Interfacial reaction and mechanical reliability of eutectic Sn–0·7Cu/immersion Ag-plated Cu solder joint

Abstract

In this study, the interfacial reaction and joint reliability of immersion Ag-plated Cu substrate with the Sn–0·7Cu (wt-%) ball–grid array (BGA) solder was investigated. During reflow, the Ag plating layer was dissolved completely into the molten Sn–Cu solder and some of the Cu layer was also dissolved into the molten solder. The dissolved Ag and Cu were precipitated as Ag₃Sn and Cu₆Sn₅ intermetallic compounds (IMCs) in the solder matrix. Upon reflow, the Sn–Cu solder exhibits an off-eutectic reaction to produce the eutectic phase and precipitate (Cu₆Sn₅ and Ag₃Sn). The Cu–Sn IMC layer was formed at the solder/Cu interface after reflow, and the IMC layer grew during aging treatment. During the shear tests, the failure mode switched from a bulk-related failure to an interface-related failure. After aging for 250 h, the joint failed partially at the solder/Cu₆Sn₅ interface. The brittle fracture was linked to the formation of thick Cu–Sn IMC layer.     

Design and implementation of automatic shading device for diffuse radiation measurement

Considering the problem of too large area the shading disc covered,complex shadow band coefficients and too big diffuse radiation measurement bias,an automatic shading device for diffuse radiometer is designed and realized. Set a shading ball on the automatic sun tracker,drive linkage parallelogram structure with the declination axis arm,the shading ball can rotate synchronously with the motion of the sun and shade beam radiation measured with pyranometer,thus shading beam radiation and measuring diffuse radiation can be realized automatically. The comparison test results show that the automatic shading device can realize diffuse radiation measurement automatically,the accuracy of diffuse radiation readings can get a 18. 7% improvement compared with traditional measure system,greatly improves the reliability and accuracy of the diffuse radiation measurement.     

Synthesis and characterisation of Si3N4p/Cu nanocomposite powders by high energy ball milling

Abstract

The present work reported the preparation of Cu–25 wt-%Si₃N₄ nanocomposite powders via high energy ball milling (HEBM). The phases and morphologies of as-milled powders with various milling times were investigated using X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The experimental results showed that with increasing the milling time, the irregularly shaped Cu powder became flattened, and, subsequently, refined and near spherical. After 12 h milling, the particle size of Cu–Si₃N₄ composite powders was in the range of 200–300 nm, while the grain size of Si₃N₄ particulates, 10–25 nm, was well within a nanometre scale. A uniform distribution of the nanosized Si₃N₄ reinforcing phase throughout the Cu matrix was successfully obtained. A reasonable mechanism for the formation of Cu–Si₃N₄ nanocomposite powders during HEBM was also proposed.     

Influence of casting parameters on void volume and centre segregation in continuously cast 100Cr6 blooms

Abstract

Continuously cast ball and roller bearing steel 100Cr6 exhibits comparatively strong segregation which poses a quality handicap. In the present work which was carried out in the time between 1992 and 1996 the void formation which is related to the centre segregation and the centre segregation were measured on 2 m long segments of 240 × 200 mm² blooms cast at the steel plant of Georgsmarienhütte GmbH. It was found that the segregation of carbon expressed with the ratio of C _max/C _o increases with casting speed and superheat. Many experiments were carried out to elucidate the effect of electromagnetic stirring along the lower part of the metallurgical length (F-EMS). But, unfortunately, a decrease in segregation could not be achieved by F-EMS. The only method to decrease the centre segregation in continuously cast blooms of 100Cr6 seems to be casting at low speeds with low superheat.     

Microstructure development and superplasticity in Inconel 718 sheet

Abstract

Within the range of temperatures and strain rates investigated, mechanical testing identified the optimum forming condition for Inconel 718 sheet as being 965°C with a strain rate of 10^-4 s^-1. A detailed investigation of the microstructural behaviour under these deformation conditions was carried out and is reported here. Typically superplastic deformation would generate an enhanced rate of grain growth. This was not the case with the present material; instead it was found that a slight apparent grain size reduction occurred and there was evidence of substantial dislocation activity. It was concluded that the material was deforming on the borderline between 'true' superplasticity and normal slip based deformation.     

