An overview is given of recent NPL research to characterise the early stages of crack development in environment-assisted cracking, focusing on the nature of the crack precursors, the pit-to-crack transition, and the impact of solution chemistry on growth rate in the small and long crack growth rate regime. The impact on corrosion and cracking of surface grinding-induced changes in near-surface material and mechanical properties is highlighted, noting that awareness of this aspect in the corrosion community still remains limited. A major feature is the remarkable insight into the evolution of small surface cracks, from dealloyed layers and from corrosion pits, provided by advanced 3D imaging. Finally, further evidence for the concept of the solution conductivity-dependent crack-size effect in stress corrosion cracking and corrosion fatigue is put forward.
SchwartzAJKumarMAdamsBLElectron backscatter diffraction in materials science. 2nd ed.New York (NY): Kluwer Academic / Plenum Publishers; 2000.
2.
ConnollyBJHornerDAFoxSJX-ray microtomography studies of localised corrosion and transitions to stress corrosion cracking. Mater Sci Technol.2006; 22: 1076–1085. doi: 10.1179/174328406X114199
3.
GiannuzziLAStevieFA.Introduction to focused ion beams. New York (NY): Springer; 2005.
4.
TurnbullAWrightLCrockerL.New insight into the pit-to-crack transition from finite element analysis of the stress and strain distribution around a corrosion pit. Corros Sci.2010; 52: 1492–1498. doi: 10.1016/j.corsci.2009.12.004
5.
BurnsJTLarsenJMGangloffRP.The effect of initiation feature on microstructure-scale crack propagation in Al-Zn-Mg-Cu. Int J Fatigue.2012; 42: 104–121. doi: 10.1016/j.ijfatigue.2011.08.001
6.
MaJZhangBWangJAnisotropic 3D growth of corrosion pits initiated at MnS inclusions for A537 steel during corrosion fatigue. Corros Sci.2010; 52: 2867–2877. doi: 10.1016/j.corsci.2010.04.036
7.
GangloffRPSlavikDCPiascikRSDirect current electrical potential measurement of the growth of small cracks. In: LarsenJMAllisonEA, editors. Proceedings of small crack test methods, ASTM STP 1149. 1992, p. 116-168.
8.
TurnbullAZhouSLucaszewiczMAn approach to measurement of environmentally assisted small crack growth. Proceedings of Corrosion 2013, NACE International; 2013, Paper no, C-2013-0002122.
9.
OlsztaMJThomasLEAsanoKCrack initiation precursors originating from surface grinding. Proceedings of the 14th Int. Conf. on Environmental Degradation of Materials in Nuclear Power Systems, Virginia Beach; 2009. p. 549-561.
10.
GhoshSKainV.Effect of surface machining and cold working on the ambient temperature chloride stress corrosion cracking susceptibility of AISI 304L stainless steel. Mater Sci Eng.2010; 527: 679–683. doi: 10.1016/j.msea.2009.08.039
11.
LuZShojiTDanTThe effect of roll-processing orientation on stress corrosion cracking of warm-rolled 304L stainless steel in oxygenated and deoxygenated high temperature pure water. Corros Sci.2010; 52: 2547–2555. doi: 10.1016/j.corsci.2010.03.027
12.
Lozano-PerezSYamadaTTerachiTMulti-scale characterization of stress corrosion cracking of cold-worked stainless steels and the influence of Cr content. Acta Mater. 2009; 57: 5361–5381. doi: 10.1016/j.actamat.2009.07.040
13.
TurnbullAMingardKLordJDSensitivity of stress corrosion cracking of stainless steel to surface machining and grinding procedure. Corros Sci.2011; 53: 3398–3415. doi: 10.1016/j.corsci.2011.06.020
14.
HindsGWickströmLMingardKImpact of surface condition on sulphide stress corrosion cracking of 316L stainless steel. Corros Sci.2013; 71: 43–52. doi: 10.1016/j.corsci.2013.02.002
15.
WickströmLMingardKHindsG. Microcrack clustering and coalescence in stress corrosion cracking of 22 Cr and 25 Cr duplex stainless steels. Corros Sci. 2016; 109: 86–93. doi: 10.1016/j.corsci.2016.03.024
16.
HindsGTurnbullA.Threshold temperature for stress corrosion cracking of duplex stainless steel under evaporative conditions. Corrosion. 2008; 64: 101–106. doi: 10.5006/1.3280678
17.
LynchSP.Mechanistic and fractographic aspects of stress corrosion cracking. In: RajaVSShojiT, editors. Stress corrosion cracking – theory and practice. Cambridge: Woodhead Publishing Ltd.; 2011. p. 1–201.
18.
HornerDAConnollyBJZhouSNovel images of the evolution of stress corrosion cracks from corrosion pits. Corros Sci.2011; 53: 3466–3485. doi: 10.1016/j.corsci.2011.05.050
19.
WrightLTurnbullA.Impact of microtopographical features in pits on stress and strain distribution, NPL Report MAT in preparation.
20.
TurnbullACrockerL.Finite element analysis of the effect of pit shape on the local stress and strain distribution, NPL Report MAT 51, 2011.
21.
ZhouSLukaszewiczMTurnbullA.Small and short crack growth and the solution-conductivity dependent electrochemical crack size effect. Corros Sci.2015; 97: 25–37. doi: 10.1016/j.corsci.2015.03.008
SabelkinVPerelVYMisakHEInvestigation into crack initiation from corrosion pit in 7075-T6 under ambient laboratory and saltwater environments. Eng Fract Mech. 2015; 134: 111–123. doi: 10.1016/j.engfracmech.2014.12.016
24.
NewmanJCJr.RajuIS.An empirical stress-intensity factor equation for the surface crack. Eng Fract Mech. 1981; 15: 185–192. doi: 10.1016/0013-7944(81)90116-8
25.
MurakamiYEndoM.Effect of hardness and crack geometries on ΔKth of small cracks emanating from small defects. In: MillerKJde los RiosER, editors. Proceedings of the behaviour of short fatigue cracks. Cambridge: EGF1, EGF Publication 1, Fatigue of Engineering materials Ltd., University Press; 1986. p. 275-294.
26.
ZhouSTurnbullA.Influence of pitting on the fatigue life of a turbine blade steel. Fatigue Fract Eng Mater Struct. 1999; 22: 1083–1093. doi: 10.1046/j.1460-2695.1999.00226.x
27.
HaddadMHEISmithKNTopperTH.Fatigue crack propagation of short cracks. J Eng Mater Technol ASME. 1979; 101: 42–46. doi: 10.1115/1.3443647
28.
TurnbullAWrightL.Modelling the electrochemical crack size effect on stress corrosion crack growth rate. Corros Sci. 2017.
29.
TurnbullAZhouS.Impact of solution conductivity and crack size on the mechanism of environmentally assisted crack growth in steam turbines. Corros Rev. 2017.
