针形名优绿茶固形机的研制与固形工艺优化

以6CZG-60型针形名茶固形机为试验对象，在单因素试验的基础上，对固形叶含水量（20%、25%、30%）、固形叶温（40、50、60℃）、固形投叶量（1、1.5、2 kg）三因素进行正交试验。单因素试验结果表明：固形叶含水量、固形叶温对茶多酚和叶绿素含量有显著影响；固形投叶量对茶多酚、氨基酸、可溶性糖、叶绿素含量均有显著影响；固形时间则对茶多酚和可溶性糖含量有显著影响。感官分析结果表明：随固形叶含水量的降低，茶条紧直度提高，香气品质提高，但外形色泽绿色度下降；随着固形温度的升高，茶条的直度、平伏度和绿色度下降，尤其是当固形叶温超过70℃以后，色泽明显变暗；随着固形叶量的增加，绿色度、香气和滋味品质下降；随着固形时间的延长，茶条圆直度和平伏度更好。正交试验结果表明，6CZG-60型针形名茶固形机最佳工艺参数为：固形叶含水量约20%，固形叶温50℃左右，固形投叶量1.5 kg左右，时间为15~20 min。

Effects of punch velocity on microstructure and tensile properties of thixoforged Mg2Sip/AM60B composite

The effects of punch velocity on the microstructures and tensile properties of Mg2 Sip/AM60 B composite were investigated.In comparison,the tensile properties of the permanent mold casting of this composite were also analyzed.The results indicate that the punch velocity obviously influences the microstructure through changing the secondary solidification behaviors and semisolid deformation mechanisms.The variations of the microstructures and deformation mechanisms are responsible for the changes in tensile properties and fracture modes of the composites.The best comprehensive tensile properties of this composite are obtained under the punch velocity of 60 mm/s.The resulting ultimate tensile strength and elongation of the composite are found to be 198 MPa and 10.2%,respectively.The excellent tensile properties of the thixoforged composite are ascribed to the elimination of porosities and the work hardening.

Stability assessment of the freeway over the gob of coalmine

The freeway passes over the gob area of the Zaibo coalmine or its neighbor- hood when it is built. It is a noticeable problem that the construction of freeway and the underground coal mining interact, especially the deformation and destruction of the gob area of the coalmine influence the long-term stability of the freeway. In the paper, based on the actual data of the exploration about the gob area of Zaibo coalmine and the built project of the freeway,the variety rule of the coal beds below the freeway was studied by using of FEM during the process of coal mining. The statuses of the stresses and strains,the varieties of the plastic area were simulated in the whole rock mass. The characters of stresses and deformation of the gob area of the coalmine were analyzed and evaluated after the freeway built. The long-term stability of the gob area was pre- dicted. The deformation of the gob area under the freeway has not been finished, and the relative measures must be taken.

Microstructural and mechanical behavior of blended powder semisolid formed Al7075/B_4C composites under different experimental conditions

This work aimed to fabricate B4C reinforced aluminum matrix composites via blended powder semisolid forming that is an implementation of the benefits of semisolid forming to the powder metallurgy. Al7075 elements were incrementally added to ethanol solution under mechanical mixing. Al7075 constituents and B4C particles were blended in a high energy ball mill. Cold compacted Al7075/B4C blends were pressed at semisolid state. The effects of the size of the matrix（20, 45 and 63 μm）, reinforcing volume fraction（5%, 10% and 20%） and semisolid compaction pressure（50 and 100 MPa） on the morphology, microstructure, density, hardness, compression and bending strength were thoroughly analyzed. Experimental results revealed that the highest microstructural uniformity was achieved when large B4C particles（45 μm） were distributed within the small particles（20 μm） of the matrix phase. Composites with matrix particles larger than reinforcing phase indicated agglomerations in loadings more than 10%（volume fraction）. Agglomerated regions resisted against penetration of the liquid phase to the pores and lowered the density and strength of these composites. Composites with 20 μm Al7075 and 20%（volume fraction） 45 μm B4C powder pressed under 100 MPa exhibited the highest values of hardness（HV 190） and compressive strength（336 MPa）.

