Solubility of tungsten in zirconium diboride solid solution

Zirconium diboride (ZrB2) is arguably one of the most important ceramic materials for applications involving extreme high temperatures and oxidizing environments such as those encountered in re-entry vehicles and hypersonic aircraft, among others. Accordingly, enhancing the creep resistance of ZrB2 is of critical importance. A viable approach to achieve the latter is through the addition of substitutional atoms such as tungsten. In this work, using a combination of quantum mechanics based first-principles simulations and thermodynamic modeling; we present the essential elements of the W-ZrB2 phase diagram to enable the design of enhanced creep-resistant ultra-high temperature ZrB2-alloys. In the course of the assessment, we estimate the Gibbs free energy of WB2, nonexistent in the literature to date, and based on the developed phase diagram, conclude that the solubility of tungsten in ZrB2 does not occur below ∼1380°C and that temperatures above ∼1700°C are needed to dissolve 1mol% of W in ZrB2.