机加工材料Al-Si-Mg合金超塑性变形及微观组织研究

以新型机加工材料Al-Si-Mg合金铸件为研究对象,在Instron5500电子万能材料试验机上进行超塑性拉伸试验,研究了合金在不同温度和应变速率下的超塑性变形及合金微观组织。结果表明,随着温度升高,合金的伸长率和真应力不断增加,应变速率敏感指数也随着增加,合金流动活化能不断减小,合金超塑性变好;在合金挤压过程中,铸态合金中含有纤维球状的共晶硅颗粒,随着热处理的不断进行,共晶硅颗粒不断细化且均匀分布,横向截面的共晶硅颗粒比纵向截面的共晶硅颗粒密集,经过人工时效处理后,合金中共晶硅颗粒不断增加,强度不断增加,伸长率逐渐减小。

基于金属材料机加工的高效加工工艺研究

本文探讨了基于金属材料机加工的高效加工工艺研究。首先介绍了传统机加工的优缺点,随后介绍了高效加工的理论基础,包括高速切削技术和微弱润滑技术。接着探讨了金属材料机加工中切削力、刀具磨损、刀具寿命等关键问题,以及工艺参数对机加工效率、表面效果和刀具寿命的影响。最后,提出了基于高速切削和微弱润滑技术的高效加工工艺设计方案,包括工艺参数的选择和工艺流程的设计。同时,本文还列举了几种基于高效加工工艺的实现途径,希望可以为相关研究提供一定借鉴。

ANALYSIS OF GEOSYNTHETICS REINFORCED EMBANKMENT ON SOFT SOIL BY FEM

The reinforcement effects of geosynthetics in thick soft subsoil case and thin soft subsoil case are studied in this paper,and a Duncan Chang nonlinear numerical model based on the finite element method (FEM) is developed.Moreover,an important conclusion that the thickness of soft subsoil affects greatly the geotechnical behavior of geosynthetic reinforced embankments is drawn.A series of embankment built on soft subsoil is calculated using the FEM program.The results of the computer program,such as the lateral displacements,settlements,and stress level and shear stresses in the subsoil,are presented in great detail and the comparison of those results disposes clearly the huge discrepancy of reinforce benefit between the thick subsoil embankment and thin subsoil embankment.Reinforcement mechanism of geosynthetics is also discussed in this paper and several conclusions are reached.This paper also gives recommendations for design.

Superelastic behavior of nanostructured Ti_(50)Ni_(48)Co_2 shape memory alloy with cold rolling processing

Effects of cold rolling followed by annealing on microstructural evolution and superelastic properties of the Ti50Ni48Co2 shape memory alloy were investigated. Results showed that during cold rolling, the alloy microstructure evolved through six basic stages including stress-induced martensite transformation and plastic deformation of martensite, deformation twinning, accumulation of dislocations along twin and variant boundaries in martensite, nanocrystallization, amorphization and reverse transformation of martensite to austenite. After annealing at 400 ℃ for 1 h, the amorphous phase formed in the cold-rolled specimens was completely crystallized and an entirely nanocrystalline structure was achieved. The value of stress level of the upper plateau in this nanocrystalline alloy was measured as high as 730 MPa which was significantly higher than that of the coarse-grained Ni50Ti50 and Ti50Ni48Co2 alloys. Moreover, the nanocrystalline Ti50Ni48Co2 alloy had a high damping capacity and considerable efficiency for energy storage.

Municipal Waste Plastics Conversion into Aviation Fuel

Aviation fuel is in great demand globally. The increased demand and high price for energy sources are driving efforts to convert natural non-renewable organic compounds into useful hydrocarbon fuel materials such as in form of aviation fuel. Alternate sources to these non-renewable hydrocarbon fuels are important and necessary. Much of these alternative sources are focused on biomass however, there are strong benefits of deriving fuels from waste plastic materials. Thermal processes can be used to convert waste plastics into hydrocarbon fuels like aviation fuel, which have unlimited applications in airline industries, as well as in transportation and power generation industries. These thermal processes are used to break down the long carbon chains found in plastics into the shorter chains in a temperature range from 300-450 ℃. This method has been carried out in succession in previous experiments. This simple and economically viable process has been developed to convert the hydrocarbon polymers of waste plastics into the short and medium chain hydrocarbons of liquid fuels. Based on the initial characterization, a fractionated portion of the developed fuel shows properties similar to some of the commercially available aviation fuels.

Non-spherical abrasives with ordered mesoporous structures for chemical mechanical polishing

The chemical mechanical polishing(CMP)technology has been widely used for surface modification of critical materials and components with high quality and efficiency.In a typical CMP process,the mechanical properties of abrasives play a vital role in obtaining the ultra-precision and damage-free surface of wafers for improvement of their performances.In this work,a series of fine structured rod-shaped silica(RmSiO2)-based abrasives with controllable sizes and diverse ordered mesoporous structures were synthesized via a soft template approach,and successfully applied in the sustainable polishing slurry for improving the surface quality of cadmium zinc telluride(CZT)wafers.Compared with commercial silica gel,solid and mesoporous silica spheres,the RmSiO2 abrasives present superior elastic deformation capacity and surface precision machinability on account of their mesoporous structures and rod shapes.Especially,ultra-precision surface roughness and relatively effective material removal speed were achieved by the CMP process using the RmSiO2 abrasives with a length/diameter(L/d)ratio of 1.In addition,a potential CMP mechanism of the developed polishing slurry to CZT wafer was elucidated by analyzing X-ray photoelectron spectra and other characterizations.The proposed interfacial chemical and mechanical effects will provide a new strategy for improving abrasives’machinability and precision manufacture of hard-to-machine materials.

Highly structured metal-organic framework nanofibers for methane storage

Porous materials such as metal-organic frameworks(MOFs)with high theoretical volumetric gas uptake capacity are promising materials for gas storage and separation,but the structuring for practical applications is challenging.Herein,we report a general and feasible strategy to combine electrospinning with a phase conversion method to decorate polyacrylonitrile nanofibers(PAN NFs)with CuMOF(HKUST-1).The strategy is based on the combination of surface pretreatment of the NFs with Cu(OH)_(2) and a subsequent phase conversion into HKUST-1 crystals(PCHKUST-1).A significant higher loading of HKUST-1 in the PAN NF matrix was achieved by the phase conversion method compared with direct electrospinning of MOF slurries or insitu growth of MOF crystals on NFs.As a result,the hierarchical structured PC(phase conversion)-HKUST-1 NFs revealed the highest gravimetric storage capacity of 86 cm^(3) g^(-1)(STP)at 3500 kPa and 298 K for methane(CH_(4)),which is higher than other HKUST-1 NFs reported previously.The improved CH_(4) uptake can be explained by the high loading of HKUST-1 due to the high availability of Cu-ions localized on the surface of the NFs during the phase conversion process,resulting in high surface area and excellent gas access of the phase converted HKUST-1.Thus,the developed strategy of structuring MOFs could be of interest for the fabrication of tailor-made MOF NF architectures for other energy and environmental applications.