Investigation of Tensile Properties of Bulk and SLM Fabricated 304L Stainless Steel Using Various Gage Length Specimens

The complex solidification dynamics and thermal cycling during Selective Laser Melting process is expected to result in non-equilibrium material characteristics. There is an essential need for characterization techniques which are critical towards the estimation of anisotropies. The current investigation is targeted towards establishing tensile testing methodologies and their relation to differing gage lengths. Dog-bone shaped specimen designs with gage lengths of 1”, 0.3” and 0.12” were employed in this research. The characterization was performed on hot rolled-annealed 304 stainless and SLM fabricated 304L stainless. It was theorized that smaller gage length specimens would be instrumental in mapping material property anisotropy at a better spatial resolution. The ultimate tensile and yield strength data were used to identify the material property distribution and assess the anisotropy. The material property distributions were used to successfully assess the testing methodologies and material characteristics.Mechanical Engineerin

Break-junction tunneling measurements of the high-\u3ci\u3eT\u3c/i\u3e\u3csub\u3e\u3ci\u3ec\u3c/i\u3e\u3c/sub\u3e superconductor Y\u3csub\u3e1\u3c/sub\u3eBa\u3csub\u3e2\u3c/sub\u3eCu\u3csub\u3e3\u3c/sub\u3eO\u3csub\u3e9- δ \u3c/sub\u3e

Current-voltage tunneling characteristics in a high-critical-temperature superconducting material containing predominately Y1Ba2Cu3O9- δ have been measured using the break-junction technique. Sharp gap structure was observed, with the largest superconductive energy gap measured to be Δ=19.5±1 meV, assuming a superconductor-insulator-superconductor junction. This energy gap corresponds to 2Δ/kBTc=4.8 at T=4 K, for a critical temperature of 93 K (midpoint of the resistive transition)

INFLUENCE OF STEEL ALLOY COMPOSITION ON THE PROCESS ROBUSTNESS OF AS-BUILT HARDNESS IN LASER-DIRECTED ENERGY DEPOSITION

To ensure consistent quality of additively manufactured parts, it is advantageous to identify alloys which can meet performance criteria while being robust to process variations. Toward such an end, this work studied the effect of steel alloy composition on the process robustness of as-built hardness in laser-directed energy deposition (L-DED). In-situ blending of ultra-high-strength lowalloy steel (UHSLA) and pure iron powders produced 10 alloys containing 10-100% UHSLA by mass. Thin-wall samples were deposited, and the hardness sensitivity of each alloy was evaluated with respect to laser power and interlayer delay time. The sensitivity peaked at 40-50% UHSLA, corresponding to phase fluctuations between lath martensite and upper bainite depending on the cooling rate. Lower (10-20%) or higher (70-100%) alloy contents transformed primarily to ferrite or martensite, respectively, with auto-tempering of martensite at lower cooling rates. By avoiding martensite/bainite fluctuations, the robustness was improved.Mechanical Engineerin

Institutional pedagogical waypoints : reflections on doctoral journeys between Taiwan and Australia

Spatial, social and academic journeys undertaken between Taiwan and Australia for doctoral education are the focus of reflection here. The discussion centres on the authors’ experiences of, on the one hand, the development of a Faculty of Education’s doctoral pedagogies in the early 2000s to reflect its international PhD candidature profile – especially from Taiwan – and, on the other, of Taiwanese doctoral candidates’ journeys through their PhDs in the Faculty. The authors write from their particular perspectives: Evans as an Australian academic and a manager of doctoral studies, and Liou as a Taiwanese academic pursuing her doctorate in an Australian university. The article considers the Australian and Taiwanese doctoral contexts between which the students transited. The institutional pedagogical strategies, from pre-enrolment to completion, are examined as waypoints on the doctoral journey for both staff and candidates

