Multilayer graded boron carbide-aluminum composites
Abstract
Boron carbide aluminum composites with multi-layer microstructure were developed by molten aluminum infiltration of boron carbide preforms. A centrifugal casting process was employed to obtain preforms with multiple graded layer structure, where particles were distributed gradually from fine particles on one side to coarse particles on the other side within each layer. A tape casting process was also developed. Uniform or stepwise multiple gradient layer structures were obtained by stacking like tapes or different tapes in repeated patterns. A narrow range of preform densities was obtained by varying the densification conditions according to green forms. It has been previously reported that boron carbide and aluminum can form many different reaction products and contact angles between boron carbide and aluminum vary with temperature and time. Minimizing the reaction products might lead to better performance of composites. This study found that spontaneous infiltration can be achieved in minutes under rough vacuum (<100 >μTorr) at 1200°C or higher. The amounts of reaction products could be effectively suppressed by rapid spontaneous infiltration. A low-temperature infiltration (LTI) scheme was designed and full infiltration of boron carbide by aluminum at T < 1000°C was achieved. Reaction products obtained by LTI were significantly less then that in composites obtained by spontaneous infiltration. The microstructure and mechanical properties of the resulting layered composites were evaluated and correlated to microstructure.
Degree
Ph.D.
Advisors
Bowman, Purdue University.
Subject Area
Materials science|Metallurgy
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