High Modulus, High Strength Filaments and Composites

摘要

The presence of internal stresses in boron filaments was inferred from experiments showing strain relief. In addition, measurements were made of the change in tungsten substrate length occurring during boron filament fabrication of the thermal expansion of boron filament to 1030C, and of the creep rate at 1070C. A model for filament formation is proposed in which the first significant step in filament fabrication is the formation of a continuous boron sheath around the tungsten substrate. Subsequent reaction between the boron sheath and the tungsten substrate results in the formation of tungsten borides at the interface having specific volumes much less than that of the reactants. Residual internal stresses present in boron filaments arise from three principal sources. These include core volume changes during filament fabrication, differential thermal contraction between the boron sheath and the core on cooling from filament formation temperature, and stresses in the boron sheath inherent in the vapor deposition process. Stresses were calculated for a selected filament from analysis, and values given for the filament surface, for the core interface, and for the core.