The thermodynamic assessment of the Ti–Si–N system and the interfacial reaction analysis

Nanosized and Nanostructured Hard and Superhard Materials and Coatings

“…The valence charge density difference (VCDD) of the TiN(111)/1ML-SiN/TiN (111) interface is shown in Figure 6.6. Indeed, upon tensile loading (which is relevant to crack growth and brittle fraction) these bonds will break, as shown in Figure 6.7b and c. A similar behavior was identified for deformation in shear (which is relevant for plastic deformation) for (111), (110) and the distorted Valence charge density distribution just before (b) and after (c) the tensile de-cohesion instability. It can be seen clearly that the VCDD on both the nitrogen and silicon atoms of the SiN interfacial layer is higher than that on nitrogen and titanium in TiN, respectively.…”

“…Thus, it could be shown that, by analogy to the studies of Hao et al on the Si 3 N 4 -like interfaces, the SiN interface is strengthened by valence charge transfer from the metallic TiN because of the higher electronegativity of Si as compared to Ti [56,57]. Whereas, the (111) and (110) interfaces are stable with respect to a finite displacement of about 3%, the (001) interface was unstable but could be stabilized by a distortion of the Si-atoms by about 12% in the [110] direction [57], in agreement with the later studies of Marten et al, who examined the dynamical stability within the harmonic approximation [59]. These results were also in agreement with the report that bulk fcc-SiN, as well as the 1 ML fcc-SiN (001) interface in its fully symmetric configuration, were dynamically unstable [60].…”

“…It must be remembered that pure and stoichiometric TiN and Si 3 N 4 nitrides are strongly immiscible (see e.g., Refs [48,109,110]) and that, according to the diffusion coefficients reported by Hultman [24], the diffusion time in a clean Ti-Si-N system at a distance of 5 nm and temperature of 550 C is on the order of 100 s [93]. Therefore, a stoichiometric and clean Ti 1Àx Si x N y solid solution must decompose to nc-TiN and a-Si 3 N 4 (Si 3 N 4 is amorphous below about 1100 C).…”

Prediction of the stability of theMn+1AXnphases from first principles

“…This was achieved through the use of the experimentally determined ternary phase diagrams in the literature. [50][51][52][53] The position of the M n+1 AX n alloys in the ternary diagram was determined and the competing phases identified from the nearby stable points on the diagram. The stoichiometry of the competing phases and the M n+1 AX n alloys was then used to derive the balance equations.…”

Study of the nitridation process of TiSi2 powder

“…The active fillers are aimed at reducing the volume shrinkage resulting from the pyrolytic conversion of polymer to ceramic [8][9]. Titanium disilicide (d=4.01g/cc) is identified as interesting active filler: under nitrogen atmosphere, the nitridation of TiSi 2 starts in a temperature range around 1000°C to form TiN (d=5.43g/cc) and Si 3 N 4 (d=3.19g/cc) [10]. This reaction generates a 57% volume increase.…”