Accession Number : AD0628277

Title :   FRACTOGRAPHIC ANALYSIS OF TI-7AL-2CB-1TA AND TI-6AL-4V FRACTURES DEVELOPED IN 'WET' FATIGUE.

Descriptive Note : Interim rept.,

Corporate Author : NAVAL RESEARCH LAB WASHINGTON D C

Personal Author(s) : Judy,R. W. ,Jr. ; crooker,T. W. ; Morey,R. E. ; Lange,E. A. ; Goode,R. J.

Report Date : 14 JAN 1966

Pagination or Media Count : 20

Abstract : Crack-growth-rate studies on Ti-7Al-2Cb-1Ta and Ti-6Al-4V alloys in low-cycle fatigue were performed in air and in a 3.5-percent salt-water solution. The Ti-7Al-2Cb-1Ta alloy was additionally tested in distilled water. An increase in crack-growth rate at all strain ranges was observed for the Ti-7Al-2Cb-1Ta in the 'wet' environments over that in the 'dry', whereas the Ti-6Al-4V alloys did not appear to be sensitive to a 'wet' environment. At a strain range of 8000 to 9000 microinches/inch, corresponding to about 60-percent yield strength, the crack-growth rate of Ti-7Al-2Cb-1Ta alloy accelerated and became erratic. Fractographic studies show that the increase in crack-growth rate is due to a change from the ductile mode of fatigue fracture usually found in 'dry' low-cycle fatigue tests of titanium alloys, to the brittle quasi-cleavage mode of fracture-a fracture mechanism of stress-corrosion cracking. The amount of quasi-cleavage seen on the fatigued fracture surface generally corresponds to the crack-growth-rate increase; thus, it is indicative of the degree of stress-corrosion cracking sensitivity. (Author)

Descriptors :   (*TITANIUM ALLOYS, FATIGUE(MECHANICS)), (*FRACTURE(MECHANICS), TITANIUM ALLOYS), STRAIN(MECHANICS), YIELD POINT, STRESS CORROSION, FRACTOGRAPHY, WATER, AIR

Subject Categories : Properties of Metals and Alloys

Distribution Statement : APPROVED FOR PUBLIC RELEASE