Titanium niobium alloy is a high-strength, corrosion-resistant, and superconducting special alloy material composed of titanium (Ti) and niobium (Nb).

Composition and Structure

Titanium niobium alloy is mainly composed of two elements, titanium and niobium. The titanium content is generally between 35% and 55%, and the niobium content is between 45% and 65%. The typical NbTi alloy has a titanium content of about 50% (mass fraction). Its main phase structure is the body centered cubic beta phase, and titanium exists in the form of solid solution in the alloy, forming a good solid solution strengthening effect.

Physical and chemical properties

Density: about 5.6-6.0 g/cm ³, slightly higher than pure titanium and pure niobium.

Melting point: about 1600 ℃, the melting point slightly decreases with increasing niobium content.

Conductivity and thermal conductivity: relatively low, but still applicable in specific electronic devices.

Corrosion resistance: It is stable in acidic, alkaline, salt, and seawater environments, and can form a dense oxide film on the surface.

Performance characteristics;

High strength: After heat treatment and processing, the yield strength can reach over 1000 MPa and can withstand high stress.

Good toughness: It still has impact resistance under high strength and is suitable for complex stress conditions.

Superconductivity: It exhibits superconducting properties at low temperatures (8-10 K) and is an important superconducting material widely used in superconducting magnets.

Fatigue resistance: It can maintain stable performance under repeated stress and is not easily broken.

Biocompatibility: Suitable for medical device applications such as implants and surgical instruments.

Niobium titanium alloy superconductors have been widely used among thousands of known superconductors due to their excellent comprehensive properties, and are currently key materials in medical nuclear magnetic resonance and large scientific device superconducting magnets. Niobium titanium alloy is a typical binary alloy composed of transition group elements. In previous studies on high entropy alloy superconductors (TaNb) 0.67 (HfZrTi) 0.33 composed of multiple transition metal elements, it was found that under ultra-high pressure (pressure above one million atmospheres is considered ultra-high pressure, and one million atmospheres equals 100 GPa), the alloy exhibits abnormally stable superconductivity [PNAS 114 (2017) 13144]. Due to niobium and titanium being the main constituent elements of this high entropy alloy, studying the superconductivity of niobium titanium alloy under ultra-high pressure can deepen our understanding of the microscopic mechanism of superconductivity in high entropy alloys.

Recently, associate researcher Guo Jing and researcher Sun Liling from the Institute of Physics of the Chinese Academy of Sciences/State Key Laboratory of Superconductivity of the National Research Center for Condensed Matter Physics, in cooperation with Professor Robert J. Cava of Princeton University, academician Zhang Yuheng, researcher Zhang Changjin and researcher Xi Chuanying from the Institute of Physics of the Chinese Academy of Sciences, and researcher Wang Qiuliang from the Institute of Electrical Engineering of the Chinese Academy of Sciences, have systematically studied the superconductivity of niobium titanium alloy superconductors under ultra-high pressure. It was found that niobium titanium alloy maintains zero resistance superconductivity under pressures up to 261.7 GPa, indicating that niobium titanium alloy is currently the most pressure resistant superconductor known among all superconductors. This pressure is the highest pressure reported for the existence of superconductivity. Under this pressure, the superconducting transition temperature of niobium titanium alloy superconductors increased from 9.6K at normal pressure to 19.1K. The results of the Hefei high magnetic field and high pressure magnetoresistance experiment showed that the critical magnetic field increased from 15.4T to 19T at 211GPa pressure and 1.8K temperature. This is the highest superconducting transition temperature and critical magnetic field found in transition metal element alloy superconductors. The high-pressure XRD experiment results of Shanghai Light Source synchrotron radiation show that there is no crystal structure change at a pressure of 200 GPa, but its volume is compressed by about 43%.

The above study reveals that alloy superconductors composed of transition group metal elements have the characteristic of stable existence under high pressure, which can resist large deformation. This is in sharp contrast to the high sensitivity of the superconductivity of copper oxide and iron-based superconductors to volume changes, and is also significantly different from the behavior of the superconducting transition temperature of post transition group metal element superconductors (full shell of d electrons in valence state) decreasing with volume compression. This achievement was published in Advanced Materials 2019 1807240.

In addition, in terms of experimental technology, this study successfully combines experiments on large scientific devices such as high-voltage extreme conditions, strong magnetic fields, and synchrotron radiation, providing a new example for China to jointly carry out cutting-edge scientific research using its own large scientific devices.