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Jihong Gu,1,&ast; Shucheng Shen,1,&ast; Mengyuan Xiong,1,2 Jin Zhao,1,2 Hongpan Tian,1 Xiao Xiao,1,3 Yirong Li1– 3 1Department of Laboratory Medicine, Zhongnan Hospital of Wuhan University, Wuhan, People’s Republic of China; 2Wuhan Research Center for Infectious Diseases and Tumors of the Chinese Academy of Medical Sciences, Wuhan, People’s Republic of China; 3Hubei Engineering Center for Infectious Disease Prevention, Control and Treatment, Wuhan, People’s Republic of China&ast;These authors contributed equally to this workCorrespondence: Yirong Li, Department of Laboratory Medicine, Zhongnan Hospital of Wuhan University, Wuhan, 430061, People’s Republic of China, Tel +8618602718052, Email liyirong838@163.comBackground: Staphylococcus aureus (S. aureus) was able to rapidly evolve and adapt under the pressure of antibiotics, host immune and environmental change. After Corona Virus Disease 2019 (COVID-19) epidemic in Wuhan, China, a large number of disinfectants were used, which might result in rapid evolution of S. aureus.Methods: A total of 619 S. aureus isolates were collected from Zhongnan Hospital, Wuhan University from 2018 to 2021, including group BEFORE (309 strains collected before COVID-19 pandemic) and group AFTER (310 strains collected after COVID-19 pandemic), for comparing the changes of molecular epidemiology. The molecular characteristics of isolates were analyzed by Multi-locus sequence typing (MLST), spa, chromosomal cassette mec (SCCmec) typing, virulence genes were screened by the PCR, antibiotic susceptibility test was carried out by the VITEK system.Results: Thirty-six sequence types (STs) belonging to 14 clone complexes (CCs) were identified. ST5 was the most prevalent clone in both groups, and ST7, ranking the sixth in group BEFORE, became the second dominant clone in group AFTER (6.5% vs 10.0%), whereas ST239 decreased from the seventh to the fourteenth (5.8% vs 1.9%). ST7 in group AFTER had a higher positive rate of virulence genes, including hlb, fnbB, seb, lukDE, sdrE and the proportion of ST7-t091 MRSA strains increased from 19.1% to 50% compared with group BEFORE. Though no significant difference of MRSA proportion was found between two groups, SCCmec type-III in group AFTER decreased (p< 0.01). Though the rate of multidrug-resistance (MDR) decreased, the virulence genes hlb, hlg, fnbB, seb and pvl carrying rates were significantly elevated in MRSA strains of group AFTER.Conclusion: After COVID-19 pandemic, ST7 becomes one of the predominant S. aureus clones in Wuhan and the carrying rate of SCCmec and virulence genes is on the rise. Therefore, it is essential to strengthen the surveillance of ST7 S. aureus clone.Keywords: Staphylococcus aureus, molecular characterization, antimicrobial resistance, virulence gene, disinfectant

The high-manganese steels are important structural materials, owing to their excellent toughness at low temperatures. However, the microstructural causes for their unusual properties have not adequately been understood thus far. Here, we report a reversal relationship between impact toughness and grain size in a high-manganese steel and its unrevealed microscopic mechanisms, which result in an excellent low-temperature toughness of the steel. Our investigations show that with increasing grain size the impact toughness of the steel can be improved drastically, especially at low-temperatures. Advanced electron microscopy characterization reveals that the enhanced impact toughness of the coarse-grained steel is attributed to the twinning induced plasticity and transformation induced plasticity effects, which produce large quantities of deformation twins, ehcp-martensite and α′bcc-martensite. Inversely, in the fine-grained steels, the formation of deformation twins and martensite is significantly inhibited, leading to the decrease of impact toughness. Microstructural characterizations also indicate that ehcp-martensite becomes more stable than α′bcc-martensite with decreasing temperature, resulting in characteristic microstructures in the coarse-grained samples after impact deformation at liquid nitrogen temperature. In the coarse-grained samples under impact deformation at -80 °C, ehcp-martensite transformation, α′bcc-martensite transformation and deformation twinning all occur simultaneously, which greatly improves the toughness of the steel.

The crystallography of phase transformation is an important issue for studying metallic alloys. Here, we demonstrate an abnormal orientation relation between face-centered cubic (fcc) and hexagonal close-packed (hcp) phases due to the intersection of two ehcp-martensite variants in a high manganese steel. The corresponding crystallographic characteristics, including invariant line, habit plane and atomic steps, have been characterized by transmission electron microscopy and the quasi-O-line model. In addition, the models of phase transformation about the intersection are proposed based on transmission mechanisms of dislocations. Our findings enrich the theories of phase transformation and implicate the possibility to fabricate stronger and tougher steel.

In this paper, a new preparation method of metal matrix composites is presented. The W/FeNiMnAlW high-entropy alloy (HEA) matrix composite materials have been prepared by a simple and efficient technology. The HEA matrix consists of a face-centered cubic (FCC) phase, an ordered body-centered cubic (BCC) phase and W2C phase. The volume fraction and average grain size of the reinforcing phase W particles, uniformly distributed in the microstructure of HEA matrix, are 30.9% and 13.57 µm, respectively. Good metallurgical bonding between W particle and matrix is achieved, and the formation mechanism of near spherical tungsten particles is discussed, and the density of the composites is 10.55 g/cm3. The hardness of W-phase, B2 phase and FCC phase was 681.48 HV, 533.82 HV and 286.70 HV, respectively. The yield strength (σ0.2) of the W/FeNiMnAlW composites is 1241 MPa, the maximum compressive strength (σmax) and the maximum plastic strain (ep) are over 2530 MPa and 15% respectively, which showed superior mechanical properties. The effective combination of FCC phase and ordered BCC phase and the uniform distribution of W particles without edges are the main reasons for its good mechanical properties. The volume wear loss and wear rate of the W/FeNiMnAlW composites are respectively 0.42 mm3 and 4.95 × 10−3 mm3/N m, and the worn mechanism is mainly adhesive wear and abrasive wear.

In this work, resistance spot welding (RSW) was used to weld dissimilar metals of cemented carbide (WC–10Co) and high strength steel (RM80). The mechanical property and microstructure of welded joints were analyzed by shear test, scanning electron microscopy and micro X-ray diffraction, establishing the corresponding relationship between the mechanical property of welded joints and microstructure. The results show that with the increase of welding current, the shear strength of welded joints first increased and then decreased, the maximum of which under the optimal welding process was 924 MPa. The characteristics of five interface bonding types were clarified, whose proportion under different welding currents was calculated, and the contribution of each interface bonding type to the performance of welded joints was studied based on the mechanical property and fracture mechanism.