Abstract

The kinetics and mechanisms of the hydrogen-free chemical-vapor-deposition (CVD) method for protective tantalum coatings in the TaBr₅–Cd system on St3, tungsten, and copper substrates in the temperature range of 700–950°C are investigated by X-ray diffraction, scanning electron microscopy, glow-discharge optical emission spectroscopy, and polarization curves. The thickness of the coatings obtained on St3, tungsten, and copper is 2.8–15.7, 2.2–5.3, and 2.0 µm respectively. The calculated activation energy of the CVD process during deposition onto St3 and tungsten (68 and 28 kJ/mol, respectively) indicates a diffusion-limiting stage. In the series of copper-tungsten-St3 substrates, the deposition rate of the tantalum coating increases and agrees with the negative enthalpy of formation of intermetallic compounds ΔH_MeTa (Me is the substrate metal), which is associated with an increase in the adsorption interaction between the substrate and TaBr₅ in it. It is shown that dense α-Ta-based coatings are deposited onto St3 at T = 700–750°C, and loose coatings based on face-centered cubic (fcc) tantalum with an admixture of lamellar hexagonal close-packed (hcp) tantalum crystals are deposited at T = 800°C and higher. Accordingly, dense body-centered tetragonal (bct) β-Ta-based coatings are deposited onto tungsten at T = 700–750°С; at 800–900°С, loose α-Ta-based coatings are deposited. A coating consisting of a mixture of α and β phases is obtained on copper at 800°C. The sums of the probabilities of deformation (α) and twinning (β) stacking faults (SFs) (1.5α + β) in deposited bcc ({112} planes) and fcc ({111} planes) tantalum are calculated by the harmonic analysis of diffraction lines according to Warren, and they range from 0.04 up to 1.2 and from 0.03 to 2%, respectively. The discovered SFs are likely to be closely related to the formation mechanisms of nonequilibrium bct, fcc, and hcp tantalum phases. Additional annealing (1000°С) of the β-Ta-based coating (tungsten substrate) leads to the formation of α-Ta, while annealing of the α-Ta-based coating (St3 substrate) leads to the formation of fcc tantalum. The formation of fcc tantalum crystals on an St3 substrate at T ≥ 725°C during CVD or as a result of annealing is assumed to be due to the α → γ phase transition in St3. The obtained α-Ta-based coatings demonstrate high corrosion properties.

中文翻译：

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保护性钽涂层的无氢 CVD 机理和动力学

摘要

_{TaBr 5}中保护性钽涂层的无氢化学气相沉积 (CVD) 方法的动力学和机制通过 X 射线衍射、扫描电子显微镜、辉光放电发射光谱和偏振曲线研究了温度范围为 700–950°C 的 St3、钨和铜基板上的 –Cd 系统。在 St3、钨和铜上获得的涂层厚度分别为 2.8–15.7、2.2–5.3 和 2.0 µm。在沉积到 St3 和钨（分别为 68 和 28 kJ/mol）期间计算的 CVD 过程的活化能表明扩散限制阶段。在铜-钨-St3系列基材中，钽涂层的沉积速率增加，与金属间化合物的负生成焓ΔH _MeTa（Me为基材金属）一致，这与吸附相互作用的增加有关在基板和 TaBr 之间₅在里面。结果表明，在T = 700–750°C 时，致密的 α-Ta 基涂层沉积在 St3 上，而基于面心立方 (fcc) 钽的松散涂层与层状六方密堆积 (hcp) 钽的混合物晶体在T = 800°C 及更高温度下沉积。因此，致密的体心四方 (bct) β-Ta 基涂层在T沉积到钨上= 700–750°С; 在 800–900°С 时，会沉积松散的 α-Ta 基涂层。在 800°C 下在铜上获得由 α 相和 β 相的混合物组成的涂层。通过谐波分析计算沉积的 bcc ({112} 面) 和 fcc ({111} 面) 钽中变形 (α) 和孪晶 (β) 层错 (SFs) (1.5α + β) 的概率之和根据 Warren 的衍射线，它们的范围分别为 0.04 到 1.2 和 0.03 到 2%。发现的SFs可能与非平衡bct、fcc和hcp钽相的形成机制密切相关。β-Ta 基涂层（钨基体）的额外退火（1000°С）导致形成 α-Ta，而 α-Ta 基涂层（St3 基体）的退火导致 fcc 钽的形成。T ≥ 725°C 在 CVD 期间或作为退火的结果被认为是由于 St3 中的 α → γ 相变。获得的 α-Ta 基涂层表现出高腐蚀性能。