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In this study, the effect of composite shear flow casting (CSFC) on microstructure and hot deformation process of Ni-based superalloy Udimet720Li has been investigated. Udimet720Li superalloy was produced by using CSFC and conventional casting methods, followed with the same isothermal forging process. The microstructures of both CSFC and conventionally solidified (CS) samples were characterized using optical microscope, scanning electron microscope, energy dispersive X-ray spectroscopy and electron backscatter diffraction. Results show that the CSFC sample owns excellent microstructural uniformity with a reduced area fraction of segregation regions, leading to a wider processing window for subsequent deformation, compared to the CS sample. Besides, the deformation resistance and the thermal workability of CSFC sample are significantly improved because of the homogeneous microstructure, resulting in the uniform deformation during subsequent isothermal forging. • Ni-based superalloy Udimet720Li was produced by using composite shear flow casting. • The microstructure evolution of Udimet720Li was investigated. • The fracture mechanism of forged microstructure was analyzed. • The CSFC-processed Udimet720Li has homogeneous microstructure and superior deformation workability. [ABSTRACT FROM AUTHOR]

In order to demonstrate the transformation relation of two primary Al 13 Mn 4 Si 8 and Al 15 Mn 3 Si 2 phases during solidification of Al-12Si-4Cu-2Mn (in wt%) alloy, verification experiments through controlling cooling rate of solidification and quenching at different stages during solidification were designed and the microstructure was characterized by optical microscope, scanning electron microscope and transmission electron microscope. The cooling rate during solidification plays a decisive role in the formation of primary Mn-rich phases. Fast cooling rate favors the slender rod-like Al 13 Mn 4 Si 8 phase and slow cooling rate leads to the formation of dendritic Al 15 Mn 3 Si 2 phase. A great number of symbiotic complexes, constituted with inner Al 13 Mn 4 Si 8 and outer Al 15 Mn 3 Si 2 phases, are found in the transition area of the surface and center of the casting with a middle cooling rate. Microstructure observation of the liquid quenching samples demonstrates that the first phase formed during solidification must be 2D lath-like Al 13 Mn 4 Si 8 phase whether with high cooling rate or with slow cooling rate. And 3D dendritic Al 15 Mn 3 Si 2 phase is transformed from 2D Al 13 Mn 4 Si 8 by a peritectic reaction: L+ Al 13 Mn 4 Si 8 →Al l5 Mn 3 Si 2 , which is dependent of the cooling rate during solidification. A schematic model with double nose curves was established to exhibit the influence of cooling rate on the peritectic reaction. With sufficient high cooling rate, this peritectic reaction will be suppressed completely. When the cooling rate is slow enough, the peritectic reaction will proceed completely. However, in case of middle rate, the peritectic reaction will happen but incompletely. [ABSTRACT FROM AUTHOR]

Powder bed fusion using a laser beam (PBF-LB) is a promising additive manufacturing (AM) technology, used to produce components with complex geometry and design freedom. The parts are built in a layer-by-layer fashion during PBF-LB, and changing the processing parameters within different layers can lead to the modification of microstructures and finally a great impact on the mechanical properties. Thus, PBF-LB provides the possibility for the customization of material properties by changing the microstructures of layers using different processing parameters. In this investigation, a twin PBF-LB system, i.e., with a low-power laser beam and a high-power laser beam in a machine, is used to produce fine and coarse microstructures using the Inconel 718 (IN718) alloy, respectively. The fine and coarse microstructures are alternately printed to form different heterogeneous structures. Correspondingly, different mechanical properties are achieved. The microstructures are analyzed using optical microscope (OM), scanning electron microscope (SEM), electron backscatter diffraction (EBSD) and numerical calculation. The defects generated by these 2 laser beams are simultaneously discussed. This study facilitates the tailoring of alloy properties using the PBF-LB technology to meet the users' needs of multiple service conditions. • IN718 heterogeneous structures are built by PBF-LB using 2 different laser systems. • A fine microstructure is formed using the low-power laser beam. • The high-power laser beam tends to produce the samples with coarse grains. • The different sizes of microstructures are ascribed to the different cooling rates. • The heterogeneous structures have effects on the mechanical properties. [ABSTRACT FROM AUTHOR]

Abstract: The thermit reaction sequence of MoSi2 formation from Mo and Si powder mixtures was investigated by SEM using quenching techniques. It was observed that the mechanism of MoSi2 formation depends on the Mo particle size. In the case of small particles, the final structure consists of equiaxed MoSi2 grains. The large particles, however, cannot be completely dissolved and remain unreacted surrounded by thin solid-state diffusional layers of Mo5Si3 and Mo3Si. [Copyright &y& Elsevier]

Abstract: Platinum-based alloys are being developed which have microstructures that are analogous to the γ/γ′ microstructure of the nickel-based superalloys. These Pt-based superalloys have the potential to substitute Ni-based superalloys for even higher temperature applications. The Pt–Cr–Ru system has been studied experimentally as part of this project. The alloys were studied in the as-cast condition, using scanning electron microscope (SEM) and X-ray diffraction (XRD). A solidification projection and liquidus surface were constructed. The major phases were (Ru), (Pt) and ∼CrPt, with ∼Cr2Ru (D8b), ∼Cr3Ru (A15) and ∼Cr3Pt (A15) being minor in extent. Both the tetragonal (L10) and cubic (A1) forms of ∼CrPt were observed. Two invariant reactions were identified in the Pt–Cr–Ru system. [Copyright &y& Elsevier]

Medium alloyed as-cast nickel base superalloy was subjected to two different cooling rates (fast and slow) after homogenization which resulted in mono-modal and bi-modal distribution of gamma prime (γ′) precipitates. Both the materials were subjected to high temperature deformation over a range of temperatures and strain rates. Irrespective of the strain rate used, the material subjected to fast cooling exhibited high compressive yield strength and flow softening characteristics when compared to the slow cooled material in the sub-solvus regime. Detailed microstructural investigation carried out using scanning and transmission electron microscope to ascertain the micro-mechanism revealed varying precipitate – dislocation interaction mechanism in both the materials. Higher flow softening and cracking in the fast cooled material is attributed to glide plane softening due to planar slip and the presence of fine network of carbides along the grain boundaries respectively. In the super-solvus regime, the flow stress of both the materials was comparable and both the materials exhibited discontinuous dynamic recrystallization (DDRX). Further, the slow cooled material exhibited lower critical strain for DDRX initiation and also better recrystallization kinetics irrespective of the processing conditions. Higher recrystallization kinetics in the slow cooled material is attributed to the concurrent particle simulated nucleation (PSN) at the coarse MC type carbide boundaries. • Effect of cooling rate on microstructure evolution and its effect on high temperature deformation behaviour evaluated. • Varying dislocation – precipitate interaction mechanisms captured and reported. • Softening & cracking in the fast cooled material is attributed to planar slip, glide plane softening & grain boundary carbides. • Homogenous deformation in slow cooled material is attributed to wavy slip. • Higher DRX kinetics in slow cooled material is ascribed to concurrent particle stimulated nucleation. [ABSTRACT FROM AUTHOR]