Effect of heat input on nanomechanical properties of wire-arc additive manufactured Al 4047 alloys

Heat input is one of the most important process parameters during additive manufacturing (AM). It is of great significance to understand the effect of heat input on the microstructure and nanomechanical properties, as well as the underlying mechanisms. Wire-arc additive manufactured (WAAM-ed) Al 4047 alloys under different heat inputs were produced and studied in this work. The as-manufactured Al alloys showed hypoeutectic microstructure that consisted of primary Al (α-Al) dendrite and ultrafine Al–Si eutectic. The effect of heat input on hardness and strain rate sensitivity (SRS) were investigated through nanoindentation. The nanohardness decreased with the increasing heat input, in accordance with the trend of yield strength and microhardness in the previous studies, in which the mechanism was usually explained by the grain growth model and Hall-Petch relationship. This work suggests a distinct mechanism regarding the effect of heat input on nanohardness, which is the enhanced solid solution strengthening produced by lower heat input. In addition, the heat input had little effect on the SRS and activation volume. It is hoped that this study leads to new insights into the understanding of the relation between heat input and nanomechanical properties, and further benefits to improve the targeted mechanical properties and engineering applications of the AM-ed materials.publishedVersio

Stochastic Stabilization for Discrete-Time System with Input Delay and Multiplicative Noise in Control Variable

The stabilization problems for time-delay stochastic systems with multiplicative noise in the control variable are investigated in this paper. The innovative contributions are described as follows. Since the past work on stabilization is based on some delay-dependent algebraic Riccati equation (DARE), how to numerically calculate the stabilizing solution remains an unsolved and open problem. On the one hand, an iterative algorithm for computing the unique stabilizing solution of DARE is proposed, while the convergence property is also proved. On the other hand, the concepts of critical stabilization and essential destabilization are proposed as a supplement to stochastic stabilization in terms of spectrum technique. Moreover, the Lyapunov-based necessary and sufficient conditions are developed

Microstructure and nanomechanical behavior of an additively manufactured (CrCoNiFe)94Ti2Al4 high-entropy alloy

Recent substantial studies indicate that high-entropy alloys (HEAs) possess superior mechanical performance, including exceptional strength, high creep resistance, etc. However, additive manufacturing (AM), a burgeoning manufacturing method, may induce extraordinary impacts on the resulting mechanical properties. For the additively manufactured (AM-ed) HEAs, the nanoscale mechanical performance and deformation mechanisms in accordance with the microstructural properties remain unclear. In this work, the microstructure and nanomechanical properties of an AM-ed (CrCoNiFe)94Ti2Al4 HEA were investigated. The local mechanical properties including hardness, elastic modulus, and nanoscale creep deformation, were explored by nanoindentation-based measurement. Simultaneously, the crystallographic orientation dependence on the mechanical behavior of AM-ed HEA was carried out by combining with electron backscattered diffraction (EBSD). It is found that the {101}-grain has the highest hardness and elastic modulus, whereas the creep resistance of {111}-grain is the greatest, with the indicators of the creep mechanism showing lattice diffusion is the dominant mechanism. Two different states of HEA, as-printed and heat-treated, were utilized to explore the effect of heat treatment. Heat treatment in the current study can increase the hardness and elastic modulus but decrease the creep resistance slightly. This work elucidates the underlying mechanisms of grain orientation dependence on nanomechanical properties and the effects of heat treatment. Moreover, it also sheds light on the particular creep behavior at the nanoscale and creep mechanism of the AM-ed (CrCoNiFe)94Ti2Al4 HEA

Microstructure and nanomechanical behavior of an additively manufactured (CrCoNiFe)94Ti2Al4 high-entropy alloy

Recent substantial studies indicate that high-entropy alloys (HEAs) possess superior mechanical performance, including exceptional strength, high creep resistance, etc. However, additive manufacturing (AM), a burgeoning manufacturing method, may induce extraordinary impacts on the resulting mechanical properties. For the additively manufactured (AM-ed) HEAs, the nanoscale mechanical performance and deformation mechanisms in accordance with the microstructural properties remain unclear. In this work, the microstructure and nanomechanical properties of an AM-ed (CrCoNiFe)94Ti2Al4 HEA were investigated. The local mechanical properties including hardness, elastic modulus, and nanoscale creep deformation, were explored by nanoindentation-based measurement. Simultaneously, the crystallographic orientation dependence on the mechanical behavior of AM-ed HEA was carried out by combining with electron backscattered diffraction (EBSD). It is found that the {101}-grain has the highest hardness and elastic modulus, whereas the creep resistance of {111}-grain is the greatest, with the indicators of the creep mechanism showing lattice diffusion is the dominant mechanism. Two different states of HEA, as-printed and heat-treated, were utilized to explore the effect of heat treatment. Heat treatment in the current study can increase the hardness and elastic modulus but decrease the creep resistance slightly. This work elucidates the underlying mechanisms of grain orientation dependence on nanomechanical properties and the effects of heat treatment. Moreover, it also sheds light on the particular creep behavior at the nanoscale and creep mechanism of the AM-ed (CrCoNiFe)94Ti2Al4 HEA

