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2 µm - eTheses Repository - University of Birmingham

2 µm - eTheses Repository - University of Birmingham

Y-Z Z Y X 10mm X-Y X-Z

Y-Z Z Y X 10mm X-Y X-Z Figure 4.70 Virtual cuts through the central layer of the Y-Z, X-Y and X-Z planes of AODY30IS infiltrated in the ISQC20 mode at v0 = 0.72 m/s. When comparing the Y-Z plane view of AODY30IS (Figure 4.70) with that of AOPC20IS (Figure 4.71) the deformation of the preform as a result of the infiltration process is apparent. The preform before infiltration had an rectangular cross-sectional shape which was preserved during infiltration of AODY30IS. Here a maximum compression, assessed as the reduction of the cross-sectional area in the X-Z plane, was 3% compared to 27% in AOPC20IS. Y-Z Z Y X 10mm X-Y X-Z Figure 4.71 Virtual cuts through the central layer of the Y-Z, X-Y and X-Z plane of AOPC20IS infiltrated in the ISQC20 mode at v0 = 0.72 m/s. 169

In the Y-Z plane section in Figure 4.71 there was an increased fraction of porosity in the pure infiltration alloy on top of the MMC compared to that in AODY30IS in Figure 4.70 and it was mainly concentrated on and close to the surface of the MMC. The porosity originated from shrinkage of the metal due to reduced metal flow during feeding after solidification started. The voxel resolution of the 3D-CT was 64 µm and so finer porosity could not be detected by this method. The MMC appeared uniform at this resolution. Brightness was reduced in the outer volumes of the MMC since this material absorbed less X- ray radiation than the inner volumes. This layer is marked in the X-Z plane view in Figure 4.71. The depth of this layer ranged between 2 mm and 3 mm in the z-and the y-directions respectively. These layers are of different density and were found in all MMCs. They have been compressed by more than 15%. a) b) c) Figure 4.72 Micrographs of TOPC10IS infiltrated in ISQC at 0.72 m/s in the X-Z plane. a) Overview with markers defining the position of the higher magnification micrographs b) and c). The lines in a) mark roughly the borderline between lighter and darker MMC areas. 170 Z X

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