Research on laser welding of cast Ni-based superalloy K418 turbo disk and alloy steel 42CrMo shaft

Exploratory experiments of laser welding cast Ni-based superalloy K418 turbo disk and alloy steel 42CrMo shaft were conducted. Microstructure of the welded seam was characterized by optical microscopy (OM), scanning electron microscopy (SEM), X-ray diffraction (XRD), energy-dispersive spectrometer (EDS). Mechanical properties of the welded seam were evaluated by microhardness and tensile strength testing. The corresponding mechanisms were discussed in detail. Results showed that the laser-welded seam had non-equilibrium solidified microstructures consisting of FeCr0.29Ni0.16C0.06 austenite solid solution dendrites as the dominant and some fine and dispersed Ni3Al gamma' phase and Laves particles as well as little amount of MC short stick or particle-like carbides distributed in the interdendritic regions. The average microhardness of the welded seam was relatively uniform and lower than that of the base metal due to partial dissolution and suppression of the strengthening phase gamma' to some extent. About 88.5% tensile strength of the base metal was achieved in the welded joint because of a non-full penetration welding and the fracture mechanism was a mixture of ductility and brittleness. The existence of some Laves particles in the welded seam also facilitated the initiation and propagation of the microcracks and microvoids and hence, the detrimental effects of the tensile strength of the welded joint. The present results stimulate further investigation on this field. (c) 2006 Elsevier B.V. All rights reserved.

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.

Dissimilar autogenous full penetration welding of superalloy K418 and 42CrMo steel by a high power CWNd : YAG laser

Experiments of autogenous laser full penetration welding between dissimilar cast Ni-based superalloy K418 and alloy steel 42CrMo flat plates with 3.5 mm thickness were conducted using a 3 kW continuous wave (CW) Nd:YAG laser. The influences of laser welding velocity, flow rate of side-blow shielding gas, defocusing distance were investigated. Microstructure of the welded seam was characterized by optical microscopy (OM), scanning electron microscopy (SEM) and X-ray diffraction (XRD) and energy dispersive spectrometer (EDS). Mechanical properties of the welded seam were evaluated by microhardness and tensile strength testing. Results show that high quality full penetration laser-welded joint can be obtained by optimizing the welding velocity, flow rate of shielding gas and defocusing distance. The laser-welded seam have non-equilibrium solidified microstructures consisting of gamma-FeCr0.29Ni0.16C0.06 austenite solid solution dendrites as the dominant and very small amount of super-fine dispersed Ni3Al gamma' phase and Laves particles as well as MC needle-like carbides distributed in the interdendritic regions. Although the microhardness of the laser-welded seam was lower than that of the base metal, the strength of the joint was equal to that of the base metal and the fracture mechanism showed fine ductility. (c) 2007 Elsevier B.V. All rights reserved.

塑料压力管道热板焊接接头瞬时应力有限元分析

基于热粘弹性积分型本构关系,考虑材料性能依赖于温度变化及相变潜热的影响,利用有限元软件ANSYS热-力耦合及载荷步功能模拟结晶型高密度聚乙烯塑料压力管道热板焊接过程。并对焊接接头的应力分布进行有限元分析,得到了环向、轴向及径向瞬态应力分布规律。采用盲孔法和锯切法测量焊后残余应力,实测结果与数值分析基本吻合。

高密度聚乙烯塑料压力管道热板焊接头应力分布有限元分析

基于热粘弹性积分型本构关系,考虑材料性能依赖于温度变化及相变潜热的影响,利用AN SYS热-力耦合及载荷步功能模拟结晶型高密度聚乙烯(HDPE)塑料压力管道热板焊接过程,并对焊接接头的应力分布进行有限元分析,得到了环向、轴向以及径向瞬态应力分布的基本规律。采用盲孔法和锯切法测量焊后残余应力,实测结果与数值分析基本符合

Thermal-mechanical interface crack behaviour of a surface mount solder joint

The effect of thermal-mechanical loading on a surface mount assembly with interface cracks between the solder and the resistor and between the solder and the printed circuit board (PCB) was studied using a non-linear thermal finite element analysis. The thermal effect was taken as cooling from the solder eutectic temperature to room temperature. Mechanical loading at the ends of the PCB was also applied. The results showed that cooling had the effect of causing large residual shear displacement at the region near the interface cracks. The mechanical loading caused additional crack opening displacements. The analysis on the values of J-integral for the interface cracks showed that J-integral was approximately path independent, and that the effect of crack at the solder/PCB interface is much more serious than that between the component and solder.

