Coating of Cubic Boron Nitride Powder with TiN in a Rotating Drum via Gas Phase Processes

To improve the performance of superhard ceramic composites, this study aims to develop a dense, phase-pure, and uniform TiN coating on cubic boron nitride (cBN) particles with a target thickness of at least 150 nm. TiN coatings were applied using atomic layer deposition (ALD) alone, as well as a combined ALD/chemical vapor deposition (CVD) process. While ALD produced uniform and dense coatings, the thickness remained below 50 nm. The combined ALD/CVD approach achieved greater thicknesses up to 500 nm, though coating homogeneity remained a challenge. Optimization efforts, including increased ALD cycles and reduced CVD pressure, led to improved coating uniformity, with 25%-30% of particles coated to thicknesses ≥ 80 nm. Structural analysis confirmed dense, pore-free TiN1-x layers for all synthesized powders. In contrast, the commercial reference powder showed a non-uniform, multiphase coating (α - Ti, Ti2N, and TiN0.53) with defects. While the ALD/CVD powders exhibited better phase purity than the commercial sample, further optimization is needed to achieve consistent coatings above 150 nm. These results suggest the ALD/CVD route is promising for producing coatings suitable for use in ceramic matrix composites.