The composite processing technology of Nb-Ti superconducting materials
Superconducting materials are widely used in many fields due to their unique properties, such as zero electrical resistance, high temperature superconductivity and so on. Among them, Nb-Ti alloys are the most widely used and widely studied. Nb-Ti alloy is extremely anisotropic in the low temperature state and its electrical and mechanical properties are closely related to its microstructure transformation during the processing. This article introduces the Nb-Ti alloy composite processing technology from the aspects of powder metallurgy, hot deformation and cold deformation processing, and analyzes the effect of microstructure transformation on the mechanical properties of Nb-Ti alloy.
Nb-Ti alloy can combine high temperature superconducting properties and mechanical properties. In order to obtain such combination, different composite processing methods need to be applied to obtain different microstructures.Among them, powder metallurgy processing is the main method of Nb-Ti alloy processing. Powder metallurgy mainly includes mechanical alloying, hot pressing sintering and spark plasma sintering (SPS). Mechanical alloying can significantly improve the microstructure of Nb-Ti alloy. The particle size can be reduced to nanometer level. Hot pressing sintering can obtain a relatively dense microstructure but the particle size and distribution are not uniform.The SPS method can obtain nanoscale Nb-Ti alloy with good electrical and magnetic properties, and it can also improve mechanical properties through double-sintering process, which is mainly due to the uniformity of particles and the greatly improved grain boundary strength.
In order to obtain higher strength of Nb-Ti alloy, hot deformation and cold deformation processing are usually used to obtain ultrafine and high microstructure structure through multi-directional deformation.Hot deformation can obtain a finer microstructure than that obtained by cold deformation, but the problem of axial contraction often occurs.Cold deformation has higher deformability than hot deformation and can obtain semi-globular or ultrafine recrystallized grains.As a result of cold deformation, the internal stress of Nb-Ti alloy is reduced, so that the strength is further improved, and the Youngs modulus is also enhanced.
The transformation of the microstructure of Nb-Ti alloy during composite processing mainly affects the mechanical properties.The microstructure of the Nb-Ti alloy changes in response to temperature, strain, strain frequency and strain rate during hot and cold deformation processing.The grain size and distribution of the alloy will be fine, so that the Youngs modulus, yield strength, ultimate strength and other mechanical properties are improved.However, the intergranular separation and porosity will increase significantly as the strain increase, resulting in a decrease of the strength properties.At the same time, due to the difference of strain in different directions, the mechanical properties are not uniform.
In short, Nb-Ti alloy is an important superconductor material, and its electrical and magnetic properties and mechanical properties are closely related to its microstructure. In order to obtain the material with highest performance, different composite processing methods, such as powder metallurgy, hot deformation and cold deformation, must be used.The understanding of the relationship between microstructure and mechanical properties is the key to obtaining Nb-Ti alloy superconducting material with higher performance.
