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The effect of post-weld heat treatment on microstructure and mechanical properties of electron beam welded IN738LC joint has been investigated. The fusion zone consists of γ-Ni matrix, bimodal-size γʹ particles, granular MC carbides (Ti-rich) and Cr-rich M23C6 carbide chain in IN738LC joint subjected to post-weld heat treatment. The secondary γʹ particle in fusion zone precipitates and grows ceaselessly with the increased aging time. The coarsening of γʹ particle follows the Lifshiitz-Slyozov-Wagner coarsening theory with a constant coarsening rate of 1.003 × 10−27m3/s. The secondary γʹ particle in base metal shows a similar size with that of fusion zone, but a lower volume fraction (52%) than that of fusion zone (54%). M23C6 carbide is easier to precipitate along high angle grain boundaries. As aging time increases, the morphology of M23C6 carbide changes from discrete granular shape to continuous chain. The thickness of M23C6 carbide also increases dramatically. Owing to smaller grain size and higher solute concentration in fusion zone, more M23C6 carbides form in FZ than that of base metal. With the increased aging time, the tensile strength of IN738LC joint at 900°C decreases gradually, while the elongation of joint firstly increases and then decreases, which is attributed to the increased channel width of γ-Ni matrix. Due to the formation of continuous M23C6 carbide chain, the rupture life of IN738LC joint firstly increases and then decreases as aging time increases. Combined with the mechanical properties and size stability of γʹ precipitates in IN738LC joint, 1125°C/2 h + 850°C/24 h is an optimized post-weld heat treatment regime.

The effect of post-weld solution treatment (PWST) on microstructure and mechanical properties of electron beam welded IN738LC joint has been investigated. The fusion zone (FZ) of IN738LC joint consisted of γ-Ni matrix, fine γʹ particles, granular MC carbides and a bit of M23C6 carbides after PWST. With the increased solution temperature, the area percent of MC carbides decreased while the content of γʹ particles increased gradually. The solvus temperature of γʹ phase in FZ and base metal (BM) was 1150 °C and 1175 °C, respectively, which was due to the different size of primary γʹ particles. When the complete dissolution of primary γʹ particles in FZ and BM occurred, the micro-hardness of FZ and BM reached the peak values (509.5 HV and 503.9 HV). As the solution temperature increased, the tensile strength of IN738LC joint initially increased and then decreased, while the stress-rupture life of IN738LC joint decreased steadily. The joint with bimodal-size γ′ particles and moderate MC carbides after 1125 °C/2 h heat treatment showed the excellent comprehensive mechanical performance, and the average strength and stress-rupture life of IN738LC joints were 686 MPa (900 °C) and 2.395 h (900 °C/350 MPa), respectively. Consequently, 1125 °C/2 h has been proposed as an optimized PWST process for IN738LC joint.

In this paper we present sufficient conditions for convergence of projection and fixed-point algorithms used to compute dynamic user equilibrium with elastic travel demand (E-DUE). The assumption of strongly monotone increasing path delay operators is not needed. In its place, we assume path delay operators are merely weakly monotone increasing, a property assured by Lipschitz continuity, while inverse demand functions are strongly monotone decreasing. Lipschitz continuity of path delay is a very mild regularity condition. As such, nonmonotone delay operators may be weakly monotone increasing and satisfy our convergence criteria, provided inverse demand functions are strongly monotone decreasing. We illustrate convergence for nonmonotone path delays via a numerical example.

Refractory metal diboride is a kind of excellent ultra-high temperature ceramics and could be applied as thermal shielding material for supersonic aircraft. In this paper, a two-step reaction process for the synthesis of refractory metal diboride powders was proposed using refractory metal oxide, carbon black (C), B4C, and calcium Ca as raw materials. Firstly, the carbothermal reduction reaction between oxides and C was taken place at 1773 K; and then, the reduction product was reacted with B4C and Ca for the purposes of boronization and decarburization. After acidic leaching, pure diboride was prepared. The experimental results indicated that diborides of Ti, Zr, Hf, V, Nb and Ta with low residual carbon content can be prepared by this method. In addition, the inheritance relationship of particle size between raw oxide and finally prepared diboride was revealed. By this method, ultra-fine TiB2 (123 nm) and ZrB2 (76 nm) powders were also successfully prepared, with the raw materials of nano TiO2 and nano ZrO2, respectively.

Summary Background & aims How anthropometric and nutrition status indicators relate to cognitive function in the oldest old adults is an issue that needs to be explored. This study aimed to analyze the association of parameters and nutrition status indicators (waist circumference, BMI, calf circumference, and waist–calf circumference ratio [WCR]) with cognitive functions in centenarians. Methods A cross-sectional observational study was conducted with the full sample of 1002 centenarians from Hainan. The mini-mental state examination (MMSE) was used to identify cognitive impairment. Multiple logistic regression analysis was used to examine the strength of association between each anthropometric index and the risk of cognitive impairment or severe cognitive impairment identified by MMSE. Locally Weighted Scatterplot Smoothing (LOWESS) curve was used to visualize the linear or non-linear relationship of each pair. Results The risk of cognitive impairment identified by MMSE for centenarians was reduced by 12% for every 1 cm thickening of the calf circumference (OR = 0.88, 95% CI: 0.81–0.95) and the increase in each unit of WCR increased cognitive impairment the risk by 1.60 times (OR = 2.60, 95% CI: 1.31–5.13) after adjusting for demographic characteristics (i.e., gender, age, ethnicity, marital status, education level, and type of residence) and lifestyle (i.e., smoking, drinking, and exercise) related variables. Conclusions Results suggest that calf circumference is negatively associated with the risk of cognitive impairment identified by MMSE in centenarians. Older adults with lower calf circumference should pay attention to their cognitive function.