A Low TCR Nanocomposite Strain Gage for High Temperature Aerospace Applications

Ceramic strain gages are being developed to monitor the structural integrity of gas turbine engine components employed in aerospace propulsion and power generation systems. Specifically, ceramic thin film strain gages based on indium-tin-oxide (ITO) and refractory metal (Pt, W, Ni, NiCoCrAlY) nanocomposites were investigated to achieve very low TRC´s in the active strain element. Nanocomposite sensor elements were prepared from a number of ITO/Pt combinatorial libraries by co-sputtering onto alumina substrates placed in between ITO and Pt sputtering targets. Temperature coefficient of resistance (TCR) measurements of the resulting nanocomposites were made by thermally cycling the strain sensors from room temperature to 1000degC and measuring the piezoresistive response from room temperature to 1200degC at strain levels up to 1000 muepsiv. The chemical composition of the most promising combinatorial libraries was analyzed by EDS /SEM. Preliminary results indicated that a near zero TCR could be achieved over an extended temperature range in nanocomposite strain sensors containing less than 10% ITO. Even though EDS revealed that the bulk of the nanocomposite strain sensor was platinum, a relatively large gage factor (~26.0) and low drift rate (0.018%/hr) were realized with the nanocomposite. Based on these results, other combinatorial libraries employing ITO-refractory metal nanocomposites including ITO-W, ITO-Ni and ITO-NiCoCrAlY were investigated for high temperature strain gage applications. These combinations did not perform as well as ITO-Pt in terms of TCR and piezoresistive response when compared to those established for the ITO-Pt nanocomposite gages.