Structure and Stress Evaluation of Diamond Films Deposited on Ti-6A1-4V Alloy at Low Temperature Using CH 4 /0 2 /H 2 an
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Mat. Res. Soc. Symp. Proc. Vol. 505 ©1998 Materials Research Society
interfacial structure, film stress, growth rate, and surface roughness. EXPERIMENT The Ti-6AI-4V substrates were polished to 1 plm using A12 0 3 slurry, ultrasonically seeded in a methanol/diamond slurry (using 1 gxm diamond powder), electrophoretically seeded [5] in an acetone/diamond solution for 60 sec. at 950 V, and then cleaned thoroughly with methanol. The 7 mm diameter, 1 mnm thick Ti-6A1-4V disks were placed in a molybdenum "cup" substrate holder such that the substrate surface was level with or just slightly protruding from the top of the holder (see Fig. 1). This geometry provided very good temperature uniformity across the surface of the substrate. The 0.5 inch diameter substrate holder was threaded into a copper heat sink whose internal hollowed cavity was continuously flushed with 10 degree water from a Neslab water chiller/recirculator. The diamond films were grown in a MPCVD system with a double-walled stainless steel vacuum chamber with a base pressure of -150 mT. The chamber dimensions are 6 inches in diameter and 18.5 inches in length. For each experiment using CH 4 /0 2/H 2 gas mixtures the chamber pressure and microwave power were maintained at 80 Torr and 740 W, respectively. The pressure and power for the CO/H 2 experiment was fixed at 90 Torr and 700 W, respectively. The substrate temperature was measured with a 'Mikron M77LS Infraducer' two color pyrometer () 1 = 1.55 gm, )2= 1.64 pgm) which has a temperature range from 500 to 2000 C. This two color pyrometer provided accurate measurement of the substrate temperature without requiring correction of the emissivity of the surface during growth. The pyrometer was oriented 57 degrees from the substrate normal. Micro-Raman spectra were taken using an argon-ion laser at 514.5 nm excitation and 100 mW power on an EG &G Dilor Raman system. Glancing angle x-ray diffraction (XRD) was performed using a Philips 'XPERT' diffractometer with thin film attachment and Cu Ka radiation. The glancing angle was I degree for all experiments. All the films described in this paper remained fully adhered after deposition. RESULTS A summary of the processing conditions and experimental results for each sample is provided in Table I. Growth rate, film thickness and surface roughness information was obtained by in-situ monitoring of the apparent temperature oscillations as measured by the optical pyrometer.
Molybdenum Substrate Holder
.
Figure
-oTi-6a-4V Substrate
Figure 1. Photograph showing molybdenum substrate holder and Ti-6A1-4V substrate.
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TABLE I. Processing Conditions and Results for Diamond Films on Ti-6A1-4V
Sample
(sccm)
Substrate Temperature (C)
Avg. Growth Rate (jim/hr)
Film Thickness (tm)
Avg. Film Stress (GPa)
A
[CH 4 ] = 5 [H2 ] = 500
710
0.164
3.6
3.8±0.9
B
[02] = 0.5 [CH 4 ] = 5, [H2] = 500
710
0.124
2.4
5.4±0.9
C
[CH 4] = 5, [H2 ] = 500
705
-
0.84
4.9±1.0
D
[02] = 1.5 [CH 4 ] = 5, [H2] = 500
710
0
E
[02] = 0.5 [CH 4 ] = 5, [H2] = 500
625
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