Plasma Assist Gas Alloying And Mechanical Properties Of TiZrHfNb Series Multi-principal Alloy

As a new type of high-strength,high-temperature-resistant and high-temperature oxidation resistant material,refractory high-entropy alloys are expected to replace traditional high-temperature alloys,but it has low plasticity at room temperature and poor deformation limit,most refractory high-entropy alloys need to be hot-worked forming.however,high deformation temperature,high flow stress,and some other shortcomings in hot processing limit the application of refractory high-entropy alloys.Hydrogen,as a temporary alloying element,can improve the hot workability of titanium alloys,titanium aluminum alloys and other materials,which has received widespread attention in recent years.In this paper,the plasma assisted gas alloying method is adopted,that is,a mixed atmosphere of H₂/Ar is introduced into the smelting atmosphere.The arc ionization causes the decomposition of hydrogen molecules,and the hydrogen enters the TiZrHfNbMo refractory high-entropy alloy.The effects of hydrogen on the microstructure and properties of TiZrHfNbMo refractory high-entropy alloy were studied.The results show that:?1?TiZrHfNbMo refractory high-entropy alloys under different hydrogen contents are composed of a single BCC phase,and the amount of hydrogen does not change the crystal structure and preferred orientation of the alloy.?2?The microstructures of TiZrHfNbMo refractory high-entropy alloys before and after hydrogenation are all typical dendritic morphologies.The solid solution of H significantly reduces the number of secondary and multiple dendrites and refines the dendrites.?3?Under high temperature deformation conditions,the structure of TiZrHfNbMo refractory high-entropy alloy before and after hydrogenation decreases with the decrease of strain rate and the increase of deformation temperature,that is,with the increase of Z,the structure becomes more uniform,and the degree of dynamic recrystallization is high,so high temperature rheological resistance is lower.?4?The thermal deformation behavior of TiZrHfNbMo refractory high-entropy alloy at 1100-1250?and0.001-0.5s^-1 before and after hydrogenation was studied.The flow stress decreases as the deformation temperature increased and the strain rate decreased?Z parameter increased?.The deformation activation energy before and after hydrogen was 326.111kJ/mol and 286.277kJ/mol.The Arrhenius constitutive equation of TiZrHfNbMo refractory high-entropy alloy before and after hydrogenation is deduced.?5?Processing map of TiZrHfNbMo refractory high-entropy alloy without hydrogen was established at?=0.6.In this experiment,the optimal deformation temperature is 1110-1170?,the strain rate is 10^-3-10^-2.5s^-1;the corresponding structure is relatively uniform and the grain size is moderate,and no instability such as cracks and holes occurs.?6?The peak stress of TiZrHfNbMo refractory high-entropy alloy with hydrogen shows strain rate sensitivity.The corresponding peak stress increases at larger strain rates of 0.5 and0.1s^-1,which is due to the solid solution strengthening of H,microstructures appear uneven.When the lower strain rate at 0.01s^-1,the peak stress greatly reduced,and the drop in high-temperature flow stress can reach to 20%.At the lowest strain rate of 0.001s^-1,the stress value is very low,so the change is not obvious.?7?Analyze the reason of peak stress softening at a strain rate of 0.01s^-1,the grain size and area ratio of dynamic recrystallization under hydrogen are significantly higher than those without hydrogen,which proves that H promotes the formation of dynamic recrystallization and high-temperature rheological structure.Under the conditions of low strain rate of 0.01 and 0.001s^-1,a precipitated phase of?m order was found at the deformation band,and the composition of the precipitated phase was similar to that of the matrix.The existence of both makes the peak softening of high-entropy alloys with H contents at low strain rates.?8?The deformation mechanism of TiZrHfNbMo refractory high-entropy alloy before and after hydrogen is mainly discontinuous dynamic recrystallization,the preferred orientation is<001>or<111>,and the orientation is more prominent after hydrogen.