Universal scaling laws of keyhole stability and porosity in 3D printing of metals

We leverage ultrahigh-speed synchrotron x-ray imaging and high-fidelity multiphysics modeling to identify strikingly simple yet universal scaling laws for keyhole stability and porosity in metal three-dimensional (3D) printing. The laws apply broadly and remain accurate for different materials, processing conditions, and printing machines. We define a new dimensionless number, the Keyhole number, to predict aspect ratio of a keyhole and the morphological transition from stable at low Keyhole number to chaotic at high Keyhole number. Furthermore, we discover inherent correlation between keyhole stability and porosity formation in metal 3D printing. By reducing the dimensions of the formulation of these challenging problems, the compact scaling laws will aid process optimization and defect elimination during metal 3D printing, and potentially lead to a quantitative predictive framework.

Low-cement concrete dams: construction, structures and innovations

Introduction. Low-cement concrete dams are water-retaining structures frequently used in modern hydraulic engineering. The number of facilities of this type goes up every year due to their simple design, speedy construction and high economic efficiency. However, a number of problems may arise in the construction and operation of such facilities. In particular, reduced strength and water permeability of interlayer joints may constitute a problem. Temperature effects arising in the course of construction and operation may cause additional deformation of their structure, changes in their stress-strain state, opening of existing cracks and further cracking. The study of the design experience, building and operation of dams made of low-cement concrete will lay the groundwork for the development of similar structures and defect elimination methods. It will also provide an opportunity to learn more about thebehaviour of structures exposed to various conditions, including climatic ones. Materials and methods. Data on existing dams made of low-cement concrete, research articles, technical reports and conference proceedings, including those issued by the International Commission on Large Dams (ICOLD), have been collected and analyzed. Results. The comparative analysis of designs of dams in operation and future-oriented solutions is performed. The co-authors have demonstrated the need for an integrated approach to solving temperature cracking problems by using filtration through the dam body. Conclusions. The results can be used as the basis for further detailed studies. The comparative analysis of traditional and innovative waterproofing liners will help to effectively choose the protection solution for an upstream face of a facility. New forecasting methods and recommendations aimed at the reduction of negative temperature effects on the operation of facilities can solve the temperature cracking problem.

High Pressure Heat Treatment of AM Parts—Combining HIP and Heat Treatment

Hot Isostatic Pressing (HIP) has been used for several decades within different industries for a wide variety of applications [1]. During the recent years HIP has become an important post process for metal additive manufacturing (AM) to secure material performance and quality. The HIP process uses a high isostatic pressure and elevated temperature to densify additively manufactured material by eliminating internal defects. The elimination of defects results in improved material properties such as fatigue, creep, ductility and fracture toughness [2-8]. HIP have historically been used only for densification and defect elimination and any modification and optimization of a material’s microstructure is usually performed after the HIP process in a separate heat treatment step in separate equipment e.g. a vacuum furnace. The main reason that these processes have been performed separately is that the achievable cooling rates in HIP systems have traditionally been relatively low, lower than what many materials require for heat treatment to for example create martensite or a super saturated condition.