Laser Beam Welding of a Low Density Refractory High Entropy Alloy

The effect of laser beam welding on the structure and properties of a Ti1.89NbCrV0.56 refractory high entropy alloy was studied. In particular, the effect of different pre-heating temperatures was examined. Due to the low ductility of the material, laser beam welding at room temperature resulted in the formations of hot cracks. Sound butt joints without cracks were produced using pre-heating to T >= 600 degrees C. In the initial as-cast condition, the alloy consisted of coarse bcc grains with a small amount of lens-shaped C15 Laves phase particles. A columnar microstructure was formed in the welds; the thickness of the grains increased with the temperature of pre-heating before welding. The Laves phase particles were formed in the seams after welding at 600 degrees C or 800 degrees C, however, these particles were not observed after welding at room temperature or at 400 degrees C. Soaking at elevated temperatures did not change the microstructure of the base material considerably, however, "additional" small Laves particles formed at 600 degrees C or 800 degrees C. Tensile test of welded specimens performed at 750 degrees C resulted in the fracture of the base material because of the higher hardness of the welds. The latter can be associated with the bcc grains refinement in the seams.