Failure modes in high strength and stiffness to weight scaffolds produced by Selective Laser Melting

The production of porous scaffold structures using additive manufacturing is becoming widespread, however a detailed understanding of the scaffold failure mechanisms is lacking. In this research, Selective Laser Melting (SLM) is used to produce Ti–6Al–4V scaffold structures consisting of a regular array of unit cells previously designed using topology optimisation. Interrupted compression testing and subsequent X-Ray Micro Tomography (XMT) characterisation is used to study the deformation and failure of the scaffolds for a range of solid fractions. Further, the XMT data of the unloaded scaffolds is used to generate meshes for finite element analysis which allowed direct comparison of desired and as built behaviour. Likely failure sites predicted from the finite element analysis compare favourably with the experimentally observed ones. Failure is initiated in areas that exhibit the greatest tensile stress, while the onset of the commonly observed layered failure occurs afterwards. The XMT of the unloaded scaffolds also highlights the inaccuracies in the SLM build process, which contributes to stress concentrations in the horizontal arms within the scaffolds. The results indicate that although the strength of the topology optimised structures is very high, further refinement in both the unit cell design and build quality would further increase the strength

On the role of tin in the infiltration of aluminium by aluminium for rapid prototyping applications

The use of tin as an alloying element in the production of freeformed infiltrated aluminium components is explored. Tin slows the growth of the aluminium nitride skeleton which provides dimensional stability, as well as increasing the rate of infiltration of the aluminium liquid into the aluminium nitride skeleton. (C) 2004 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved

The effect of trace elements on the sintering of Al-Cu alloys

Trace additions of Sn, In, Bi, Sb and Pb have been used to activate the liquid phase sintering of an Al-4Cu-0.15Mg alloy. Additions of as little as 0.05 wt% (similar to 0.01 at.%) increases the sintered density from 88 to 92% of the theoretical density. The elements which aid sintering have both high vacancy binding energies and high diffusivities in Al. It is suggested that the trace element diffuses into the Al, and forms trace element-vacancy clusters. This reduces the diffusivity of the Cu in the Al matrix, delaying Cu dissolution therefore causing the liquid to persist for longer times. This enhances sintering and therefore densification. (C) 1999 Acta Metallurgica Inc. Published by Elsevier Science Ltd. All rights reserved

On the role of tin in the nitridation of aluminium powder

The role of tin in the mechanism by which aluminium nitride grows on aluminium powder is explored. In the absence of tin, the aluminium powder nitrides rapidly, with growth occurring both into and out from the surface of the particles. In contrast, nitridation occurs more slowly in the presence of tin, which is incorporated in the growing nitride. When the tin is depleted, rapid nitridation occurs. The initial tin concentration determines the point at which the growth rate changes. (c) 2006 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved

Liquid phase sintering of aluminium alloys

The principle that alloys are designed to accommodate the manufacture of goods made from them as much as the properties required of them in service has not been widely applied to pressed and sintered P/M aluminium alloys. Most commercial alloys made from mixed elemental blends are identical to standard wrought alloys. Alternatively, alloys can be designed systematically using the phase diagram characteristics of ideal liquid phase sintering systems. This requires consideration of the solubilities of the alloying elements in aluminium, the melting points of the elements, the eutectics they form with aluminium and the nature of the liquid phase. The relative diffusivities are also important. Here we show that Al-Sn, which closely follows these ideal characteristics, has a much stronger sintering response than either Al-Cu or Al-Zn, both of which have at least one non-ideal characteristic. (C) 2001 Elsevier Science B.V. All rights reserved

The role of a low-energy-density re-scan in fabricating crack-free Al85Ni5Y6Co2Fe2 bulk metallic glass composites via selective laser melting

status: publishe

Processing and properties of topologically optimised biomedical Ti-24Nb-4Zr-8Sn scaffolds manufactured by selective laser melting

status: publishe

Selective laser melting of an Al86Ni6Y4.5Co2La1.5 metallic glass: Processing, microstructure evolution and mechanical properties

status: publishe

A selective laser melting and solution heat treatment refined Al-12Si alloy with a controllable ultrafine eutectic microstructure and 25% tensile ductility

status: publishe