Effect of Ti and Ta content on the oxidation resistance of Co-Ni-based superalloys

Co-Ni-based superalloys are known for their capability to function at elevated temperatures and superior hot corrosion and thermal fatigue resistance.Therefore,these alloys show potential as crucial high-temperature structural materials for aeroengine and gas turbine hot-end components.Our previous work elucidated the influence of Ti and Ta on the high-temperature mechanical properties of alloys.However,the intricate interaction among elements considerably affects the oxidation resistance of alloys.In this paper,Co-35Ni-10Al-2W-5Cr-2Mo-1Nb-xTi-(5−x)Ta alloys(x=1,2,3,4)with varying Ti and Ta contents were designed and compounded,and their oxidation resistance was investigated at the temperature range from 800 to 1000℃.After oxidation at three test conditions,namely,800℃for 200 h,900℃for 200 h,and 1000℃for 50 h,the main structure of the oxide layer of the alloy consisted of spinel,Cr_(2)O_(3),and Al_(2)O_(3)from outside to inside.Oxides consisting of Ta,W,and Mo formed below the Cr_(2)O_(3)layer.The interaction of Ti and Ta imparted the highest oxidation resistance to 3Ti2Ta alloy.Conversely,an excessive amount of Ti or Ta resulted in an adverse effect on the oxidation resistance of the alloys.This study reports the volatilization of W and Mo oxides during the oxidation process of Co-Ni-based cast superalloys with a high Al content for the first time and explains the formation mechanism of holes in the oxide layer.The results provide a basis for gaining insights into the effects of the interaction of alloying elements on the oxidation resistance of the alloys they form.

GaN based ultraviolet laser diodes

In the past few years,many groups have focused on the research and development of GaN-based ultraviolet laser diodes(UV LDs).Great progresses have been achieved even though many challenges exist.In this article,we analyze the challenges of developing GaN-based ultraviolet laser diodes,and the approaches to improve the performance of ultraviolet laser diode are reviewed.With these techniques,room temperature(RT)pulsed oscillation of AlGaN UVA(ultraviolet A)LD has been realized,with a lasing wavelength of 357.9 nm.Combining with the suppression of thermal effect,the high output power of 3.8 W UV LD with a lasing wavelength of 386.5 nm was also fabricated.

Modeling core-spreading of interface dislocation and its elastic response in anisotropic bimaterial

Interracial dislocation may have a spreading core corresponding to a weak shear resistance of interfaces. In this paper, a conic model is proposed to mimic the spreading core of interfacial dislocation in anisotropic bimaterials. By the Stroh formalism and Green＇s function, the analytical expressions of the elastic fields are deduced for such a dislocation. Taking Cu/Nb bimaterial as an example, it is demonstrated that the accuracy and efficiency of the method are well validated by the interface conditions, a spreading core can greatly reduce the stress intensity near the interfacial dislocation compared with the compact core, and the elastic fields near the spreading core region are significantly different from the condensed core, while they are less sensitive to a field point that is 1.5 times the core width away from the center of the spreading core.

Fabrication of Superhydrophobic–Hydrophilic Patterned Cu@Ag Composite SERS Substrate via Femtosecond Laser

Ultralow concentration molecular detection is critical in various fields,e.g.,food safety,environmental monitoring,and dis-ease diagnosis.Highly sensitive surface-enhanced Raman scattering(SERS)based on ultra-wettable surfaces has attracted attention due to its unique ability to detect trace molecules.However,the complexity and cost associated with the preparation of traditional SERS substrates restrict their practical application.Thus,an efficient SERS substrate preparation with high sensitivity,a simplified process,and controllable cost is required.In this study,a superhydrophobic–hydrophilic patterned Cu@Ag composite SERS substrate was fabricated using femtosecond laser processing technology combined with silver plating and surface modification treatment.By inducing periodic stripe structures through femtosecond laser processing,the developed substrate achieves uniform distribution hotspots.Using the surface wettability difference,the object to be measured can be confined in the hydrophilic region and the edge of the hydrophilic region,where the analyte is enriched by the coffee ring effect,can be quickly located by surface morphology difference of micro-nanostructures;thus,greatly improving detec-tion efficiency.The fabricated SERS substrate can detect Rhodamine 6G(R6G)at an extraordinarily low concentration of 10^(−15)mol/L,corresponding to an enhancement factor of 1.53×10^(8).This substrate has an ultralow detection limit,incurs low processing costs and is simple to prepare;thus,the substrate has significant application potential in the trace analysis field.

