Microstructure,Properties and Crack Suppression Mechanism of High-speed Steel Fabricated by Selective Laser Melting at Different Process Parameters

To enrich material types applied to additive manufacturing and enlarge application scope of additive manufacturing in conformal cooling tools,M2 high-speed steel specimens were fabricated by selective laser melting(SLM).Effects of SLM parameters on the microstructure and mechanical properties of M2 high-speed steel were investigated.The results showed that substrate temperature and energy density had significant influence on the densification process of materials and defects control.Models to evaluate the effect of substrate temperature and energy density on hardness were studied.The optimized process parameters,laser power,scan speed,scan distance,and substrate temperature,for fabricated M2 are 220 W,960 mm/s,0.06 mm,and 200℃,respectively.Based on this,the hardness and tensile strength reached 60 HRC and 1000 MPa,respectively.Interlaminar crack formation and suppression mechanism and the relationship between temperature gradient and thermal stress were illustrated.The inhibition effect of substrate temperature on the cracks generated by residual stresses was also explained.AM showed great application potential in the field of special conformal cooling cutting tool preparation.

A Nomogram for Predicting the Severity of COVID-19 Using Laboratory Examination and CT Findings

Background: The outbreak of COVID-19 has a significant impact on the health of people around the world. In the clinical condition of COVID-19, the condition of critical cases changes rapidly with a high mortality rate. Therefore, early prediction of disease severity and active intervention play an important role in the prognosis of severe patients. Methods: All the patients with COVID-19 in Taizhou city were retrospectively included and segregated into the non-severe and severe group according to the severity of the disease. The clinical manifestations, laboratory examination results, and imaging findings of the 2 groups were analyzed for comparing the differences between the 2 groups. Univariate and multivariate logistic regression were used for screening the factors that could predict the disease, and the nomogram was constructed. Results: A total of 143 laboratory-confirmed cases were included in the study, including 110 non-severe patients and 33 severe patients. The median age of patients was 47 years (range, 4 - 86 years). Fever (73.4%) and cough (63.6%) were the most common initial clinical symptoms. By using the method of multivariate logistic regression, the variables to construct nomogram include age (OR: 1.052, 95% CI: 1.020 - 1.086, P = 0.001), body temperature (OR: 2.252, 95% CI: 1.139 - 4.450, P = 0.020), lymphocyte count (OR: 1.128, 95% CI: 1.000 - 1.272, P = 0.049), ADA (OR: 1.163, 95% CI: 1.023 - 1.323, P = 0.021), PaO2 (OR: 0.972, 95% CI: 0.953 - 0.992, P = 0.007), IL-10 (OR: 1.184, 95% CI: 1.037 - 1.351, P = 0.012), and bronchiectasis (OR: 3.818, 95% CI: 1.694 - 8.605, P = 0.001). The AUC of the established nomogram was 0.877. Conclusions: This study analyzed the cases of patients with COVID-19 in Taizhou city and constructed a model to predict the illness severity. When patients showed the features including older age, high body temperature, low lymphocyte count, low ADA value, low PaO2, high IL-10, and bronchiectasis sign in CT predicts a greater likelihood of severe COVID-19.

Timing and mechanism of opening the Neo-Tethys Ocean:Constraints from mélanges in the Yarlung Zangbo suture zone

The evolution and final closure of the Neo-Tethys Ocean are one of the most important geological events that have occurred on Earth since the Mesozoic.However,the evolution of the Neo-Tethys is not well constrained,in particular whether its opening occurred in the Permian or the Triassic and whether a plume was involved with its opening or not.In this study,we present geochronological and geochemical data for mafic igneous rocks in mélanges along the Yarlung Zangbo suture zone(YZSZ)in southern Tibet to constrain the timing and mechanism of opening the Neo-Tethys Ocean.Based on field observations,the YZSZ mélanges can be divided into three segments.The western(west of Zhongba)and eastern(Sangsang-Renbu)segments are composed of ocean plate stratigraphy representing accretionary complexes that formed during subduction of Neo-Tethyan oceanic lithosphere beneath the southern margin of the Asian continent.Mélanges in the central segment(Zhongba-eastern Saga)typically have a siliciclastic matrix,and represent Tethyan Himalayan strata that were structurally mixed with the southern margin of the Asian continent.Based on our and previously published geochemical data,the mafic rocks in the YZSZ mélanges are ocean island basalt(OIB)-like,with ages in the Late Permian-Middle Triassic,the Middle-Late Jurassic,and the Early Cretaceous,respectively.An OIB-like block with an age of ca.253 Ma is identified from the Zhongba mélanges in the western segment,and it is the oldest OIB lithology yet identified in the YZSZ mélanges related to the evolution of the Neo-Tethys Ocean.Geochemical features indicate that this OIB-like block is distinct from typical OIBs and would be formed during continental rifting to incipient seafloor spreading.In the framework of plate divergent-convergent coupling systems and based on literature data for early Middle Triassic seamounts,radiolarian cherts,and normal mid-ocean ridge basalt-like oceanic crust,we conclude that opening of the Yarlung Zangbo Neo-Tethys Ocean would mainly occur at~250–243 Ma in the Early Triassic,not later than the early phase of Middle Triassic.In addition,a mantle plume was not involved in opening the Yarlung Zangbo Neo-Tethys Ocean.On the other hand,we have also identified a suite of ca.160 Ma OIB-like basaltic sills from the Bainang mélanges in the eastern segment,which is the same age as the OIB lithologies previously reported in the Zhongba mélanges.Based on the sill-like occurrence and absence of plume-related rock associations in this region,the Bainang OIB-like rocks might result from Middle-Late Jurassic continental rifting in northern Gondwana.Magmatism related to this tectonic event is preserved in both the YZSZ mélanges and Himalayan strata,but its tectonic significance requires further investigation.Based on this study of the YZSZ mélanges and the previous studies of YZSZ ophiolites,Gangdese belt igneous rocks,and sedimentary rocks,we have reconstructed the entire Wilson Cycle of the Yarlung Zangbo Neo-Tethys Ocean,mainly involving continental rifting and ocean opening,subduction initiation,ultraslow-spreading ridge-trench conversion,subduction re-initiation,and oceanic closure and initial India-Asia collision for the tectonic emplacement of ophiolites.These processes were associated not only with magmatic flare-ups and lulls in the Gangdese belt but also with two stages of ophiolite obduction.Our data therefore provide new insights into the evolution of the Yarlung Zangbo Neo-Tethys Ocean and related Tethyan geodynamics.