Papers by Author: Gang Ji

Abstract: Cold spraying (CS) is a solid-state layer-by-layer deposition technique, allowing to fabricate complex-shaped metallic components, such as metal matrix composites (MMCs). It has been demonstrated that introduction of a nacre-like nanolaminated architecture in man-made MMCs can perfectly beat the conflict between strength and ductility (toughness). In this work, the fully dense carbon nanotubes (CNTs) reinforced Al6Si (hereafter called CNT/Al6Si) MMC with the nanolaminated architecture is successfully realized by flake powder metallurgy followed by CS. It is revealed that the nanolaminated architecture, containing nanosized grains, is properly created in the CNT/Al6Si flaky powder by ball milling, which is then conserved in the CS-processed component. The harmful excessive formation of Al₄C₃ due to interfacial reaction is limited and structural integrity of initially incorporated CNTs is well retained.

Abstract: The current medical technology necessitates the usage of biodegradable metals like Magnesium (Mg) as the future implant material due to the numerous benefits it can provide. Therefore, new Magnesium-based rare earth alloys targeting biomedical applications were synthesized using Disintegrated Melt Deposition (DMD) technique followed by hot-extrusion. In this investigation, Zinc (Zn) and Erbium (Er) were chosen as alloying elements to provide suitable strengthening effect and Mg-2Zn, Mg-2Zn-2Er alloys were synthesized. With the addition of alloying elements, the grain size was reduced and several MgZn intermetallics were formed. Corrosion studies of as-extruded materials were done in 0.5 wt.% NaCl solution to elucidate the microstructure-corrosion relationship. Improved corrosion resistance is seen in the alloys in comparison to pure Magnesium. Addition of Erbium is seen to improve the protectiveness of the surface film formed during immersion. Both these elements have proven to increase the corrosion potential of Mg in NaCl solution.

Abstract: Strength and ductility are the two most important mechanical properties of a structural material. However, they are often mutually exclusive. In this study, a 6 wt. % TiB₂ nanoparticle reinforced 7075Al (i.e. TiB₂/7075Al) composite was designed and produced by the processing route combining casting, friction stir processing, hot extrusion and T6 heat treatment. The result of tensile testing demonstrates that the as-processed composite sample presents an ultimate tensile strength of 677 MPa and a total elongation to failure of around 15 %, being higher than any Al or Al based materials ever reported. The typical microstructure contains the TiB₂ reinforcement nanoparticles uniformly distributed in the equiaxed Al grain matrix (2 μm in average grain size). In addition to the dispersed nanoprecipitates of the 7075Al (Al-Zn-Mg-Cu) matrix, the integrated TiB₂ nanoparticles are systematically decorated by a shell corresponding to (Zn_1.5Cu_0.5)Mg. This finding challenges our understanding and opens a door for further enhancing strength and ductility being easily scalable for industrial applications.

Abstract: Al and Al12Si matrix composites reinforced with synthetic diamond particles have been developed by using conventional powder metallurgy and emerging additive manufacturing techniques, i.e. vacuum hot pressing (VHP) and selective laser melting (SLM), respectively. Relative density and interface structure have been evaluated to relate to measured thermal conductivity (TC) of the composite. Despite very different physical and metallurgical mechanisms (VHP vs. SLM), the diamond/Al interface can be tailored allowing to form a ‘clean’ and tightly-adhered interface at the micrometer scale in both cases. This so-called diffusion-bonded interface is the most favorable for enhancing overall TC which demonstrates the potential of SLM for processing multifunctional Al matrix composites. However, how to realize full densification and simultaneously maintain such an interface structure during SLM remains a key technical problem to figure out.

Abstract: The current work focuses on the particular case of dissimilar 6082 Al alloy/pure copper butt-friction stirred joints. It takes advantage of voluntarily non optimized welding conditions in order to test the potential of an original approach of identification of the welding defects by means of a single tensile test. The sequence and mechanism of the fracture events arise from their localization on the fracture surfaces thanks to strain maps obtained by digital image correlation. This technique of flaws identification is proved to be particularly efficient at least with the present highly damaged welds.