Process-property-microstructure relationships in laser-powder bed fusion of 420 stainless steel.

Laser-powder bed fusion (L-PBF) is an additive manufacturing technique for fabricating metal components with complex design and customized features. However, only a limited number of materials have been widely studied using L-PBF. AISI 420 stainless steel, an alloy with a useful combination of high strength, hardness, and corrosion resistance, is an example of one such material where few L-PBF investigations have emerged to date. In this dissertation, L-PBF experiments were conducted using 420 stainless steel powders to understand the effects of chemical composition, particle size distribution and processing parameters on ensuing physical, mechanical and corrosion properties and microstructure in comparison to wrought and metal injection molding (MIM). The density of the fabricated specimens increased, and their surface roughness decreased as the layer thickness and median particle size was decreased and energy density was increased. Following heat treatment, the ultimate tensile strength and elongation of L-PBF specimens with Nb (1.2 %) and Mo (0.57 %) improved to 1750 ± 30 MPa and 9.0 ± 0.2 %, which were higher than the previously reported values in L-PBF, MIM and wrought 420 stainless steel. Tempering of martensite during heat treatment and nanoscale NbC precipitation were consistent with improvement in properties. L-PBF specimens fabricated with deagglomerated fine powder (D50: 12 µm) exhibited similar spreadability, mechanical properties and microstructure to specimens fabricated with coarse powder (D50: 28 µm). In the presence of Nb (1.2 %) and Mo (0.57 %), corrosion properties improved over wrought 420 stainless steel

Risk factors of coronary heart disease and correlates of type 2 diabetes among Cuban Americans

Cuban Americans, a minority Hispanic subgroup, have a high prevalence of type 2 diabetes. Persons with diabetes experience a higher rate of coronary heart disease (CHD) compared to those without diabetes. The objectives of the National Institute of Diabetes and Digestive and Kidney Disease (NIDDK) are to investigate the risk factors of CHD and the etiology of diabetes among diabetics of minority ethnic populations. No information is available on the etiology of CHD risks for Cuban Americans. This cross-sectional study compared Cuban Americans with (N = 79) and without (N = 80) type 2 diabetes residing in South Florida. Data on risk factors of CHD and type 2 diabetes were collected using sociodemographics, smoking habit, Rose Angina, Modifiable Activity, and Willet\u27s food frequency questionnaires. Anthropometrics and blood pressure (BP) were recorded. Glucose, glycated hemoglobin, lipid profile, homocysteine, and C-reactive protein were assessed in fasting blood. Diabetics reported a significantly higher rate of angina symptoms than non-diabetics (P = 0.008). After adjusting for age and gender, diabetics had significantly (P \u3c 0.001) larger waist circumference and higher systolic BP than non-diabetics. There was no significant difference in major nutrient intakes between the groups. One quarter of subjects, both diabetics and non-diabetics, exceeded the intake of percent calories from total fat and almost 60% had cholesterol intake \u3e200 mg/d and more than 60% had fiber intake \u3c20 gm/d. The pattern of physical activity did not differ between groups though, it was much below the recommended level. After adjusting for age and gender, diabetics had significantly (P \u3c 0.001) higher levels of blood glucose, glycated hemoglobin, triglycerides, and homocysteine than non-diabetics. In contrast, diabetics had significantly (P \u3c 0.01) lower levels of high-density lipoprotein cholesterol (HDL-C). Multivariate logistic regression analyses showed that increasing age, male gender, large waist circumference, lack of acculturation, and high levels of triglycerides were independent risk factors of type 2 diabetes. In contrast, moderate alcohol consumption conferred protection against diabetes. The study identified several risk factors of CHD and diabetes among Cuban Americans. Health care providers are encouraged to practice ethno-specific preventive measures to lower the burden of CHD and diabetes in Cuban Americans

Effect of Post Processing Heat Treatment Routes on Microstructure and Mechanical Property Evolution of Haynes 282 Ni-Based Superalloy Fabricated with Selective Laser Melting (SLM)

