Microstructure and Wear Behavior of In-Situ NbC Reinforced Composite Coatings

In the present study, plasma spray welding was used to prepare an in-situ niobium carbide (NbC) reinforced Ni-based composite coating on the low carbon steel, and the phase composition and the microstructure of the composite coatings were studied. The wear resistance and the wear mechanism of the composite coatings were also researched by the wear tests. The results showed that the main phases of the composite coating were NbC, γ-Ni, Cr23C6, Ni3Si, CrB, Cr5B3, Cr7C3 and FeNi3. A number of fine in-situ NbC particles and numerous chromium carbide particles were distributed in the γ-Ni matrix. The increase in the mass fraction of Nb and NiCr-Cr3C2 could lead to the increase in NbC particles in the composite coatings. Due to the high hardness of NbC and chromium carbides, the micro-hardness and the wear resistance of the composite coatings were advanced. The composite coating with the powder mixtures of 20% (Nb + NiCr-Cr3C2) and 80% NiCrBSi had the highest micro-hardness and the best wear resistance in this study. The average micro-hardness reached the maximum value 1025HV0.5. The volume loss was 39.2 mm3, which was merely 37% of that of the NiCrBSi coating and 6% of that of the substrate under the identical conditions

Ecological Shifts of Supragingival Microbiota in Association with Pregnancy

Pregnancy is a physiological process with pronounced hormonal fluctuations in females, and relatively little is known regarding how pregnancy influences the ecological shifts of supragingival microbiota. In this study, supragingival plaques and salivary hormones were collected from 11 pregnant women during pregnancy (P1, ≤14 weeks; P2, 20–25 weeks; P3, 33–37 weeks) and the postpartum period (P4, 6 weeks after childbirth). Seven non-pregnant volunteers were sampled at the same time intervals. The microbial genetic repertoire was obtained by 16S rDNA sequencing. Our results indicated that the Shannon diversity in P3 was significantly higher than in the non-pregnant group. The principal coordinates analysis showed distinct clustering according to gestational status, and the partial least squares discriminant analysis identified 33 genera that may contribute to this difference. There were differentially distributed genera, among which Neisseria, Porphyromonas, and Treponema were over-represented in the pregnant group, while Streptococcus and Veillonella were more abundant in the non-pregnant group. In addition, 53 operational taxonomic units were observed to have positive correlations with sex hormones in a redundancy analysis, with Prevotella spp. and Treponema spp. being most abundant. The ecological events suggest that pregnancy has a role in shaping an at-risk-for-harm microbiota and provide a basis for etiological studies of pregnancy-associated oral dysbiosis

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<p>Pregnancy is a physiological process with pronounced hormonal fluctuations in females, and relatively little is known regarding how pregnancy influences the ecological shifts of supragingival microbiota. In this study, supragingival plaques and salivary hormones were collected from 11 pregnant women during pregnancy (P1, ≤14 weeks; P2, 20–25 weeks; P3, 33–37 weeks) and the postpartum period (P4, 6 weeks after childbirth). Seven non-pregnant volunteers were sampled at the same time intervals. The microbial genetic repertoire was obtained by 16S rDNA sequencing. Our results indicated that the Shannon diversity in P3 was significantly higher than in the non-pregnant group. The principal coordinates analysis showed distinct clustering according to gestational status, and the partial least squares discriminant analysis identified 33 genera that may contribute to this difference. There were differentially distributed genera, among which Neisseria, Porphyromonas, and Treponema were over-represented in the pregnant group, while Streptococcus and Veillonella were more abundant in the non-pregnant group. In addition, 53 operational taxonomic units were observed to have positive correlations with sex hormones in a redundancy analysis, with Prevotella spp. and Treponema spp. being most abundant. The ecological events suggest that pregnancy has a role in shaping an at-risk-for-harm microbiota and provide a basis for etiological studies of pregnancy-associated oral dysbiosis.</p