| Gradient materials belong to a new class of inhomogeneous material that the composition, structure and property gradually change along the thickness. Gradient materials have been widely used to in the areas of aerospace, electromagnetism, nuclear engineering and electro-optical engineering for they can simultaneously have two contradictory properties, which are impossible in the homogeneous materials. In the present dissertation, tape casting combined vacuum hot-pressure sintering has been explored to prepare Al-Cu gradient materials to solve the problems such as difficult to control the gradient structure and highly densify Al-Cu gradient materials.Firstly, a series of tapes with different Al-Cu powder mixtures were fabricated. To form slurry, 0.6wt.% Hypermer KD-1 was chosen as dispersant, 2.7wt.% Polyvinyl Butyral(PVB) as binder, 3wt.% glycerinum as plasticizer, 33.7wt.% ethanol and butanone as solvent, the residuals were powders. The slurry was then cast onto a double-blade casting machine to form tapes. The first blade height was 200?m, the second blade height was 100?m and the rotation of baseband was 2.5mm/s. The tapes were homogeneous without obvious sedimented particles, the thickness distributions of tapes were close to normal distribution, within 40-61?m.After removing organics, the powders were explored to fabricate Al-Cu composites by vacuum hot-pressure sintering. Also, the structure of Al-Cu composites was studied systematically. The results revealed that Al-Cu composites were highly densified at 500oC-300MPa-2h, the relative density exceeds 95.63%. Except for Al and Cu, there was some residual carbon which exists in the form of organic, and elemental carbon. Bonding of Al/Cu interface were mainly Al-Cu diffusion layers, the thickness of diffusion layers were within 2-3.5?m and no obvious intemetallic compounds were found.Direct mixing method was explored to study the effect of tape casting on the structure and properties of Al-Cu composites. The results demonstrated that the residual carbon had little influence on the phase, microstructure and Vicker hardness of Al-Cu composites. However, the residual carbon decreased the relative density of Al-Cu composites because it reduced the density. For example, the porosity of 100%Cu was almost 0 while the relative density was just 95.63%. Also, the residual carbon reduced the acoustic impedance of Al-Cu composites, among which the maximum cut was 100%Cu(19.56%). The bending strength of Al-Cu composites prepared by tape casting decreased sharply and increased with increasing Cu content, from 47.9MPa for terminal Al to 227.11 MPa for terminal Cu.At last, 8-layer Al-Cu gradient composite materials with Cu increasing from 0wt.% to 66.03 wt.% were fabricated by the method. The composition and thickness of each layer were accurately controlled, with deviations within 0.19%-2.9% and 0.3%-9.6%, respectively. Al-Cu gradient composite materials were highly densified, Al and Cu phases were dispersed uniformly and well compacted in all layers. No obvious pores or gaps between the layers were found. The flatness of Al-Cu gradient materials was good, with Al surface flatness 6.06?m and high Cu content surface 7.64?m. Scanning Acoustic Microscopy(SAM) revealed that the parallelism of Al-Cu gradient composite materials was excellent and no obvious pores were found in the samples. |
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