Yong W. Bae

Preparation and friction characteristics of self-lubricating TiN-MoS2 composite coatings

Abstract Composite coatings consisting of discrete phases of TiN and MoS 2 were codeposited on graphite and Ti-6Al-4V substrates from Ti((CH 3 ) 2 N) 4 /NH 3 /MoF 6 /H 2 S gas mixtures. Chemical composition and microstructure of the coatings were characterized by Auger electron spectroscopy, X-ray diffraction, and transmission electron microscopy. Friction coefficients at room temperature in air were typically in the range of 0.07 to 0.3. The friction coefficients remained comparable at 573 K, but increased to 0.7 to 1.0 at 673 K. A friction coefficient value of ∼0.3 was, however, obtained from a composite coating tested at 973 K.

Nanoscale hardness and microfriction of titanium nitride films deposited from the reaction of tetrakis (dimethylamino) titanium with ammonia

Nanocrystalline titanium nitride films with very low carbon and oxygen content were deposited on single‐crystal silicon substrates from the reaction of tetrakis (dimethylamino) titanium, Ti[(CH3)2N]4, with ammonia at 633 K and a pressure of 665 Pa. The film consisted of ∼10 nm grains. The hardness of the film, measured by nanoindentation, was 12.7±0.6 GPa. The average kinetic friction coefficient, against type 440C stainless steel, was determined using a friction microprobe to be 0.43.

Na2SO4-lnduced Corrosion of Si3N4 Coated with Chemically Vapor Deposited Ta2O5

Hot isostatically pressed Si{sub 3}N{sub 4} was coated with chemically vapor-deposited Ta{sub 2}O{sub 5}, and subjected to oxidative and corrosive environments to determine the feasibility of using a Ta{sub 2}O{sub 5} coating for protecting Si{sub 3}N{sub 4} from hot corrosion. The coated structure was relatively stable at 1,000 C in pure O{sub 2}. However, the Ta{sub 2}O{sub 5}-Si{sub 3}N{sub 4} system became unstable in an environment containing Na{sub 2}SO{sub 4} and O{sub 2} at 1,000 C because (1) Ta{sub 2}O{sub 5} and Na{sub 2}SO{sub 4} reacted rapidly to form NaTaO{sub 3} and (2) subsequently NaTaO{sub 3} interacted destructively with the underlying Si{sub 3}N{sub 4} substrate to form a molten phase.

Na{sub 2}SO{sub 4}-induced corrosion of Si{sub 3}N{sub 4} coated with chemically vapor deposited Ta{sub 2}O{sub 5}

Hot isostatically pressed Si{sub 3}N{sub 4} was coated with chemically vapor-deposited Ta{sub 2}O{sub 5}, and subjected to oxidative and corrosive environments to determine the feasibility of using a Ta{sub 2}O{sub 5} coating for protecting Si{sub 3}N{sub 4} from hot corrosion. The coated structure was relatively stable at 1,000 C in pure O{sub 2}. However, the Ta{sub 2}O{sub 5}-Si{sub 3}N{sub 4} system became unstable in an environment containing Na{sub 2}SO{sub 4} and O{sub 2} at 1,000 C because (1) Ta{sub 2}O{sub 5} and Na{sub 2}SO{sub 4} reacted rapidly to form NaTaO{sub 3} and (2) subsequently NaTaO{sub 3} interacted destructively with the underlying Si{sub 3}N{sub 4} substrate to form a molten phase.

Synthesis and selected micro-mechanical properties of titanium nitride thin films by the pyrolysis of tetrakis titanium in ammonia

Thin films of titanium nitride were chemical vapor deposited on (100)-oriented single-crystal silicon substrates from tetrakis (dimethylamino) titanium, Ti((CH{sub 3}){sub 2}N){sub 4}, and ammonia gas mixtures in a cold-wall reactor at 623 K and 655 Pa. The films were characterized by Auger electron spectroscopy, X-ray diffraction, and transmission electron spectroscopy. The nano-scale hardness of the film, measured by nanoindentation, was 12.7 {plus_minus} 0.6 GPa. The average kinetic friction coefficient against unlubricated, type 440C stainless steel was determined using a computer-controlled friction microprobe to be {approximately}0.43.

Self-Lubricating, TiN-MoS 2 Composite Coatings Produced by Simultaneous Deposition from Ti((CH 3 ) 2 N) 4 /NH 3 /MoF 6 /H 2 S GAS Mixtures

Composite coatings consisting of discrete phases of TiN and MoS 2 were codeposited on graphite substrates from Ti((CH 3 ) 2 N) 4 /NH 3 /MoF 6 /H 2 S gas mixtures in a cold-wall reactor at 1073 K and 1.3 kPa. Chemical composition and microstructure of the coatings were characterized by Auger electron spectroscopy, X-ray diffraction, and transmission electron microscopy. Kinetic friction coefficients of the coatings were determined by a computer-controlled friction microprobe and values less than 0.2 were obtained with a type-440C stainless-steel counterface under ambient condition.

Friction and wear of self-lubricating TiN-MoS{sub 2} coatings produced by chemical vapor deposition

The purpose of the work reported here was to develop special chemical vapor deposition (CVD) methods to produce self-lubricating ceramic coatings in which the lubricating and structural phases were co-deposited on Ti-6Al-4V alloy substrates. These novel composite coatings are based on a system containing titanium nitride and molybdenum disulfide. The method for producing these coatings and their sliding behavior against silicon nitride counterfaces, in the temperature range 20--700 C in air, are described. The initial sliding friction coefficients for the composite coatings at room temperature were 0.07--0.30, but longer-term transitions to higher friction occurred, and specimen-to-specimen test variations suggested that further developments of the deposition process are required to assure repeatable friction and wear results. Friction and wear tests at 300 and 700 C produced encouraging results, but tests run at an intermediate temperate of 400 C exhibited friction coefficients of 1.0 or more. Oxidation and a change in the nature of the debris layers formed during sliding are believed to be responsible for this behavior.