Accession Number : AD0728239

Title :   Mechanisms of Fatigue in Mill-Annealed Ti-6Al-4V at Room Temperature and 600F.

Descriptive Note : Technical rept. 1 Apr 70-28 Feb 71,

Corporate Author : MIDWEST RESEARCH INST KANSAS CITY MO

Personal Author(s) : Benson,David K. ; Grosskreutz,J. Charles ; Shaw,Gordon G.

Report Date : APR 1971

Pagination or Media Count : 51

Abstract : The mechanisms of the fatigue of mill-annealed Ti-6Al-4V were studied at 600F and room temperature. Early crack initiation (N sub o approximately = or < 0.14 Nf) was found to occur in HCP alpha-grains by a slip-band mechanism under all but the least severe conditions of cyclic stress. Under stresses near the fatigue limit at room temperature, fatigue cracks began much later (No approximately 0.4 Nf) at the interface between HCP alpha- and BCC beta-grains without detectable slip. Under all conditions, Stage 1 fatigue crack growth occupied 50-80% of the total life. Although mechanical twins were produced in profusion near the growing Stage 2 fatigue cracks, they appeared to play no role in crack initiation or Stage 1 crack growth; nor did they facilitate Stage 2 growth. A very thin polygonized layer (approximately 1 micrometer thick) was discovered adjacent to the Stage 2 fatigue crack surfaces. Neither this nor any other of the observations could be interpreted as evidence for a metallurgical instability or strain-induced phase transformation which might be harmful to the fatigue resistance of the alloy. (Author)

Descriptors :   (*TITANIUM ALLOYS, FATIGUE(MECHANICS)), ALUMINUM ALLOYS, VANADIUM ALLOYS, CRACK PROPAGATION, CRACKS

Subject Categories : Metallurgy and Metallography

Distribution Statement : APPROVED FOR PUBLIC RELEASE