Influence of thin coatings deposited by a dynamic ion mixing technique on the fatigue life of TITANIUM ALLOYS

• Published in: Journal of materials science 1999-03, Vol.34 (5), p.1003-1008
• Main Authors: PERAUD, S, VILLECHAISE, P, MENDEZ, J, DELAFOND, J
• Format: Article
• Language: English
• Subjects: Applied sciences; Coatings; Crack initiation; Deformation mechanisms; Diamond pyramid hardness; Exact sciences and technology; Fatigue life; Fatigue strength; Fatigue tests; Film thickness; Fracture mechanics; Intermetallic compounds; Ion implantation; Low cycle fatigue; Materials science; Mechanical properties; Metal fatigue; Metallic coatings; Metals. Metallurgy; Microstructure; Modulus of elasticity; Nickel titanides; Physical vapor deposition; Production techniques; Resonant frequencies; Substrates; Surface treatment; Tensile tests; Thin films; Titanium alloys; Titanium base alloys
• ISSN: 0022-2461; 1573-4803
• DOI: 10.1023/A:1004535709821

The technique of dynamic ion mixing involving a physical vapour deposition method and a simultaneous ion implantation has been used in order to improve the fatigue resistance of two titanium alloys. This process allows the deposition of adherent NiTi and SiC amorphous coatings of the order of 1 μm 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 materials and largely suppress or delay crack initiation. These effects depend, 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 characterized by different techniques: scratch-tests, micro-Vickers indentations, Young's modulus measurements by a resonant frequency method and “fracture stress” determination by in situ tensile tests. The results have shown that their mechanical properties are very different to those of the corresponding classically deposited solid materials and are influenced by the film thickness. The results are discussed according to the mechanical properties of the coatings and the substrate deformation and damage modes associated with their microstructure.