PSI - Issue 14

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

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Aman Arora/ Structural Integrity Procedia 00 (2018) 000–000

4. Experimental results and Discussion

4.1 Tensile test and Fractography As can be seen in Fig. 3 ductility of nickel sample has been reduced by almost 45 % and ultimate tensile strength by 12 % after charging it with hydrogen. A little increase in yield strength can be seen after hydrogen charging

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Stress (MPa)

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Fig.3. Stress-Strain graph of tensile test with and without hydrogen charging

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Fig. 4. Scanning Electron Micrographs of fractured surface after tensile testing. (a) Uncharged specimen showing dimpled surface typical of ductile material. (b) Hydrogen charged sample showing intergranular facets like brittle material . which could be due to resistance or pinning of dislocation nucleation by hydrogen cottrell atmospheres (Latanision et.al. 1974). We have also analysed fractured surface of uncharged nickel sample and hydrogen charged nickel sample as shown in Fig. 4. Uncharged nickel sample fractured with dimple on its surface that are typically due to coalescence of micro voids in ductile material like nickel. However, hydrogen charged sample fractured in a brittle manner as can be seen in Fig. 4(b) with completely granular faceted surface along with slip bands. 4.2 Grain configurations favouring crack initiation in uncharged and Hydrogen charged Nickel Sample The associated EBSD map of annealed and uncharged nickel sample has been shown in Fig. 5 which gives an idea