*Communication* **Synthesis and Characterization of Mechanically Alloyed Nanostructured (Ti,Cr)C Carbide for Cutting Tools Application**

**Mohsen Mhadhbi <sup>1</sup> and Wojciech Polkowski 2,\***


**\*** Correspondence: wojciech.polkowski@kit.lukasiewicz.gov.pl; Tel.: +48-12-2618-324

**Abstract:** (Ti,Cr)C is a novel additive for high-performance cermets. In this work, a (Ti0.8Cr0.2)C nanostructured solid solution was synthesized via Mechanical Alloying (MA) from the mixture of of Ti, Cr, and C powders. The MA process was carried out at room temperature under argon atmosphere with a duration limited to 20 h. Phase changes and microstructure evolution of the powders during the MA process were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM) techniques. The results of XRD analysis demonstrated the synthesis of (Ti,Cr)C solid solution with a crystallite size of about 10 nm that were micro-strained to about 1.34%. The crystallite size displays a decreasing trend with increasing milling time. The results of direct observations of structural features by TEM method in 20 h MAed samples shows a good agreement with the results from the XRD analyses.

**Keywords:** Nano (Ti,Cr)C powder; mechanical alloying (MA); nanostructure; X-ray diffraction

#### **Citation:** Mhadhbi, M.;

Polkowski, W. Synthesis and Characterization of Mechanically Alloyed Nanostructured (Ti,Cr)C Carbide for Cutting Tools Application. *Crystals* **2022**, *12*, 1280. https://doi.org/10.3390/ cryst12091280

Academic Editor: Umberto Prisco

Received: 16 August 2022 Accepted: 7 September 2022 Published: 9 September 2022

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#### **1. Introduction**

Titanium carbide (TiC) is widely used in industrial applications as a hard coating to protect the surface of cutting tools from wear and erosion, resulting in an extended tool life [1]. It exhibits high strength, high hardness, good wear resistance, high melting point, high chemical stability, and low friction coefficient [2–5]. In particular, nanosized TiC particles are considered as promising microstructural modifiers and mechanical strengtheners for particle dispersed composite alloys, since fine TiC dispersoids in the metallic matrix improve the overall properties of the materials without an adverse effect on their ductility or toughness [6,7].

So far, several methods have been used to prepare nanostructured carbides including a carbothermal reduction [8], mechanical alloying (MA) [9], spark plasma sintering (SPS) [10], chemical vapor deposition (CVD) [11], etc. Among the aforementioned techniques, the MA is an easy and cost-efficient route usually used to prepare nanostructured materials, and especially for manufacturing composite powders [12].

As described in literature reports, the main idea behind using a (Ti,*M*)C (*M* = transition refractory metal) solid solution instead of TiC is to improve the toughness of cermets. Park and Kang [13] have synthesized nanocrystalline (Ti1-xWx)C solid solutions, with a homogenous microstructure and improved properties by the SPS process. Kim et al. [14] fabricated homogeneous (Ti,W)C nanocomposite powders by a high-energy ball milling of a mixture of Ti, W, and C powders. The obtained nanopowders were then SPSed to receive fully densified sinters having a uniform microstructure with a mean grain size of 500 nm. Kwon et al. [15] prepared (Ti,V)C solid solution powders by the MA of Ti-V alloy and graphite powder mixture. The MA process was carried out in a high-energy planetary ball mill for up to 20 h under an argon atmosphere. Additionally, Bandyopadhyay et al. [16] investigated the effect of Ti substitution by W on the microstructure of the Ti0.9W0.1C carbide. They reported that TiWC alloy was formed after 50 min of milling and a fully

nanocrystalline single phase cubic Ti0.9W0.1C compound with a particle size of 11 nm was formed after 8 h of milling. Hence, the effect of ball milling on microstructural change of (Ti,W)C solid solution was experimentally studied by Yang et al. [17]. They found that with increasing milling time up to 108 h, the initial crystallite size decreased from 38.6 to 19.2 nm. Analogously, Dutta et al. [18] reported the formation of Ti0.9Al0.1C nano-carbide after 3 h of milling. They found that that the results of crystal structure examinations obtained by TEM technique are in a good agreement with those derived from the XRD measurements. Wang et al. [19] also produced a (Ti, Mo)C carbide reinforced Fe-based surface composite coating by the laser cladding technique. It has been concluded that (Ti, Mo)C particles with the FCC structure and various shapes are obtained after the solidification. Recently, Yildiz et al. [20] prepared via the SPS a novel multi-component (Ti,Zr,Hf,W)C ceramic with a nano-hardness of 32.7 GPa and a fracture toughness of 5 MPa m1/2. Recently, Vorotilo et al. [21] proposed that a solid solution (Ti,Cr)C, while retaining the main advantages of TiC, possesses higher oxidation resistance owing to the formation of Cr2O3. The (Ti,Cr)C cermets have been produced by a combustion synthesis driven by the Self-propagated High Temperature Synthesis (SHS) [21] or by High-Velocity Air Plasma Spraying [22]. However, to our best knowledge, there are no available reports on the MA synthesis of this type of solid solution-based cermet. Therefore, by taking into account a documented feasibility of the SPS process in a fabrication of high performance cermets, as well as a high impact of the batch powders on the resulted properties of final sinters; the main goal of our this work is to obtain a (Ti0.8C0.2)C composite powder with a suitable particle size that can be employed in the SPS process. Specifically, we are showing for the first time the results of systematic studies on the effect of milling time on the structural evolution of a novel mechanically alloyed (Ti0.8Cr0.2)C powders.
