F. S. Cohen, Pratt & Whitney, Hartford, CT
The high cycle fatigue properties of Ti-6Al-4V with six different microstructure/texture combinations were investigated. Only material with lamellar microstructure exhibited linear Goodman relationship on the constant fatigue life diagram. Material with coarse bimodal and equiaxed microstructures had pronounced mean stress sensitivity, with HCF strength at mean stresses being significantly lower than predicted by Goodman relationship.Investigation of fatigue crack initiation process by replication technique showed that in most cases crack first initiates in the alpha grain, resulting in formation of flat alpha facet on the fracture surface. Results of fractography analysis indicate that most likely these facets are formed by cleavage on the basal plane.
Predictive model for the effects of microstructure and texture on the fatigue strength of a/b titanium alloys have been developed based on the statistical analysis of fatigue data.
Mean Stress Sensitivity Parameter was introduced as a measure of convexity in the Goodman construction and related to the texture characteristics of the material.
Summary: The high cycle fatigue properties of Ti-6Al-4V with six different microstructure/texture combinations were investigated. Only material with lamellar microstructure exhibited linear Goodman relationship on the constant fatigue life diagram. Material with coarse bimodal and equiaxed microstructures had pronounced mean stress sensitivity, with HCF strength at mean stresses being significantly lower than predicted by Goodman relationship.
Investigation of fatigue crack initiation process by replication technique showed that in most cases crack first initiates in the alpha grain, resulting in formation of flat alpha facet on the fracture surface. Results of fractography analysis indicate that most likely these facets are formed by cleavage on the basal plane.
Predictive model for the effects of microstructure and texture on the fatigue strength of ƒÑƒ}ƒÒƒntitanium alloys have been developed based on the statistical analysis of fatigue data.
Mean Stress Sensitivity Parameter was introduced as a measure of convexity in the Goodman construction and related to the texture characteristics of the material.
