Nitridation of Ti/Nb alloys and solid-state properties of delta-(Ti,Nb)N

The formation of microstructures and diffusion layers in the Ti-Nb-N system was investigated by annealing compact Ti/Nb alloys (0-100 at% Ti) in a high-purity nitrogen atmosphere (3 and 30 bar N2) in the temperature range 1300-1600 degrees C. The alloy starting material was in the form of wedge-type samples as well as in the form of plane sheets. After nitridation all samples showed a yellow colour which is characteristic for the fee delta-(Ti,Nb)N phase, the layer growth rate of which was a minimum at 75 at% Ti. The nitride layer as well as the precipitates were rich in Ti whereas in the beta alloy an Nb increase was observed. During nitridation needles with different length and width grew from the inner layer boundary into the original alloy. Electron probe microanalysis (EPMA) was performed to gain insight into the time evolution of the diffusion profiles of Ti, Nb and N. Homogeneous plane-sheet samples were used for measurements of the microhardness, the superconducting transition temperature and the lattice parameter of delta-(Ti,Nb)N.