Characteristics of deep penetration laser welding of dissimilar metal Ni-based cast superalloy K418 and alloy steel 42CrMo

Experimental trials of autogenous deep penetration welding between dissimilar cast Ni-based superalloy K418 and alloy steel 42CrMo flat plates with 5.0 mm thickness were conducted using a 3 kW continuous wave (CW) Nd:YAG laser. The influences of laser output power, welding velocity and defocusing distance on the morphology, welding depth and width as well as quality of the welded seam were investigated. Results show that full keyhole welding is not formed on both K4.18 and 42CrMo side, simultaneously, due to the relatively low output power. Partial fusion is observed on the welded seam near 42CrMo side because of the large disparity of thermal-physical and high-temperature mechanical properties of these two materials. Tile rnicrohardness of the laser-welded joint was also examined and analyzed. It is suggested that applying negative defocusing in the range of Raylei length can increase the welding depth and improve tile coupling efficiency of the laser materials interaction. (c) 2007 Elsevier Ltd. All rights reserved.

Small scale, grain size and substrate effects in nano-indentation experiment of film-substrate systems

The mechanical properties of film-substrate systems have been investigated through nano-indentation experiments in our former paper (Chen, S.H., Liu, L., Wang, T.C., 2005. Investigation of the mechanical properties of thin films by nano-indentation, considering the effects of thickness and different coating-substrate combinations. Surf. Coat. Technol., 191, 25-32), in which Al-Glass with three different film thicknesses are adopted and it is found that the relation between the hardness H and normalized indentation depth h/t, where t denotes the film thickness, exhibits three different regimes: (i) the hardness decreases obviously with increasing indentation depth; (ii) then, the hardness keeps an almost constant value in the range of 0.1-0.7 of the normalized indentation depth h/t; (iii) after that, the hardness increases with increasing indentation depth. In this paper, the indentation image is further investigated and finite element method is used to analyze the nano-indentation phenomena with both classical plasticity and strain gradient plasticity theories. Not only the case with an ideal sharp indenter tip but also that with a round one is considered in both theories. Finally, we find that the classical plasticity theory can not predict the experimental results, even considering the indenter tip curvature. However, the strain gradient plasticity theory can describe the experimental data very well not only at a shallow indentation depth but also at a deep depth. Strain gradient and substrate effects are proved to coexist in film-substrate nano-indentation experiments. (c) 2006 Elsevier Ltd. All rights reserved.

Atomistic investigation of the effects of temperature and surface roughness on diffusion bonding between Cu and Al

Molecular dynamics (MD) simulations are carried out to analyze the diffusion bonding at Cu/Al interfaces. The results indicate that the thickness of the interfacial layer is temperature-dependent, with higher temperatures yielding larger thicknesses. At temperatures below 750 K, the interface thickness is found to increase in a stepwise manner as a function of time. At temperatures above 750 K, the thickness increases rapidly and smoothly. When surface roughness is present, the bonding process consists of three stages. In the first stage, surfaces deform under stress, resulting in increased contact areas. The second stage involves significant plastic deformation at the interface as temperature increases, resulting in the disappearance of interstices and full contact of the surface pair. The last stage entails the diffusion of atoms under constant temperature. The bonded specimens show tensile strengths reaching 88% of the ideal Cu/Al contact strength. (c) 2007 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

负超载对Al-2024疲劳裂纹扩展的影响

本文讨论了负超载对Al-2024铝合金材料疲劳裂纹扩展的影响,试验发现在大量负超载循环周次之后也有裂纹停滞现象发生。这种停滞现象的产生与剪切唇的形成有关。本文发现负超载期间的剪切唇(简称剪切唇Ⅰ)和负超载之后的剪切唇(简称剪切唇Ⅱ)对疲劳裂纹扩展速率影响的程度不同。从裂纹闭合的观点建立了负超载对疲劳裂纹扩展影响的计算模型。

