Coupled effect of heat input and beam oscillation on mechanical properties of alloy 718 electron beam weldments

Abstract

Autogenous full penetration electron beam welds were made on alloy 718 with and without beam oscillation technique. Weldments were subjected to two types of post-weld heat treatments: direct aging (DA) and solution treatment at 980°C followed by aging (STA). When the welds were prepared using different heat inputs in the welding processes with and without beam oscillation, the influence of beam oscillation could not be studied in isolation but the coupled effect of heat input and beam oscillation was studied. Laves particles were finer in size and lower in amount in unoscillated welds compared with those in beam oscillated welds subjected to DA condition. δ phase needles were observed around Laves particles in the welds subjected to STA condition. The amount of Laves particles was less and that of δ phase was more in unoscillated welds compared with those in beam oscillated welds subjected to STA condition. Unoscillated weldments exhibited longer fatigue lives compared with beam oscillated weldments in both DA and STA conditions owing to less amount of Laves in the former. Weldments in STA condition had longer lives compared with those in DA condition. The role of δ phase needles in fatigue life could not be identified.     

Bright zinc–nickel alloy deposition from alkaline non-cyanide bath

Abstract

Zinc–nickel alloy deposition with polyvinyl alcohol and piperonal as bath additives has been investigated. The effects of additive concentration, triethanolamine concentration and other parametric variables on the deposit and solution properties have been studied. Polarisation studies were carried out under different conditions to understand the effect of triethanolamine and the brighteners on the co-deposition. Results indicated that the additives lead to bright alloy deposition containing ～10% nickel. The deposit produced at the optimum conditions with the additives has a nanograined structure with a γ phase.     

医用加速器电子治疗模式的BEAM程序分析

医用电子直线加速器XHA9在水模体中的实测曲线显示出其标称能量低、表面剂量偏高等现象。为寻求解决途径,用蒙特卡罗程序BEAM对XHA97MeV电子治疗模式E7建立了初始电子束模型,并计算了水模中的百分深度剂量（PDD）曲线,分析了各部件产生的电子对治疗电子束的贡献,确定限光筒产生的大量低能电子是导致出现标称能量低、表面剂量偏高等现象的主要原因。通过修改限光筒、散射箔等部件,分步优化了治疗头结构。模拟计算结果表明：优化方案提高了加速器的标称能量,降低了表面剂量和轫致辐射剂量,使剂量均匀性得到明显改善。     

Optimised running system design for bottom filled aluminium alloy 2L99 investment castings

Abstract

This research has evaluated the effect of surface turbulence introduced during the filling of moulds on the reliability of Al-7Si-Mg alloy (2L99)investment castings. Four different running systems were designed to provide different amounts of surface turbulence: top filled, uncontrolled bottom filled, and controlled bottom filled with and without a filter. Computer modelling has been used to simulate the filling of the different designs and the results have been compared with the actual flow behaviour established using real time X-ray radiography. Castings have been produced using the different running systems, tested in four point bending, and the results analysed using the Weibull statistical technique. It has been shown that top filling produces significant turbulence, which results in the least reliable castings (Weibull modulus of 25.5). There was no significant difference between this and the Weibull modulus of 27 found for uncontrolled bottom filled systems. This indicates that a poorly controlled bottom filled system is no better than a top filled system. Both were inferior to the controlled bottom filled systems without and with filters, which had Weibull moduli of 38 and 54 respectively. SEM examination and oxygen analysis of representative fracture surfaces has provided supporting evidence for the important role that oxide films played in reducing properties.     

Method for welding highly crack susceptible magnesium alloy ZK60

Abstract

The highly crack susceptible magnesium alloy ZK60 plates of 2 mm thickness were successfully welded by laser beam welding (LBW) with filler strip, which has the advantages of low heat input and capability of adjusting the compositions of weld metal to a less susceptible level. The effects of the compositions of filler strips on the microstructures and mechanical properties of the joints were investigated. Compared with autogenous LBW, LBW with filler strip can produce a narrower joint and avoid the cracks and pits, which severely worsen mechanical properties of the joints. When the filler strip of ZK40 alloy is employed, the grains in fusion zone can be refined, and a high quality joint, with the ultimate tensile strength of 322 MPa up to 90·7% of the base metal, is obtained.     

