S. Peraud et al., Influence of thin coatings deposited by a dynamic ion mixing technique on the fatigue life of titanium alloys, J MATER SCI, 34(5), 1999, pp. 1003-1008
The technique of dynamic ion mixing involving a physical vapour deposition
method and a simultaneous ion implantation has been used in order to improv
e the fatigue resistance of two titanium alloys. This process allows the de
position of adherent NiTi and SIC amorphous coatings of the order of 1 mu m
thick. Both treated substrates have been tested at room temperature in the
low cycle fatigue range, revealing significant fatigue life improvement..
NiTi and SiC films modify the surface deformation mechanisms of fatigued ma
terials and largely suppress or delay crack initiation. These effects depen
d, however, on the nature! of the film, the microstructure of the substrate
and the stress amplitude applied during the fatigue tests. To explain the
fatigue results, the mechanical properties of these thin films have been ch
aracterized by different techniques: scratch-tests, micro-Vickers indentati
ons, Young's modulus measurements by a resonant frequency method and "fract
ure stress" determination by in situ tensile tests. The results have shown
that their mechanical properties are very different to those of the corresp
onding classically deposited solid materials and are influenced by the film
thickness. The results are discussed according to the mechanical propertie
s of the coatings and the substrate deformation and damage modes associated
with their microstructure. (C) 1999 Kluwer Academic Publishers.