Break-junction tunneling measurements of the high-\u3ci\u3eT\u3c/i\u3e\u3csub\u3e\u3ci\u3ec\u3c/i\u3e\u3c/sub\u3e superconductor Y\u3csub\u3e1\u3c/sub\u3eBa\u3csub\u3e2\u3c/sub\u3eCu\u3csub\u3e3\u3c/sub\u3eO\u3csub\u3e9- δ \u3c/sub\u3e

Current-voltage tunneling characteristics in a high-critical-temperature superconducting material containing predominately Y1Ba2Cu3O9- δ have been measured using the break-junction technique. Sharp gap structure was observed, with the largest superconductive energy gap measured to be Δ=19.5±1 meV, assuming a superconductor-insulator-superconductor junction. This energy gap corresponds to 2Δ/kBTc=4.8 at T=4 K, for a critical temperature of 93 K (midpoint of the resistive transition)

Effect of Optimizing Particle Size in Laser Metal Deposition with Blown Pre-Mixed Powders

Functionally Graded Material (FGM) is often fabricated by Laser metal deposition with pre-mixed multiple powders (PMM-powder). Since the supplied PMM-powder directly affects FGM’s composition, investigation on PMM-powder’s property is greatly needed. This paper employed experimental method to observe an important problem: PMM-powder separation in fabricating FGM. A novel particle size optimization method was introduced as solution to eliminate the powder separation. Pre-mixed pure Cu and 4047 Al powders were used to do two experiments. The first experiment result disclosed the existence of powder separation. By optimizing the particle size, the PMM-powder separation was effectively solved in the second experiment result.Mechanical Engineerin

Achieving junction stability in heavily doped epitaxial Si:P

Producción CientíficaJunction stability and donor deactivation in silicon at high doping limit has been a long-standing issue in advanced semiconductor devices. Recently, heavily doped epitaxial Si:P layer with phosphorus concentrations as high as 3 × 1021 at./cm3 has been employed in nanowire field-effect transistor (FET) devices for sub-3 nm technology node as low resistance source-drain and channel stressor. In such highly doped Si:P, the actual dopant activation is much less than nominal phosphorus concentration due to inactive phosphorus atoms arising from dopant-vacancy defects (PnV) clustering phenomenon. Even with state-of-the-art high temperature millisecond annealing, this epitaxial film is thermally unstable upon subsequent thermal treatments. To overcome this limitation, we demonstrate a selective dopant activation scheme which results from the dipole moments of inactive PnV structures within the crystal lattice and their direct energy coupling with the external electric field. It's found that superior stability in dopant activation can be achieved through microwave annealing when a specific temperature and field conditions are met using a triple-parallel-susceptor setup in the microwave cavity. Based on experimental results and ab-initio calculation, we proposed a model, whereas the microwave-PnV interactions result in a specific distribution of dopant defect dominated by thermally stable P4V clusters through elimination of unstable low order PnV, leading to the suppression of donor deactivation and achieving thermally stable junction.Ministerio de Ciencia, Innovación y Universidades (Project MOST-109-2628-M-008-004-MY3

Laser Metal Deposition of Functionally Gradient Materials from Elemental Copper and Nickel Powders

This work deals with the planning and fabrication of a functionally gradient copper-nickel composition via Laser Metal Deposition (LMD). Various compositions of copper and nickel were made by blending different weight percentages which were then sequentially deposited to fabricate functionally gradient copper-nickel thin-wall structures. Analyses were performed by sectioning the thin-wall samples for metallographic, hardness, X-ray diffraction (XRD) and Energy Dispersive X-ray Spectroscopy (EDS) studies. The fabrication was studied for identifying and corroborating the deposited compositions and their corresponding gradients. XRD analyses were performed to identify the crystal structure of the deposit. EDS analysis was instrumental in identifying the variation in composition and realizing the gradient in between compositions. Consequences of using different laser beam intensity profiles and varying laser power duty cycles were realized by analyzing the copper-nickel concentration trends obtained from EDS analyses. Hardness testing was successful in capturing the decreasing trends in strength with decreasing nickel concentration.Mechanical Engineerin