Microstructural evolution of nanostructured Ti 0.7 Ni 0.3 N prepared by reactive ball-milling Ujjwal Kumar Bhaskar a , S.K. Pradhan b, * a Department of Physics, Sreegopal Banerjee College, Bagati, Magra, Hooghly 712148, India b Department of Physics, The University of Burdwan, Golapbag, Burdwan 713104, India 1. Introduction Ti-based metal nitrides such as TiN, TiCN, TiAlN, and TiNiN are technologically important because of their extremely high hardness (2500 Vickers’ hardness), stability at high temperatures (3200 K), high chemical inertness, excellent corrosion and wear resistance, high electrical and thermal conductivities, excellent infrared (IR) reflectivity properties. Because of these excellent properties they are being used in a number of applications such as coatings on cutting tools especially for dry and high speed machining for obtaining improved hardness and wear resistance, self-heating crucibles, electronic conductor, diffusion barrier in electronic devices, and optical coatings [1–5]. Ni is one of the promising metals to improve the properties of the TiN x coatings. Zhang et al. and Akbari et al. obtained the nanocomposite TiN films with an amorphous nickel matrix by co-sputtering or dual ion beam sputtering of titanium and nickel targets under nitrogen environment [6–8]. Akbari et al. observed only the TiN crystalline phase. The grain size, which was calculated using the Scherrer equation from the (2 0 0) peaks, decreases from 16 to 4 nm as the Ni content varies from 0 to 22 at.%. A texture evolution of TiN crystallites from (1 1 1) to (2 0 0) was observed when increasing the temperature and the Ni concentration. Nanoindentation tests indicate that the hardness of the coatings is around 40 GPa. The hardness slightly increases with the Ni concentration and the maximum value roughly corresponds to an intergranular distance of 0.5 nm [7]. Stock et al. reported the deposition of the Ti–Ni–N coating by unbalanced reactive magnetron sputtering and characterized the coating materials in terms of their composition, morphology and hardness. The hardness of the Ti–Ni–N coatings with an average nickel content of 8 at.% increases with increasing nitrogen content from 7 to 17 GPa [9]. Todaka et al. [10] produced Ti–Ni–N composite ultra fine particles (UFPs) of size larger than 40 nm by DC plasma jet method and their work focused on the nanostructures and morphologies of the prepared composite UFPs. It is evident from the XRD pattern and HRTEM micrograph of their sample that Ti–Ni–N composition was not obtained in prepared UFPs. However, the room temperature synthesis of single phase nanocrystalline (Ti–Ni)N powder has not been reported yet. The nanocrystalline powder can be consolidated to almost zero porosity bulk specimens for structural applications or may be intended as the sputtering target for thin film deposition on any substrate of specific design. Synthesis of metal nitrides by any conventional methods of preparation requires huge instrumenta- tions and in most of the cases it is very difficult to achieve the required stoichiometric chemical composition through deposition process [6–10]. In contrast, nanocrystalline metal nitride powders with required particle size and chemical composition can be synthesized easily at room temperature in a large scale by Materials Research Bulletin 48 (2013) 3129–3135 A R T I C L E I N F O Article history: Received 11 December 2012 Accepted 25 April 2013 Available online 3 May 2013 Keywords: A. Nitrides A. Nanostructures C. X-ray diffraction D. Microstructure A B S T R A C T Nanocrystalline stoichiometric Ti 0.7 Ni 0.3 N powder has been synthesized by ball-milling the a-Ti (hcp) and Ni (fcc) powders under N 2 gas at room temperature. The a-Ti phase partially transforms to the transient (-Ti phase after 1 h of milling. After 5.5 h of milling, very broad reflections of Ti 0.7 Ni 0.3 N phase is noticed. Complete formation of Ti 0.7 Ni 0.3 N phase is observed after 9 h of milling. Microstructure in terms of lattice imperfections of unmilled and all ball-milled powder mixtures are primarily characterized by analyzing the X-ray powder diffraction patterns employing the Rietveld structure refinement procedure. It clearly reveals the presence of Ti 0.7 Ni 0.3 N phase and inclusion of nitrogen atoms into the a-Ti–Ni matrix on the way to formation of nitride phase. Microstructure of the ball milled nitride powders is also characterized by HRTEM. Particle size of Ti 0.7 Ni 0.3 N phase obtained from XRD method of characterization is 5 nm which is very close to that obtained from HRTEM. ß 2013 Elsevier Ltd. All rights reserved. * Corresponding author. Tel.: +91 3422657800; fax: +91 3422657800. E-mail addresses: skp_bu@yahoo.com, skpbu2012@gmail.com (S.K. Pradhan). Contents lists available at SciVerse ScienceDirect Materials Research Bulletin jo u rn al h om ep age: ww w.els evier.c o m/lo c ate/mat res b u 0025-5408/$ – see front matter ß 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.materresbull.2013.04.061