In situ X-ray stress analysis at high temperatures in CVD steel-substrate compounds

Thin hard coatings deposited by chemical vapour deposition (CVD) techniques on to various substrate materials lead to considerable improvement in the tribological and corrosion behaviour of coated components, provided that su itable residual stresses are present. The distinction between deposition in duced intrinsic and thermally induced residual stresses in coated parts is well accepted. Thermal stresses were introduced into the coating-substrate compound upon cooling to room temperature from the high temperatures applie d in CVD processes. The resulting residual stress states, which affect the mechanical and tribological behaviour of the coatings, are attributed to th e different thermal expansion coefficients of substrate materials and hard coatings. The calculation of residual stresses in CVD hard coatings often d iffers from the experimentally examined stresses measured by X-ray diffract ion. The development of residual stresses in steel substrates coated with C VD TiCN was studied in situ while heating specimens from 21 up to 800 degre es C, with subsequent cooling to room temperature. The measurements clearly show non-linear behaviour in the development of residual stresses in the s ubstrate resulting from plastic deformation. (C) 1999 IoM Communications Lt d.