Fatigue of metallic microdevices and the role of fatigue-induced surface oxides

• Published in: Acta materialia 2004-04, Vol.52 (6), p.1609-1619
• Main Authors: Boyce, B.L., Michael, J.R., Kotula, P.G.
• Format: Article
• Language: English
• Subjects: Analytical electron microscopy; Applied sciences; Condensed matter: structure, mechanical and thermal properties; Electronics; Electroplating; Exact sciences and technology; Fatigue; Fatigue, brittleness, fracture, and cracks; Mechanical and acoustical properties of condensed matter; Mechanical properties of solids; Micro- and nanoelectromechanical devices (mems/nems); Nickel; Oxidation; Physics; Semiconductor electronics. Microelectronics. Optoelectronics. Solid state devices
• ISSN: 1359-6454; 1873-2453
• DOI: 10.1016/j.actamat.2003.12.032

A new method for fatigue testing of metallic micro-electro-mechanical systems has been developed and applied to characterize the high-cycle fatigue behavior of nickel microspecimens formed by the LIGA process. Cantilever microbeams with a cross-section of 26 × 250 μm were tested under fully reversed loading conditions at 20 Hz. The observed stress-life curve and fatigue limit was similar to what has typically been reported for conventional bulk nickel. SEM inspection of the fatigue surface revealed that failure initiated in zones of localized extrusions and intrusions associated with persistent slip bands (PSBs). Focused ion beam machining was used to extract a cross-sectional TEM foil from the deformation zone, revealing an unexpected thick (up to 400 nm) oxide on the surface of the PSBs. This PSB oxide thickening mechanism appears to be the source of crack initiation.