Metal Ti–Cr alloy powders nitriding under atmospheric pressure by microwave heating

In the presence of microwave radiation, nitridation of metallic titanium in air becomes possible instead of the thermodynamically favorable oxidation. In this study, β-Ti–Cr alloy powders were synthesized to these nitrides by microwaves, using the fact that a solid solution of β-Ti–Cr is similar to pure β-Ti in terms of the electronic structure. The alloy powders were heated to a temperature of 1000 °C or higher by microwaves at a high oxygen partial pressure (PO2=2×10-1atm), and were analyzed by both wavelength-dispersive X-ray spectroscopy and X-ray diffraction. Nitridation was achieved for the β-Ti–Cr alloy, but not for a Ti–Fe alloy. The results can be explained using the average energy of electrons in 3d orbitals. Furthermore, multilayer structures made of nitrides and oxides were observed. The powders had a temperature–space distribution in the microwave field and the multi-layer structures corresponded to this distribution.

► Ti–Cr alloy powder compacts are different from that of pure Ti in heating behavior.
► Microwaves nitride Ti–Cr alloy instead of thermodynamically preferable oxidation.
► The powder compacts shows multilayer structures made of nitrides and oxides.
► The nitriding can be explained by average energy of 3d orbital (Md numbers).