Field-induced anisotropic magnetic phase transitions and tricritical phenomena in GdCr_(6)Ge_(6)

The interaction between complex magnetic structures and non-trivial band structures in ternary rare-earth GdCr_(6)Ge_(6) induces exotic and abundant electro-magnetic phenomena.In this work,we perform a systematical investigation on critical behaviors and magnetic properties of the single-crystal GdCr_(6)Ge_(6).The temperature,field,and angle dependence of magnetization unveils strong magnetic anisotropy along the c-axis and isotropic characteristic in the ab-plane.Critical exponentsβ=0.252(1),γ=0.905(9),δ=4.606(3)for H//ab,andβ=0.281(3),γ=0.991(8),δ=4.541(5)for H//c are obtained by the modified Arrott plot method(MAP)and critical isotherm(CI)analysis.The determined exponents for both directions are consistent with the theoretical prediction of a tricritical mean-field model.Based on detailed magnetization measurements and universality scaling,comprehensive magnetic phase diagrams of GdCr6Ge6for H//ab and H//c are constructed,which reveal that the external field induces a ferromagnetic(FM)transition for H//ab while a ferrimagnetic(FIM)one for H//c.Two tricritical points are determined for H//ab(11.2 K,266.3 Oe)and H//c(11.3 K,3.3 kOe)on the phase diagrams,respectively.The field-induced anisotropic magnetic configurations and multiple phases are clarified,where the moments of Gd and Cr form FM coupling for H//ab while FIM one for H//c via the interaction between Gd and Cr sublattices.

Porphyrin-based heterogeneous photocatalysts for solar energy conversion

In recent years,porphyrins with a similar structure to chlorophyll are often used as photosensitizers or reaction centers to improve the light absorption capacity or catalytic selectivity of existing photocatalytic systems.However,photocatalytic reactions include photoelectric conversion,photocarrier transport,and surface reaction,which requires the overall design of porphyrin-based photocatalysts.In this paper,the research work of porphyrin molecular design in heterogeneous photocatalysis in recent years is reviewed.Besides,the application of interface control and spatial confinement effect in porphyrin-based hybrid photocatalyst is introduced.Finally,the future development direction of porphyrin-based photocatalysts is prospected and the main challenges in the research of porphyrin-based photocatalysts are given.

Assessing OSM building completeness for almost 13,000 cities globally

OpenStreetMap(OSM)is an essential source for acquiring building data,although such data may suffer from quality issues.Many studies have focused on assessing OSM building data quality but few have been carried out on a global scale.This study aims to assess OSM building completeness(a quality measure)for 12,975 cities across the globe.This was achieved by employing population grid data as a proxy for reference building data.Not only the completeness of each city but also that of the grids within that city was assessed.The assessment results were evaluated based on calculating the overall accuracy and the r-square value between estimated and reference OSM building completeness values.Results showed that for 75%of cities,the completeness is lower than 20%;no more than 9%of cities have an estimated completeness higher than 80%.The overall accuracies of most countries were higher than 80%.The estimated completeness was also highly correlated with the reference completeness,which verifies the effectiveness of our approach.These results may be useful for acquiring and updating building data in OSM.A global and open dataset related to OSM building completeness has been made available for public use.

Carrier balance and linear magnetoresistance in type-II Weyl semimetal WTe2

Unsaturated magnetoresistance （MR） has been reported in type-II Weyl semimetal WTe2, manifested as a perfect compensation of opposite carriers. We report linear MR （LMR） in WTe2 crystals, the onset of which was identified by constructing the MR mobility spectra for weak fields. The LMR further increased and became dominant for fields stronger than 20 T, while the parabolic MR gradually decayed. The LMR was also observed in high-pressure conditions.