PSI - Issue 14

Aman Arora et al. / Procedia Structural Integrity 14 (2019) 790–797

797

8

Aman Aror / St uctural Integ ity Procedia 00 (2018) 000–000

275

Uncharged Sample Hydrogen Charged Sample

120

Uncharged Sample Hydrogen Charged Sample

100

250

-20 Elastic Modulus Difference  GPa) 0 20 40 60 80

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175

150

Elastic Modulus (GPa)

125

0.00

0.05

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0.28

0.32

0.36

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Schmid Factor Difference

Schmid factor

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(b)

Fig. 8. (a) Elastic modulus and schmid factor of crack neighbouring grains (b) Limit of elastic modulus difference and schmid factor difference of crack neighbouring grains in uncharged and hydrogen charged nickel sample 5. Conclusion In the present work, effect of hydrogen on fatigue crack nucleation mechanism in polycrystalline pure nickel samples is shown. Tensile test and fractography confirms the hydrogen embrittlement of nickel specimens. Crack nucleation sites under fatigue loading were characterized using EBSD. Schmid factor and elastic modulus maps of the neighbouring area surrounding the fatigue crack nucleation sites provided better understanding of the effect of hydrogen. It was observed that in uncharged nickel sample, cracks nucleate from grain boundaries with neighbouring grains having high schmid factor and large difference in elastic modulus. However, when hydrogen is present there is local plasticity and negligible elastic modulus difference suggesting grain boundary decohesion irrespective of the type of crack neighbouring grains. References Birnbaum H.K. (2003). Hydrogen Effects on Deformation and Fracture: Science and Sociology. MRS Bulletin, 28(7), 479-485. Cowles B.A. (1989) High cycle fatigue in aircraft gas turbine–an industry perspective. Int J Fract 80(2–3):147–163. Kumar A., Torbet C.J., Pollock T.M., Jones J.W. (2010). In situ characterization of fatigue damage evolution in a cast Al alloy via nonlinear ultrasonic measurements. Acta Mater 58(6):2143–2154. Milligan W.W., Orth E., Schirra J., Savage M. (2004). Effects of microstructure on the high temperature constitutive behavior of IN100. Superalloys 2004:331–339. Latanision R.M., Opperhauser H. (1974). The intergranular embrittlement of nickel by hydrogen: The effect of grain boundary segregation. Metallurgical Transactions (1974) Volume 5: 483-492. Li K., Ashbaugh N.E., Rosenberger A.H. (2004). Crystallographic initiation of nickel-base superalloy IN100 at RT and 538 o C under low cycle fatigue conditions. Superalloys 2004:251. Pollock T.M., Tin S. (2006). Nickel-based superalloys for advanced turbine engines: chemistry, microstructure and properties. J Propuls Power 22(2):361–374. Stinville J.C., Lenthe W.C., Miao J., Pollock T.M. (2015b). A combined grain scale elastic-plastic criterion for identification of fatigue crack initiation sites in a twin containing polycrystalline nickel-base superalloy. Acta Mater 103:461–473. Stinville J.C., Lenthe W.C., Pollock T.M . , Echlin M.P., Callahan P.G., Texier D. (2017). Microstructural statistics for fatigue crack initiation in polycrystalline nickel-base superalloys Int J Fract (2017) 208:221–240. Texier D., Gómez A.C., Pierret S., Franchet J-M., Pollock .TM., Villechaise P., Cormier J. (2016). Microstructural features controlling the variability in low-cycle fatigue properties of alloy inconel 718DA at intermediate temperature. Metall Mater Trans A 47(3):1096–1109. Deng Y., Barnoush A. (2017). Hydrogen embrittlement revealed via novel in situ fracture experiments using notched micro-cantilever specimens. Acta Materialia 142 (2017) 236-247.