Effects of vacuum environment on small fatigue crack propagation in Ti–6Al–4V

Abstract

a b s t r a c tSmall fatigue crack propagation tests were conducted on Ti-6Al-4V in ultrahigh vacuum, air, and argon to clarify the effects of vacuum on crack propagation processes. The crack propagation rate in vacuum was significantly lower than that in air. The crack propagation rate in argon agreed with that in air in the small crack regime; however, it became similar to that in vacuum in the long crack regime. This indicates that the existence of gases has significant effects in the small crack regime, even if they are chemically inert. These results led us to conclude that, in addition to chemical inactivity, the absence of physical adsorption plays an important role in the retarding effect of vacuum on small crack propagation.

Vacuum effects on fatigue crack growth in submicrometre‐thick freestanding copper films

“…In the middle‐Δ K region, d a /d N was smaller in vacuum than in air: d a /d N in vacuum was roughly one‐fourth of that in air. These results of a decrease in d a /d N in vacuum are consistent with that observed in bulk metals . However, as shown in Figure B, d a /d N in air and vacuum was reversed as Δ K decreased in the low‐Δ K region: d a /d N rapidly decreased in air as Δ K decreased and reached a fatigue threshold, Δ K th,air , of 1.3 to 1.5 MPam 1/2 (indicated by downward arrows in Figure ).…”

“…These results of a decrease in da/ dN in vacuum are consistent with that observed in bulk metals. 7,9,11,[18][19][20] However, as shown in Figure 7B, da/ dN in air and vacuum was reversed as ΔK decreased in the low-ΔK region: da/dN rapidly decreased in air as ΔK decreased and reached a fatigue threshold, ΔK th,air , of 1.3 to 1.5 MPam 1/2 (indicated by downward arrows in Figure 7). By contrast, da/dN was larger in vacuum than in air even for ΔK ≲ 1.4 MPam 1/2 , and the crack still propagated below ΔK th,air .…”

Effect of forging process on high cycle and very high cycle fatigue properties of TC4 titanium alloy under three‐point bending

“…The fracture SEM analysis shows that as the maximum stress decreases, the crack initiation position shifts from the surface to the subsurface, and the fatigue crack initiation is the result of the competition between surface slip and internal cleavage. Due to the complexity of the titanium alloys' very high cycle fatigue damage mechanism, scholars in China and abroad have also studied the effects of microstructure, 13,14 surface treatment, 15,16 loading environment, 17,18 and test frequency 19–22 …”

The fatigue crack growth behaviour of 2524‐T3 aluminium alloy in an Al2O3 particle environment

“…Besides, with the increase of air humility, the FCGR of Al alloy usually increases, 9,10 because the fresh fracture surface of Al alloy can react with the moisture in the air to produce hydrogen, thus inducing hydrogen embrittlement. Compared with those in air, the FCGR of Al alloy exhibits significant degradation in vacuum or inert gas environments especially in the early stage of crack propagation, 11 which is believed to be due to promotion of the reverse-slip process caused by isolating the oxygen from Al alloy. In addition, many studies indicated that 12 the FCGR of Al alloy generally increases in saline solution due to the pitting caused by the corrosion reaction between the inclusions and chloride ions.…”