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In contrast to subtractive manufacturing processes, such as machining, and forming processes, additive manufacturing (AM), which is also called 3-D printing, direct digital manufacturing or free form fabrication, is a process of joining materials to make objects from 3D model data, usually layer by layer. Although additive manufacturing was mainly used in the production of prototypes from polymeric materials initially, the production of metallic parts with this manufacturing technology has attracted great interest in recent years. This innovative technology is commonly referred to metal additive manufacturing (MAM) and is presently being applied in various industries such as aeronautics-space, energy, automotive, medicine, various tools and customer goods. Metal parts are produced in three different ways by MAM methods. These are powder bed fusion, powder feed fusion and wire feed fusion systems. In the first two of these additive manufacturing methods, metal or alloy powders are used as raw materials, while in the third method, the filler wire made of metals or alloys is the starting material. However, metal powders, especially alloy powders, are quite costly. This in turn makes the production of metal parts using filler wire very attractive. Another advantage of wire feed additive manufacturing systems, particularly of wire arc additive manufacturing (WAAM), is its potential to produce small- and medium-sized metallic parts economically with high deposition rate. Nowadays, this innovative manufacturing technology is being considered as a promising fabrication technology for manufacturing several products from various engineering materials including aluminum and its alloys. In this paper, studies on WAAM of Al-alloy parts will be discussed. In addition, the most common defect (i.e., porosity) encountered in Al-alloy parts produced by WAAM will be considered as well as the precautions taken against its formation.

Austenitic stainless steels exhibit excellent properties such as outstanding formability even at cryogenic temperatures, high mechanical properties and good corrosion performance. This makes them attractive for use in various industries ranging from petro-chemical industries, food industry, medical-dental equipments, and pressure vessels to LNG tanks and welding is often required in most of these applications. Especially with the increase in energy crisis in recent years, the production of LNG tanks using conventional arc welding processes is important. In this study, the weldability of 10 mm thick 316 L stainless steel plates used in the production of LNG tanks by gas tungsten arc welding was investigated. The effect of multi-pass welding on the microstructural evolution and thus on mechanical behavior of the joint produced was studied. Optical microscopy and scanning electron microscopy as well as energy dispersive spectroscopy were employed to investigate the microstructural evolution in the weld region of the joint fabricated. In addition, microhardness measurements and tensile testing were conducted to mechanical characterization. As a result of the study, a slight hardness increase was observed within the weld region of the joint compared to that of the base material. The welded joint exhibited higher yield and tensile strength values, namely 329 and 630 MPa respectively, than the base plate which displayed a yield strength of 308 MPa and a tensile strength of 603 MPa.

Low alloy steel plates containing 9% Ni are generally preferred in the production of LNG storage tanks, due to their outstanding combination of properties such as excellent toughness, high ductility and crack re-sistance at very low temperatures. Welding is an indispensable manufacturing method in the production of LNG storage tanks. Thus, there is a need for reliable welding procedures which do not diminish low tem-perature properties of this steel grade. This study introduces the result of microstructural evolution in the weld region and the mechanical properties of the gas tungsten arc welded 10 mm thick 9 Ni steel joint produced by using a Ni-based filler wire, which is widely used in LNG storage tanks. The microstructures evolved in the weld region were examined by extensive optical microscopy and SEM investigations. Mechanical properties and joint performance values of the welded joints were determined by detailed microhardness measurements and transverse tensile tests. Moreover, fracture toughness of the joint fab-ricated was also determined at - 196 degrees C by Charpy V-notch test. (c) 2021 CIRP.