Study on the technology of surface strengthening Ti–6Al–4V alloy by near-dry multi-flow channel electrode electrical discharge machining

Titanium alloy has excellent performance and wide application prospects in the aerospace, energy, chemical industry, and other areas. However, low hardness and poor wear resistance severely limit the application range of titanium alloys. Therefore, in the present research, multi-flow channel electrode and gas-liquid atomization medium are used for surface strengthening of Ti–6Al–4V alloy by electrical discharge machining (EDM). Benefiting from the multi-flow channel electrode, the gas-liquid atomization medium passes into the discharge gap uniformly. Under the environment of transient high-temperature and high-pressure generated by discharge, the ionized element N and molten titanium in the atomizing medium are induced to undergo in-situ synthesis reactions and generate a nitride reinforcement layer. Influence parameters such as peak current, pulse on time (Ton), and pulse off time (Toff) on the surface characteristics are optimized through single-factor experiments. Scanning electron microscope (SEM) and X-ray diffractometer (XRD) are adopted to investigate the hardness and wear resistance characteristics of the strengthening surface. The results indicate that a continuous and uniform reinforcement layer with fewer defects can be obtained. TiN and other hard phases are observed in the strengthened surface. The hardness of the strengthening layer is about 3–5 times as much as that of the substrate, and the wear resistance is increased by more than 40 %. Electrochemical analysis shows that the corrosion tendency of the strengthened layer decreased by 72 % compared to that of the substrate

Effect of reverse pulse current density on microstructure and properties of supercritical Ni-GQDs nanocomposite coatings

In this study, Ni-GQDs nanocomposite coatings were prepared by double-pulse electrodeposition under supercritical CO2 with graphene quantum dots (GQDs) as the second phase additive. The effects of supercritical CO2 conditions and reverse pulse current density on microstructure, crystal orientation, grain size, GQDs quality, mechanical properties, and corrosion resistance of Ni-GQDs nanocomposite coatings were investigated. The results show that when the reverse pulse current density is 0.8 A /dm2, the surface of Ni-GQDs-Ⅱ nanocomposite coating is compact and flat, GQDs is uniformly dispersed in the coating, and GQDs is closely bound to Ni grains. Compared with the coating prepared at normal temperature and pressure. The grain size of the Ni-GQDs-Ⅱ nanocomposite coating is 4.58 nm, and the grain size is reduced by 75.3 %. The quality of GQDs in the coating was improved. The coating hardness is 867.22 HV, which is significantly increased by 53.7 %. The roughness is 0.236 μm, which is significantly reduced by 37.2 %. The friction coefficient and volume wear were 0.262 and 3.395 × 107 μm3, respectively, which were significantly reduced by 27.4 % and 57.9 %. After electrochemical corrosion, the self-corrosion voltage of the coating was −139 mV, and the self-corrosion current density was 3.19 × 10−7 A/cm2. The self-corrosion voltage was significantly increased by 61.2 %, and the self-corrosion current density was significantly decreased by 71.2 %. The Rct value and Ndl value of the coating are 31594.53 Ω·cm2 and 0.862, respectively. Significantly increased by 226.2 % and 67.1 %, respectively. The coating has excellent mechanical properties and corrosion resistance

Pinocembrin Protects Blood-Brain Barrier Function and Expands the Therapeutic Time Window for Tissue-Type Plasminogen Activator Treatment in a Rat Thromboembolic Stroke Model

Tissue-type plasminogen activator (t-PA) remains the only approved therapy for acute ischemic stroke but has a restrictive treatment time window of 4.5 hr. Prolonged ischemia causes blood-brain barrier (BBB) damage and increases the incidence of hemorrhagic transformation (HT) secondary to reperfusion. In this study, we sought to determine the effect of pinocembrin (PCB; a pleiotropic neuroprotective agent) on t-PA administration-induced BBB damage in a novel rat thromboembolic stroke model. By assessing the leakage of Evans blue into the ischemic hemisphere, we demonstrated that PCB pretreatment 5 min before t-PA administration significantly reduced BBB damage following 2 hr, 4 hr, 6 hr, and even 8 hr ischemia. Consistently, PCB pretreatment significantly decreased t-PA infusion-resulting brain edema and infarction volume and improved the behavioral outcomes following 6 hr ischemia. Mechanistically, PCB pretreatment inhibited the activation of MMP-2 and MMP-9 and degradation of tight junction proteins (TJPs) occludin and claudin-5 in the ischemic hemisphere. Moreover, PCB pretreatment significantly reduced phosphorylation of platelet-derived growth factor receptor α (PDGFRα) as compared with t-PA alone. In an in vitro BBB model, PCB decreased transendothelial permeability upon hypoxia/aglycemia through inhibiting PDGF-CC secretion. In conclusion, we demonstrated that PCB pretreatment shortly before t-PA infusion significantly protects BBB function and improves neurological outcomes following prolonged ischemia beyond the regular 4.5 hr t-PA time window. PCB pretreatment may represent a novel means of increasing the safety and the therapeutic time window of t-PA following ischemic stroke

