A Nitride-Reinforced NbMoTaWHfN Refractory High-Entropy Alloy: Unlocking Potential for Ultra-High-Temperature Engineering Applications

Key Highlights :

1. A new generation of refractory alloys with excellent high-temperature performance is urgently demanded.

2. Traditional superalloys can hardly fulfill the temperature demands.

3. Mainly composed of refractory metal elements, refractory high-entropy alloys (RHEAs) exhibit enhanced strength at temperatures above 1,200° C, causing them to attract a great deal of attention.

4. If a large number of solute atoms gather around dislocations, they will hinder the movement of dislocations.

5. When a moving dislocation encounters the second phase, a dislocation ring will form, increasing the required external force, which provides the deformation force.

6. Besides, high-temperature strength is generally related to softening temperature.

7. The softening temperature for an alloy is approximately 0.6T m (where the melting temperature , T m , is given in K).

8. Unfortunately, little has been reported about alloys showing promising engineering application strengths at 1,800° C or above thus far.

9. Considering the high-temperature strength of the NbMoTaWHf RHEA and the excellent thermal stability of nitrides, the secondary strengthening of nitrides on a NbMoTaWHf-base alloy seems to be an efficient approach to realize the "win–win" situation of high temperature and high strength at ultra-high temperatures.

10. A research team at the Defense Innovation Institute of China led by Professor Xiubing Liang has designed a nitride-reinforced NbMoTaWHfN refractory high-entropy alloy, which shows extremely high compressive yield strengths at temperatures between 1,000 and 1,800° C.

     As the service temperature of hot-ends in aero-engines, gas turbines, and nuclear power plants is reaching 1800 °C or even higher, traditional superalloys can hardly fulfill the temperature demands. Refractory high-entropy alloys (RHEAs) composed of refractory metal elements have been gaining attention due to their enhanced strength at temperatures above 1,200° C. A research team at the Defense Innovation Institute of China has designed a nitride-reinforced NbMoTaWHfN refractory high-entropy alloy, which shows extremely high compressive yield strengths at temperatures between 1,000 and 1,800° C. The findings of their study have been published in Engineering.

     The NbMoTaW(HfN)x alloys, with x = 0, 0.3, 0.7, and 1, consist of multiple phases of body-centered cubic (BCC), hafnium nitride (HfN), or multicomponent nitride (MN) phases. As the x contents increase, the grain size becomes smaller, and the strength gradually increases. The compressive yield strengths of the NbMoTaWHfN RHEA at ambient temperature, 1,000° C, 1,400° C, and 1,800° C were found to be 1,682 MPa, 1,192 MPa, 792 MPa, and 288 MPa, respectively. This strength exceeds the high temperature and strength of most known alloys, including high-entropy alloys, refractory metals, and superalloys.

     The phase formation mechanism of the HfN and MN phases and the strengthening mechanism of NbMoTaW(HfN)x at ambient and elevated temperatures were studied. The HfN phase has a significant effect on the alloy's high-temperature strength due to its high structural stability and sluggish grain coarsening. The superior mechanical properties of the NbMoTaWHfN RHEA compared with various alloys endow it with potential for wide-ranging engineering applications at ultra-high temperatures.

     The development of this nitride-reinforced refractory high-entropy alloy is an important breakthrough in the field of engineering at ultra-high temperatures. It provides a “win–win” situation of high temperature and high strength, thus unlocking potential applications for aero-engines, gas turbines, and nuclear power plants. The research team is now carrying out further studies to further optimize the mechanical properties of the alloy and extend its application scope.

Continue Reading at Source : phys