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The formation of intermetallic compounds (IMCs) at the joint interface between dissimilar metals has been the focus of recent research, since joint properties are largely determined by these interfacial IMCs. In this study, FeCoCrNiMn high entropy alloy (HEA) was joined to traditional 1060Al alloy by friction stir lap welding (FSLW) for the purpose of reducing the excessive cost of HEAs. Microstructural characterization shows the interfacial layer is continuous but varies in thickness from 1.3 to 1.7 μm. The interfacial structure can be divided into three types. Close to the Al side are STR I and II, confirmed to be of same monoclinic Al₁₃Fe₄ type IMC, but showing sharp difference in composition with simultaneous co-depletion of Cr and Mn and co-enrichment of Co and Ni in STR I. Close to the HEA side is STR III, consisting of parallelly arranged ultra-fine columnar grains, identified to be orthorhombic Al₅Fe₂ type IMC.

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Microstructure-sensitive fatigue crack growth in 304 metastable austenitic stainless steel containing nanotwin bundles was studied using a miniature compact tension specimen combined with post-fatigue metallographic examinations. The single-variant nanotwinned specimens exhibited high crack growth resistance compared to the coarse-grained specimen without nanotwin bundles, regardless of lamellar orientation. In the nanotwin bundles, martensite variants are formed with the habit plane parallel to the twin plane during crack propagation. Even when the crack propagates along the twin boundary, it tends to proceed by activation of multiple slip systems into the formed martensite phase, which inhibits brittle twin boundary separation. Post-fatigue transmission electron microscopy revealed that detwinning occurred ahead of the crack tip. Therefore, introducing nanotwin bundles into the metastable austenitic steel changes the course of damage accumulation through detwinning and martensite formation, enhancing the fatigue crack growth resistance.

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A multi-modal, multi-scale correlative tomography investigation of Al-TiC metal matrix composites processed via flux-assisted reaction synthesis is reported. Synchrotron X-ray microradiography is utilized to visualize the reaction and particle evolution in real-time. Changes in particle diameter and areal number density suggest that the process is nucleation- rather than growth-dominated. At 950 °C, the bulk of the reaction takes place in a relatively short time span of less than 600 s. The microstructure is imaged at higher resolution in 2D (scanning electron microscopy) and 3D (synchrotron X-ray nanotomography), revealing the formation of carbide particles with a hexagonal platelet morphology. We propose that the morphology arises due to the incorporation of Si impurities during the experiment. It is expected that the correlative tomography workflow and analysis may guide future metal matrix composite (MMC) processing strategies.

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Boron is known to influence the grain boundary microchemistry and thereby improve the mechanical performance of superalloys; however, the form in which boron exists at the grain boundary is debatable. We show from electron microscopy characterization that in a directionally solidified Ni-base superalloy boron is present in the form of nearly spherical nano-sized metal borides. We also report the existence of a gradient in composition of Cr, and W within the nano-sized boride precipitates located along the grain boundaries. These borides are present discretely and suppress the agglomeration of mostly reported M₂₃C₆ carbides at the columnar grain boundaries. This could be a possible reason for the reported improvement in transverse creep properties of boron modified directionally solidified superalloys.

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A high strain rate compressed Mg-Y alloy is prepared for the study of <1-100> symmetric tilt grain boundary. A twin-like {33-64} tilt boundary, which is formed via the evolution of {11-21} twin boundary, is commonly found for the first time in the deformed Mg-Y alloy. Via combining high-angle annular dark-field scanning transmission electron microscopy and density functional theory calculations, the formation of {33-64} tilt boundary and the associated segregation of Y atoms are rationalized. Such a finding provides a new vision on twinning behavior for the design of new high-performance Mg alloys.

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