A Quantitative Assessment of Microtexture in Titanium Alloys using Destructive and Nondestructive Methods
Microscopy and Microanalysis
Due to the need to balance high performance with safety, ultrasonic inspection is routinely performed on many critical aerospace components at various stages of manufacturing. For instance, cylindrical titanium billets are inspected to look for nitrogen-stabilized defects (hard alpha). After forging, the material is machined into its sonic shape which enables rapid analysis using scanning ultrasound (or phased array) systems. While these inspections are generally pass/fail with very little
... th very little additional information being stored or utilized, there is actually a wealth of information in the ultrasound data related to microstructure. In the case of titanium alloys, mostly owing to the two-phase structure and elastic anisotropy, the microstructure evolution mechanisms are generally of the non-classical type, i.e. there is no classical nucleation and growth of high angle grain boundaries, but rather dislocation climb and glide result in continuous evolution of the microstructure and texture from the initial to final condition. Based on this knowledge, Semiatin and co-workers  have developed a series of microstructure and texture evolution models for sub-ß-transus worked two-phase titanium alloys. The final critical aspect to consider in titanium alloys is the effect of microtexture, or large clustered regions of primary alpha particles of similar orientation. These microtextured regions (MTRs) are particularly deleterious to dwell fatigue properties in near-alpha titanium alloys, but also impact fatigue lifetime variability in general as well. From the perspectives of location specific design and serial-number based lifing, it would be beneficial to develop quantitative relationships between the size, shape, spatial orientation, crystallographic orientation and range of alpha particle c-axis misorientations within each MTR which all have first order effects on dwell fatigue properties  . In this paper, we describe a method to obtain size, shape and an effective one-dimensional orientation distribution for MTRs (spread in alpha particle size) by inversion of ultrasound attenuation and backscattering data collected in three-directions. The results are compared to similar measurements obtained from EBSD data.