抄録
The micro-electro-mechanical systems (MEMS) market requires the development and increased understanding of new micro-scale materials in order to continue to push its capabilities into new markets. Many of the applications of MEMS devices require the material to provide a high yield stress, superior creep strength and increased Young's modulus. These properties should be provided by material with a low density and the ability to be produced in a manner consistent with complicated, small scale components. For MEMS applications, requiring the retention of properties at temperatures in excess of 400℃, the application of compositions based upon the high temperature intermetallic γ-TiAl phase is being considered. A high strength alloy of this type, which has received significant attention in bulk form, is the composition Ti-46Al-5Nb-1W (at %). In this case this material is in the near fully lamellar form, having being produced with a colony size of 75μm. In this work samples with a cross section of ≈ 100μm x 10mm and micro sized cantilever beam samples, measuring ≈ 18μm x 6μm, were used to provide information upon the effect of thickness reductions upon the fracture toughness and fatigue properties of this alloy. This was completed using a specially developed testing machine which utilises a 250mN load cell to provide accurate loading through a diamond tip to such small cantilever beams. The paper includes both a comparison between these micro sized values and those of the thin film material as well as information upon the orientation dependence of these properties resulting from trans- and inter-lamellar failure modes.
