0«DTXC QUÄLTET IK'SKüuxiiii) 3
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ABSTRACT (Maximum 200 words)A comprehensive investigation of the nature of fatigue in beta titanium alloys, especially in Ti-10V-3Fe-3Al alloy, emphasizing the crack initiation and crack growth aspects in controlled microstructural conditions, was performed. A detailed survey of literature of past work in this area, was also conducted. It has been found that the fatigue limit in this alloy is independent of the size, shape and volume fraction of the primary alpha particles. The matrix condition, as determined by the aging treatment had a strong influence on the fatigue behavior. It has been found that fatigue resistance could be improved only by controlling the aging treatment, that resulted in changes in the matrix microstructure. A mysterious fatigue behavior, exhibiting dual stress versus number of cycles to failure was also found in one microstructural condition. Aging treatments that resulted in omega phase precipitation, decreased the fatigue strength. In terms of fatigue crack growth response, omega phase increased the resistance to crack growth. Additionally, a strong sensitivity of fatigue crack growth to mean stress was also found with the omega precipitation. An evaluation of fatigue behavior of various titanium alloys was also made. It was concluded that microstructural refinement led to the minimal mean stress sensitivity in conventionally aged beta alloys, in comparison to other titanium alloys. The results are discussed in the light of microstructure, electron microscopy, fractography and quantitatitve determination of chemistry by energy-dispersive chemical analysis.
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SUMMARYA comprehensive investigation of the nature of fatigue in beta titanium alloys, especially in Ti-10V-3Fe-3Al alloy, emphasizing the crack initiation and crack growth aspects in controlled microstructural conditions, was performed. A detailed survey of literature of past work in this area, was also conducted. It has been found that the fatigue limit in this alloy is independent of the size, shape and volume fraction of the primary alpha particles. The matrix condition, as determined by the aging treatment had a strong influence on the fatigue behavior. It has been found that fatigue resistance could be improved only by controlling the aging treatment, that resulted in changes in the matrix microstructure. A mysterious fatigue behavior, exhibiting dual stress versus number of cycles to failure was also found in one microstructural condition.Aging treatments that resulted in omega phase precipitation, decreased the fatigue strength. In terms of fatigue crack growth response, omega phase increased the resistance to crack growth.Additionally, a strong sensitivity of...