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The dendrite morphologies of the cast nickel-based superalloy CMSX-4® (CMSX-4® is registered trademarks of the Cannon-Muskegon Corporation) and the austenitic stainless steel HP microalloy have been obtained via an automated serial-sectioning process which allows three-dimensional (3D) microstructural characterization. The dendrite arm spacing, volume fraction of segregation, and fraction of porosity have been determined. This technique not only increases the depth, scope, and level of detailed microstructural characterization but also delivers microstructural data for modeling and simulation.

The reliability of 2L99 (Al–7Si–0˙4Mg) alloy investment castings produced using gravity and vacuum counter-gravity mould filling processes has been compared. Large numbers of bars have been cast and tested in four point bending and the scatter in their strengths characterised using the Weibull statistical technique to give the Weibull modulus λ. Both top and bottom gated designs of gravity poured moulds produced unreliable castings (λ=17 for both). This contrasted with previous work which showed much higher moduli for bottom gated moulds (49 and 54); this discrepancy has been attributed to poor control over mould filling and evidence for this was wide variation in filling times in the present work. The standard CLA vacuum counter-gravity filling process significantly improved the reliability (λ=29), but this was marginally reduced (λ=27) when a filter was introduced into the sprue. Possible reasons for this are discussed. A modification to the mould design further increased the reliability (λ=44)...

The influence of the casting filling technique and hot isostatic pressing (hipping) on the fatigue-life distribution of Al-7Si-Mg alloy castings has been studied. To vary the number density and size of oxide-film defects in the castings, test bars were cast using bottom-gated filling systems with and without filtration. Some unfiltered castings were subjected to a hipping treatment of 100 MPa at 500 °C for 6 hours. Test pieces were machined from the castings and were fatigue tested in pull-pull sinusoidal loading, at maximum stresses of 150 and 240 MPa under a stress ratio of R=+0.1. The fatigue lives at any probability of failure and Weibull statistical parameters of the filtered castings were higher than those of the unfiltered and nonhipped castings, illustrating the importance of the casting technique. However, the unfiltered but hipped castings exhibited higher performance. It is proposed that the significant improvement in fatigue life after hipping is due to the deactivation of entrained double oxide-film defects as fatigue-crack initiators.

Entrainment defects occur frequently in aluminium alloy castings during mould filling, and are very detrimental to both mechanical properties and reliability. The formation mechanisms and influences of these defects have been discussed previously, but the behaviour of the defects in the liquid metal and their evolution during solidification has not been studied in detail. In this research, samples of Al-Si-Mg alloy A356 that contained entrainment defects were scanned using ultra-fast synchrotron-based X-ray tomographic microscopy at the TOMCAT beamline of the Paul Scherrer Institut. The samples were directly viewed at both room temperature and in a fully liquid state. The reconstructed images showed three different entrainment defect morphologies, namely, entrained pores, tangled double oxide films and closed cracks. The evolution of the morphology of the entrainment defects was studied to better understand morphological changes of the defects, and the relationship between entrainment defects and microporosity.

The increased use of microsoldered circuits has brought with it concern over the reliability of the Pb–Sn solder joints in such assemblies. It is well known that bulk samples of the eutectic Pb–Sn alloy solidify as a lamellar eutectic. This has often been assumed to be the microstructure of considerably smaller volumes of the same alloy, although studies of atomised drops in the Pb–Sn and other systems have shown that non-equilibrium structures commonly develop in alloy systems during the solidification of small volumes. In the present work the solidification of small volume truncated sphere flip-chip microsolder bonds was studied using differential scanning calorimetry of the arrays of bonds, and the microstructures were assessed. Cooling traces obtained using differential scanning calorimetry revealed under coo lings up to 31 K before solidification, although the integrated solidification exotherm is insufficient to encompass the solidification of the entire array of bonds examined. Metallograp...