A novel use of the electron backscattered diffraction (EBSD) characterization technique for study of fracture has been demonstrated. This new approach has been employed for characterization and analysis that contribute to the understanding of crack initiation in Ti-6242 under dwell-fatigue loading conditions. A faceted crack initiation site is typically observed on the dwell-fatigue fracture surface of Ti-6242. The level of microtexture has a major influence on the dwell-fatigue failures in near-␣ titanium alloys, such as Ti-6242. In this study, serial sectioning and EBSD techniques were used to obtain the orientation images of almost the entire specimen cross section at different depths below the fracture surface. The orientation images are color coded on three different bases: the angle between the loading axis and basal plane normal, the Schmid factor for prism slip, and the Schmid factor for basal slip. The aim was to determine the important aspects of the crystallographic orientation and the size of the microtextured region that is associated with the faceted initiation site. The results of this study are used to explain the possible locations of crack initiation in a test specimen under dwell-fatigue loading condition. These results are also used to better understand the role of size of microtextured regions in determining which crack will outgrow the other cracks (for the case of multiple cracking typically observed in the alloy of current study under the dwell-fatigue loading conditions) to become the dominant crack that leads to eventual specimen failure. This understanding has important practical implications because the dominant crack effectively determines the specimen life.

Af aceted initiation site is observed in Ti-6242 alloy for both the cyclic and static-loading test conditions. In thise xperimental study, the crystallographic orientation of the facets has been determined usingt he electron backscattered diffraction (EBSD) technique in conjunction with the quantitativetilt fractography in ascanning electron microscope (SEM).Quantitative tilt fractography analysis has been used to determinethe spatial orientation of fracture facets.The results indicatethat the normal-fatigue (no-dwell) fracture facets are oriented at ; 5d eg with respect to the basal plane; the dwell-fatigue fracture facets are oriented at ; 10 to 15 deg with respect to the basal plane and the static-loading fracture facets are oriented at ; 20 degw ith respect to the basal plane. These crystallographic orientation determinations of the fracture facets at the crack-initiation site can be used to obtain an idea about the type of loading that produced them.

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This article presents the results of a recent study of the response of an ␣/␤-forged Ti-6Al-2Sn-4Zr-2Mo alloy during static, normal-fatigue, and dwell-fatigue loading. The plastic-strain accumulation under different loading conditions is reported. The failure modes and associated fractographic features under static, normal-fatigue, and dwell-fatigue loading conditions are also discussed. These results are used to obtain a better understanding of the relative contributions of the cyclic and creep processes to the overall damage under dwell-fatigue conditions.

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