Hardness and Tribological Effects of Ion Implantation on Electroplated Chromium
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Mat. Res. Soc. Symp. Proc. Vol. 356 0 1995 Materials Research Society
1.3 cm long, 6.4 mm in diameter tapering to a 3.2 mm diameter tip, were used for the hardness measurements and secondary ion mass spectrometry (SIMS) analysis. The base material for the samples was made from a heat treated, AISI 4340 grade steel. The samples were electroplated using a chromium plating solution consisting of 250 g/V chromic acid and 2.5 g/A sulfuric acid. The hard chromium was deposited using a cathodic current of 30 A/dm 2 at a plating solution temperature of 55 'C. The low contraction chromium was deposited using a cathodic current of 120 A/dm 2 at a plating solution temperature of 85 'C. The resulting films were 99.97 wt% chromium and 99.92 wt% chromium for the hard chromium and low contraction chromium, respectively. The plating time was chosen to produce a film thickness of approximately 75 - 100 /um. The samples were mechanically polished to an average surface roughness of around 14 nm Ra/20 nm RMS. The chromium plated samples were then subjected to ion implantation using an Extrion Model 400 implanter. The implantations were performed using an N2' or Ar' ion beam at ion energies of 150 keV and 75 keV, respectively. The doses ranged from 9.4 x 1015 to 3.1 x 1018 N atoms/cm 2 and from 9.4 x 1015 to 3.1 x 1017 Ar atoms/cm 2. The implantations were carried out at both room temperature (sample temperature did not exceed 180 'C) and 500 'C at a background pressure of 10-6 torr and beam current density of 3 - 4 .A/cm 2. SIMS was combined with Auger electron spectroscopy (AES) to characterize the implantation profiles and chemical composition of the implanted chromium films, using a Perkin Elmer 6300 SIMS instrument and a Perkin Elmer Model 660 AES instrument at Evans East, Plainsboro, NJ. The SIMS profiling was done using a 5.0 keV Cs' ion beam and observing the positive secondary ion yield from the sample as a function of time. Depth scales were determined from post bombardment craters using a Dektak stylus profilometer. Surface hardness was measured using a Leitz optical microscope with a Knoop diamond indenter. Several different loads were used ranging from 5 - 200 grams. On every sample, at least ten measurements were taken at each of the two lighter loads and at least six to eight measurements were taken at the remaining loads. Wear testing was performed using a pin-on-disk geometry in accordance with ASTM test method G-99 at Implant Sciences Corporation, Wakefield, MA on an ISC-200PC Tribometer System. 3.2 mm diameter alumina balls were used as the pins to wear against the chromium plated disks. Each test was conducted at room temperature without lubrication for 60 minutes with the ball rotating on the sample at a sliding velocity of 10 cm/sec at a constant load of 50 grams. The friction coefficient was recorded during wear testing and the wear rate measurements were calculated from the disk volume loss measured by profilometry. RESULTS AND DISCUSSION Nitrogen and Argon Concentration Depth Profiles For a given implantation
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