Electron beam welding (EBW) of two important engineering alloys, Ti–6Al–4V and 21Cr–6Ni–9Mn, was studied experimentally and theoretically. The temperatures at several monitoring locations in the specimens were measured as a function of time during welding and the cross-sections of the welds were examined by optical microscopy. The theoretical research involved numerical simulation of heat transfer and fluid flow during EBW. The model output included temperature and velocity fields, fusion zone geometry and temperature versus time results. The numerically computed fusion zone geometry and the temperature versus time plots were compared with the corresponding experimentally determined values for each weld. Both the experimental and the modelling results were compared with the corresponding results for the keyhole mode laser beam welding (LBW).Both experimental and modelling results demonstrate that the fusion zone size in Ti–6Al–4V alloy was larger than that of the 21Cr–6Ni–9Mn stainless steel during both the electron beam and laser welding. Higher boiling point and lower solid state thermal conductivity of Ti–6Al–4V contributed to higher peak temperatures in Ti–6Al–4V welds compared with 21Cr–6Ni–9Mn stainless steel welds. In the EBW of both the alloys, there were significant velocities of liquid metal along the keyhole wall driven by the Marangoni convection. In contrast, during LBW, the velocities along the keyhole wall were negligible. Convective heat transfer was important in the transport of heat in the weld pool during both the laser and the EBW. The computed keyhole wall temperatures during EBW at low pressures were lower than those during the LBW at atmospheric pressure for identical heat input.

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During laser-arc hybrid welding, plasma properties affect the welding process and the weld quality. However, hybrid welding plasmas have not been systematically studied. Here we examine electron temperatures, species densities, and electrical conductivity for laser, arc, and laser-arc hybrid welding using optical emission spectroscopy. The effects of arc currents and heat source separation distances were examined because these parameters significantly affect weld quality. Time-average plasma electron temperatures, electron and ion densities, electrical conductivity, and arc stability decrease with increasing heat source separation distance during hybrid welding. Heat source separation distance affects these properties more significantly than the arc current within the range of currents considered. Improved arc stability and higher electrical conductivity of the hybrid welding plasma result from increased heat flux, electron temperatures, electron density, and metal vapor concentrations relative to arc or laser welding.

The electrical resistivity and magnetic susceptibility of allotropically pure P-Ce and y-Ce and some two-phase (a+P or P+ y} samples, which were predominantly P-Ce, were measured from 2 to 300 K. Because P-Ce transforms to a-Ce between 15 and 50 K, several unusual experimental techniques were used to obtain reliable data. Our results show that the electrical resistivity of P-Ce remains unusually large, & 50 ILLA cm down to 40 K and below this temperature it drops an order of magnitude. The magnetic-susceptibility data show that P-Ce obeys the Curie-gneiss law down to near its Neel temperature, -12.5 K. Low-field susceptibility data, & 800 Oe, show a Neel temperature at 12.5 K and that the magnetic susceptibility near the ordering temperatures decreases with increasing field. X-ray metallographic data indicate that when P-Ce transforms to a-Ce the initial growth occurs at the surface and grows inward. The unusual temperature dependence of the electrical resistivity of P-Ce could not be explained by several existing models pand-spin fluctuation or crystalline field) which have been used to explain large increases in the resistivity for other materials. However, a recently developed model based on Kondo scattering which is quenched by magnetic ordering appears to account for the observed results.