The effects of load and substrate hardness on the development and maintenance of wear-protective layers during sliding at elevated temperatures

Transitions to low wear rates often occur during sliding between contacting metal surfaces, due to the establishment of high-resistance load-bearing l ayers. Such layers are developed from compaction of wear debris particles, with adhesion between the particles being an important factor in determinin g whether the layers are maintained, leading to wear protection, or break d own, leading to abrasive wear. They are formed more easily and retained mor e effectively at higher temperatures, due to increased sintering and adhesi on between the debris particles and to enhanced oxidation of these particle s. This paper presents the results of a study of the reciprocating sliding wear and friction of dissimilar combinations of pin and disc steel specimen s (high-speed steel and high-chrome steel pins and carbon steel discs) at t emperatures of 500-600 degreesC, with emphasis on the influence of load and substrate hardness on the development and maintenance of such wear-protect ive particulate layers. Complex relationships occur between the effects of increased load in producing larger debris particles, in decreasing the crit ical particle size for establishing the layers and in decreasing the separa tion between the sliding surfaces, and the effects of hardness of the subst rates on the sizes and amounts of wear particles and on the topographies of the wear scars. The relationships are complicated further by oxidation and sintering of debris particles, leading to development of oxide or oxide-co ntaining 'glaze' surfaces, and subsequent breakdown of the layers during sl iding. (C) 2001 Elsevier Science B.V. All rights reserved.