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Anisotropic dimensional change on sintering may strongly affect the precision of parts produced by press and sinter. In previous work a design procedure accounting for anisotropic dimensional change of axi-symmetric parts (disks and rings) has been developed on the basis of experimental data. In this work the procedure has been applied to predict the anisotropic dimensional change of real parts produced in industrial conditions, providing that coaxial rings were identified in the geometry of the actual parts. Parts were highly different for material, complexity of geometry, green density and process conditions. Parts were measured in the green and sintered state and the measured dimensional changes were compared to the predicted ones, finding a good agreement. The procedure was also adapted to predict dimensional change of an oval feature, and highly satisfactory results were obtained.

Alumina coatings deposited onto steel substrates by plasma spraying were studied using transmission electron microscopy. A number of allotropes of alumina distinct from the alpha-alumina of the starting powder were identified. The as-sprayed coatings consist primarily of metastable gamma-alumina and amorphous/nanocrystalline material. Areas of alpha-alumina were observed, generally in conjunction with the twinned metastable phases delta-and theta-alumina, and these were interpreted as resulting from solid-state transformation from the gamma phase, due to the annealing action of subsequent passes of the plasma torch. The absence of such phases from the first-and last-deposited layers is further evidence for such a mechanism. ]

The anisotropic dimensional changes during sintering was investigated for rings made of eight different materials with different green densities and H/(Dext-Dint) ratio. Dimensional changes are affected by green density, as shown in previous works, while the geometrical parameter does not display a clear influence. The anisotropy parameter K defined in a previous work does not describe anisotropy of dimensional change unambiguously, due to the anisotropy of shrinkage/swelling in the compaction plane. A new anisotropy parameter (K3D) was therefore defined considering the dimensional changes of internal diameter, external diameter, and height. This parameter display an unambiguous dependence on the equivalent isotropic dimensional change and will be used in further work to develop a predictive model for the prediction of the anisotropic dimensional change during sintering of parts with different green density and geometry.

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