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T h ic k-Bou nda r y-F i I m Form at ion by Friction Modifier Additives-The addition of friction modifiers to lubricants has been the subject of study for a number of years. Two main models have emerged, a thick-film and a thin-film or monolayer model, but it is uncertain which materials and conditions produce which results. The present work, therefore, looked at whether certain additives form thin or thick films in rolling and I or rolling-sliding contacts; the practical effect of any thick-film formation behaviour; and the nature and structure of boundary films formed. Using ultrathin-film interferometry, tests were performed on a rig, with two commercial friction modifiers, a copper carboxylate soap, and a dimerised unsaturated carboxylic acid, i n hexadecane and in a solvent-refined mineral oil. The results showed that both additives formed thick films in high-pressure rolling and sliding contacts at slow speeds. However, the nature of the films is determined by temperature and speed, and under certain conditions they can be destroyed.

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The microstructure of additively manufactured Ti-6Al-4V (Ti64) produced by a laser powder bed fusion process was studied during post-build heat treatments between 1043 K (770 °C) and just above the b transus temperature 1241 K (1008 °C) in situ using high-energy X-ray diffraction. Parallel studies on traditionally manufactured wrought and annealed Ti64 were completed as a baseline comparison. The initial and final grain structures were characterized using electron backscatter diffraction. Likewise, the initial texture, dislocation density, and final texture were determined with X-ray diffraction. The evolution of the microstructure, including the phase evolution, internal stress, qualitative dislocation density, and vanadium distribution between the constituent phases were monitored with in situ X-ray diffraction. The as-built powder bed fusion material was single-phase hexagonal close packed (to the measurement resolution) with a fine acicular grain structure and exhibited a high dislocation density and intergranular residual stress. Recovery of the high dislocation density and annealing of the internal stress were observed to initiate concurrently at a relatively low temperature of 770 K (497 °C). Transformation to the b phase initiated at roughly 913 K (640 °C), after recovery had occurred. These results are meant to be used to design post-build heat treatments resulting in specified microstructures and properties.