Levels of Phthalate Metabolites in Urine of Pregnant Women and Risk of Clinical Pregnancy Loss

Toxicological studies have shown that phthalate esters (PAEs), a class of widely used and environmentally prevalent chemicals, can increase the abortion rate in animals, but epidemiological evidence is scarce. This study aimed to explore the relationship between the urinary concentration of phthalate metabolites and the risk of clinical pregnancy loss. A total of 132 women who underwent clinical pregnancy loss (cases) and 172 healthy pregnant women (controls) were recruited from Beijing, China. Eight phthalate metabolites in urine were determined by ultraperformance liquid chromatography tandem mass spectrometry (UPLC–MS/MS). Five phthalate metabolites, monomethyl phthalate (MMP), monoethyl phthalate (MEP), monoisobutyl phthalate (MiBP), mono-<i>n</i>-butyl phthalate (MnBP), and mono­(2-ethlyhexyl) phthalate (MEHP), were detected in at least 95% of the urine samples, with the highest median concentration of 51.0 μg/g of creatinine for MnBP of all participants. The differences in urinary concentrations of phthalate metabolites between cases and controls were evaluated using the Mann–Whitney <i>U</i> test. The concentrations of MEP (median of 18.7 μg/g of creatinine), MiBP (23.3 μg/g of creatinine), and MnBP (58.2 μg/g of creatinine) detected in the cases were significantly higher than those (15.7 μg/g of creatinine for MEP, 19.4 μg/g of creatinine for MiBP, and 43.9 μg/g of creatinine for MnBP) in the controls (<i>p</i> < 0.05). Increasing risks of clinical pregnancy loss were observed from the first to fourth quartiles of the MEP, MiBP, and MnBP concentrations (<i>p</i> < 0.05 for trend). We concluded that exposure to MEP, MiBP, and MnBP was associated with an increased risk of clinical pregnancy loss

Ubiquitous Occurrence of Chlorinated Byproducts of Bisphenol A and Nonylphenol in Bleached Food Contacting Papers and Their Implications for Human Exposure

The occurrence of bisphenol A (BPA), nonylphenol (NP), and their six chlorinated byproducts were investigated in 74 food contacting papers (FCPs) from China, the U.S.A., Japan, and Europe using a sensitive dansylation LC-MS/MS method. BPA

Levels of Blood Organophosphorus Flame Retardants and Association with Changes in Human Sphingolipid Homeostasis

While a recent toxicological study has shown that organophosphorus flame retardants (OPFRs) may disrupt sphingolipid homeostasis, epidemiologic evidence is currently lacking. In this study, a total of 257 participants were recruited from Shenzhen, China. Eleven OPFRs were for the first time simultaneously determined in the human blood samples by ultraperformance liquid chromatography and tandem mass spectrometry. Six OPFRs, tributyl phosphate (TNBP), 2-ethylhexyl diphenyl phosphate (EHDPP), tris­(2-chloroisopropyl) phosphate (TCIPP), tris­(2-butoxyethyl) phosphate (TBOEP), triethyl phosphate (TEP), and TPHP, were detectable in at least 90% of participants, with median concentrations of 37.8, 1.22, 0.71, 0.54, 0.49, and 0.43 ng/mL, respectively. Sphingomyelin (SM) levels in the highest quartile of EHDPP, TPHP, TNBP, TBOEP, TEP, and TCIPP were 45.3% [95% confidence interval; 38.1%, 53.0%], 51.9% (45.5%, 58.6%), 153.6% (145.1%, 162.3%), 20.6% (14.5%, 27.0%), 59.0% (52.1%, 66.2%), and 62.8% (55.2%, 70.6%) higher than those in the lowest quartile, respectively, after adjusting for covariates. Sphingosine 1-phosphate (S1P) levels in the highest quartile of EHDPP, TPHP, and TNBP were 36% (−39%, −33%), 16% (−19%, −14%), and 36% (−38%, −33%) lower than those in the lowest quartile, respectively. A similar pattern emerged when exposures were modeled continuously. We for the first time found the associations between OPFRs and changes in human sphingolipid homeostasis