Growth Mechanism And Joint Structure Of Zno Tetrapods

Regular zinc oxide (ZnO) tetrapods with a flat plane have been obtained on Si(1 0 0) substrate via the chemical vapour deposition approach. The x-ray diffraction result suggests that these tetrapods are all single crystals with a wurtzite structure that grow along the (0 0 0 1) direction and corresponding electron backscatter diffraction analysis reveals the crystal orientation of growth and exposed surface. Furthermore, we find some ZnO tetrapods with some legs off and the angles between every two legs are measured with the aid of scanning electron microscopy and image analysis, which benefit to reveal the structure of ZnO tetrapods joint. The structure model and growth mechanism of ZnO tetrapods are proposed. Besides, the stable model of the interface was obtained through the density-functional theory calculation and the energy needed to break the twin plane junction was calculated as 5.651 J m(-2).

High efficiency operation of butt joint line-defect-waveguide microlaser in two-dimensional photonic crystal slab

Butt joint line-defect-waveguide microlasers are demonstrated on photonic crystal slabs with airholes in a triangular lattice. Such microlaser is designed to increase the output power from the waveguide edge directly. The output power is remarkably enhanced to 214 times higher by introducing chirped structure in the output waveguide. The lasing mode operates in the linear dispersion region of the output waveguide so that the absorption loss due to the band-edge effect is reduced. The laser resonance is illustrated theoretically using the finite difference time domain method. A practical high power efficiency of 20% is obtained in this microlaser. (C) 2008 American Institute of Physics.

A novel butt-joint scheme for the preparation of electro-absorptive lasers

A 1.55 mu m InGaAsP/InGaAsP multiple-quantum-well electro-absorption modulator (EAM) monolithically integrated with a distributed feedback laser (DFB) diode has been realized based on a novel butt-joint scheme by ultra-low metal-organic vapour phase epitaxy for the first time. The threshold current of 25 mA and an extinction ratio of more than 30 dB are obtained by using the novel structure. The beam divergence angles at the horizontal and vertical directions are as small as 19.3 degrees x 13 degrees, respectively, without a spot-size converter by undercutting the InGaAsP active region. The capacitance of the ridge waveguide device with a deep mesa buried by polyimide was reduced down to 0.30 pF.

Butt-Joint Monolithicaily Integrated DFB-LD/EA-MD Light Source for 10Gbit/s Transmission

This paper reports on the design, fabrication, and performance of an integrated electro-absorptive modulated laser based on butt-joint configuration for 10Gbit/s application. This paper mainly aims at two aspects. One is to improve the optical coupling between the laser and modulator; another is to increase the bandwidth of such devices by reducing the capacitance parameter of the modulator. The integrated devices exhibit high static and dynamic characteristics. Typical threshold current is 15mA,with some value as low as 8mA. Output power at 100mA is more than 10mW. The extinction characteristics,modulation bandwidth, and electrical return loss are measured. 3dB bandwidth more than 10GHz is monitored.

Integrated electroabsorption-modulated DFB laser by using an improved butt-joint method

An improved butt coupling method is used to fabricate an electroabsorption modulator (EAM) monolithically integrated with a distributed feedback (DFB) laser. The obtained electroabsorption-modulated laser (EML) chip with the traditional shallow ridge exhibits very low threshold current of 12 mA, output power of more than 8 mW, and static extinction ratio of -7 dB at the applied bias voltage from 0.5 to -2.0 V.