Interface phenomena in (super)hard nitride nanocomposites: from coatings to bulk materials

Abstract

Mechanical properties of nanocomposites usually surpass the mechanical properties of their micro-structured and single-crystalline counterparts. This is mainly due to an extremely high density of internal interfaces in nanocomposites like grain, crystallite and phase boundaries. When compared to diamond, carbides and borides, nitrides are of interest because of their high temperature oxidation resistance and compatibility with iron containing alloys. This tutorial review classifies the contributions of various internal interfaces to the hardness of the nanocomposites, and appreciates the outstanding role of partially coherent phase boundaries in the hardness enhancement. With selected examples of transition metal nitrides containing aluminium and silicon as well as of boron nitrides, it is explained how the nanocomposites with partially coherent phase boundaries and thus with enhanced hardness can be synthesised. As the possible ways of the formation of coherent phase boundaries, the local epitaxial growth of phases with limited mutual solubility, the production of supersaturated solid solutions followed by the segregation of elements during the spinodal decomposition and the incomplete phase transformation are discussed. The most important techniques, used for synthesis of nitride nanocomposites, like CVD, PVD, precursor-based methods, mechanical alloying and high-pressure-high-temperature synthesis are briefly reviewed. Besides, a short overview on hardness definitions and hardness measurements is included.

Structural and mechanical evolution of reactively and non-reactively sputtered Zr–Al–N thin films during annealing

“…As XRD suggests only for a single-phase face centred cubic ZrN based structure, Fig. 1, we refer to our coatings with r-Zr 0.66 Al 0.34 N and nr-Zr 0.68 Al 0.32 N. The XRD peaks of the reactively sputtered coatings are broader having an integral width Γ 200 of the (200) peak of ~ 2.7°, whereas Γ 200 ~ 1.3° for nr-Zr 0.68 Al 0.32 N. In combination with the higher background level, the broad XRD peaks for r-Zr 0.66 Al 0.34 N suggest for the presence of an additional phase, similar to the observations made for Ti 1 − x Al x N [52]. A comparable XRD pattern with an increased background level is also presented for single-phase face centred cubic Zr 1 − x Al x N with x = 0.15, 0.35, 0.38, and 0.43 [33,49].…”

Understanding hardness evolution of Zr–Si–N nanocomposite coatings via investigating their deformation behaviors

“…Transition metal nitrides are often deposited on the surface of ductile materials to fabricate a thin, yet protective coating against wear and corrosion during operation [1][2][3][4][5]. The mechanical properties such as hardness and adhesion strength are often considered as the principle requirements of the hard coatings, which have been extensively used to improve the lifetime and working efficiency of cutting tools.…”

Phase transformations on nanometre scale

“…One prominent example of the nanostructured materials are multiphase nanocomposites. One way how to prepare multiphase nanocomposites with the particle size of about 10 nm or even smaller is to employ controlled phase transformations on the nanometre scale in order to fragment originally larger particles to the desired size [1,2]. In this contribution, it will be shown how the crystallography in conjunction with X-ray powder diffraction and transmission electron microscopy can help to predict and to understand the phase transformations on nanometre scale and to explain the effect of the local strain fields in nanocomposites on the thermodynamic stability of the participating phases and/or on the stabilisation of metastable phases [3].…”