Development of multicomponent hybrid powders based on titanium and niobium carbides as a promising material for laser cladding

. Multicomponent hybrid TiC-NbC(Zr, Si) powder was developed and manufactured by mechanosynthesis in a high-energy vibratory ball mill. High-purity fragmented TiC, NbC, Zr and Si powders were selected and mixed in a ratio of 60:15:10:15 at.%, respectively, to manufacture the above powder. Several modes of mechanosynthesis were chosen for the experiment: 3, 6, 9 and 12 hours. Scanning electron microscopy (SEM) and X-Ray diffraction (XRD) analyzes were used to study the morphology, chemical and phase compositions of the obtained TiC-NbC(Zr, Si) powder. The SEM analysis confirmed the presence of all TiC, NbC, Zr and Si components in the final powder regardless of the mechanosynthesis time. However, the XRD analysis showed that after 9 and 12 hours of mechanosynthesis, the Zr and Si diffraction lines are completely absent. This occurs due to the dissolution of the Zr and Si elements in titanium and niobium carbides. In addition, it has been established that more than 6 hours are required to synthesize finely dispersed TiC-NbC(Zr, Si) powder. The study results can be useful for optimization of the mechanosynthesis process.


Introduction
The development and synthesis of metal powders with a complex of improved physicomechanical characteristics is an important and urgent task in a rapidly developing economy. One of the traditional and approved methods to obtain multicomponent composite powders is mechanosynthesis (mechanoactivation) in vibration, planetary-ball, rotor-stator mills [1 -3].
During mechanosynthesis only 2-3 % of useful energy is spent on mechanical dispersion and 97-98 % -on structural changes in the crystal lattice. In particular, an accumulation of crystal lattice deformations, an increase of dislocations, a break or weakening of interatomic bonds and shear strains occur upon mechanosynthesis [4][5][6][7].
The study goal is to obtain multicomponent hybrid TiC-NbC(Zr, Si) powder by mechanosynthesis in a high-energy vibratory ball mill, as well as its characterization using SEM and XRD analyzes.

Materials and methods
High-purity fragmented TiC, NbC, Zr and Si powders were selected to obtain a multicomponent hybrid TiC-NbC(Zr, Si) powder by mechanosynthesis in a high-energy vibratory ball mill with a controlled Ar atmosphere. The initial powders were mixed in a ratio of 60:15:10:15 at.%, respectively, and then placed in brass mortars with 12 brass balls for mechanosynthesis. The total mass of powders in each mortar is 3 g: mTiC=1.54 g; mNbC=0.74 g; mZr=0.49 g and mSi=0.23 g. Several modes of mechanosynthesis were chosen for the experiment: 3, 6, 9 and 12 hours.
The morphology and chemical composition of the initial and obtained powders were studied using the SEM Tescan Vega II XMU (Tescan, Czech) with a tungsten cathode equipped with an energy dispersive microanalyzer INCA Energy 450 XT (Oxford Instruments, United Kingdom).
The XRD analysis of all the above-mentioned powders was carried out by Shimadzu XRD-7000 diffractometer (Shimadzu Corporation, Japan) coupled with graphite monochromator in CuK radiation. The diffraction spectrum was recorded in the angular range 2 = 30-120° with the scanning step  = 0.03° and the pulse accumulation for 2 seconds. The XRD reflections were identified using the X'Pert High Score software (Malvern Panalytical, United Kingdom).

Results and discussion
The morphology and phase composition of the initial fragmented TiC, NbC, Zr and Si powders are shown in Figures 1 and 2, respectively. The diffraction lines of the elements are indicated with certain colors: TiC -red, NbC -blue, Zr -green and Si -orange.    The interpretation of XRD patterns established the presence of all TiC, NbC, Zr and Si elements in TiC-NbC(Zr, Si) powder obtained by mechanosynthesis for 3 and 6 hours. However, after 9 and 12 hours of mechanosynthesis, the diffraction lines of Zr and Si are completely absent, which presumably occurs due to the dissolution of Zr and Si in titanium and niobium carbides. Further characterization of the TiC-NbC(Zr, Si) powder is required to confirm this assumption.
The morphology and chemical composition of the TiC-NbC(Zr, Si) powder after 3, 6, 9 and 12 hours of mechanosynthesis are shown in Figure 4 and Table 1, respectively. The SEM analysis confirmed the presence of all TiC, NbC, Si and Zr components in the obtained powder regardless of the mechanosynthesis time.  The spectra of various sections of the obtained TiC-NbC(Zr, Si) powder were taken to determine its chemical composition after each time interval of the mechanosynthesis process. According to Table 1, different time intervals of the mechanosynthesis lead to a significant change in the chemical composition and refinement of the TiC-NbC(Zr, Si) powder, which indicates the effectiveness of the mechanosynthesis method in the context of obtaining finely dispersed powders with desired concentration of elements.

Conclusions
The paper presents the development and manufacture of multicomponent hybrid TiC-NbC(Zr, Si) powder by mechanosynthesis using different time intervals. The SEM and XRD analyzes were used to determine the morphology, chemical and phase compositions of the obtained powder. It has been established that more than 6 hours are required for complete dissolution of Zr and Si in titanium and niobium carbides and obtaining finely dispersed TiC-NbC(Zr, Si) powder. The study results can be useful for optimization of the mechanosynthesis process.