Precipitations of W/Cu metallic phases in ZrC in the reactive melt infiltrated ZrC/W composite

Abstract W and Cu rich precipitates have been found in ZrC ceramic grains in the reactive melt infiltrated ZrC/W composite prepared at 1300 °C. The microstructures of the precipitates have been identified using transmission electron microscopy and energy dispersive X-ray spectroscopy. The substantial mechanism of the precipitation was studied by calculating and analyzing the lattice parameters of ZrC (aZrC). First-principles calculations were also used to evaluate the formation energies of carbon sub-stoichiometric ZrC (ZrCx) with substitutional W or Cu atoms. The precipitates in ZrC are identified as W, Cu, CuW3 and Cu5Zr phases. The increase in C/Zr ratio in reaction formed ZrC grains causes the loss of W and Cu solutes in ZrCx, which gives rise to an increment in aZrC. The presence of C vacancies is energetically favorable to the solid dissolutions of W and Cu atoms in ZrCx lattice. Thus, the initial formed ZrCx with a large number of C vacancies has an ability to dissolve W and Cu solutes. And the metallic precipitates in ZrC grains are attributed to the reducing solubility limits of W and Cu with the increasing C content in ZrCx.