Reliable and cost effective design of intermetallic Ni2Si nanowires and direct characterization of its mechanical properties

We report that a single crystal Ni2 Si nanowire (NW) of intermetallic compound can be reliably designed using simple three-step processes: casting a ternary Cu-Ni-Si alloy, nucleate and growth of Ni2 Si NWs as embedded in the alloy matrix via designing discontinuous precipitation (DP) of Ni2 Si nanoparticles and thermal aging, and finally chemical etching to decouple the Ni2 Si NWs from the alloy matrix. By direct application of uniaxial tensile tests to the Ni2 Si NW we characterize its mechanical properties, which were rarely reported in previous literatures. Using integrated studies of first principles density functional theory (DFT) calculations, high-resolution transmission electron microscopy (HRTEM), and energy-dispersive X-ray spectroscopy (EDX) we accurately validate the experimental measurements. Our results indicate that our simple three-step method enables to design brittle Ni2 Si NW with high tensile strength of 3.0 GPa and elastic modulus of 60.6GPa. We propose that the systematic methodology pursued in this paper significantly contributes to opening innovative processes to design various kinds of low dimensional nanomaterials leading to advancement of frontiers in nanotechnology and related industry sectors.1

Customizing the mechanical properties of additively manufactured metallic meta grain structure with sheet-based gyroid architecture

The use of cellular structures has led to unprecedented outcomes in various fields involving optical and mechanical cloaking, negative thermal expansion, and a negative Poisson’s ratio. The unique characteristics of periodic cellular structures primarily originate from the interconnectivity, periodicity, and unique design of the unit cells. However, the periodicity often induces unfavorable mechanical behaviors such as a “post-yielding collapse”, and the mechanical performance is often limited by the design of the unit cells. Therefore, we propose a novel structure called a meta grain structure (MGS), which is inspired by a polycrystalline structure, to enhance flexibility in design and mechanical reliability. A total of 138 different MGSs were built and tested numerically, and the correlations between the design parameters (e.g., the relative density) and mechanical properties of the MGSs were rigorously analyzed. A systematic design methodology was developed to obtain the optimal design of the MGS with the target Young’s modulus. This methodology makes it possible to build a unique structure that offers various design options and overcomes the current limitations of cellular structures. Furthermore, a systematic inverse design methodology makes it possible to produce an MGS that satisfies the required mechanical performance. © 2022, The Author(s).TRU

Properties of Pure Ti Implants Fabricated by Additive Manufacturing

This study was carried out to evaluate the aspect of microstructure and mechanical property development on additive manufactured pure Ti at elevated heat-input. For this work, pure Ti powder (commercial purity, grade 1) was selected, and selective laser melting was conducted from 0.5 to 1.4 J/mm. As a result, increase in heat-input led to the significant grain growth form 4 μm to 12 μm, accompanying with the change of grain shape, correctly widmanstätten structured grains. In addition, Vickers microhardness was notably increased from 228 Hv to 358 Hv in accordance with elevated heat-input, which was attributed to the increased concentration of oxygen and nitrogen mainly occurred during selected laser melting process

Correlation of cryogenic deformation mechanisms to excellent strength-ductility of CrCoNi medium entropy alloy processed by selective laser melting

The present study investigated the cryogenic mechanical properties and microstructure of CrCoNi medium entropy alloy (MEA) fabricated by selective laser melting (SLM) with hot isostatic pressing (HIP). The SLM processing parameters were optimized with respect to the relative density and micro-hardness of as-built CrCoNi specimens. The cryogenic (150 K) deformation mechanisms (compared to room (298 K) temperature) of SLM CrCoNi MEA were characterized by uniaxial tensile test, electron backscatter diffraction (EBSD) and transmission electron microscopy (TEM). At 150 K, it reveals superior mechanical properties with the noticeable increase in both strength and ductility by 6.5% and 10.0% (as-built), 22.7% and 6.6% (HIP-treated), respectively. It is found that the high cooling rate of 3.2 × 106 K/s obtained from the simulation results in the fine microstructure and high dislocation density, accordingly the high yield strength of SLM CrCoNi MEA. The steady work hardening, which postpones the onset of necking instability, is attributed to the pronounced dislocation activity and deformation twinning. In addition, a new phase with hexagonal closed-packed (HCP) substructure is apparently observed. Thus, a synergistic effect of dislocations, deformation twinning and HCP substructures contributes to the simultaneous enhancement of strength and ductility. These findings reveal that the CrCoNi MEA fabricated by SLM exhibits an excellent strength and ductility at cryogenic temperature. Furthermore, the SLM CrCoNi MEA with HIP shows significant improvement in the ductility with exceptional strength at 150 K. It demonstrates that a combination of SLM and HIP promotes the CrCoNi MEA to be promising for the cryogenic applications

Effect of heating scan strategy using low energy density on relief of thermal residual stress in L-PBF process for CoCrMo alloy

