The influence of internal hydrogen and temperature on the second stage fatigue-crack-growth rate da/dN of Ti-5Al-2.5 Sn(ELI) was studied. Between 293K and 413K, da/dN increases with increasing hydrogen contents. with samples containing 82ppm hydrogen, da/dN increase with increasing temperature between 293K and 333K and decrease with increasing temperature between 333K and 413K. With samples containing 420ppm or 795ppm hydrogen, da/dN decrease with increasing temperature between 293K and 413K. In the region of lower stress intensity factor range (ΔK< 36MPa-m~(1/2)), the second stage fatigue-crack-growth is discontinuous, which is a alternate course of growing and stagnating. The growing length is about three times larger than the size of plastic zone ahead of the crack tip, which is approximate to the size of stress ()trains-induced hydrides' zone. Stagnating cycles ΔN-bar increases with increasing temperature and decreases with increasing hydrogen. It was proposed that the apparent crack-growth-rate consists of three parts: da/dN = (da/dN)_M + (da/dN)_I + (da/dN)_(II) (da/dN)_M is determined by pure mechanical effect. (da/dN)_I + (da/dN)_(II) is resulted from the hydrogen effect. (da/dN)_I is as a function of stress (strain)-induced hydrides and (da/dN)_(II) is as a function of original hydrides. The influence of temperature and the stagnating phenomenon in the lower ΔK region are thinked as (da/dN) -controlling, and the influence of hydrogen contents and original hydrides are thinked as (da/dN)_(II)-controlling. The fractographs of Ti-5Al-2.5Sn (ELI) vary as a function of stress intensity level, temperature and hydrogen contents. For small values of ΔK, there are no apparent fatiguestriations. The fractographs identified as cleavage-like characteristic, which is more apparent with more hydrogen. With increasing values of ΔK, fatigue-striations are more and more apparent and the spacing of the striations is larger and larger.
修改评论