Grain growth and particle pinning in a model Ni-based superalloy

Nanocrystalline Al-Mg with extreme strength due to grain boundary doping

“…Second-phase particles 3 and drag elements inhibit grain growth through a process known as Zener pinning, where fine particulates reside in the grain boundaries and prevent migration by exerting pressure opposite to the driving forces [13]. Both images taken using bright field transmission electron microscopy (BF TEM) in Fig 1.1 show second-phase particles pinning grain boundaries and restricting grain boundary movement [13,14]. Zener pinning therefore increases the activation energy for grain growth and allows a material to preserve fine grain size.…”

“…Zener pinning therefore increases the activation energy for grain growth and allows a material to preserve fine grain size. [13] and (b) four types of inert particles in a Ni-based alloy where they reside in and pin grain boundaries [14].…”

“…When the solute atom is smaller than that of the matrix, it is called small substitutional where tensile stress is imposed on surrounding atoms [35]. Similarly in interstitial solid solution, a solute atom bigger than that of the matrix generates tensile stress on surrounding atoms; and a smaller solute atom generates 14 compressive stress on surrounding atoms. Shear stress is also applied on all strained atoms.…”

“…and (b) four types of inert particles in a Ni-based alloy where they reside in and pin grain boundaries [14] ………………………………………………………………………………………………10 Fig. 2.1 Segregation enthalpy map for binary systems where red scale represents positive enthalpy or tendency of the solute to segregate to the grain boundary, blue scale represents negative enthalpy or antisegregation, black scale represents lack of data for calculation, a black dot represents non-Miedema or other data source, and a "x" represents sources not useful for segregation calculation [24] ……………………………………………………………………..13 Material Matters.…”

Selective Growth of Low Stored Energy Grains During δ Sub-solvus Annealing in the Inconel 718 Nickel-Based Superalloy

“…All nickel-based superalloys contain secondary-phase particles that can be exploited to limit grain growth during annealing through the Smith-Zener pinning effect. [4,5] In the case of Inconel 718, the presence of d phase particles (Ni 3 Nb) hinders grain growth during d sub-solvus annealing. [6] Nonetheless, during complex hot forging cycles, critical thermomechanical conditions can result in what has been referred to as abnormal grain growth during d sub-solvus annealing stages.…”