Part 2. Metallurgical factors governing the H-assisted intergranular cracking of peak-aged Ti-3Al-8V-6Cr-4Mo-4Zr (Beta-C)
A previous study (Part 1) showed that the solution-treated and aged (STA) (i.e., peak-aged) condition of Beta-C Ti, ({sigma}{sub 0.2 pct y} = 865 MPa), as measured by reductions in the fracture initiation stress with predissolved H content and the introduction of an intergranular (IG) fracture mode. It was also shown that yield-strength elevation and the subsequent enhancement in the local hydrostatic stresses within the notch root are not the controlling factors in the H-assisted IG fracture initiation of the STA condition. Previous work (Part 1) implicates a microstructural feature or condition associated with the 500 C aging treating. In this study, it is shown that localized internal hydride precipitation at the grain boundaries or alpha beta interfaces was not detected by a variety of experimental methods over the range of internal H contents for which IG fracture initiation was observed. It was also shown that grain-boundary alpha colonies or films are not responsible for the IG fracture initiation in the STA condition. A measured increase in hydrogen embrittlement (HG) susceptibility as a function of aging time at 500 C is consistent with the segregation or depletion of a critical species at the grain boundary. However, grain-boundary segregation/depletion could not be detected with Auger electron spectroscopy (AES) of specimens fracturing in a vacuum. Compression tests used to characterize and compare the alloys' slip behavior showed that plastic deformation is concentrated at or near the grain boundaries in the STA condition. Therefore, a possible intergranular fracture initiation mechanism that includes the effects of hydrogen and localized deformation is discussed.
- Research Organization:
- Naval Surface Warfare Center, West Bethesda, MD (US)
- OSTI ID:
- 20014047
- Journal Information:
- Metallurgical and Materials Transactions. A, Physical Metallurgy and Materials Science, Journal Name: Metallurgical and Materials Transactions. A, Physical Metallurgy and Materials Science Journal Issue: 1 Vol. 31; ISSN MMTAEB; ISSN 1073-5623
- Country of Publication:
- United States
- Language:
- English
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