Introduction

The detection of defects in titanium billets present challenges that are considerably different from those encountered in traditional aerospace materials. This means that the proven non-destructive testing (NDT) techniques that exist for inspection of defects in more traditional aircraft structures are not appropriate for use in this application. Furthermore, existing NDT techniques currently applied have diminishing usefulness as increased production rates, operator subjectivity, and fatigue drastically decreases the probability of defect detection (POD). The crash of flight UA 232 at Sioux City, Iowa, USA in July 1989, with 111 fatalities, was directly attributable to a fatigue crack initiating from a hard alpha inclusion on the surface of a turbine disc that was not detected during manufacture. Other reports, of similar aircraft incidents involving fatalities have concluded that the current in service NDT inspections had failed to detect defects created during the manufacturing process that subsequently became responsible for the loss of life. This clearly illustrates an obvious and urgent need to develop advanced NDT technologies for application during the manufacture of titanium destined for aircraft components.

The QualiTi project is a collaborative research endeavour pursuing new techniques for reliable and comprehensive inspection of titanium billets. Two NDT technologies are being developed and deployed in parallel in order to achieve these objectives. The inspection of the near surface of the billet is being undertaken using a new eddy current system, while the interior of the billet will be inspected using tailor made 2D phased array (PA) ultrasound system. The following sections will present a detailed view of both systems and their integration.