Selective laser melting (SLM) is one of the most widely used additive manufacturing technologies. Fabricating nickel-based superalloys with SLM has garnered significant interest from the industry and the research community alike due to the excellent high temperature properties and thermal stability exhibited by the alloys. Haynes-282 alloy, a γ′-phase strengthened Ni-based superalloy, has shown good high temperature mechanical properties comparable to alloys like R-41, Waspaloy, and 263 alloy but with better fabricability. A study and comparison of the effect of different heat-treatment routes on microstructure and mechanical property evolution of Haynes-282 fabricated with SLM is lacking in the literature. Hence, in this manuscript, a thorough investigation of microstructure and mechanical properties after a three-step heat treatment and hot isostatic pressing (HIP) has been conducted. In-situ heat-treatment experiments were conducted in a transmission electron microscopy (TEM) to study γ′ precipitate evolution. γ′ precipitation was found to start at 950 °C during in-situ heat-treatment. Insights from the in-situ heat-treatment were used to decide the aging heat-treatment for the alloy. The three-step heat-treatment was found to increase yield strength (YS) and ultimate tensile strength (UTS). HIP process enabled γ′ precipitation and recrystallization of grains of the as-printed samples in one single step

Reversible Transition between Excimer and J‑Aggregate of Indocarbocyanine Dye in Langmuir–Blodgett (LB) Films

In the present Article, a reversible transition behavior from J-aggregates to excimer of an indocarbocyanine dye 1,1′-dioctadecyl-3,3,3′,3′-tetramethylindocarbocyanine perchlorate (DiI) in Langmuir–Blodgett (LB) films was reported. Surface pressure–area (π–<i>A</i>) isotherms, UV–vis, and fluorescence spectroscopies as well as atomic force microscopy (AFM) were used for characterizations of the films. π–<i>A</i> isotherms suggest a balance of interactions between DiI and fatty acids in the mixed monolayer at DiI mole fraction <i>X</i>_DiI = 0.4, resulting in a stable and ideally mixed monolayer. It has been observed that pure DiI formed excimer in LB films, whereas both J aggregates and excimer were formed in LB films when DiI was mixed with long chain fatty acids, viz., stearic acid or arachidic acid. In fatty acid matrix at <i>X</i>_DiI = 0.4, only J aggregates were formed in the LB films. This has been confirmed using deconvolution of spectroscopic results as well as using excitation spectroscopy. The coherent size of the J aggregate was found to be a maximum for the mixed film at the mole fraction 0.4 of DiI in fatty acid matrix. The J-aggregate domain in the LB film contains approximately (20 ± 5) coherent sizes. However, J aggregates were totally absent when DiI was mixed with cationic surfactant, polymer, or nanoclay

Properties of Water Atomized 25Cr7Ni Stainless Steel Processed by Laser-Powder Bed Fusion

The 25Cr7Ni stainless steel is characterized by its two-phase microstructure consisting of ferrite and austenite, contributing to an excellent combination of mechanical and corrosion properties. The present study examined the effects of laser energy density and laser powder bed fusion (L-PBF) process parameters on the physical, mechanical and corrosion properties of a water atomized 25Cr7Ni stainless steel powder processed through L-PBF. The results from the study saw that a combination of L-PBF process parameters (laser scan speed and laser scan spacing at a constant layer thickness) as critical factors affecting the mechanical and corrosion properties of the printed samples. The Archimedes density, mechanical and corrosion properties of samples improved with increase in energy density. The as-printed samples displayed single-phase ferritic microstructure and higher mechanical strength (1050 MPa) compared to wrought, metal injection molded (MIM), powder metallurgically sintered (PM) 25Cr7Ni stainless steel (super duplex stainless steel) alloys. The samples exhibited comparable corrosion resistance to that of a wrought 25Cr7Ni stainless steel despite the presence of only ferritic microstructure