Effect Of Melt Hydrogenation On Microstructure And Mechanical Properties Of Refractory TiZrNbHf_0.5Mo_0.5 Matrix High-entropy Alloys

The refractory high-entropy alloys（RHEAs）based on refractory elements have become a hot spot in the aspect of high-temperature structural materials with its unique structures and properties.However,refractory high-entropy alloys has relatively low room-temperature ductility and high density which limited its application prospects.In order to solve the problem of low room temperature ductility of refractory high-entropy alloys and develop new high-plasticity and high-strenhgth refractory high entropy alloys,two hydrogen-containing TiZrNbHf_0.5Mo_0.5 and TiZrNbHf_0.5Mo_0.5C0.2 refractory high entropy alloys were prepared by arc melting with melt hydrogenation process.The effect and mechanism of melt hydrogenation on the microstructure and me chanical properties were investigated.Firstly,the hydrogen-absorbing behavior of two refractory high-entropy alloys are studied.The hydrogen contents in the two alloys increase with the increase of hydrogen partial pressure.The hydrogen element is exist in the alloy in the form of atoms and is evenly distributed.The hydrogenated and unhydrogenated TiZrNbHf_0.5Mo_0.5 refractory high-entropy alloys are composed of a single disordered BCC phase,and the hydrogenated and unhydrogenated TiZrNbHf_0.5Mo_0.5C0.2 refractory high entropy alloys are composed of one matrix BCC phase and the secondary FCC phase.Both the phase of two alloys have very high structural stability with or without hydrogenation.Hydrogen do not change the crystal structure of the two refractory high-entropy alloy,but increase the lattice distortion.Hydrogenation refines the dendrite structure and makes the composition distribution of TiZrNbHf_0.5Mo_0.5 refractory high-entropy alloy more uniform.Hydrogenation increases the composition difference between the matrix and the reinforcing phase of TiZrNbHf_0.5Mo_0.5C0.2 refractory high entropy alloy,and it also produces a small amount of Zr element segregation.Besides,hydrogenation slightly increases the average size of the reinforcing phase.In addition,with the increase of hydrogen partial pressure,the morphology of the reinforcing phases in the alloy changed from uniformly distributed to long clusters.Hydrogenation can significantly improve the plastic of TiZrNbHf_0.5Mo_0.5 refractory high-entropy alloys.The high-strength and high-ductility TiZrNbHf_0.5Mo_0.5 refractory high-entropy alloy can be obtained by melt hydrogenation process.Hydrogenation can reduces the yield strength of TiZrNbHf_0.5Mo_0.5C0.2 refractory high-entropy alloy,but it can slightly increase the peak strength of TiZrNbHf_0.5Mo_0.5C0.2 refractory high-entropy alloy.Besides,melt hydrogenation can slightly reduce the hardness of TiZrNbHf_0.5Mo_0.5 and TiZrNbHf_0.5Mo_0.5C0.2 refractory high-entropy alloys.In addition,melt hydrogenation can effectively increase the strength of TiZrNbHf_0.5Mo_0.5 and TiZrNbHf_0.5Mo_0.5C0.2 refractory high entropy alloys at elevated temperature,while does not change the compressive ductility.And hydrogenation can improve the dynamic recrystallization ability of TiZrNbHf_0.5Mo_0.5 refractory high-entropy alloys after deformation at elevated temperature.The hydrogen induced ductilizastion mechanism of TiZrNbHf_0.5Mo_0.5 refractory high-entropy alloy was studied.When deformation at low compressive strain,crack growth in the region with high density of dislocations is the fracture failure mechanism of unhydrogenation RHEAs.While hydrogenation can reduce the number of cracks and dislocation density of the RHEAs during plastic deformation.And the hindering effect of hydrogen atoms on the formation of supersaturated vacancies during cold deformation and thus delaying vacancy collapse is the ductilizastion mechanism of TiZrNbHf_0.5Mo_0.5 refractory high-entropy alloy.When deformed at relatively high compressive strain,the plastic deformation mechanism of hydrogenated RHEA is shifted to a twin deformation.Hydrogen can induce the formation of twins so that some of the slip systems that were originally in an unfavorable orientation changed to a position that is conduciv e to slippage,thus increasing the plastic deformation ability,thereby realizing the ductilizastion of TiZrNbHf_0.5Mo_0.5 refractory high-entropy alloy.