Enhanced mechanical properties of molybdenum alloy originating from composite strengthening of Re and CeO_(2)

To enhance the mechanical properties of molybdenum alloys at both room and high temperatures,Mo-14Re-1CeO_(2)alloy was synthesized using the powder metallurgy method,and the corresponding microstructure and mechanical properties were characterized.The results indicate that the ultimate tensile strength of Mo-14Re-1CeO_(2)reaches 657 MPa,with a total elongation of 35.2%,significantly higher than those of pure molybdenum(453 MPa,and 7.01%).Furthermore,the compression strength of Mo-14Re-1CeO_(2)at high temperature(1200℃)achieves 355 MPa,which is still larger than that of pure molybdenum(221 MPa).It is revealed that there is a coherent interface between CeO_(2)and the Mo-14Re matrix with CeO_(2)particles uniformly distributed in both intergranular and intragranular regions.The improvements in mechanical properties are primarily attributed to the formation of Mo-Re solid solution,grain refinement,and dispersion strengthening effect of CeO_(2).

空心球壳状MoS_(2)/WS_(2)异质结构的制备及其电催化析氢性能

系统研究一种由空心WS_(2)球壳和花瓣状MoS_(2)组成的异质结构。结果表明,空心球壳结构使活性位点更容易暴露,异质结构的形成有助于激发WS_(2)和MoS_(2)之间的协同效应,从而提高析氢反应性能,具有更好的电子转移能力。更重要的是,密度泛函理论计算进一步阐明了协同机理,表明MoS_(2)/WS_(2)异质结构可有效调节氢吸附自由能,使之在W/Mo原子比为2꞉25时达到最小值。因此,优化后的WMo-2/25催化剂表现出优异的电催化析氢活性,Tafel斜率低,为53 mV/dec,并具有良好的稳定性。

Optimal dose of busulfan for depleting testicular germ cells of recipient mice before spermatogonial transplantation

Successful spermatogonial transplantation requires depletion of the host germ cells to allow efficient colonization of the donor spermatogonial stem cells. Although a sterilizing drug,busulfan （Myleran）,is commonly used for preparing a recipient mouse before transplantation,the optimal dose of this drug has not yet been defined.The present study investigated the effects of different doses of busulfan （10-50 mg per kg body weight） on survival rate,testicular mass and histomorphology,and on the haploid spermatids and spermatozoa of male BALB/c mice.The results suggest that a dosage of 30 mg kg^-1 is optimal for the ablative treatment withbusulfan used to prepare the recipient mice. This dose results in an adequate depletion of the host germ cells for colonization of donorderived spermatogonial stem cells and causes the lowest death rate of the animals.

Microwave sintering of Mo nanopowder and its densification behavior

In order to prepare high-performance Mo with fine and homogeneous microstructure to meet the demand of high-technology applications such as metallurgical,mechanical,national defense,aerospace and electronics applications,the microwave sintering process and densification mechanism of Mo nanopowder were studied.In this experiment,Mo nanopowder and micropowder were used for conventional sintering and microwave sintering at different sintering temperatures and sintering time,respectively.The results showed that with the increase in the sintering temperature,the increase rates of the relative density and hardness increased rapidly at first and then slowed down.The relative density rapidly reached 95%,followed by a small change.Mo nanopowder with a relative density of 98.03% and average grain size of 3.6 μm was prepared by microwave sintering at 1873 K for30 min.According to the analysis of the sintering kinetics,its densification is attributed to the combination of volumetric diffusion and grain boundary diffusion mechanisms.The calculated sintering activation energy of Mo nanopowder was 203.65 kJ/mol,which was considerably lower than that in the conventional sintering,suggesting that the microwave sintering was beneficial to the enhancement in the atom diffusion and densification for the powder.The results confirm that the microwave sintering is a promising method to economically prepare molybdenum with high properties.

Effects of cross rolling on texture,mechanical properties and anisotropy of pure Mo plates

To clarify the influence of the deformation texture on the mechanical properties,pure Mo plates were processed by various cross rolling procedures,and the relation among texture,microstructure and mechanical properties was discussed.The results show that cross rolling of the Mo plates is beneficial for the formation of the rotated cube component,i.e.,{001}<110>.The corresponding orientation density exhibits a positive correlation with the total rolling deformation and the current-pass deformation.When the total deformation is 96%or greater,the Mo plates form a texture orientation dominated by{001}<110>,whereas theγ-fibre texture becomes weaker and the cube texture{100}<100>disappears completely.The presence of{001}<110>has great effects on the properties of cross-rolled Mo plates,which is beneficial for strength enhancement and plasticity reduction in both the rolling direction(RD)and the transverse direction(TD).

Effects of shape and size of second phase on mechanical properties of sintered Mo-Y_(2)O_(3) alloys

The morphology and size of second phase greatly influence the strengthening effect on oxidation dispersion strengthened Mo alloys.In this work,a novel nanostructuring strategy is adopted to modify the second phase of Y_(2)O_(3),and the corresponding effects of particle shape and size on mechanical properties of sintered Mo−Y_(2)O_(3) alloys were investigated.It is found that spherical particles with sizes below 200 nm are preferred due to the dominant intragranular distribution of second phases associated with better strengthening effect originating from dislocation pinning.With smaller particle size of Y_(2)O_(3) nanospheres(105 nm),the tensile strength of corresponding Mo alloy is enhanced by about 43.8%,much higher than that(8.3%)reinforced by second phase nanospheres with larger particle size(322 nm).Meanwhile,with similar particle size(around 100 nm),the spherical shape exhibits better strengthening effect than the one reinforced by one-dimensional rod-like second phase.

Preparation of highly dispersed superfine W-20 wt% Cu composite powder with excellent sintering property by highly concentrated wet ball-milled process

The ball milling process and the CuWO-WOprecursors were investigated, and a new highly concentrated wet ball-milled process(HWM) was designed. W-20 wt% Cu composite powders with excellent sintering property were synthesized by highly concentrated wet ballmilled process and co-reduction. The powders were characterized by scanning electron microscopy(SEM), X-ray diffraction(XRD), field electron transmission electron microscopy(FESEM) and laser-diffraction diameter tester.The results indicate that particle size of W03-CuO powder mixtures decreases to 390 nm rapidly with the milling time increasing to 5 h. The CuWOprecursors promote the microstructural homogeneity of W and Cu. W-Cu composite powders have a highly dispersed and well sintering property. The particle size of W-Cu powders milled by HWM for 5 h is about 680 nm. High-resolution transmission electron microscopy(HRTEM) result suggests that W phase and Cu phase are mixed at nanometer scale. The above W-Cu composite powders reach the relative density of about 99.3%.

Porous nickel–titanium alloy prepared by gel-casting

To explore the preparation of porous nickel- titanium alloy with excellent properties, larger size and complex shape, the premixed powder of Ni and Ti with atomic ratio of 1：1 was shaped by gel-casting. The effects of solids loading and the content of dispersant on flow ability of nickel-titanium slurry and the mechanical properties of nickel-titanium sintered body were studied. The drying models under different solids loading were also discussed. The results show that the viscosity of slurries significantly increases with an increase in solids loading. After a proper process of drying, the green body with complex shape is obtained. The sintered body with porosity rate reaching up to 49.5 % and compression strength reaching to 364.74 MPa could meet the basic demands of implant materials.