摘要: Set the Refractive Indexes of the One-Dimensional Photonic Crystals (1-D Pcs) were n2 and n3, Keeping n2=1.5 Unchanged and Adjusting n3 in the Range of 2.5--3.5, the Dispersion Curves were Obtained through Characteristic Matrix Method (CMM). The Results Show that when n3 Increased from 2.5 to 3.5, the Band Gap Width Also Increased from about 0.086 to 0.140 Correspondingly. Furthermore, the Results Show that it’s a Linear Growth Process between the Refractive Index Difference and the Band Gap Width of the 1-D Pcs, for the First Propose Quantitatively, there is a Relationship Equation Δω=0.0537(Δn)+0.0336(Δn=n3-n2) Approximately.
摘要: Fe62 alloy coating was fabricated on the surface of #45 steel cutting edges with 2kW all-solid-state laser and powder feeding device. The substrate and forming layer are characterized by optical microscope and scanning electron microscope for microstructure, and tested by micro-hardness tester for micro-hardness. The results show that the forming layer combined with the substrate metallurgically. The microstructure of substrate is eutectoid ferrite and pearlite. The microstructure of layer is uniform and compact, with hard precipitation. The content of Cr, the hard phase generated element, at the grain boundary, is higher than that of grain inside and many hard phases were generated at the grain boundary. Compared with the substrate, the micro-hardness of forming layer increases by about 2 times. All these results show that application of laser additive enhancing technology in the field of cutting tools has larger potential.
摘要: Metallographic analyses on microstructure of squeeze cast magnesium alloy AM50 with different levels of calcium addition are performed via optical microscopy (OM), and scanning electron microscopy (SEM). The OM results show the calcium has a grain refining effect on the base alloy AM50 with the level of Ca addition up to 2 wt.%. As the Ca content further increases, its grain refining effect becomes limited. The SEM observation reveals the addition of 2 wt.% Ca to the AM50 alloy leads to the formation of a continuous network of eutectic phases along grain boundaries while the discontinuous divorced secondary eutectic β-Mg12Al17 is present in the microstructure of AM50 containing also the primary α-Mg, and Mn-Al intermetallic particles. The elemental mapping by the energy dispersive spectroscopy (EDS) indicates the presence of the major alloying elements of Al and Ca along grain boundaries in the squeeze cast AM50 alloy with Ca addition.
摘要: Quartz glass is a typical hard and brittle material. During the manufacturing process of quartz glass components, ultra-precision grinding is widely used due to its high throughput and good dimensional accuracies. However, grinding will unavoidably induce large surface and subsurface damage. In this study, the surface and subsurface damage characteristics of quartz glass substrates ground by diamond wheels with different grit sizes were investigated in terms of surface roughness, surface topography, subsurface microcrack characteristic, and subsurface damage depth. Discussion was also provided to explore corresponding reasons of surface and subsurface damage induced by diamond grinding wheels with different grit sizes of #1500 and #2000. The experiment results showed that the surface roughness, surface damage, and subsurface damage depth induced by #2000 quartz glass was ground by #1500 diamond grinding wheel, and in ductile mode when ground by #2000 diamond grinding wheel.
摘要: Aluminum foam sandwich structure is a new type of composite material with excellent mechanical and functional properties. As it is known that properties of aluminum foam sandwiches (AFS) vary if the foam core is sandwiched between different face sheets. To study the effects of face-sheet materials on the mechanical properties of AFS and enable a better understanding of the usage of such AFS structures under flexural load, AFS sandwiched by 6061-aluminum alloy face-sheets and 304 stainless steel face-sheets were fabricated and investigated under three-point bending by using WDW-T100 electronic universal tensile testing machine. Results showed that 6061-aluminum alloy reinforced AFS had the same peak load value with 304-stainless steel reinforced one almost so long as the thicknesses of the face-sheet material were the same and the foam core densities were the same too, but the energy absorption ability of 304-stainless steel reinforced AFS was much higher than that of 6061-aluminum alloy reinforced. However, the integrality of the 6061-sandwiched AFS was better than 304-sandwiched AFS. Deformation modes of the two types of AFS were also discussed in the present study.
摘要: The hot compressive deformation behaviors of ZHMn34-2-2-1 manganese brass are investigated on Thermecmastor-Z thermal simulator over wide processing domain of temperatures (923K-1073K) and strain rates (0.01s-1-10s-1). The true stress-strain curves exhibit a single peak stress, after which the stress monotonously decreases until a steady state stress occurs, indicating a typical dynamic recrystallization. A revised constitutive model coupling flow stress with strain, strain rate and deformation temperature is established with the material constants expressed by polynomial fitting of strain. Moreover, better prediction ability of the constitutive model is achieved by implementation of a simple approach for modified the Zener-Hollomon parameter considering the compensation of strain rate and temperature increment. By comparing the predicted and experimented values, the correlation coefficient and mean absolute relative error are 0.997 and 2.363%, respectively. The quantitative statistical results indicate that the proposed constitutive model can precisely characterize the hot deformation behavior of ZHMn34-2-2-1 manganese brass.
摘要: Understanding inner corrosion property of casing steel is fundamental to safe and economic exploitation of oil & gas. In this present work, a series of corrosion tests were conducted on 3%Cr coupons derived from 9-5/8” casing. Analyses of weight loss, product morphology and composition were carried out, to investigate the corrosion behaviors caused by sweet CO2. Analysis on the weight loss showed that, with an increment of temperature from 45°C to 105°C, the corrosion rate of 3%Cr coupon firstly ascends and then arrives to the maximum at 65°C. SEM analysis demonstrated the formation of a compact corrosion product layer on the specimen surface. While increasing the exposed time increases, the corrosion rate gradually descends. The main compositions of corrosion product are Fe-Cr and Cr5O12, which can effective hinder corrosion reaction in the CO2 environment.
摘要: Surface finish plays a critical role in functional performance of machined components. This study investigates machining finish of Ti-6Al-4V alloy prepared by Additive Manufacturing (AM) with a series of slot-milling experiments. The study compares the machined AMed part with that made of the conventional wrought Ti-6Al-4V. The microstructure of AMed parts is acicular α and Widmanstatten α lath structures compared to lamellar α structure of that in the wrought parts. Due to the unique microstructure from AM process, the AMed parts present higher strength and lower ductility. Therefore, a lower surface roughness is obtained in the milling of AMed parts compared to its counterpart of wrought parts. In addition, the machined surface of AMed parts possesses a topography of discontinued ridges. It is believed that the topography is due to low ductility of AMed part. The results show that the machined AMed part presents better surface finish. The study provides a guidance to optimization of machining parameters for AMed Ti-6Al-4V alloys.
摘要: Carbon fiber/epoxy resin composites (C/E composites) are wildly used in manufacture of aircraft fuselages and wings in aerospace industry, due to their excellent properties. However, hole making of C/E composites always results in machining damage, such as burr, tearing, delamination and so on. Milling tools with different shapes were used to conduct helical milling experiments on C/E composites. The influence of tool shape on machining damage was analyzed by measuring the damage area of burr, tearing and delamination. And then the feed speed, axial feed per orbital revolution and spindle speed was changed respectively to study the effect of processing parameters on machining damage. The machining damage can be reduced by choosing appropriate tool shape and processing parameters.