Cooling rate dependent as-cast microstructure and mechanical properties of Zr-based metallic glasses

In this article, wedge chill casting is used to provide a variation of the cooling rate for the study of cooling rate-dependent as-cast microstructure and mechanical properties of Zr-based metallic glasses with and without yttrium doping. In-situ formed crystalline phases and crystallization sequence are realized in the context of the cooling rate. Macro-hardness is studied via the Brinell ball indentation and the contact morphology is discussed on the basis of microstructure analysis

Influence of build layout and orientation on microstructural characteristics of electron beam melted Alloy 718

Effects of build layout and orientation consisting of (a) height from the build plate (Z-axis), (b) distance between samples, and (c) location in the build plate (X-Y plane) on porosity, NbC fraction, and hardness in electron beam melted (EBM) Alloy 718 were studied. The as-built samples predominantly showed columnar structure with strong Ë\u82001Ë\u83 crystallographic orientation parallel to the build direction, as well as NbC and ÎŽ-phase in inter-dendrites and grain boundaries. These microstructural characteristics were correlated with the thermal history, specifically cooling rate, resulted from the build layout and orientation parameters. The hardness and NbC fraction of the samples increased around 6% and 116%, respectively, as the height increased from 2 to 45 mm. Moreover, by increasing the height, formation of ÎŽ-phase was also enhanced associated with lower cooling rate in the samples built with a greater distance from the build plate. However, the porosity fraction was unaffected. Increasing the sample gap from 2 to 10 mm did not change the NbC fraction and hardness; however, the porosity fraction increased by 94%. The sample location in the build chamber influenced the porosity fraction, particularly in interior and exterior areas of the build plate. The hardness and NbC fraction were not dependent on the sample location in the build chamber. © 2018, The Author(s).First Online: 17 September 2018</p

Predictors of bronchopulmonary dysplasia or death in premature infants with a patent ductus arteriosus

BACKGROUND: Preterm infants with a PDA are at risk for death or development of BPD. However, PDA treatment remains controversial. We investigated if PDA treatment and other clinical or echocardiographic (ECHO) factors were associated with the development of death or BPD. METHODS: We retrospectively studied clinical and ECHO characteristics of preterm infants with birth weight <1500 g and ECHO diagnosis of a PDA. Logistic regression and classification and regression tree (CART) analyses were performed to assess variables associated with the combined outcome of death or BPD. RESULTS: Of 187 preterm infants with a PDA, 75% were treated with indomethacin or surgery and 25% were managed conservatively. Death or BPD occurred in 80 (43%). Logistic regression found lower gestational age (OR 0.5), earlier year of birth during the study period (OR 0.9), and larger ductal diameter (OR 4.3) were associated with the decision to treat the PDA, while gestational age was the only variable associated with death or BPD (OR 0.6, 95% CI 0.5-0.8). CONCLUSION: Only lower gestational age and not PDA treatment or ECHO score was associated with the adverse outcome of death or BPD. Further investigation of PDA management strategies and effects on adverse outcomes of prematurity is needed