Microstructural Stabilization
A thermal treatment process executed after thin film deposition stabilizes the crystalline structure and reduces the electrical drift of the sensor. Through post deposition annealing, the sputtered film is heated to a controlled temperature to promote grain growth and remove crystal defects. This thermal process ensures that the sensor has stable electrical properties during subsequent service.
Annealing Process
Inconel substrates and platinum sensing elements are typically heated in a vacuum or controlled atmosphere to prevent oxidation of the metal. The annealing temperature is selected to be higher than the intended operating temperature to ensure that further structural changes do not occur in the field. This heating profile is maintained for a specified duration before cooling at a slow rate.
This slow cooling rate prevents the formation of new thermal stresses that could weaken the bond between the ceramic and the superalloy substrate.
Stress Relief
Internal stresses developed during sputtering are relieved during this thermal treatment as the atoms rearrange into more stable lattice positions. Sputtered films often contain high compressive or tensile stresses that can cause delamination if not addressed. The reduction of these stresses improves the adhesion and long term mechanical reliability of the sensor assembly.
Verification Testing
X ray diffraction analysis confirms the phase purity and grain size modification resulting from this thermal treatment. This analysis verifies that the crystal structure has stabilized, which correlates with a lower rate of sensor drift during subsequent high temperature operation. This measurement completes the manufacturing and quality assurance cycle.
