Metrological Error
The introduction of systematic inaccuracy into tilt measurements during x ray diffraction strain analysis degrades the validity of calculated residual stress states. When analyzing thin films, tilt calculation corruption arises when specimen misalignment or instrument drift shifts the diffraction peak position. This error leads to incorrect stress values and can result in the rejection of acceptable coatings.
Error Source
Misalignment of the sample stage along the axis of rotation is the primary physical cause of this measurement error. If the sample surface does not coincide with the goniometer center, tilting the sample shifts the peak position independently of any strain in the film. This geometric shift mimics the effect of residual stress, causing a false gradient in the analysis.
This problem is particularly severe in thin film testing, where the diffracted signal is weak and the peak positions are already difficult to resolve.
Systemic Influence
Analysis of the sin2 psi plot reveals this error by showing a non linear or asymmetric relationship that deviates from the expected straight line. This distortion makes it difficult to extract the true slope, which represents the residual stress. The resulting uncertainty can obscure the true mechanical state of the sensor layers, leading to incorrect performance predictions.
Correction Practice
Precise mechanical alignment and the use of reference specimens are utilized to detect and correct for this error. Regular verification of the stage center of rotation ensures that peak shifts are due only to lattice strain. This correction ensures that the residual stress measurements remain accurate and comparable.
