to produce SS components in net shape, 5-7 circumventing the requirement of traditional manufacturing methods such as casting, rolling, welding, machining, forging, etc. Selective Laser Melting (SLM) is one such additive manufacturing method, which can produce dense products by laser processing of metal powders. In SLM, metal powder layers are successively fused in a layer-by-layer manner into the requisite 3D structure, employing a fiber laser. [8][9][10][11] The metallic component in essence is therefore 3D printed into the requisite shape, by additive manufacturing processes like SLM. The process takes place in chamber of well-controlled inert atmosphere (either nitrogen or argon). The primary parameters that govern the microstructure of a 3D printed specimen are the laser power and the laser scan speed, as they influence the thermal gradients and growth rate of the metal at the solid-liquid interface (in the melt pool). 12 The porosity that may develop in 3D printed specimens depends upon the heating and cooling rates of the melt pool. 13 The laser scan speed relates to the duration for which the laser beam is in contact with ...

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High-strength aluminum alloys are important for lightweighting vehicles and are extensively used in aircraft and, increasingly, in automobiles. The highest-strength aluminum alloys require a series of high-temperature “bakes” (120° to 200°C) to form a high number density of nanoparticles by solid-state precipitation. We found that a controlled, room-temperature cyclic deformation is sufficient to continuously inject vacancies into the material and to mediate the dynamic precipitation of a very fine (1- to 2-nanometer) distribution of solute clusters. This results in better material strength and elongation properties relative to traditional thermal treatments, despite a much shorter processing time. The microstructures formed are much more uniform than those characteristic of traditional thermal treatments and do not exhibit precipitate-free zones. These alloys are therefore likely to be more resistant to damage.

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