Effect of heating rate on dielectric and pyroelectric properties of double doped PZT

Abstract

Double doped lead zirconium titanate (PZT) was synthesised by solid state reaction method. Calcination and sintering was carried out at various heating rates in order to study the effect of heating rate on the extent of phase formation of double doped PZT. Furthermore, the effect of heating rate on dielectric and pyroelectric properties was also investigated. Rhombohedral perovskite phase was confirmed in the double doped PZT samples. Quantitative X-ray diffraction (XRD) analysis suggests that the extent of PZT formation decreases beyond 8°C min^?1 heating rate. The crystallite and grain sizes calculated from Scherrer's equation and field emission scanning electron microscope (FE-SEM) photographs respectively show the decreasing behaviour with increasing heating rate. Dielectric and pyroelectric properties show the increasing behaviour up to 8°C min^?1 and decreasing behaviour beyond this heating rate.     

Modeling study of the hydrodynamic arc breaking mechanism in BEAM

Blasting erosion arc machining (BEAM) utilizes thermal effect of the arc rather than spark to remove workpiece material. This paper investigates the expansion and distortion rules of the discharge channel based on the analysis of high speed photography and the micrographs of craters to study mechanism of BEAM. Based on these investigations, a thermal finite element model is developed. Then the temperature distributions in workpieces, both with and without flushing, are obtained. The comparisons of the obtained temperature distributions explain the formation of the trailing crater and the effect of hydrodynamic arc breaking mechanism on the efficiency of BEAM.     

Nanocrystalline zinc–nickel alloy deposition using pulse electrodeposition (ped) technique

Abstract

Zinc–nickel alloy was electrodeposited on stainless steel using pulse current deposition (PED) from a chloride–sulphate bath. Duty cycles were varied between 10 and 80% and frequency was changed from 10 to 100 Hz. The deposit characteristics were analysed using SEM, XRD and AFM and the results are presented in this paper. The corrosion resistance of zinc–nickel alloy deposited from direct current deposition (DCD) has been compared with that of the deposit obtained by pulse current using the electrochemical impedance spectroscopy method.     

Stress Generated on Aluminum During Anodization as a Function of Current Density and pH

Anodic oxidation is accompanied by stressgeneration during the growth of the oxide. The presentstudy focuses on the stress-generation mechanism onaluminum as a function of the applied current density in acidic solutions of sulfuric acid ofdifferent strengths giving variable pH. Abeam-deflection technique was utilized for thedetermination of the magnitude and direction of stressesgenerated during the anodic oxidation process. Generally,thickness of the oxide determines whether the stress iscompressive or tensile in nature. The results have beeninterpreted in terms of the formation and annihilation of anion (O^2-) and cation(Al³⁺) vacancies. A reduction in thealuminum-ion vacancy concentration (V Al ³ ) results in a compressive stressdeflection, whereas tensile-stress deflection isintroduced by an increase in the oxygen vacancy(Vo²⁺) concentration. The mechanism isfurther elucidated by current-density jump/dropexperiments. The results show that stress in this caseis affected by the dissolution of the oxide at the oxide-electrolyteinterface.     

Monitoring localised corrosion in inhibited solutions using wire beam electrode–noise signatures method

Abstract

The objective of this work is to determine the nature of localised corrosion in inhibited solutions by establishing possible relationships between characteristic features in electrochemical noise and corrosion processes using an electrochemically integrated multielectrode system, namely the wire beam electrode (WBE) in combination with noise signatures method. Experiments have been carried out to simultaneously measure electrode potential noise and WBE current distribution maps from stainless steel (SS316L) WBE exposed to inhibited solutions containing 6%FeCl₃ solution with inorganic inhibitors including 2 wt-% sodium chromate (Na₂CrO₄), cerium chloride (CeCl₃) and lanthanum chloride (LaCl₃). Characteristic electrochemical noise signatures were found to correlate with characteristic changes in WBE current distribution maps that show corrosion rates distributions and the degree of localised corrosion. A new concept namely localisation parameter (LP) has been proposed to identify the degree of inhibition. Na₂CrO₄ effectively inhibited the pitting corrosion process and the LP successively decreased through out the corrosion process. With the presence of CeCl₃ and LaCl₃, pits on stainless steel in 6%FeCl₃ solution were not repassivated and an increase in the LP was observed for both inhibitors. The results suggest that the WBE method could be used in combination with the noise signatures as a sensitive technique for monitoring inhibiting effect on localised corrosion.