Determining the pattern of direction and distribution of intermetallic phase in the eutectic of the weld material after electron-beam welding of titanium and niobium alloys

Abstract

This paper reports a study whose object was material of the weld. The nature of changes in the microstructure of the weld material, which are caused by changes in the supplied energy, alloying elements and heat removal from the melt area, was investigated. Welding was performed with an electron beam at Uacc=60 kV, Ieb=90 mA, with an elliptical sweep of 3×4 mm. The speed of electron beam movement veb was varied from 7 to 15 mm·s-1. The temperature of the experimental welded samples T0 was varied from 300 K to 673 K. Ti-TiB alloy (a microcomposite alloy with reinforcing TiB fibers) was welded with Ti-TiB alloys, T110, and with niobium. One of the tasks of welding this alloy was to preserve and optimize the structure of this type in the weld. Grinding of boride fibers, loss of their initial orientation, and formation of a dendritic or cellular microstructure was observed in the weld. Using the methods of raster electron microscopy and micro-X-ray spectral analysis, the microstructure of the weld material was investigated and the dimensional characteristics of TiB fibers under different welding conditions were determined. The analysis of changes in the microstructure of the weld material, the average length ᶏ and the thickness ȩ of the boride fibers in the material of the joints made at different velocities of electron beam movement and initial temperatures T0 was carried out. It was established that the growth of the ratio ȩ/ᶏ from 0.04–0.07 to 0.1–0.27 is accompanied by significant changes in the microstructure and the mechanism of formation of eutectic phases. It is shown that the process that determines the formation of the microstructure of the weld material was the eutectic breakdown with the determining influence of the temperature gradient, crystallization rate, supercooling, concentration inhomogeneities, and alloying impurities.