CVD of Carbide Multi-Phased Coatings
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embedded within a TiC matrix is achieved. In the study below, CVD is used to deposit Ti-W-C films of varying compositions. The study consists of two parts. First, the effect of CVD processing parameters are modeled against TiC film composition using a statistically significant factorial design. Then, film properties, including atomic composition, deposition rate, crystallinity, film orientation, and morphology of various Ti-W-C compositions are reported. EXPERIMENT TiC and Ti-W-C films were deposited on 440C steel by CVD using a gas mixture of TiC14 , CH4 , H 2, Ar, and W(CO) 6 for W films. The reactor chamber was a quartz tube with inner diameter of 135mm, heated by a resistance furnace. For the TiC deposition studies, total furnace pressure, reaction temperature, total mass flow, C:Ti input ratio and H:Ti ratios were adjusted for each experiment according to the fractional 25 1 factorial design. The C:Ti and H:Ti variables were the ratio of mass flow rates of the individual reactants. A total of 22 experiments were completed, 16 different experiments varying the low or high value of each variable were completed and 6 replications of the midpoint experiment were completed. The software program "JMP" was used to analyze the composition fractional factorial design [3]. Table I lists the deposition variables and their low, mid-point, and high values. 339
Mat. Res. Soc. Symp. Proc. Vol. 581 © 2000 Materials Research Society
Table I. Deposition Variables and Values Mid-point Low value Factor 1000 950 Reaction Temperature (QC) 2 1 C:Ti input 9 0 H:Ti input 175 50 Reaction Pressure (Torr) 265 130 Total Mass Flow (sccm)
High value 1050 3 18 300 400
For the Ti-W-C deposition studies, the reactor temperature and pressure were 1050'C and 150 Torr respectively. The total flow rates were varied in the range of 235-275 sccm. The theoretical inlet ratio of metal to carbide or (TiCl 4+W(CO) 6)/CH 4 was determined by the mass flow rates of TiCl 4, W(CO) 6 and CH 4. The films of varying atomic composition were deposited by varying mass flow rate of TiCI4 while maintaining the mass flow rate of W(CO) 6 at constant. The thickness of the deposits was determined by abrasion through the film, obtained by
dimpling together with an abrasive agent (diamond 3jtm). The thickness values were calculated from the diameters of the ring prints measured by optical microscopy. The deposition rate was then obtained by the thickness divided by the deposition time. X-ray diffraction was used to characterize phase formation in the films. The composition of the films was determined by auger electron spectroscopy (AES) and by X-ray photoelectron spectroscopy (XPS). The morphologies of the film surface were observed with scanning electron microscopy (SEM). The roughness of the films was obtained by atomic force microscopy (AFM). RESULTS AND DISCUSSION PART 1- The Deposition of TiC: How Deposition Variables Affect TiC Film Composition through Fractional Factorial Design Titanium At.% The reactor pressure, total mass flow, and H:Ti input exhibit signi
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