Fatigue Crack Nucleation and Propagation in Alpha-Beta Titanium Alloys.
POLYTECHNIC INST OF NEW YORK BROOKLYN
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Observations have been made of crack path behavior of alpha-beta Titanium alloys on the surface and in interiors. The fracture surface for an alphaTi-0.4Mn a betaTi-10.2Mn, and an alpha-beta alloy Ti-5.2Mn, have been examined, TEM examiniation of alpha and beta alloys carried out and a study of slip line reversal during load reversal was made. Surface cracking occurs along alpha-beta interfaces and these cracks and joined by link-up. In the interior the crack proceeds along the lines of easiest slip with the result that cracks do not necessarily follow interfaces. The concentration of the crack path in alpha or along alpha-beta interfaces is attributed to higher strain in these regions. Striations are found to be more prominent in beta than in alpha and this is attributed to the higher strain hardening of the alpha phase. Hardening in alpha was attributed to an increase in dislocation density and interaction between twins and dislocations. It was not possible to ascertain whether softening in beta was due to an increase in dislocation density, a decrease in density of the structure giving rise to streaking on diffraction patterns or both. Slip line reversal during reverse straining was found to occur preferentially at grain boundaries.
- Properties of Metals and Alloys