An Advanced Process Of Improving Rolling Ability Of Spray Deposition Porosity Material-Ceramic Rolling Technology

As an advanced material preparation technology, spray deposition has been widely used to produce alloys and metal matrix composites. In principle, the spray deposited preforms usually exhibit limited mechanical properties due to the porosity and a lack of sound metallurgical bond between the particles. Higher performance can be achieved by further densification and deformation. The densification and plastic deformation behaviors and fracture behaviors of the as-spray deposited porous performs were investigated in this thesis. The involved deformation process is rolling. A novel rolling methods named as"Ceramic Rolling"developed based on pseudo-HIP technology is applied.The main conclusions are as follows:(1) The effects of processing conditions during"Ceramic Rolling"technique were investigated.Seven kinds of"Ceramic Rolling"experiments have been experimentally verified to improve the formability of the porous 8009/SiCP alloy performs.The experimental results show that the shape of the pressure transfer medium and the rolling method has obvious effect on the deformation of the spray deposited performs. The densification and plastic deformation behaviors and the fracture behaviors of the as-spray deposited porous performs are related with the effects of particulate characteristics during"Ceramic Rolling"process. The ceramic particulates, especially the Al2O3 particle with the size of about 200 meshes, can serve as the medium for transferring pressure, thus to provide a more homogenous severe hydrostatic stress field to handicape the flowing of the metals in the longitudinal and transverse directions and to avoid cracking during the rolling process.(2) The influence of the processing conditions on the densification and deformation behaviors of the porous 5A06 and 8009/SiCp alloy perform during"Ceramic Rolling"process were investigated. The experimental results show that comparing with the fully dense materials, the deformation behavior of spray deposited preforms is very complicated and difficult because of the existence of porosity in the preforms and oxidation film on the surface of the alloy particles in the matrit. During the conventional rolling process, the porous preform is liable to cracking or tearing. During Ceramic Rolling, the ceramic particulates may serve the dual functions of a compactible pressure transfer medium and also as a medium for heat preservation in workpiece body, thus helps to maintain the necessary temperature levels for the deformation during rolling. It is obvious that the ceramic particles can retard the flowing of the metal in the longitudinal and the transverse during Ceramic Rolling when the thickness reduction is up to 25%-30%, which is important in avoiding the cracks. Since severe hydrostatic stress field benefits the formability, extrusion is widely adopted for the densification and deformation of the as-spray deposited preforms.(3) The processing parameters such as packing materials, ceramic particulate size and kind should be paid more attention in order to improve the densification effect to so as to and obtain large dimension sheet free of crack. The results show that the"Ceramic Rolling"technique is an effective method to speed up the densification and improve the formability of porous spray deposition alloy preforms, which is thought to be resulted from the severe hydrostatic and homogenous stress. As the immature manufacture technique to process spray deposited aluminum alloys, great efforts will be stimulated for further investigation, and significant progress is expected. Nevertheless, extrusion can not produce large dimension plates limited by the facility.