Al及Al合金粉末颗粒表面氧化膜厚度对爆炸烧结体质量的影响

本文借助光学显微镜、扫描电镜分析研究了水雾化、氮气雾化al粉和超声氩气雾化Al-Li合金粉爆炸烧结体的显微结构, 结果表明: 只有Al及Al合金粉的表面氧化膜厚度小于30nm时, 才可以得到性质优异的爆炸烧结体。

Microstructures of explosively consolidated rapidly solidified aluminum and Al-Li alloy powders

The microstructures and the characteristics of water-atomized, nitrogen gas-atomized Al powders and ultrasonic argon gas-atomized Al-Li alloy powder were investigated by means of metallography, SEM, Auger electron spectroscopy and X-ray diffraction techniques. Rapidly solidified powders were explosively consolidated into different sized cylinders under various explosive parameters. The explosively consolidated compacts have been tested and analysed for density microhardness, retention of rapidly solidified microstructures, interparticle bonding, fractography and lattice distortion. It is shown that the explosive consolidation technique is an effective method for compacting rapidly solidified powders. The characteristics of surface layers play a very important role in determining the effectiveness of the joints sintered, and the Al-Li alloy explosive compacts present an abnormal softening appearance compared to the original powder.

SiC颗粒对Al-Zn合金激光快凝晶粒组织的影响

Al-Zn合金和SiCp/Al-Zn复合材料的激光重熔晶粒组织的对比研究表明 ,SiC颗粒对凝固初生相的生长具有阻碍作用。在颗粒尺寸较大和颗粒含量较高的条件下 ,激光熔池中会形成非外延生长的晶粒

原位生成TiC粒子在快凝Al-Fe合金中变化行为的研究

通过OM，SEM和TEM等手段研究了在常规铸态以及快速凝固Al-8wt％Fe合金中原位生成TiC粒子时棚组成及显微组织的变化。同时结合利用外加法制备的常规铸态和快速凝固Al-8wt％Fe/TiC合金的娃微组织变化，得出了原位反应TiC粒子的生成及其在合金熔体中的变化行为：在常舰铸态下生成的尺寸较大的八岍体TiC颗粒在快速凝固过程中将发生全部或部分溶解，在随后的怏冷过程中将重新析出并形成细小的TiC粒子，原位生成的TiC粒子在快速凝固过程中同样可以对α-Al起到促发形核的作用。

激光熔覆原位合成αFe(Al)/Fe_3Al涂层的研究

通过寻求工艺参数与Fe 2 8% (at)Al粉末的最佳匹配 ,利用激光熔覆和复合材料原位合成技术 ,制备了熔覆质量好的α Fe(Al) /Fe3Al涂层。该熔覆层为α Fe(Al)固溶体胞状组织基体上分布着黑色DO3结构Fe3Al质点 ,多数质点分布在晶界上 ,颗粒尺寸为 (10 0～ 30 0 )nm。EDAX线扫描结果表明 ,Al、Fe在整个涂层中分布比较均匀 ,无宏观偏析 ;Al、Fe成分在近界面及界面处缓慢过渡 ,涂层和基体发生互扩散 ,为冶金结合。熔覆层的显微硬度为 6 39HV0 2 ,比基体高 2倍 ,多道搭接处理对熔覆层的硬度影响不大。

Thermal Residual Stresses in SiCw/Al Composite

<正> The SiCw/6061Al composites were fabricated by squeeze casting method. Varia-tions of thermal residual stresses with quenching temperature, cooling manner, aging time and thethermal-cold cycle process in thin specimens,and the distributions of thermal residual stresses alongthe distances from the surface and changes with heating temperatnres in thick specimens were stud-ied by means of X-ray diffraction (XRD). The effects of residual stresses on the mierostructure, di-mensional stability and age-hardening behavior were studied by SEM, TEM observations, and tensiletest. The results showed that there existed macrostress, microstress and thermal mismatch stress inSiCw/Al compo-site,and the presence of microstress and thermal mismatch stress has no influenceon the measurement of macrostress, but the macrostress can affect the measured value of thermalmismatch stress. Thermal res dual stress induced during the composite fabrication process, will be further in-creased when the composite were subjected to the e

