QUANTITATIVE ASSESSMENT OF THE DETECT ABILITY OF CERAMIC INCLUSIONS IN STRUCTURAL TITANIUM CASTINGS BY X-RADIOGRAPHY

摘要

Titanium HIP casting offer tremendous potential as a design option in structural applications. In damage tolerant structures, the design process must include consideration of the inherent producibility of the production process. Producibility necessarily includes the capabilities and limitation of nondestructive inspection procedures used in production and acceptance. An effects of defects analysis for each component application must be included in the design process. There are often shortfall in engineering/producibility data to support a new design application and such data must be developed as a part of the component design qualification. The capabilities of X-radiography for detection of ceramic (shell) inclusions that are inherent to the titanium casting process were not available and the data described in this paper was developed to support the component design qualification. Detection of the ceramic shell unfortunately falls below the classical limit that can be characterized by predictive models based on signal/noise margins and required experimental characterization as an image pattern recognition problem. A probability of detection (POD) design of experiment and data analysis protocol was used to quantify the capabilities of the inspection procedures and for use in the design analysis processes. The data described is the result of four independent X-radiographers capabilities to discriminate ceramic shell anomalies of varying sizes in various titanium thicknesses. Four different shell (facecoat) formulations from different vendors were characterized by this process. The results were used to improve facecoat formulations for increased detectability and the work was eventually expanded to seven different formulations and several additional X-radiographers after the data described herein was analyzed. Nondestructive inspection is often based on a causal relationship between the signal/artifact that can be generated by the inspection procedure and the desired physical condition to be quantified. In this program, the X-radiographic procedure was capable of detecting and quantifying the inherent shell size, but could not quantify the "halo" of affected area surrounding the shell inclusion. An additional task was therefor required to generate the causal relationship between the detected shell and the corresponding anomaly that was considered in damage tolerant and life-cycle (design) analyses. The combined tasks of functional design, component producibility analysis and nondestructive inspection engineering design enables design, production and life-cycle maintenance of new engineering machines and missions with a confidence level that was previously unattainable. The integrated role of design and nondestructive inspection engineering is clearly demonstrated in the work described.