Dissimilar laser welding of HfTaTi refractory medium-entropy alloy to low-entropy Ni-based superalloy

Refractory medium-entropy alloys show considerable potential for high-temperature structural applications owing to their superior mechanical properties and thermal stability. However, dissimilar welding with conventional superalloys remains challenging because of the large physical and chemical mismatches between the two kinds of materials, which tend to promote the formation of brittle phases and degrade joint performance. To overcome these issues, this study employed a Ni–Ti double-layer interlayer to conduct continuous laser welding of HfTaTi and Inconel 718 at powers of 700, 800, and 900 W. The welded joints were characterized using X-ray diffraction, scanning electron microscopy, energy-dispersive spectroscopy, and electron backscatter diffraction. The addition Ni–Ti interlayer can weld refractory high-entropy alloys and nickel-based superalloys together, and the laser power can effectively modulate microstructure and mechanical properties. The fusion zone exhibits irregular coarse grains and abundant second-phase particles, with the average grain size increasing from 1.6 to 2.2 μm as laser power increases. Correspondingly, microhardness increases from 550 ± 10 to 740 ± 10 HV, whereas bending strength decreases from 517 to 311 MPa, a trend attributed to precipitation strengthening associated with second-phase coarsening. There is an inverse relationship between the hardness of the welded joint and its overall bending strength.