Microstructural evolution and mechanical characterization of wire arc additively manufactured 2Cr13 thin-wall part

2Cr13 thin-wall part was additively deposited by robotic cold metal transfer (CMT) technology, and two traditionally manufactured counterparts in annealing (as-Aed) and quenching & tempering (as-QTed) conditions were adopted as comparison. The results show that only a strong texturing corresponding to α-Fe phase was detected for the wire-arc additively manufactured (WAAM) part, indicating an austenite-free structure. As-deposited microstructure was consisted of martensite laths and ferrite matrix, along with irregular δ-ferrite precipitation. The martensitic growth direction was non-oriented in the X–Y plane, but primarily parallel to the depositing direction in the X-Z and Y-Z planes along the maximum thermal gradient. Both nanohardness and ultimate tensile strength (UTS) for each WAAM sample were enhanced when compared with the as-Aed BM, while poorer than that of the as-QTed BM. Such mechanical evolution was a result of the intrinsic microstructural features, whereas the similar elastic modulus properties were mainly attributed to the similar 2Cr13 atomic bonding. A ductile tensile fracture behavior was dominant in the X-Z plane, while a mixed mode of ductile and brittle fracture occurred in the X–Y and Y-Z planes. The findings above reveal an isotropy in mechanical properties despite a slightly microstructural discrepancy in different planes for the as-deposited 2Cr13 WAAM part

Distinct Metabolome Changes during Seed Germination of Lettuce (Lactuca sativa L.) in Response to Thermal Stress as Revealed by Untargeted Metabolomics Analysis

Temperature strongly influences lettuce (Lactuca sativa L.) seed germination. Different lettuce genotypes respond differently to higher temperatures or thermal stress. In this study, we evaluated the germination performance of 304 lettuce accessions incubated at three temperature settings, 21 °C, 28 °C and 35 °C, respectively, for 40 h. At 21 °C, seeds of all 304 accessions germinated with very well an average germination percentage of 87.72%; at 28 °C, the average germination percentage dropped to 42.84% and at 35 °C, the germination decreased to 1.01%. Then, we investigated changes in metabolic profiles of lettuce seed response to thermal stress using an untargeted metabolomics approach. Results suggested that seeds of thermal-sensitive and thermal-tolerant cultivars employed different metabolic strategies in response to thermal stress during germination. Thermal-sensitive buds accumulated more significant amounts of organic acids, amino acids, sugars, sterols, phenolic compounds and terpenoids compared to thermal-tolerant buds at 21 °C. Thermal-tolerant lettuce cultivar accumulated higher concentrations of amino acids, organic acids, sugars, sesquiterpene lactones, sterols, and fatty acids derivatives during the germination at 35 °C compared to germinated at 21 °C. This investigation paves the way to link the metabolomics to other external and internal factors affecting lettuce seed germination under thermal stress

Behavior of Sn-3.0Ag-0.5Cu solder/Cu fluxless soldering via Sn steaming under formic acid atmosphere

Formic acid (FA) atmosphere is promising to achieve chemical reduction at the oxidized surfaces of the solder and matrix material during soldering, replacing chemical flux being challenging as the continuous decrease in the pitch of solder bump in a three-dimensional integrated circuit. Although a previous study observed the effect of Sn steaming on the wettability of the solder during FA soldering, it has not been understood yet by adequate studies. This study demonstrates the fluxless soldering behavior of Sn-3.0Ag-0.5Cu (SAC) solder/Cu under FA atmosphere. Resembling vulcanian eruption Sn steaming occurred with a solid-state Sn and promoted Sn–Cu intermetallic compound (IMC) formations obviously at temperature (210 ° C) lower than the melting temperature of Sn (231 ° C). As indicated by in-situ observations, the IMC formations led to the final spreading area of solder under FA soldering was larger than that under the soldering with rosin mildly activated (RMA) flux. The wettability of SAC solder under FA atmosphere could be improved with continuous heating

Study of a low-energy collimated beam electron source and its application in a stable ionisation gauge

Stable ionisation vacuum gauges obtain stable sensitivity by controlling both the well-defined electron trajectory and electron energy in the ionisation volume. To achieve this goal, a collimated electron beam and large ion- isation cross-section are required as the electrons enter the ionisation volume. In this paper, a low-energy electron source based on carbon nanotubes is designed to realise a collimated electron beam by the addition of specialised deceleration and focus electrodes. The experimental transmission is approximately 25%, which is in good agreement with the simulation results. Furthermore, a simulation study is carried out combining the electron source with the components of a novel stable ionisation gauge. The numerical simulation results show a sensitivity of 0.250 Pa-1. It provides an important reference for the development of stable ionisation gauge based on the field emission cathode