Factors affecting the initial nucleation of alumina on cemented-carbide substrates in the CVD process

Abstract

Alumina nuclei were deposited, using chemical vapor deposition (CVD), under varying process conditions on polished cemented-carbide substrates (WC+TiC, TaC, NbC+Co) for 60 s in order to study the nucleation stage. During the heating up of the substrates the binder of the polished surfaces diffused onto the carbide surfaces. The surface of the WC was thereby converted to η-phase, while no attack on the (Ti,W)C surfaces could be detected. After the short deposition the alumina nuclei were counted. The nucleation was always most dense on the (Ti,W)C grains. The chemical equilibria of the gas for the various process conditions were calculated and supersaturations for the components of the gas and a total one were computed. It was found that the density of nuclei increased with increasing supersaturation of the aluminum chlorides and the total supersaturation. The supersaturation of the oxygen donors, however, did not correlate with the density of nuclei. A dense nucleation is believed to be important for the adherence of the final deposit.

Chemically Vapour Deposited Alumina Coatings on High Speed Steel Cutting Tools

“…Whilst the supersaturation of the AI-donor (AlCI 3 ) decreases as the deposition temperature increases, that of the O-donor (H 2 0 vapour from CO 2 and H 2 ) increases because the H 2 0 inlet concentration is more sensitive to temperature than the H 2 0 equilibrium concentration, the resulting exponentially increased growth rate accounting for the coarser grains found to exist at the higher deposition temperatures. It is pertinent to point out that whilst Park et al refer to an increase in the supersaturation of O-donor with increasing deposition temperature (in agreement with the findings of 10hannesson and Lindstrom [41]) this is in direct contrast to the findings of Lindstrom and 10hannesson [29] and Kim et al [43], according to whom the supersaturation of O-donors decreases with increasing deposition temperature. In their work Colmet and Naslain [27] observed that AlP3 coatings deposited at a deposition temperature of 1173 K (900°C) and a total pressure of 0.8 atm, with the other deposition conditions as specified earlier in Section 2.1, were composed of nodules whilst coatings deposited at a temperature of 1323 K (10S0°C) exhibited "well-shaped", pyramidal AIP3 crystals.…”

“…In a similar investigation, 10hannesson and Lindstrom [41] 3 ) the measured saturation density of AlP3 clusters was found to be 3 x 10' cm· 2 • According to Kornmann et ai, from work carried out at different deposition temperatures with different reactant gas compositions to those previously quoted, the saturation density of Al 2 0 3 nuclei also increases with increasing AlCI 3 supersaturation.…”

“…A number of workers have investigated the effect of deposition temperature on AI,03 coatings chemically vapour deposited on various substrates, paying particular attention to its effect on nucleation [29,32,41], deposition rate [31,36,37,42,43] surface morphology [24,27,43,44,48], preferred orientation [43] and crystal structure [38,[45][46][47].…”

“…Several workers have investigated the effect of reactant gas concentration on chemically vapour deposited Al 2 0 3 coatings, in terms of either partial pressures or mole ratios, paying particular attention to the fOllowing: nucleation [29,41], deposition rate [31,36,37,38,42,43,44], surface morphology [42,43,27] and preferred orientation [44]. This section is 19 therefore divided into two parts; the first deals with the effect of partial pressure and the second with the effect of mole ratio.…”

Crystallographic Orientation and Surface Morphology of Chemical Vapor Deposited Al2 O 3

“…Since then, this new porous material has been investigated particularly because of its potential use in integrated circuit technology(3)(4)(5)(6). Since then, this new porous material has been investigated particularly because of its potential use in integrated circuit technology(3)(4)(5)(6).…”