On the growth kinetics, texture, microstructure, and mechanical properties of tungsten carbonitride deposited by chemical vapor deposition

Tungsten carbonitride [W(C,N)] was deposited on cemented carbide substrates by chemical vapor deposition (CVD) in a hot-wall reactor using tungsten hexafluoride (WF6), acetonitrile (CH3CN), and hydrogen (H-2) as precursors. Tungsten carbides and nitrides with a hexagonal 6-WC type structure are generally difficult to obtain by CVD. Here, it was found that the combination of WF6 and CH3CN precursors enabled the deposition of W(C,N) coatings with a delta-WC type structure and columnar grains. A process window as a function of the deposition temperature and precursor partial pressures was determined to establish the conditions for the deposition of such coatings. Scanning electron microscopy, x-ray diffraction, electron backscatter diffraction, and elastic recoil detection analysis were used for the investigation of the coating thickness, microstructure, texture, and composition. From the investigation of the kinetics, it was concluded that the growth was mainly controlled by surface kinetics with an apparent activation energy of 77 kJ/mol, yielding an excellent step coverage. The partial reaction orders of the reactants together with their influence on the microstructure and coating composition was further used to gain a deeper understanding of the growth mechanism. Within the process window, the microstructure and the texture of the W(C,N) coatings could be tailored by the process parameters, enabling microstructural engineering with tuning of the mechanical properties of the W(C,N) coatings. The nanoindentation hardness (36.6-45.7 GPa) and elastic modulus (564-761 GPa) were found to be closely related to the microstructure

Magnetic carbon nanocomposites via the graphitization of glucose and their induction heating

Carbon nanocomposites containing iron-based nanoparticles are attractive materials for the catalyst sup-ports used for magnetic (induction) heating catalysis. The metallic, soft-magnetic iron nanoparticles pro-vide local heating of the support in an alternating magnetic field and ensure rapid magnetic separation of the nanocomposite particles from reaction suspensions. In this work, magnetic carbon nanocomposites were prepared by annealing the precursor particles consisting of iron-oxide nanoparticles dispersed in a carbohydrate matrix. The annealing was conducted at 600 degrees C and 750 degrees C in an Ar atmosphere. At both temperatures the carbothermal reduction of iron oxide to Fe/Fe3C was observed; however, at the lower temperature the rate of reduction and the growth of the nanoparticles were considerably slower. The Fe3C was formed in negligible amounts only after a prolonged period of annealing at 600 degrees C. A detailed structural analysis showed that the Fe/Fe3C nanoparticles catalyze the graphitization of the carbonaceous precursor material already at 600 degrees C, resulting in the formation of a graphitic shell that surrounds them. This shell is tight enough to prevent the areal oxidation of the encapsulated Fe nanoparticles; their magnetic properties remained unchanged even after 1 year of storage under ambient conditions. At the higher annealing temperature, the growth of the Fe/Fe3C nanoparticles caused bursting of the graphitic shell and thus par-tially exposed their surfaces to the atmosphere. All the nanocomposites exhibited ferromagnetic behavior in accordance with their compositions. The nanocomposite that was predominantly composed of a graphitic shell, encapsulated Fe nanoparticles and a negligible amount of Fe3C, showed the highest specific ab-sorption rate (760 W/gFe at 274 kHz), even at a relatively low AC-field amplitude (88 mT).(c) 2023 Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http:// creativecommons.org/licenses/by-nc-nd/4.0/)

Kinetics of the low-pressure chemical vapor deposited tungsten nitride process using tungsten hexafluoride and ammonia precursors

Tungsten nitride (WNx) is a hard refractory material with low electrical resistance that can be deposited using multiple methods. This study focuses on the microstructrual development of low pressure chemical vapor deposition grown WNx coatings. Also, the growth kinetics is studied and discussed in terms of the resulting microstructures. Samples of WNx were deposited using WF6, NH3, and Ar at 592-887 K in a hot-wall reactor with variable gas mixture compositions (NH3:WF6 = 0.5-25). The coatings were nitrogen-rich (x similar to 1.65) and oxygen-free as determined by time-of-flight-elastic recoil detection analysis. X-ray diffraction showed that the coatings transformed from being amorphous to crystallizing as beta-W2N at 641-690 K. The morphologies changed with deposition temperature. Being very fine grained and nodular at deposition temperatures 740 K and below, increasing the deposition temperature to 789 K while employing a NH3:WF6 molar ratio of 1, large disc-shaped protrusions were formed. When increasing the NH3:WF6 molar ratio to 25, striped facets became increasingly dominant. Investigating the latter by transmission electron microscopy, a microstructure of smaller ridges formed by twinning, oriented as in the out-of-plane direction, was revealed across the facet surfaces. Transmission Kikuchi diffraction confirmed that was the texture of these coatings. The partial reaction order of WF6 and NH3 at 740 K was determined to be close to 1/6 and 1/2, respectively. The apparent activation energy ranged from 82 to 12 kJ/mol corresponding to deposition temperatures from 592 to 887 K

Chemical vapor deposition of TiN on a CoCrFeNi multi-principal element alloy substrate

The reactivity of a quaternary multi-principal element alloy (MPEA), CoCrFeNi, as a substrate in thermal halide chemical vapor deposition (CVD) processes for titanium nitride (TiN) coatings was studied. The coatings were deposited at 850 degrees C-950 degrees C using TiCl4, H-2 and N-2 precursors. The coating microstructures were characterized using X-ray diffraction (XRD), scanning and transmission electron microscopy (SEM/TEM) with energy dispersive X-ray spectroscopy (EDS). Thermodynamic calculations of substrate and coating stability for a gas phase environment of N-2 and H-2 within a temperature range relevant for the experiments showed that Cr is expected to form hexagonal Cr2N and cubic (Ti1-epsilon 1 Cr epsilon 1)N or (Cr1-epsilon 2 Ti epsilon 2)N phases. These phases could however not be discerned in the samples by XRD after the depositions. Cr was detected at the grain boundaries and the top surface by EDS for a sample synthesized at 950 degrees C. Grain boundary and surface diffusion, respectively, were the suggested mechanisms for Cr transport into the coating and onto the top surface. Although thermodynamic calculations indicated that Cr is the most easily etched component of the CoCrFeNi alloy to form gaseous chlorides in similar concentrations to that of the residual Ti-chlorides, no sign of etching were found according to the imaging of the sample cross-sections using SEM and TEM. Cross-section and top surface images further confirmed that the choice of substrate had no significant detrimental influence on the film growth or microstructure