This study investigates the effects of low energy density laser rescanning of Additive Manufacturing (AM) called Laser-Powder Bed Fusion (L-PBF) on the microstructure, residual stresses, and mechanical characteristics of CoCrMo alloy specimens. Specimens were fabricated under four conditions, i.e., secondary laser scanning with energy density 5 %, 10 %, and 20 %, compared to the first laser irradiation energy densities (AB, 19.41 J/mm3). To confirm the effect of the second laser irradiation, the phase change was analyzed using X-ray diffraction (XRD), and the shape and distribution of the face-centered cubic (FCC) and hexagonal closed packing (HCP) phases were confirmed through electron backscatter diffraction (EBSD) analysis. In particular, the correlation between microstructural stability and residual stress reduction was analyzed, and the effects of microstructural changes on mechanical properties were studied. Through this study, it was confirmed that the appropriate laser conditions during the L-PBF process can act as a heat source, resulting in a heat treatment effect

Effect on microstructural and mechanical properties of selective laser melted pure Ti parts using stress relief heat-treatment process

This study investigated the correlation between the microstructure and the mechanical properties of pure Ti specimens manufactured via selective laser melting (SLM) using the stress relief heat-treatment process. Similar heat treatments were performed at a rate of 10 °C/min with a dwell time of 2 h to reach post-treatment temperatures ranging from of 490–890 °C in intervals of 100 °C. Phase change analysis using X-ray diffraction was conducted to verify the effects of the post-treatment process, while electron backscatter diffraction analysis was conducted to study the effects of microstructural changes induced by the post-treatment process on the mechanical properties of pure Ti specimens. In addition, a comprehensive analysis was performed to analyze residual stress following the stress relief heat treatment. The findings of this study establish a clear relationship between the mechanical properties and microstructural changes in SLM-manufactured pure Ti after heat treatment across a broad temperature range. Furthermore, the study confirms that heat treatment effectively relieves the residual stress in SLM Ti specimens

Influence of Warm Isostatic Press Process on Mechanical Properties of a Part Fabricated by Metal Material Extrusion Process

Material extrusion (ME) using a filament including metal powders has recently attracted considerable attention because it allows the production of metal parts at low cost. However, like other additive manufacturing processes, metal ME suffers from the problem of internal pores. In this study, warm isostatic pressure (WIP)—a post-process used to downsize or remove the pores in polymer ME—was employed in metal ME to improve the mechanical properties of the finished part. It was confirmed experimentally that the tensile strength and the strain at the ultimate tensile strength were increased by WIP. However, from hardness tests, two different results were obtained. On a microscopic scale, there was no change in hardness because the temperature of the WIP process was not high enough to change the microstructure, while on a macroscopic scale, the hardness changed owing to the collapse of the pores within the material under the indenter load. In specimens with relatively large pores, the hardness sensitivity increases with a larger indenter. Finally, factors affecting the WIP process parameters in metal ME were discussed

Influence of Warm Isostatic Press Process on Mechanical Properties of a Part Fabricated by Metal Material Extrusion Process

Material extrusion (ME) using a filament including metal powders has recently attracted considerable attention because it allows the production of metal parts at low cost. However, like other additive manufacturing processes, metal ME suffers from the problem of internal pores. In this study, warm isostatic pressure (WIP)—a post-process used to downsize or remove the pores in polymer ME—was employed in metal ME to improve the mechanical properties of the finished part. It was confirmed experimentally that the tensile strength and the strain at the ultimate tensile strength were increased by WIP. However, from hardness tests, two different results were obtained. On a microscopic scale, there was no change in hardness because the temperature of the WIP process was not high enough to change the microstructure, while on a macroscopic scale, the hardness changed owing to the collapse of the pores within the material under the indenter load. In specimens with relatively large pores, the hardness sensitivity increases with a larger indenter. Finally, factors affecting the WIP process parameters in metal ME were discussed

Moderate-intensity versus high-intensity statin therapy in Korean patients with angina undergoing percutaneous coronary intervention with drug-eluting stents: A propensity-score matching analysis.

ObjectivesIt is unclear whether high-intensity statin therapy provides incremental clinical benefits over moderate-intensity statin therapy in Asian patients with angina. This study sought to compare the clinical outcomes of moderate- and high-intensity statin therapies in patients undergoing percutaneous coronary intervention (PCI) for angina in Korean patients.MethodsBased on the national health insurance claims data in South Korea, patients aged 18 years or older without a known history of coronary artery disease, who underwent PCI with drug-eluting stents due to angina between 2011 and 2015, were enrolled. According to the intensity of statin therapy, patients were categorized into moderate-intensity statin therapy (n = 23,863) and high-intensity statin therapy (n = 9,073) groups. The primary endpoint, defined as a composite of all-cause death and myocardial infarction, was compared between the two groups using a propensity-score matching analysis.ResultsDuring the follow-up period (median, 2.0 years; interquartile range, 1.1-3.1), 1,572 patients had 1,367 deaths and 242 myocardial infarctions. After propensity-score matching, there were 8,939 matched pairs. There was no significant difference in the incidence of the primary endpoint between the two groups (adjusted hazard ratio of high-intensity statin therapy, 1.093; 95% confidence interval: 0.950-1.259; p = 0.212).ConclusionsIn Korean patients undergoing PCI with drug-eluting stents for angina, the high-intensity statin therapy did not provide additional clinical benefits over the moderate-intensity statin therapy