Magnetic Damping Properties of Single-Crystalline Co_(55)Mn_(18)Ga_(27) and Co_(50)Mn_(18)Ga_(32) Films

We investigate the structural,static magnetic and damping properties in two Mn-deficient magnetic Weyl semimetal Co-Mn-Ga(CMG) alloy films,i.e.,Co_(55)Mn_(18)Ga_(27)(CMG1) and Co_(50)Mn_(18)Ga_(32)(CMG2),which were epitaxially grown on MgO(001) substrates.CMG1 has a mixing phase of B2and L21,larger saturation magnetization(M_(s) ~760 emu/cm^(3)),stronger in-plane magnetic anisotropy.CMG2 has an almost pure B2phase,smaller M_(s)(~330 emu/cm^(3)),negligible in-plane magnetic anisotropy.Time-resolved magneto-optical Kerr effect results unambiguously demonstrate an obvious perpendicular standing spin wave(PSSW) mode in addition to the Kittel mode for both of the CMG films.The intrinsic damping constant is about 0.0055 and 0.015 for CMG1 and CMG2,respectively,which are both significantly larger than that of the stoichiometric CMG(i.e.,Co_(2)MnGa)film reported previously.In combination with the first-principles calculations,the intrinsic damping properties of the Mn-deficient CMG films can be well explained by considering the increase of density of states at the Fermi level,reduction of M_(s),and excitation of the PSSW mode.These findings provide a new clue to tuning the magnetic damping of the magnetic Weyl semimetal film through slight off-stoichiometry.

Equivalent strain hardening exponent of anisotropic materials based on spherical indentation response

Uniaxial strain hardening exponent is not suitable for describing the strain hardening behaviors of the anisotropic materials, especially when material deforms in the multi-axial stress states. In this work, a novel method was proposed to estimate the equivalent strain hardening exponent of anisotropic materials based on an equivalent energy method. By performing extensive finite element (FE) simulations of the spherical indentation on anisotropic materials, dimensionless function was proposed to correlate the strain hardening exponent of anisotropic materials with the indentation imprint parameters. And then, a mathematic expression on the strain hardening exponent of anisotropic materials with the indentation imprint was established to estimate the equivalent strain hardening exponent of anisotropic materials by directly solving this dimensionless function. Additionally, Meyer equation was modified to determine the yield stress of anisotropic materials. The effectiveness and reliability of the new method were verified by the numerical examples and by its application on the TC1M engineering material.

Novel cemented carbide produced with TiN_(0.3) and high-entropy alloys

High-entropy alloys are suitable for use as a binder for cemented carbides duo to outstanding mechanical, oxidation and wear behavior. Therefore, high-entropy alloy was selected to replace Co and Ni metal bond in this study. The results of X-ray diffraction analysis show that CoCrNiCuMn high-entropy alloy is stabilized in the cemented carbide system. Scanning electron microscope（SEM） fractural morphologies of the cemented carbides added with CoCrNiCuMn show that CoCrNiCuMn distributes in grain boundaries, and the grains are bound tightly together. Furthermore, SEM fractural morphologies of the cemented carbides with 5 wt%, 7 wt%, and 10 wt% CoCrNiCuMn show that CoCrNiCuMn slows the growth of grains, which effectively binders the grains, prevents the generation and propagation of cracks, and finally, greatly improves the toughness of the cemented carbides.According to the results observed in the cemented carbides containing different amounts of CoCrNiCuMn, the hardness level gradually increases with the amount of CoCrNiCuMn; however, a reverse trend is seen in the toughness level. The cemented carbide with 10 wt% CoCrNiCuMn shows the highest toughness value of 7.05 MPa·m^1/2.

Influence of Initial Microstructure on Warm Deformation Processability and Microstructure of an Ultrahigh Carbon Steel

Various isothermal compression tests are carried out on an ultrahigh carbon steel （1.2% C in mass percent）, initially quenched or spheroidized, using a Gleeble-3500 system. The true stress is observed to decrease with increas ing temperature and decreasing strain rate. The true stress of the initially quenched steel is lower than that of the ini- tially spheroidized steel at high deformation temperature （700 ~C） and low deformation strain rate （0. 001 s-1 ）. The value of the deformation activation energy （Q） of the initially quenched steel （331.56 kJ/mol） is higher than that of the initially spheroidized steel （297.94 kJ/mol）. The initially quenched steel has lower efficiency of power dissipation and better processability than the initially spheroidized steel. The warm compression promotes the fragmentation and the spheroidization of lamellar cementites in the initially quenched steel. The fragmentation of lamellar cementites is the spheroidizing mechanism of the eementites in the initially quenched steel. Results of transmission electron microscope investigation showed that fine grains with high angle boundaries are obtained by deformation of the initially quenched steel.

Preparation of Water Dispersible Poly(methyl methacrylate)-based Vesicles for Facile Persistent Antibacterial Applications

We report a facile strategy for incorporating persistent and effective antibacterial property into a widely used polymer, poly（methyl methacrylate）（PMMA）, by copolymerizing methyl methacrylate（MMA） with 2-（tert-butylamino）ethyl methacrylate（TA） in one pot via atom transfer radical polymerization（ATRP）. The subsequent self-assembly of the resultant poly（methyl methacrylate）-block-poly[（2-tert-butylamino）ethyl methacrylate]（PMMA20-b-PTA15） diblock copolymer affords well-defined water-dispersible vesicles, which can be facilely sprayed on the walls in hospitals for effective inhibition and killing of bacteria. 1H-NMR and gel permeation chromatography（GPC） studies confirmed the successful synthesis of welldefined copolymer. Transmission electron microscopy（TEM）, atomic force microscopy（AFM） and dynamic light scattering（DLS） studies proved the formation of vesicles with narrow size distribution. DLS studies revealed the excellent stability of vesicles at various temperatures. Antibacterial tests showed effective antibacterial activities of polymer vesicles against both Gram-positive and Gram-negative bacteria. Moreover, this strategy may be extended for preparing a wide range of polymeric materials for facile antibacterial applications in many fields.