China
Africa
Explore chapters and articles related to this topic
High Entropy Alloys in Bulk Form
Published in T.S. Srivatsan, Manoj Gupta, High Entropy Alloys, 2020
Reshma Sonkusare, Surekha Yadav, N.P. Gurao, Krishanu Biswas
If T′L > critical gradient, where T′L=dTL/dx at the interface, a stable planar interface will form. Here, (T1−T3) is known as the equilibrium freezing range of the alloy. Microsegregation is not desirable for the alloys and it can be controlled by the proper heat treatment procedure after the alloy solidification. When we go from lab scale to industrial scale, the alloy size increases manyfold and macrosegregation comes into the picture.
Solidification and Melting
Published in Greg F. Naterer, Advanced Heat Transfer, 2018
Microsegregation refers to compositional variations at the scale of the grain diameter or interdendritic distance within the solidifying material. The dendrite arm spacing, Ld, can be related to the interfacial temperature gradient and solidification velocity according to: Ld≈C(∂T/∂x)−1/2V−1/2 where C is an empirical constant. Therefore, in manufacturing processes such as casting solidification and extrusion, the heat transfer processes during phase change have a significant influence on the thermomechanical properties of the final solidified material.
Phase Change Problems
Published in M. Necati Özişik, Helcio R.B. Orlande, Marcelo José Colaço, Renato Machado Cotta, Finite Difference Methods in Heat Transfer, 2017
M. Necati Özişik, Helcio R.B. Orlande, Marcelo José Colaço, Renato Machado Cotta
Notice that, as the solidification begins, the solid phase rejects solute and the concentration in the remaining liquid and mushy regions increases. Thus, the solid and liquid temperatures at each point of the domain must be determined as the solidification front advances. This indeed induces a buoyancy effect represented by the Oberbeck–Boussinesq equation. The rejection of the solute by the solid often leads to secondary reactions, such as formation of oxides, sulfides, oxysulfides, and nitrides during solidification, which can significantly alter microsegregation patterns (Ghosh 1990). Such reactions will not be treated in this book.
Statistical modelling of microsegregation in laser powder-bed fusion
Published in Philosophical Magazine Letters, 2020
Supriyo Ghosh, Raiyan Seede, Jaylen James, Ibrahim Karaman, Alaa Elwany, Douglas Allaire, Raymundo Arroyave
However, the full realisation of the potential of AM processes is impeded by uncertainty regarding the reliability of the final material in service [5,7,9–11]. Some 47% of manufacturers surveyed indicated that the uncertain quality of the final product was a barrier to the adoption of AM [12]. This is primarily due to rapid heating and cooling during the microstructure formation processes, leading to significant variations and distributions of the key microstructural features, and eventually uneven qualities of the final product [3,5,7,13]. Therefore, microstructural evolution during AM processes is a critical stage that needs to be assessed thoroughly. The typical morphology that often forms during laser melting solidification processes is cellular in nature [1–4,8]. The key features in a cellular microstructure that determine the properties of the final material, particularly tensile strength and low-cycle fatigue life, are cellular spacing, microsegregation, and the misorientation between cells [5,8,14]. We refer to these microstructural features as the Quantities of Interest (QoIs) critical for material properties and behaviour in service. Let us consider microsegregation for our present measurements and analysis. Microsegregation results due to solute redistribution between the solid cell core and advancing solidification front in the solidifying alloy melt-pool [15–18]. We use Ni–Nb as the sample alloy material. Ni–Nb alloys show excellent mechanical properties and creep resistance at elevated temperatures and thus are often used in gas-turbine and jet-engine components [19]. Also, Ni–Nb is the most important binary analogue of Ni-based superalloys because Nb segregates most severely due to its smallest equilibrium partition coefficient among all the elements in the superalloy, controlling the average solidification behaviour of the material [19,20]. The as-solidified microstructures are further manipulated using appropriate post-deposition heat treatment schedules to homogenise the variation and distribution of the QoIs for property and performance control [3,8,21].