Refractory High Entropy Alloys (RHEAs) have emerged as potential substitutes for the leading Ni-Superalloys, showcasing remarkable properties in elevated-temperature service conditions. The MoNbTaW system, in particular, has garnered attention for its exceptional yield strength surpassing 500 MPa at 1200 °C. Nevertheless, these alloys manifest brittle behaviour at ambient temperatures, thereby constraining their applicability.

The development of RHEAs faces several obstacles, such as alloy design and industrialisation, that must be overcome for further advancements. To tackle these challenges head-on, researchers have explored the use of high-throughput screening alloy design strategies through the combination of computational and experimental methods. Therefore, in-situ alloying of vanadium (V) and titanium (Ti) by Laser Direct Energy Deposition (L-DED) assisted by thermodynamic simulations (CALPHAD using Thermo-Calc) has been explored to accelerate the screening of promising compositions. This approach enabled the rapid production of compositionally graded parts, expediting the overall screening process.

Firstly, the effect of process parameters, mainly the laser power, was assessed on the produced parts. Subsequently, room temperature assessments of the quaternary system were conducted through scanning electron microscopy with energy dispersive spectroscopy (SEM/EDS), electron backscatter diffraction (EBSD), X-ray diffraction (XRD) characterisation, and Vickers microhardness measurements to evaluate the impact of V and Ti in both microstructure and mechanical properties. Regarding the laser power effect, it is observed that with the increase of such parameter the compositional gradient of the produced parts is lost due to the overall structure homogenization. Through the in-situ alloying strategy, it was observed that both V and Ti maintain the single-phase BCC structure of the MoNbTaW alloy, although some interdendritic segregation is present. Additionally, increasing the amount of both elements a hardness increase is observed, which is associated with a solid solution strengthening. Because the formation of second phases is avoided it is assumed that the ductility is also slightly increased. Based on these results, it was attainable to optimise the L-DED processing of RHEAs and expand the practical knowledge of RHEAs, thus accelerating the potential industrialisation of these alloys.