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Evolution of the inner microstructure of uniaxially pressed copper powders was investigated by in situ X-ray microtomography. Experiments were carried out at the European Synchrotron in Grenoble, France. Sintering was performed under reducing atmosphere at 1050 °C. Qualitative and quantitative information from the 3D images acquired along the whole sintering cycle were analyzed. From that, macro- and microstructural features of the evolving microstructure were obtained. We found that large pores can be created during sintering and then they can grow during the whole thermal cycle by reducing the initial relative density of the sample by 10 %. The effect of the pore shape and the heterogeneous distribution of the pore volume fraction inside the sample are responsible for the behavior observed during sintering. The heterogeneous deformation measured is controlled by the evolution of the porosity. [ABSTRACT FROM AUTHOR]

This work analyses the microstructure changes of various copper-based powder systems during sintering from 3D images provided by in situ synchrotron microtomography. The investigated systems include a copper powder with a wide particle size distribution of 0-63 µm poured into a quartz capillary, a pre-sintered copper compact with artificially created large pores and a mixture of copper and alumina particles. The experiments were carried out at the European Synchrotron in Grenoble, France. Powders were sintered up to 1060°C under reducing atmosphere in a furnace located between the X-ray source and the detector. During each experiment, 3D images were taken at various times of the thermal cycle. We have obtained images with a resolution of 1.5 µm and the time of acquisition of every image was ∼1 min. Quantitative analysis of these images allowed the changes of various important parameters to be followed. Such parameters characterise the sintering process at the particle length scale: interparticle coordination, pore size distribution and particle centre-to-centre distance. Moreover, by tracking the displacement of each particle centre and comparing it to the displacement predicted by classical mean field assumption, we have been able to assess the magnitude of particle rearrangement occurring during sintering. From these data, the sintering behaviour of heterogeneous powder systems is discussed with particular emphasis of collective particle phenomena. [ABSTRACT FROM AUTHOR]

Abstract: Titanium and its alloy foams have been receiving a growing interest for biomedical industry due to their biocompatibility and high potential in dental, spinal, joint and hip implant applications. Near net shape production and reproducibility of a product require a full understanding of the processing parameters’ effect on manufacturing and final properties. The shape complexity of titanium surgical implants, for example dental implants, necessitates a good control in compaction and sintering of metal skeletons containing macropores for near-net shape manufacturing. In this study, effects of processing parameters such as spacer powder size and amount on compaction, sintering and final structural properties were investigated. Commercially pure cellular titanium with porosities ranging between 35 and 75% and pore sizes between 100μm and a few millimeters were produced via powder metallurgy with spacers. Architectural parameters of the foams, before and after sintering, were quantitatively characterized via X-ray computed microtomography. Addition of fine spacer powders enhanced compaction and densification of the foam structure. Pore walls were observed to get thicker during sintering. The use of coarser space holders resulted in thicker pore walls and a wider pore wall thickness distribution. The results indicated that strength and stiffness tend to increase with increasing pore size. Among the structural features that spacer size altered, pore wall thickness and pore face roughness were found to be the most dominant effects on strength and stiffness. [Copyright &y& Elsevier]