Comparative Transcriptome Analysis Revealed Key Genes Regulating Gossypol Synthesis in Tetraploid Cultivated Cotton

Tetraploid cultivated cotton (Gossypium spp.) produces cottonseeds rich in protein and oil. Gossypol and related terpenoids, stored in the pigment glands of cottonseeds, are toxic to human beings and monogastric animals. However, a comprehensive understanding of the genetic basis of gossypol and gland formation is still lacking. We performed a comprehensive transcriptome analysis of four glanded versus two glandless tetraploid cultivars distributed in Gossypium hirsutum and Gossypium barbadense. A weighted gene co-expression network analysis (WGCNA) based on 431 common differentially expressed genes (DEGs) uncovered a candidate module that was strongly associated with the reduction in or disappearance of gossypol and pigment glands. Further, the co-expression network helped us to focus on 29 hub genes, which played key roles in the regulation of related genes in the candidate module. The present study contributes to our understanding of the genetic basis of gossypol and gland formation and serves as a rich potential source for breeding cotton cultivars with gossypol-rich plants and gossypol-free cottonseed, which is beneficial for improving food safety, environmental protection, and economic gains of tetraploid cultivated cotton

Identification of Chromosome Segment Substitution Lines of <i>Gossypium barbadense</i> Introgressed in <i>G</i>. <i>hirsutum</i> and Quantitative Trait Locus Mapping for Fiber Quality and Yield Traits

<div><p>Chromosome segment substitution lines MBI9804, MBI9855, MBI9752, and MBI9134, which were obtained by advanced backcrossing and continuously inbreeding from an interspecific cross between CCRI36, a cultivar of upland cotton (<i>Gossypium hirsutum</i>) as the recurrent parent, and Hai1, a cultivar of sea island cotton (<i>G</i>. <i>barbadense</i>) as the donor parent, were used to construct a multiple parent population of (MBI9804×MBI9855)×(MBI9752×MBI9134). The segregating generations of double-crossed F₁ and F₂ and F_2:3 were used to map the quantitative trait locus (QTL) for fiber quality and yield-related traits. The recovery rate of the recurrent parent CCRI36 in the four parental lines was from 94.3%–96.9%. Each of the parental lines harbored 12–20 introgressed segments from Hai1across 21 chromosomes. The number of introgressed segments ranged from 1 to 27 for the individuals in the three generations, mostly from 9 to 18, which represented a genetic length of between 126 cM and 246 cM. A total of 24 QTLs controlling fiber quality and 11 QTLs controlling yield traits were detected using the three segregating generations. These QTLs were distributed across 11 chromosomes and could collectively explain 1.78%–20.27% of the observed phenotypic variations. Sixteen QTLs were consistently detected in two or more generations, four of them were for fiber yield traits and 12 were for fiber quality traits. One introgressed segment could significantly reduce both lint percentage and fiber micronaire. This study provides useful information for gene cloning and marker-assisted breeding for excellent fiber quality.</p></div

Numbers and total length of the introgressed Hai1 segments in the three generations.

<p>a: Number of the introgressed Hai1 segments; b: Total length of the introgressed Hai1 segments.</p

Phenotypic analysis of fiber quality and yield traits in the three populations.

<p>Phenotypic analysis of fiber quality and yield traits in the three populations.</p

Introgressed Hai1 chromosome segments in the parents.

<p>1: MBI9804; 2: MBI9855; 3: MBI9752; and 4: MBI9134; A: genome of recurrent parent CCRI36; B: homologous Hai1 segments; H: heterozygous Hai1segments.</p

Phenotypic analysis of parent fiber quality and yield traits.

<p>Phenotypic analysis of parent fiber quality and yield traits.</p