| Conventional powder metallurgical techniques have the drawback in that metastable properties of the powder can be lost during the sintering stage. The use of shock waves to bond particles of powder together can, in principle, circumvent this drawback and produce bulk solids which retain metastable properties of the initial powder. However, the effects of the relevant shock and powder parameters on the final properties of the compacts must be understood before this technique can be used optimally.;The measured homogeneous temperatures in the copper-constantan powders varied from 150 C to 940 C as the shock energy was increased from 50 to 360 kJ/kg (shock pressure from 1.3 to 9.4 GPa). These results indicate that almost all of the energy in the shock front is converted into thermal energy. Furthermore, the rise time of the shock front is less than 23 ns which corresponds to a shock front width of less than 37 (mu)m, a dimension comparable to the powder particle diameter.;Rapidly solidified AISI 9310 steel powders were consolidated and the dependence of the microhardness and the ultimate tensile strength of the compacts on the shock energy from 94 to 770 kJ/kg (3.6 to 19.0 GPa) were measured for an initial powder distension of 1.64 and a shock duration of 2-3 (mu)s. Photomicrographs and SEM fractographs were used to study the interparticle bonding in the compacts. Results show that, for shock energies below 200 kJ/kg (4.9 GPa), the compacts have negligble strength. However, above this threshold the strength of the compact rises rapidly until a maximum value of 1.3 GPa is reached at a shock energy of 500 kJ/kg (12.4 GPa). This strength which is larger than that of wrought AISI 9310 remains constant before decreasing at the higher shock energies. In marked contrast, with increasing shock energy, the diamond pyramid hardness increases very gradually from a value of 340 for the initial powder to 500 at a shock energy of 500 kJ/kg. Microhardness also begins to decrease at higher shock energies. . . . (Author's abstract exceeds stipulated maximum length. Discontinued here with permission of author.) UMI;In the present investigation the influence of shock pressure, shock duration, and surface oxides on the mechanical and metallurgical properties of compacted steel, molybdenum, and nickel-molybdenum alloy powders were studied. In addition, to improve our fundamental understanding of shock waves in metallic powder media, the shock temperature at the junction between two layers of copper and constantan powders was measured via the thermoelectric effect for varying shock pressure and energy. |
