William A. Brainard

An XPS study of the adherence of refractory carbide silicide and boride rf‐sputtered wear‐resistant coatings

Radio frequency sputtering was used to deposit refractory carbide, silicide, and boride coatings on 440‐C steel substrates. Both sputter etched and pre‐oxidized substrates were used and the films were deposited with and without a substrate bias. The composition of the coatings was determined as a function of depth by x‐ray photoelectron spectroscopy combined with argon ion etching. Friction and wear tests were conducted to evaluate coating adherence. In the interfacial region there was evidence that bias may produce a graded interface for some compounds. Biasing, while generally improving bulk film stoichiometry, can adversely affect adherence by removing interfacial oxide layers. in all cases but the iron oxide coverage was only complete on the preoxidized substrates. The film and iron oxides were mixed in the MoSi2 and Mo2C films but layered in the Mo2B5 films. In the case of mixed oxides, pre‐oxidation enhanced film adherence. In the layered case it did not.

Adhesion and friction of PTFE in contact with metals as studied by Auger spectroscopy, field ion and scanning electron microscopy

Abstract The adhesion between PTFE and metals was studied by field ion microscopy, Auger emission spectroscopy and scanning electron microscopy. Strong adhesion between PTFE and all metals, both clean and oxidized, was observed with these techniques for both static and dynamic contact. The bonding is sufficiently strong so that for soft metals such as aluminum, pieces of metal can be pulled out of the bulk and embed in the PTFE subsequently causing severe scoring of the metal surfaces.

The effect of mechanical surface and heat treatments on the erosion resistance of 6061 aluminum alloy

The effects of both mechanical surface treatments and heat treatments on the erosion resistance of 6061 aluminum alloy were studied in order to gain a better understanding of material properties which affect erosion behavior. It was found that mechanical surface treatments have little or no effect on the erosion resistance. This is due to the formation by particle impact of a work-hardened surface layer, independent of the initial surface condition. The erosion resistance of aluminum single crystals was found to be independent of orientation, which is due to destruction of the surface microstructure and formation of a polycrystalline surface layer by the particle impact as observed by X-ray diffraction. Although on solution treatment of annealed aluminum 6061 the increase in hardness is accompanied by an increase in erosion resistance, precipitation treatment (which causes a further increase in hardness) results in a slightly lower erosion resistance.

Composition of RF-sputtered refractory compounds determined by X-ray photoelectron spectroscopy

rf‐sputtered coatings of CrB2, MoSi2, Mo2C, TiC, and MoS2 were examined by x‐ray photoelectron spectroscopy (XPS). Data on stoichiometry, impurity content, and chemical bonding were obtained. The influences of sputtering target history, deposition time, rf power level, and substrate bias were studied. Significant deviations from stoichiometry and high oxide levels were related to target outgassing. The effect of substrate bias depended on the particular coating material studied.

Dynamic SEM wear studies of tungsten carbide cermets

Dynamic friction and wear experiments were conducted in a scanning electron microscope. The wear behavior of pure tungsten carbide and composite with 6 and 15 weight percent cobalt binder was examinded. Etching of the binder was done to selectively determine the role of the binder in the wear process. Dynamic experiments were conducted as the WC and bonded WC cermet surfaces were transversed by a 50 micron radiused diamond stylus. These studies show that the predominant wear process in WC is fracture initiated by plastic deformation. The wear of the etched cermets is similar to pure WC. The presence of the cobalt binder reduces both friction and wear. The cementing action of the cobalt reduces granular separation and promotes a dense polished layer because of its low shear strength film-forming properties. The wear debris generated from unetched surface is approximately the same composition as the bulk. Presented as an American Society of Lubrication Engineers paper at the ASLE/ASME Lubrication Conference...

Friction and wear of metals in contact with pyrolytic graphite

Abstract Sliding friction experiments were conducted with gold, iron, and tantalum single crystals sliding on prismatic and basal orientations of pyrolytic graphite in various environments including, vacuum, oxygen, water vapor, nitrogen and hydrogen bromide. Surfaces were examined in the clean state and with various adsorbates present on the graphite surfaces. LEED, Auger spectroscopy, SEM, and EDXA were used to characterize the graphite surfaces. Results indicate that the prismatic and basal orientations do not contain nor do they chemisorb oxygen, water vapor, acetylene, or hydrogen bromide. All three metals exhibited higher friction on the prismatic than on the basal orientation and these metals transferred to the atomically clean prismatic orientation of pyrolytic graphite. No metal transfer to the graphite was observed in the presence of adsorbates at 760 torr. Ion bombardment of the graphite surface with nitrogen ions resulted in the adherence of nitrogen to the surface.

The atomic nature of polymer-metal interactions in adhesion, friction and wear

The polymers PTFE (polytetraf1uoroethylene) and polyimide were studied contacting various metals in adhesion and sliding friction experiments. Field ion microscopy and Auger emission spectroscopy, were used to examine the nature of the polymermetal interactions. Strong adhesion of polymers to all metals in both the clean and oxidized states was observed. Adhesive bonding was sufficiently strong with the cohesively weaker metals such as aluminum that metal transferred to the polymers. Adhesion coefficients measured approach those for clean metals in contact and field ion microscopy indicates that the polymer to metal bonds are chemical in nature. The field ion microscope also indicates that polymer fragments transferred to cohesively strong metals such as tungsten and that these fragments are highly oriented. Auger emission spectroscopy indicates that a single pass of PTFE across a metal surface is sufficient to generate a transfer film. Electron induced desorption of the PTFE from the metal surface indicates that bonding to the metal is via the carbon atom with little to no fluorine to metal interaction.

Use of a nitrogen–argon plasma to improve adherence of sputtered titanium carbide coatings on steel

Friction and wear experiments on 440‐C steel surfaces that had been rf sputtered with titanium carbide when a small percentage of nitrogen was added to the plasma were conducted. X‐ray photoelectron spectroscopy and x‐ray diffraction were used to analyze the resultant coatings. Results indicate that a small partial pressure of nitrogen (∠0.5%) markedly improves the adherence, friction, and wear properties when compared with coatings applied on sputter‐etched, oxidized surfaces or in the presence of a small oxygen partial pressure. The improvements are related to the formation of an interface containing a mixture of the nitrides of titanium and iron which are harder than their corresponding oxides.

Adherence of sputtered titanium carbides

Abstract Sputtered coatings of the refractory metal carbides are of great interest for applications in which hard wear-resistant materials are desired. The usefulness of sputtered refractory carbides is often limited in practice by spalling or interfacial separation. In this work improvements in the adherence of refractory carbides on alloys based on iron, nickel and titanium were obtained by using oxidation, reactive sputtering or sputtered interlayers to alter the coating-substrate interfacial region. X-ray photoelectron spectroscopy and argon ion etching were used to characterize the interfacial regions, and an attempt was made to correlate adherence as measured in wear tests with the chemical nature of the interface.

Improved adhesion of sputtered refractory carbides to metal substrates

Abstract Sputtered coatings of the refractory metal carbides are of great interest for applications where hard wear-resistant materials are desired. The usefulness of sputtered refractory carbides is often limited in practice by spalling or interfacial separation. In this work improvements in the adherence of refractory carbides on iron, nickel and titanium base alloys were obtained by using oxidation, reactive sputtering or sputtered interlayers to alter the coating-substrate interfacial region. X-ray photoelectron spectroscopy and argon ion etching were used to characterize the interfacial regions, and an attempt was made to correlate adherence as measured in wear tests with the chemical nature of the interface.