Grain size affecting the deformation characteristics via micro-injection upsetting

Abstract The micro-injection upsetting (MIU) experiments of commercially pure aluminium have been conducted on two groups of specimens with different grain structures. One group is of coarse grain (CG, undeformed) and the other group is of fine grain (FG) achieved via the 4th pass equal channel angular pressing in micro-meso/scale. The two groups were further processed by micro/meso-scale extrusion before conducting MIU for fabricating tiny pins. Micro-upsetting test of the tiny pins showed that the material has a good isotropic flow forming and is free of undesirable defects comparing with the CG counterparts, which can be ascribed to the decreasing of grain boundary strengthening effect in the case of FG structure

On the current research progress of metallic materials fabricated by laser powder bed fusion process:a review

Abstract Laser powder bed fusion (LPBF) is the most common metal additive manufacturing technique. Following pre-programmed designs, it employs a high-power density laser source to melt pre-alloyed or mixed powders layer by layer, allowing for complex metallic component fabrication. This technique has recently been utilised to produce superior, near-full-density three-dimensional functional parts for various industrial applications. As the LPBF technology matures, ongoing research is being conducted to increase its viability as a sustainable solution in achieving digital transformation in metallic materials and qualifying new metallic materials for digital products. This review focuses on recent developments in the LPBF technique in terms of process parameters, defects, microstructure evolution, related metallurgical phenomena, and microselective laser melting processing for miniaturised part production. First, considerable attention is given to the related parameters that affect the LPBF process, that is, powder-related and laser-related properties. Second, the metallurgical imperfections related to the LPBF products are described in terms of their types, formation mechanisms, and suppression strategies for these defects. Third, the solidification behaviour, phase transformation, and precipitation during the LPBF processing were systematically investigated. Fourth, the materials implemented in microselective laser melting for three-dimensional microfeature production on various metals are summarised. Finally, the results from this review are summarized, and future research addressing existing difficulties and promoting technical advancements are recommended

Effects of wall thickness variation on hydrogen embrittlement susceptibility of additively manufactured 316L stainless steel with lattice auxetic structures

Abstract In the present study, the hydrogen embrittlement (HE) susceptibility of an additively manufactured (AM) 316L stainless steel (SS) was investigated. The materials were fabricated in the form of a lattice auxetic structure with three different strut thicknesses, 0.6, 1, and 1.4 mm, by the laser powder bed fusion technique at a volumetric energy of 70 J·mm⁻³. The effect of H charging on the strength and ductility of the lattice structures was evaluated by conducting tensile testing of the H-charged specimens at a slow strain rate of 4 × 10⁻⁵ s⁻¹. Hydrogen was introduced to the specimens via electrochemical charging in an NaOH aqueous solution for 24 h at 80 °C before the tensile testing. The microstructure evolution of the H-charged materials was studied using the electron backscattered diffraction (EBSD) technique. The study revealed that the auxetic structures of the AM 316L-SS exhibited a slight reduction in mechanical properties after H charging. The tensile strength was slightly decreased regardless of the thickness. However, the ductility was significantly reduced with increasing thickness. For instance, the strength and uniform elongation of the auxetic structure of the 0.6 mm thick strut were 340 MPa and 17.4% before H charging, and 320 MPa and 16.7% after H charging, respectively. The corresponding values of the counterpart’s 1.4 mm thick strut were 550 MPa and 29% before H charging, and 523 MPa and 23.9% after H charging, respectively. The fractography of the fracture surfaces showed the impact of H charging, as cleavage fracture was a striking feature in H-charged materials. Furthermore, the mechanical twins were enhanced during tensile straining of the H-charged high-thickness material

Enhancement of strength in laser-joined Al-TRIP and Si-TRIP steels:microstructural insights and deformation analysis

Abstract This study highlights the strengthening mechanisms observed during the metal joining of high-strength grade steels (Al-TRIP and Si-TRIP) by providing a concise investigation of microstructural features, mechanical strength evaluation, and employing Finite Element Method (FEM) analysis to understand the deformation behaviour in the joint. The base metals (BMs), Al-TRIP and Si-TRIP are cold-rolled sheets with thicknesses of 0.9 mm and 1.3 mm, respectively. Al-TRIP contains 2.4 wt% Al, while Si-TRIP contains 1.5 wt% Si. The Al-/Si-TRIP joint was processed by laser welding at low energy input 24 J/mm. Electron backscattering diffraction and transmission electron microscopy extensively characterized the microstructural features in the fusion zone (FZ) and heat-affected zone (HAZ) to study strengthening mechanisms induced by welding. Uniaxial tensile tests examined joint mechanical strength, while microindentation hardness (HIT) measurements evaluated mechanical response in the weld zones. The FZ showed a fully martensitic structure, while the HAZs displayed refined grains. Ultrafine-grained structures with an average size of 1 μm were observed in the HAZs, resulting in higher HIT hardness values (∼6.7 GPa) compared to the FZ (∼6.3 GPa). Interestingly, the mechanical tensile properties of the joint were unaffected as failure occurred in the thinner Al-TRIP steel. Finite Element Method (FEM) analysis simulated the tensile testing, revealing localized plasticity in the thinner Al-TRIP and explaining the observed fracture

Influence of nanoparticles addition on the fatigue failure behavior of metal matrix composites:comprehensive review

Abstract Light-weight, high-strength metal matrix composites (MMCs) have been gaining prominence in various industrial applications in which the materials are exposed to static and dynamic loading conditions. Unfortunately, micron-sized MMCs frequently encounter challenges such as particle breakage and debonding at the reinforcement-matrix interface, resulting in premature failure due to the decline in their mechanical properties, making them impractical to be utilized in some crucial applications. On the other hand, metal matrix nanocomposites (MMNCs) have been proven to improve strength, ductility, and fracture toughness characteristics, which are greatly beneficial in various industrial applications such as automotive, aerospace structures, and biomaterials. This review provides a comprehensive insight into the effect of nanoparticle addition on the fatigue performance of metals and alloys. Firstly, special attention has been given to the factors influencing the fatigue life of MMNCs. Secondly, the effect of nanoparticle incorporation on the fatigue performance of common metal matrixes, including aluminum, magnesium, titanium, and steel alloys, is reviewed in detail. Finally, a summary of this review and the future aspects related to the behavior of metals with nanoparticles at cyclic loading is provided