Interatomic Interaction Modulated NbMoTaW Refractory High-entropy Alloy Thin Films

Multicomponent alloys in near-equal molar ratios are considered to be disordered solid solutions with simple crystal structures,the local structure is the key factor that determines the performance.High-entropy alloy films have more uniform composition and disordered structure,which is conducive to the study of modulating the properties of high entropy alloys through the local structural changes caused only by the interactions between atoms.The weak interaction component V and strong interaction component O were selected to modulate the local structure in this paper.A series of(NbMoTaW)_100-xV_x(x=0?30.5,at%)and(NbMoTaWV)_100-xO_x(x=0?53.63,at%)thin films were prepared by radio frequency magnetron sputtering.Their microstructure/composition,mechanical properties,electrical conductivities and resistivity-temperature behavior were systematically studied.Furtherly,in accordance with the“cluster-plus-glue-atom”model,the present paper interpreted the local structure evolution with the film components changing.Adding weak interaction component V does not change the body-centered-cubic(BCC)structure of the films,whereas the hardness,elastic modulus,and the ratio of hardness to elastic modulus(H/E)show a tendency of slight increase first and then gradual decrease.The maximum value occurs in the(NbMoTaW)_91.5V_8.5film,exhibiting 13.62±1.36GPa,234.35±13.85GPa,and 0.058,respectively.The(NbMoTaW)_100-xV_x films possess a relative low resistivity(52.92?84.84??·cm),which can stay stable from room temperature to nearly 900K.The excellent thermal stability of the films is originate form the enthalpy interaction,and the high stability of the refractory element itself.Combining with the theoretical calculation and experimental measurement,the presence of V brings two-fold effects.The main one is the enhancement of the microstructural homogeneity by increasing the disorder degree.The other is weakening interatomic interactions as well as enabling the films more unstable due to the increasing system energy.An entropy-stabilized refractory metal oxide film can be produced by adding strong interaction component O.With increasing the oxygen content,the films gradually transform from BCC solid solutions to the amorphous oxides.The hardness and modulus of the thin films increase first and then decrease,reaching a maximum of 15.5 GPa and 215.6 GPa,respectively.The room temperature resistivity can be tuned in the range of 55?1.26×10⁶??·cm.Resistivity-temperature behavior of the films have significant differences,films with low oxygen contents show good resistivity stability in a wide temperature range,however the stability decreases rapidly with the increase of oxygen content.Simultaneously,the conductive mechanism gradually changes from the metallic type to amorphous oxide semiconductor type(a near TiO₂ type ionic crystal type).This study demonstrates that the local structure and properties of thin films can not only be modulated by adding weakly interacting elements to a small extent,but also can be modulated in a large range by adding strong interacting elements,which can cover metal solid solution to amorphous oxide semiconductor.Providing a new means for controlling the structure-property relationship of advanced materials on the basis of atomic configuration.The refractory high entropy film and its oxide have excellent mechanical properties and high temperature resistance,and their properties can be adjusted in a wide range,which is conducive to high temperature bearing structures,micro-electronic devices,heating protection systems,diffusion barriers and film resistors and other applications of high temperature resistance,high hardness and wear resistance.