Effect of MnS powder additions and vibratory ball peening on corrosion resistance of sintered 316LSC stainless steels

Abstract

As sintered parts are to be machined after sintering, the MnS powder is usually added to improve the machinability. Vibratory ball peening is used for deburring and improving the surface finish of sintered components in local PM industries. The effect of the MnS powder content and vibratory ball peening on the corrosion resistance of the sintered 316LSC alloys was investigated. Experimental results show that the addition of MnS powder slightly decreases the sintered density. The weight loss rate of the sintered specimens immersed in the 10%FeCl₃ corrosion test solution increases slightly with increas- ing MnS content, but decreases with increasing sintering temperature. Vibratory ball peening effec- tively decreases the weight loss rate of the sintered stainless steels. The chromium atoms actively migrate across the phase boundary and diffuse into the MnS particles during sintering. This intensive chromium diffusion affects the corrosion performance of the sintered alloys with MnS added. The surface morphology of the as sintered and the ball peened specimens before and after the corrosion test were studied with a SEM.     

Synthesis of nanosized WC/MgO powders by high energy ball milling and analysis of reaction thermodynamics

Abstract

In the present work, a powder mixture of pure WO₃, graphite and Mg with a definite atomic ratio was milled at room temperature using a high energy ball mill method, and ball milled powders were analysed by X-ray diffraction, scanning electron microscopy and transmission electron microscopy. The results indicated that after ball milling for a period of time, an oxidation–reduction reaction was successfully achieved among the Mg, graphite and WO₃ powders to obtain MgO and WC. The extension of the ball milling led to the refinement of the powders. After ball milling 50 h, nanocrystalline WC grains (25 nm) were embedded into the fine matrix of MgO and formed fine nanocomposite MgO/WC powders (～100 nm in diameter). The experimental results and thermodynamic analysis showed that the formation of nanocomposite MgO/WC was a mechanically induced self-propagating reaction, and very short milling time was needed to complete the reaction.     

Compression tests of carbon steel ball mould for casting

Abstract

In this study, the carbon steel boll mould that has merit of the metal mould and the sand mould was produced. Steel balls were heated and joined to produce the steel ball mould. The compressive strength was measured for the strength of the mould. The compression specimen was manufactured after putting steel balls into the carbon vessel and heating to join. The compression specimen was 10 mm in diameter and about 10 mm in height. The influence of the diameter of the steel ball and temperature of heating on the strength of the steel ball mould was examined. The compressive strength decreased as the ball diameter became large. Steel balls were oxidised and joined by heating. Melted aluminium was cast into the carbon steel ball mould. The macrostructure of the solidified specimen was observed.     

Flavescence dorée elimination from dormant wood of grapevines by hot-water treatment

Flavescence dorée (FD) and other types of grapevine yellows are serious diseases of grapevines caused by phytoplasmas. FD is spread by a leafhopper species, and it has been shown to be transmitted by using infected cuttings. Data are presented for the effective use of hot-water treatment to eliminate FD. Immersion time has to be increased logarithmically when temperature is reduced linearly. The effective treatments range from 10 h at 40°C to 10 min at 55°C. The eggs of the leafhopper vector of FD, Scaphoideus titanus , are also killed by immersion at 50°C for 45 minutes. This temperature/time combination is recommended for treating dormant cuttings of grapevines for the elimination of FD.     

Measurement and modelling of hollow rubber spheres: surface-normal impacts

Abstract

The performance of natural rubber sports balls under impact conditions is dominated by the material's behaviour under high strain rate conditions dictated by the impact velocity and ball dimensions. To design improved products, sports ball manufacturers need to better understand the physical phenomena associated with ball impact against both rigid and deformable surfaces. This understanding will provide the foundation for performance prediction and optimisation design tools as well as more appropriate product and ultimately material testing techniques. Rebound characteristics of pressurised and pressureless tennis balls and their respective rubber cores subject to normal impacts are presented for a range of incident velocities. High-speed video analysis has been used to measure coefficient of restitution, impact duration and 'whole ball' deformation to validate a surface-normal impact finite element method based predictive model as the first step towards a more comprehensive oblique impact model. Accounting for strain rate dependent stiffness and damping material properties has achieved close correlations between model predictions and observed impact behaviour. The propagation of dominant bending and hoop-strain waves through the ball during the impact is revealed to illustrate the methodology's effectiveness in predicting ball performance associated with difficult to observe impact phenomena.