Numerical simulation of solidification morphologies of Cu-0.6Cr casting alloy using modified cellular automaton model

The purpose of this study is to predict the morphologies in the solidification process for Cu-0.6Cr(mass fraction,%)alloy by vacuum continuous casting(VCC)and verify its accuracy by the observed experimental results.In numerical simulation aspect, finite difference(FD)method and modified cellular automaton(MCA)model were used to simulate the macro-temperature field, micro-concentration field,nucleation and grain growth of Cu-0.6Cr alloy using real data from actual casting operations.From the observed casting experiment,the preliminary grain morphologies are the directional columnar grains by the VCC process.The solidification morphologies by MCAFD model are in agreement with the result of actual casting experiment well.

Deformation mechanism and forming properties of 6061Al alloys during compression in semi-solid state

The 6061 semi-solid aluminium alloy feedstocks prepared by near-liquidus casting were compressed in semi-solid state by means of Gleeble-3500 thermal-mechanical simulator.The relationship between the true stress and the true strain at different temperatures and strain rates was studied with the deformation degree of 70%.The microstructures during the deformation process were characterized.The deformation mechanism and thixo-forming properties of the semi-solid alloys were analyzed.The results show that the homogeneous and non-dendrite microstructures of semi-solid 6061Al alloy manufactured by near-liquidus casting technology could be transformed into semi-solid state with the microstructure suitable for thixo-forming which are composed of near-spherical grains and liquid phase with eutectic composition through reheating process.The deformation temperature and strain rate affect the peak stress significantly rather than steady flow stress.The resistance to deformation in semi-solid state decreases with the increase of the deformation temperature and decrease of the strain rate.At steady thixotropic deformation stage, the thixotropic property is uniform, and the main deformation mechanism is the rotating or sliding between the solid particles and the plastic deformation of the solid particles.

Mechanocaloric materials for solid-state cooling

This article reviews the up-to-date progress in mechanocaloric effect and materials near ambient temperature. For elastocaloric materials, we focus on directly measured temperature change and its entropy origin in nonmagnetic and magnetic shape memory alloys. In terms of barocaloric materials, change in magnetic state, volume and shift of transition temperature due to hydrostatic pressure are systematically compared. We propose advantages and challenges of elastocaloric materials for solidstate cooling. Strategies to enhance elastocaloric and mechanical stability under long-term mechanical cycles are presented. Finally, we conclude with an outlook on the prospect of elastocaloric cooling application.

Solid catalytic growth mechanism of micro-coiled carbon fibers

Micro-coiled carbon fibers were prepared by catalytic pyrolysisof acetylene with nano-sized nickel powder catalyst using the substrate method. The morphology of micro-coiled carbon fibers was observed through field emission scanning electron microscopy. It was found that the fiber and coil diameter of the obtained micro-coiled carbon fibers is about 500—600 nm and 4—5 μm, respectively. Most of the micro-coiled carbon fibers obtained were regular double carbon coils, but a few irregular ones were also observed. On the basis of the experimental observation, a solid catalytic growth mechanism of micro-coiled carbon fibers was proposed.

Solidified morphology and mechanism of bulk nanocrystalline Fe_(80)P_(13)C_7 alloy at isothermal undercooling

The molten Fe80P13C7 alloys can achieve a large undercooling up to 320 K by fluxing technique. With the help of fluxing technique, the molten Fe80P13C7 alloys can be solidified at different undercooling （△T） through isothermal undercooling experiment It is indicated that the microstructure of the solidified Fe80P133C7 alloy specimens is refined significantly with the increasing undercooling and the grain size is about 20 μm, 10 μm, 200 nm and 70 nm for △T=50 K, 150 K, 250 K and 320 K, respectively The solidification morphologies of the solidified Fe80P13C7 alloy specimens under different undercooling are quite different. When △T=50 K, it presents a traditional solidification microstructure under a undercooling condition, composed of the primary dendrite and anomalous eutectic within the dendrites. When △T=150 K, a cell-like solidification morphology can be found, which can be proposed to be formed based on the nucleation and growth of spinodal decomposition mechanism. When △T=250 K, there is a strong direction of the solidification under an optical micrograph, two zones can be divided, and the microstructure of each zone presents a network which results from a liquid spinodal decomposition. When △T=320 K, the microstructure presents a random network completely. Microhardness test shows that the hardness of the solidified specimens increases with the undercooling.