Study On Nanostructure Stability Of Cu/Nb Immiscible Thin Films

Extreme service environments such as nuclear power impose increasingly stringent requirements on materials.Nanocrystallization of structures is an effective way to improve the performance of materials.However,the stability of nanomaterials is always a technical challenge that limits its application.The immiscible material system is considered to have the potential to obtain a thermally stable nanomaterial system due to its thermodynamic characteristics.Cu-Nb is a typical immiscible system.In this paper,Cu/Nb nano-multilayer composite films were prepared by Modulated Pulsed Power Magnetron Sputtering（MPPMS）and Pulsed DC magnetron sputtering（PDCMS）.The changes of film structure and mechanical properties of Cu/Nb nano-multilayer composite film before and after vacuum annealing were compared.Study on the thermal stability of Cu/Nb nano-multilayer composite film structure.The main conclusions were as follows:1)When the substrate is in floating state,maintain the average power of the PDCMS at 1kW,and change the pulse on time(τ_on)of the MPPMS strong ionization phase from 7μs to 11μs,the average power increased from 1.0 kW to 2.4 kW,and the Nb content increased from29.76 at.%to 43.55 at.%,the film exhibits characteristic diffraction peak of Nb（110）and Cu（111）,forming Nb and Cu broaden peaks between the two peaks and separating whenτ_on is 11μs.All films exhibit a certain layered structure and have a distinct columnar crystal growth structure.In addition,with the increase ofτ_on,the film hardness increased from 6.3 GPa to 8.2GPa,and the residual stress exhibited tensile stress and increased from 129.8 MPa to 183.3MPa.2)Substrate applied-50 V bias,maintain the average power of the PDCMS at 1 kW,and change the pulse on time(τ_on)of the MPPMS strong ionization phase from 7μs to 11μs,Its discharge characteristics are consistent with those under floating.Nb content increased from 27.89 at.%to 38.33 at.%,the film exhibits characteristic diffraction peak of Nb（110）and Cu（111）,forming Nb and Cu broaden peaks between the two peaks and separating whenτ_on is 11μs.All the films showed a distinct layered structure,and the columnar crystal growth structure gradually changed into a glass-like state.In addition,with the increase ofτ_on,the film hardness increased from 6.86 GPa to 8.98 GPa,and the residual stress exhibited compressive stress and was-39.8 MPa.Increase to-413.5 MPa.3)Because of the better performance of the sample prepared under bias conditions,the stability and mechanical properties of the structure were further studied by annealing experiments.Film with a bias of-50 V and aτ_on of 8μs is annealed at 200°C,300°C,and400°C.The microstructure,grain size,two-phase distribution,hardness and Young’s modulus did not change much,indicating that the Cu/Nb nano-multilayer composite film prepared under this condition has high thermal stability.However,after the annealing of the film with a bias voltage ofτ_on of 11μs,the microstructure changed which Nb and Cu produce two-phase segregation.The grain size does not increase with the increase of the annealing temperature,and the hardness and Young’s modulus of the film did not change greatly.The above research results show that the Cu/Nb nano-multilayer composite film with high thermal stability is obtained when the experimental parameters are-50 V bias andτ_on is 8μs.The grain size of the film is nano-sized and exhibits a nano-multilayer structure.After annealing at 400°C for 3 h,its microstructure and mechanical properties can maintain good stability.