No abstract

No abstract

No abstract

Although TiN and NbN are known to form a complete quasibinary solid solution, it was found that upon nitridation of Ti/Nb or annealing of (Ti,Nb)N alloys the formation of large lamellae occurs, which could be optically distinguished by their golden yellow (Ti-rich) and light yellow (Ti-poor) colour. Such structures at much smaller scales are known to result from spinodal decomposition.In order to characterize the decomposition process, the samples were investigated by wavelength-dispersive electron probe microanalysis. The measurement conditions were adjusted in order to account for the Ti Ll and N Ka overlap, as well as to take an appropriate mass absorption coefficient for N in Nb into consideration. Different acceleration voltage for electron probe microanalysis were applied, which showed that the problem can be overcome by tuning the measurement conditions.

Hardmetals and cermets are alloys with a complicated microstructure of hard-phase constituents such as WC, TiC, TiN,. . . and its combinations. A variety of microstructural constituents can form in these alloys, which define their performance to a large extent. Some hard-phase particles occur in a core-and-rim type structure in which the element concentration differs substantially between the core and the rim. In order to investigate the microstructural features of hardmetals and cermets in detail, model alloys in the form of diffusion couples were prepared. X-ray investigations using state-of-the-art wavelength-dispersive x-ray mapping procedures implemented on a Cameca SX 50 microprobe were performed for all the elements, both light and heavy, occurring in these alloys. Line coincidences were treated by comparison with chemically analysed standards and by subtracting interfering radiations.After 1008 h, W-rich rims were found around Ti-rich cores inside the Ti(C,N) phase of the Ti(C,N)/(Ti,W)C diffusion couple. The thickness of these rims did not change with time. When W was substituted by Mo it was observed that the well-known core-rim structure is built by diffusion of Mo into the Ti(C,N) grains. But with time the Mo diffuses into the core of the Ti(C,N) phase and homogenizes, showing that the core-rim structure is not stable.