The improvement in wear and corrosion resistanceinduced by vapour-deposited coatings whether chemical (CVD) orphysical (PVD) are well-known. In fact when the applied coating isthick enough it tends to be essentially pore free and denseproviding an excellent barrier protection both in terms ofcorrosion and wear resistance. A typical application area forvapour-deposited coatings on ferrous alloys is the surfacemodification given by TiN or TiC PVD coatings to improve theservice life of high speed steels used for manufacturing cuttingtools. As a surface modification technique PVD is attractivebecause the different procedures proposed in the literature andindustrially developed allow coatings to be obtained of controlledcomposition and strength thus making possible the extended use ofcoated tools for wider application fields such as the die-castingprocess in which die casting dies must withstand thermal shock,thermal fatigue and resistance to molten metals. In the presentpaper both nucleation and propagation of fatigue cracks induced bythermal fatigue cycling on AISI H11 hot work tool steel PVDcoated with chromium nitride and titanium/aluminium nitride havebeen investigated. A farther coating given by a dense film ofmagnetite (Fe_3O_4), employed as corrosion barrier and obtainedby surface oxidation of the same AISI H11 hot work tool steel, hasalso been studied. The obtained thermal fatigue results have beencompared with previous data from tests on the same uncoated steeland have been related to the morphology, chemical compositionand physical proprieties of the tested coatings.
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