Production, characterization and weldability of boron doped high entropy alloys by arc melting

High entropy alloy (HEA) is a new generation material group that consists of five or more principal elements in equal or equimolar proportions and can be produced by many different processes and in a ternary phase diagram, the composition lines of HEAs are in the center of diagram unlike the conventional alloys. This situation completely changes the thermodynamic structure, microstructure, type of phases, and thus its physical and mechanical properties of the alloy. In this study, equimolar FeNiCoCrCuBx (x=1, 2, 3, 4, and 5 at. %) HEAs were produced by using conventional/microwave sintering and vacuum arc melting techniques in order to determine the synthesis-structure-property-performance relationships. The effects of boron ratio and sintering method on microstructure and mechanical properties of HEAs were examined, and then the weldability were determined by tungsten inert gas method. As a result of experimental studies, it was determined that all HEAs contain three different face centered cubic (FCC) solid solution phases in dendritic microstructure. The size of spherical and Cu-rich FCC phase increased and the phases agglomerated in inter-dendrite region with the increasing boron addition in conventional sintered HEAs. However, this situation didn't occur in microwave sintered HEAs and more regular and homogeneous microstructure formed. While the three-point bending strength and elongation of microwave sintered HEAs increased with the boron addition rate, this increase up to 3 at. % for conventional sintered HEAs. The highest strength (3150 MPa) and elongation (0.19 mm/mm) values were obtained in 5 at. % boron doped and microwaved sintered HEA. It has been concluded that microwave sintering process before vacuum arc melting creates positive effects on solidification and provides to form more stable phases. According to results of welded HEAs, there is no intermetallic phase were observed in the microstructure, however, the hardness that increased with boron addition decreased the three-point strength. It was concluded that the weldability of HEAs is good and mechanical properties can be improved with convenient heat treatment.