Microcracks Propagation in One Al/SiCp under Impact Loading

Numerous microcracks propagation in one metal matrix composite, Al/SiCp under impact loading was investigated. The test data was got with a specially designed impact experimental approach. The analysis to the density, nucleating locations and distributions of the microcracks as well as microstructure effects of the original composite was received particular emphasis. The types of microcracks or debonding nucleated in the tested composite were dependent on the stress level and its duration. Distributions of the microcracks were depended on that of microstructures of the tested composite while total number of microcracks in unit area and unit duration, was controlled by the stress levels. Also, why the velocity was much lower than theoretical estimations for elastic solids and why the microcracks propagating velocities increased with the stress levels' increasing in current experiments were analysed and explained.

The Effect of the Thickness of Fe2 Al5 Phase Layer at Fe/Al Interface on the Mechanics Behavior of Hot Dip Aluminizing Coating

Hot Dip Aluminized Coatings with different thickness were prepared on Q235 steel in aluminum solutions with different temperature for certain time. Through tensile tests and in-situ SEM observations, the effect of the coating's microstructure on the tensile strength of the samples was studied. It was disclosed at certain aluminum solution temperature,transaction layers mainly composed of Fe2 Al5 phase got thicker with time prolonging, and this changed initial crack's extending direction from parallel with to vertical with stretching direction. The change in crack direction decreased tensile strength of samples, thus made the coating easy to break. It was concluded that the existence of thick Fe2 Al5 phase layer was the basic reason for the lowering of tensile strength of the coating.

Adsorption of formaldehyde molecule on the intrinsic and Al-doped graphene: a first principle study

To search for a high sensitivity sensor for formaldehyde (H2CO), We investigated the adsorption of H2CO on the intrinsic and Al-doped graphene sheets using density functional theory (DFT) calculations. Compared with the intrinsic graphene, the Al-doped graphene system has high binding energy value and short connecting distance, which are caused by the chemisorption of H2CO molecule. Furthermore, the density of states (DOS) results show that orbital hybridization could be seen between H2CO and Al-doped graphene sheet, while there is no evidence for hybridization between the H2CO molecule and the intrinsic graphene sheet. Therefore, Al-doped graphene is expected to be a novel chemical sensor for H2CO gas. We hope our calculations are useful for the application of graphene in chemical sensor.

Numerical Study On Transient Flow In The Deep Naturally Fractured Reservoir With High Pressure

According to the experimental results and the characteristics of the pressure-sensitive fractured formation, a transient flow model is developed for the deep naturally-fractured reservoirs with different outer boundary conditions. The finite element equations for the model are derived. After generating the unstructured grids in the solution regions, the finite element method is used to calculate the pressure type curves for the pressure-sensitive fractured reservoir with different outer boundaries, such as the infinite boundary, circle boundary and combined linear boundaries, and the characteristics of the type curves are comparatively analyzed. The effects on the pressure curves caused by pressure sensitivity module and the effective radius combined parameter are determined, and the method for calculating the pressure-sensitive reservoir parameters is introduced. By analyzing the real field case in the high temperature and pressure reservoir, the perfect results show that the transient flow model for the pressure-sensitive fractured reservoir in this paper is correct.

Effects of volumetric allocation on heave response of semisubmersible in deep sea

The configuration of semisubmersibles consisting of pontoons and columns and their corresponding heave motion response in incident progressive waves are examined. The purpose of the present study is to provide a theoretical approach to estimating the effects of volumetric allocation on natural period and response amplitude operator (RAO) in heave motion. We conclude that the amplitude of heave motion response can be considerably suppressed by appropriately adjusting volumetric allocation so that the natural heave period keeps away from the range of wave energy. The theoretical formulae are found in good agreement with the corresponding computational results by WAMIT.