Mechanical and Tribological Properties of ZrC/VC Alloy Films Deposited by Sputtering and Pulsed Laser Deposition
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However, despite their attractive properties, the hardness level of these carbides (20-30 GPa) are well below that of competitive materials such as diamond (80 GPa). Improving the hardness levels of carbides can be achieved by alloying two or more transition metal carbide mixtures. Using PLD and RF magnetron sputtering, we have investigated the effects of various deposition conditions, including substrate, substrate temperature, laser fluence, and deposition pressure on the resultant film properties. Using a time-of-flight quadrupole mass spectrometer (TOFQMS), mass and kinetic energy distributions and collision dynamical effects of the background gas were measured. By correlating the spectrometry studies with the materials properties, our ability to control the microstructure and in-plane film texture is greatly improved. These capabilities can open up new opportunities for the fabrication of tough and wear-resistant coatings. EXPERIMENTAL Pulsed laser deposition of the carbide alloy was conducted in a high-vacuum chamber using a rotating target and heated substrate holder. The target-substrate distance was 4.6 cm. The target was hot-pressed from high-purity (99.9%) carbide powders, with a nominal composition of 36% VC and 64% ZrC. A KrF excimer laser beam (248 nm, 30 nsec FWHM, 9 Hz) was focused through a 0.5 m focal length lens onto the target. Laser energy densities ranged from 4.0 - 7.0 J/cm 2. The base pressure for the ablation chamber was typically 5.0 x 10-3 mT and was backfilled to 5.0 - 60.0 mT with ultra-pure argon gas during ablation. Films were deposited directly onto Si substrates at 20', 200', and 400'C. The gas flow rate was held between 2.0-4.0 sccm and the pressure was adjusted by throttling the pump speed. Film thickness measurements were achieved using masked-off sections under an atomic force microscope (AFM). This yield261 Mat. Res. Soc. Symp. Proc. Vol. 505 ©1998 Materials Research Society
ed a deposition rate of 0.2 A per shot at an energy density of 5.2 J/cm 2 . The nominal film thickness was 0.6 4am (30,000 shots). X-ray diffraction (XRD) using CuKot radiation was used for phase and crystal orientation analysis of the films. Wear-testing was conducted using a pin-ondisk apparatus which revealed the friction coefficient and left a visibly observable wear-track. Hardness tests were conducted with a Nanoindentor II. The sputtered films were deposited by RF magnetron sputtering in high-vacuum. The background pressure was held at 5.0 mT of ultra-high purity argon. The substrates were oriented 400 off-axis and heated to 20', 2000, and 400' C, respectively. The target-to-substrate distance was 6 inches and the nominal film thickness was 0.6 4tm. TOF The time of flight apparatus consisted of a laser ablation chamber attached to a quadrupole mass spectrometer by a 0.8 m gas manifold tube. The total distance from the target to the channeltron/dynode detector array was 1.2 m. The KrF excimer laser was focused using a 0.5 m focal length lens at a 450 incidence angle onto a rotating target holder. The
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