Search

Yttria-stabilized zirconia (YSZ, Y2O3-ZrO2) ceramic with titanium dioxide nanoparticle (nanoTiO2) is prepared using conventional pressureless and two-step sintering (TSS) methods. The microstructure, phase composition, and mechanical properties of TSS-TiO2-ZrO2-Y2O3 nanocomposite ceramics are compared to those of the ceramics sintered using conventional sintering. The effect of TSS and nanoparticles on the sintering densification of the YSZ ceramics is investigated. X-ray diffractometry revealed that nanoTiO2 destabilizes c-ZrO2 and stabilizes t-ZrO2 in the YSZ. In addition, TSS is more conducive for grain refinement and sintering densification of the TiO2-ZrO2-Y2O3 nanocomposite ceramics; the average grain size of the samples decreased from 1.446 (conventional sintering) to 0.492 μm (TSS). Meanwhile, the relative density and sintering shrinkage of the TSS-1450 sample reached the maximum (98.23% and 22.92%, respectively) at a nanoTiO2 fraction of 7 wt%. The maximum microhardness and bending strength of the TSS-1450 ceramic matrix with 7-wt% nanoTiO2 were 1823 HV and 505 MPa, respectively. The nanoparticles distributed in the grain boundary induce the crack to the matrix, which induces the transgranular fracture, and nanoTiO2 improves the densification and mechanical properties of YSZ ceramics more than titanium dioxide microparticles. [ABSTRACT FROM AUTHOR]

Vacuum brazing of TC4 titanium alloy and 316L stainless steel was conducted using Ag70.5Cu27.5Ti2 filler metal, the effects of microstructure and mechanical properties of brazing temperature on interface were investigated, and the bonding mechanism of brazed joint was also established. The results show that the filler metal and the base metal on both sides were completely diffused and bonded well. The microstructure of brazed joint interface is as follows: TC4 titanium alloy/diffusion layer(α-Ti + Ti2Cu)/reaction layer (including TiCu and Ti2Cu)/joint center area/TiFe layer/316L stainless steel. When the holding time lasted for 15 min, the shear strength of brazed joint first increased and then decreased as the brazing temperature rose. When the brazing temperature upped to 870 °C, the maximum of shear strength reached 190 MPa, and then the fracture occurred in the center of the brazed joint. The hardness of the joints gradually increased as the temperature rose, and the mean value reached maximum of 323 HV at 930 °C. [ABSTRACT FROM AUTHOR]

Plants belonging to family Paeoniaceae are not only economically important ornamental plants but also medicinal plants used as an important source of traditional Chinese medicine. Owing to the complex network evolution and polyploidy evolution of this family, its systematics and taxonomy are controversial and require a detailed investigation. In this study, three complete chloroplast genomes of sect. Paeonia, one of the sections of Paeonia, were sequenced and then analysed together with 16 other published chloroplast genomes of Paeoniaceae species. The total lengths of the chloroplast genomes of these species were 152,153–154,405 bp. A total of 82–87 protein-coding genes, 31–40 tRNA genes and 8 rRNA genes were annotated. Bioinformatics analysis revealed 61–74 simple sequence repeats (SSRs) in the chloroplast genomes, most of which have A/T base preference. Codon usage analysis showed that A/U-ending codons were more positive than C/G-ending codons, and a slight bias in codon usage was observed in these species. A comparative analysis of these 19 species of Paeoniaceae was then conducted. Fourteen highly variable regions were selected for species relationship study. Phylogenetic analysis revealed that the species of sect. Paeonia gathered in one branch and then divided into different small branches. P. lactiflora, P. anomala, P. anomala subsp. veitchii and P. mairei clustered together. P. intermedia was related to P. obovata and P. obovata subsp. willmottiae. P. emodi was the sister to all other species in the sect. Paeonia. [ABSTRACT FROM AUTHOR]