Titanium and its alloys with open cellular structures such as mesh and foam are characterized by low Young's modulus similar to that of human bone. Moreover, they provide the space required for bone tissue in-growth. These characteristics render them suitable for use as an implant. [1] However, to ensure long-term endurance and the ability to withstand abrupt impact fracture, the artificial cellular materials are expected to possess adequate strength in conjunction with high energy absorption capability. [2,3] As regard bone ingrowth, recent studies indicated that cellular structures need to have high porosity, but such structures generally lack adequate mechanical strength and energy absorption, [4,5] These mutually opposing requirements of high porosity and mechanical strength in conjunction with high energy absorption have hindered the application of cellular structure as biomedical devices.Thus, to alleviate the aforementioned demerits of cellular structures, graded/gradient cellular titanium and titanium alloys structures are considered appropriate. If we can optimize the distribution of pore size, pore morphology, and relative density, the open cellular structures will exhibit a combination of high porosity and high strength, optimized in-growth of tissues, and the ability to withstand varying mechanical stress at specific regions. [6][7][8] Recent efforts were directed in fabricating functionally graded cellular titanium alloys, with the possibility for consideration in biomedical applications. [9][10][11] Additive manufacturing process using electron beam melting (EBM) technique has been recently developed to fabricate titanium alloy cellular mesh and foam structures. [12,13] The approach provides accurate control of internal pore architecture and complex-shapes, and thereby provides the opportunity to tailor and fabricate bulk functionally graded cellular structures and elucidate their mechanical behavior. In the study presented here, graded/gradient Ti-6Al-4V mesh structures were fabricated by EBM with the objective to elucidate compressive deformation behavior, Young's modulus, strength, and the underlying deformation mechanisms. It is demonstrated that through appropriate design of graded/gradient cellular mesh structure with high strength and high energy, absorption combination can be fabricated, which have mechanical properties superior to those previously reported for uniform metallic cellular structures. Figure 1 is a computer-aided design (CAD) model for reticulated mesh with radial dual-density. The unit cell of the mesh is rhombic dodecahedron (Figure 1a). The macroscopic images of these graded meshes are presented in Figure 1f. Scanning electron microscopy (SEM) studies suggested that the strut thickness of mesh was %500 mm (Figure 1f). In a manner similar to previous studies, the strut surfaces were rough, [14] and the mesh struts had acicular microstructure consisting primarily of a 0 -martensite and a small amount of b-phase (Figure 1f) because of rapid cooling experienced by the thin isola...
Gas-phase synthesized binary nanoparticles (NPs) possess ultraclean surfaces, which benefit versatile uses in sensors and catalysts. However, precise control of their configuration and properties is still a big challenge because the growth mechanism and phase evolution dynamics in these NPs are very hard to unveil. Here, we report a strategy to investigate the phase evolution dynamics in binary NPs by using e-beam assisted ultrafast local heating and cooling inside a transmission electron microscope. With this strategy, the phase segregation and corresponding shape evolution of PbBi NPs are in situ revealed. It is found that the as-prepared PbBi alloy NPs will transform into heterostructures under e-beam stimulated structural relaxation, leading to the formation of featured Janus configurations with faceted Bi polyhedron parts and intermetallic hemisphere parts. During phase segregation, Pb 1 Bi 1 and Pb 7 Bi 3 phases are captured and identified, and a model of phase and shape evolution of PbBi nanoalloys is developed and contrasted with that of their bulk counterparts. These findings benefit the understanding of the phase dynamics of binary NPs and can provide in-depth information for engineering their structures for practical applications.
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