Jianchuan Wang

Effects of pressure and vibration on the thermal decomposition of cubic Ti1-xAlxN, Ti1-xZrxN, and Zr1-xAlxN coatings: a first-principles study

Thermodynamic properties as well as the miscibility gap (binodal) and spinodal decompositions of the cubic Ti1-xAlxN, Ti1-xZrxN, and Zr1-xAlxN coating alloys have been computed using first-principles calculations. Herein, the cluster expansion method and especially the special quasirandom structure are employed to describe the disordered alloys. The effects of pressure and lattice vibration on the miscibility gaps and spinodal decompositions of the above alloys have been investigated by means of Helmholtz free energy with the vibrational contribution depicted with the Debye-Grüneisen model. It is found that the application of hydrostatic pressure promotes the isostructural decomposition of Ti1-xAlxN, Ti1-xZrxN, and Zr1-xAlxN alloys, whereas the vibrational contribution decreases the consolute temperature of the phase separation. Our results indicate that the improved age-hardening behavior of cubic Ti1-xAlxN coatings with the addition of Zr arises from the enlarged composition range of binodal and spinodal curves at specified temperatures. Our results are in good agreement with the available experimental data and provide a useful insight into the investigation of age-hardening and characterization of Ti–Al–Zr–N-based coatings for high-temperature applications.

Diffusion of hydrogen vacancy in Na3AlH6

We perform first-principles calculations to investigate neutral and charged H vacancies dynamics involving vacancy formation and diffusion in Na3AlH6. We find that the activation barrier for local diffusion (diffusion within AlH5 unit) is smaller than that of nonlocal diffusion (diffusion between AlH6 and AlH5 units) for all types of H vacancies; H diffusion in Na3AlH6 is dominated by mobility of positively charged H vacancies. Furthermore, our results confirm that the observed highly mobile species by anelastic spectroscopy measurements is probably the positively charged H vacancies in the form of local diffusion.

A New Relationship Among Self- and Impurity Diffusion Coefficients in Binary Solution Phases

A new relationship among self- and impurity diffusion coefficients has been proposed for binary solution phases and verified via 30 solid solutions. In terms of this model, one impurity diffusion coefficient in a binary phase can be predicted once the other three diffusion coefficients are available. The application of the present model is exemplified in the Al-Mg system.