Development of gasless thermite foils for bonding dissimilar metals

Thermites;Brazing;Materials Science & Engineering

Kinsey, Alex HEl-Awady, Jaafar ;

Johns Hopkins University

关键词: Thermites;    Brazing;    Materials Science & Engineering;   

Others  :  https://jscholarship.library.jhu.edu/bitstream/handle/1774.2/60199/Alex%20Kinsey%20Dissertation.docx?sequence=2&isAllowed=y

瑞士|英语

来源: JOHNS HOPKINS DSpace Repository

【 摘 要 】

One major challenge in increasing fuel efficiency of automobiles is introducing more lightweight components into vehicle structures. One of the technological gaps for adding more lightweight materials is the lack of cost-effective joining methods of dissimilar metal combinations. As such, this work describes the development of a novel joining technique of using fully dense thermite foils, named Redox Foils, which exothermically react to produce a molten metal braze capable of joining dissimilar metal combinations.The development process is described in detail, specifically, explaining the three ;;generations” of foils fabricated. At each stage of development, the fabrication process is adjusted with the goal of producing a gasless propagating foil capable of brazing dissimilar metals. The fabricated foils are characterized using a variety of techniques to understand the behavior of the self-propagating foils.First, a new powder metallurgy technique for consolidating thermites is developed and explained with initial chemistries tested. The thermite compositions are systematically diluted with excess metal to increase the metal content of the braze and suppress gas formation upon reaction. Very early in the process it was determined that gas formation and reactivity of the foils are critical parameters that must be optimized, as gas generation results in porous braze layers.To that end, reactivity of the foils is enhanced by altering the fabrication process in a second generation of Redox Foils, by introducing ball milled nanocomposite powders to fabrication process. The microstructures of these foils, more specifically, length scales of reactive and inert material, are critically analyzed and compared with finite element heat transfer simulations to determine critical length scales required to suppress metal vapor production.To demonstrate the ability to suppress gas, thin film reactive multilayers are fabricated as an ideal microstructure for comparison. Due to the fine control of layer thickness with multilayer foils, the inert diluent is homogenously placed between reactive components. The propagation of the foils demonstrated that metal vapor suppression is possible by placing the diluent in the proper place.Lastly, the third of generation Redox Foils were fabricated with milling the fuel, oxide, and diluent together to more uniformly distribute the diluent in the microstructure. Foils are analyzed and used to join metals producing a gasless propagating foil.