Influence of Process Conditions on the Growth and Texture of CVD Alpha-Alumina

Abstract

In the present study, the influence of experimental variables on the growth characteristics and texture development in chemically vapour deposited α-Al2O3 coatings was investigated. The emphasis was on the effects of H2S. The α-Al2O3 layers were deposited from the AlCl3-H2-CO2-HCl-H2S precursor system onto intermediate Ti(C,N) layers. The substrate was cemented carbide. The coatings were characterized with respect to microstructure and texture using X-ray diffraction, scanning electron microscopy and electron back-scattering diffraction. The observations were unpredictable, suggesting that in addition to the growth rate, H2S strongly affected the texture of the α-Al2O3 coatings. The uncatalyzed α-Al2O3 coatings (H2S = 0) developed (11 2 ¯ 0) texture. With the increment of H2S concentration the texture changed from (11 2 ¯ 0) texture through (10 1 ¯ 0), (10 1 ¯ 2) and (10 1 ¯ 4) textures to (0001) texture. Growth regimes for (11 2 ¯ 0), (10 1 ¯ 0), (10 1 ¯ 2), (10 1 ¯ 4) and (0001) textures were depicted as a function of the H2S/CO2 ratio. Examples of grain-boundary and microstructural manipulation of CVD α-Al2O3 layers by applying texture control were presented.

Tribological Properties of Multilayer CVD Coatings Deposited on SiAlON Ceramic Milling Inserts

“…CVD coating techniques are preferred for coating SiAlON inserts because of the strength of the bonds that are created between the SiAlON substrate and the interatomic bonding layer. Previous studies [20][21][22][23][24][25] deduced that chemical vapour deposition is the most suitable method for creating thin-film coatings that have high durability and high wear resistance at high cutting temperatures. The benefit of the chemical vapour deposition coating process is that it allows for a high enough temperature to be reached on the surface of the heated substrate.…”

Characteristics and Cutting Performance of CVD Al2O3 Multilayer Coatings Deposited on Tungsten Carbide Cutting Inserts in Turning of 24CrMoV5-1 Steel

“…8% due to the heat generated during thermal CVD process and metal cutting [10]. It was also reported that the mechanical properties of CVD α-Al 2 O 3 coatings could be enhanced by choosing an optimized texture for the α-Al 2 O 3 phase [11]. Consequently, CVD Al 2 O 3 coatings have continuously been optimized with respect to the phase and film texture control.…”