Influence of substrate pre-treatment on the tribological properties of hard coatings during sliding : doctoral thesis
Podgornik, Bojan, 1970-
Hard PVD coatings are usually very thin and brittle and so the substrate must carry the main part of the applied load. If the substrate has insufficient deformation will occur, leading to premature ...failure of the coating. In this thesis, the influence of the substrate pre-treatment on the tribological properties of hard PVD coatings was studied in terms of microhardness, residual stress, scratch adhesion and the dry sliding wear resistance. Surface treatment of the steel substrate involved hardening with two different tempering temperatures and plasma nitriding with or without a compound layer, while three PVD coatings were deposited on the pre-treated steel substrate: TiN, TiAlN and a hydrogen-free hard-carbon coating. Special emphasis was put on the influence of the hardness and residual stress distribution in the substrate as well as the interfacial bonding on the load carrying capacity and durability of the hard coating. Therefore, results of a number of wear tests in which flat-ended duplex-treated pins were mated to hardened ball bearing steel discs including various surface and subsurface analyses are presented in this thesis. In order to verify the suggested influence of the residual stress present in the pre-treated steel substrate, calculations of contact stress were carried out. The results of this investigation show improved wear properties of the plasma-nitrided hardcoated specimens compared with uncoated and pre-hardened ones. Increased hardness of the substrate, obtained by plasma nitriding, improves the load-carrying capacity of the substrate, which can then effectively support the coating, while interdiffusion between the iron-nitride at the nitrided surface and the thin Ti interlayer deposited at the beginning of the coating process most probably improves coating-to-substrate adhesion. Although previous investigation showed a negative effect of the compound layer, it was found that a precisely controlled plasma nitriding process can lead to a dense, uniform and highly adherent compound layer with a positive effect on the wear properties of pre-nitrided and hard-coated steel.
Type of material - dissertation
; adult, serious
Publication and manufacture - Ljubljana : [B. Podgornik], 2000
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