No abstract

The lifetime of thermal barrier coating (TBC) systems on gamma titanium aluminides was determined in the temperature range between 850°C and 950°C under cyclic oxidation conditions in air. Coupons of the alloy Ti-45Al-8Nb (at.%) were coated by pack aluminizing. A subset of samples was subsequently annealed at 910°C for 312 h in argon. During this heat treatment, the two-phase (Nb,Ti)Al 3 plus TiAl 2 microstructure of the coating transformed into single phase c-TiAl. On pre-oxidised aluminized, annealed and bare samples, TBCs of yttria partially stabilized zirconia were deposited using electron-beam physical vapour deposition (EB-PVD). No spallation of the TBCs was observed in cyclic oxidation tests at 850°C for up to 3,000 cycles of 1 h dwell time at high temperature. The two-phase aluminide coating provided effective oxidation protection due to the formation of a continuous alumina scale. The lifetime of this TBC system exceeded 1,400 cycles at 950°C, whereas an aluminized and annealed sample failed after approximately 500 cycles. The TBC on bare substrate failed when thermally cycled at 900°C. In contrast, no spallation occurred with an aluminized and annealed specimen at this temperature during the maximum exposure length of 1,000 cycles, probably related to an increased aluminium concentration in the subsurface region.EB-PVD zirconia top coats were well adherent to the alumina scale and the thermally grown mixed oxides. Failure of the TBC systems observed with bare and annealed samples was associated with spalled oxide scales formed on c-TiAl.

No abstract

A standard complementary metal‐oxide‐semiconductor (CMOS) process is successfully modified to encompass the preparation of suspended TiN membranes of only 50 nm thickness from one of the metal layer stacks of the back‐end flow. The layers’ elastomechanical constants are determined with high precision by laser Doppler vibrometry. Residual stress gradients are compensated and a state of moderate tensile strain is introduced into the membranes. Test systems of TiN beams and bridges operating in a capacitive coupling scheme are optimized for the low voltage range attainable with CMOS devices. TiN actuators are particularly suited for applications in biotechnology like sensing of pressure or viscosity in microfluidic devices due to their high corrosion resistance in liquid electrolyte surroundings. The established inclusion of the process in a CMOS pilot line enables the production of cheap and monolithically integrated microelectromechanical systems (MEMS) and bio‐microelectromechanical systems (BioMEMS) devices.

No abstract