The Researches On Technology And Deformation Mechanism Of Porous Materials Prepared By Spray Deposition During Frame-Confined Rolling

As an advanced material preparation technology, spray deposition has an advantage in producing high performance alloys and metal matrix composites. However, the workability and mechanical properties of spray deposited preforms are poor owing to the porosity formed during the deposition processing. So, further densification and plastic deformation treatment are needed to prepare fully dense products with high mechanical properties.In this thesis, a novel rolling technology, termed as"Frame-Confined Rolling"was investigated for the continuous densification of the as-spray deposited preforms.Firstly, the processing conditions of the frame-confined rolling technique and the influence factors on the densification effect were analyzed. The effects of the processing variables on the microstructures, the density distribution in the preforms and the evolution of the pore shapes during rolling were investigated. The experimental results show that the frame-confined rolling technique can greatly improve the workability of spray deposited preforms and avoid cracks whcich easily occur during the conventional rolling processing. The best gaps size in length and width wereθB=4-6% andθL=7.5-10% for the densification and workability of spray deposited preforms. The maximum thickness reductionεh of each pass should be under 10% during the first 2-3 passes. When the total thickness reductionεwas larger than 30%,εh can reach up to 10-20%. When theεis larger than 80%, the maximum relative density of the spray deposited preforms can reach up to 98.0% and this kind of plate preformd can be cold rolling, but the thickness reductionεh of each pass should be controlled in the range of 5-10%.Based on the above results, the densification and deformation mechanism, evolution regularities of the pores and microstructures during the frame-confined rolling processing are discussed. The mechanical properties of the as-rooled sheets were examined. At the beginning of the rolling processing, the distribution of thickness reduction in the as-rooled sheets were not uniform, the thickness reductionεon the surface layer of the sheet was smaller than that in the center layers. When the preforms fully filled the frame, the thickness reduction distribution will tend to be uniform. The densification rate of the surface layer of the preforms was the most fast. The three-dimensional compressive stress at the center of the preforms was beneficial to the deformation of the pores. During rolling of the 8009Al/SiCp preforms, the SiC particles easily break up into finer pieces and the distribution state tend to be more uniform. The frame-confined rolling technique can effectively speed up the densification of the spray deposited performs and improve the rolling workability of the porous preforms. So, the mechanical properties of the spray deposited sheets by frame-confined rolling technique are superior to that of the sheets by the conventional rolling tecnique.