Abstract
The effect of residual hydrogen on mechanical properties and fracture behavior of Ni 3(Si,Ti) single crystals and polycrystals is investigated by tensile tests, using materials with a low level (<0.5 mass ppm) and high level (∼2 mass ppm) hydrogen content, and also with and without a trace amount of boron (50 ppm). Furthermore, the effect of pre-plastic deformation on these phenomena is investigated. Tensile elongation and fracture mode of the Ni 3(Si,Ti) single crystals are primarily insensitive to the hydrogen content. The tensile elongation of the Ni 3(Si,Ti) polycrystals are markedly reduced by a high level of hydrogen content, and associated fractography shows a mainly brittle intergranular fracture pattern. However, boron-doped Ni 3(Si,Ti) polycrystals are not embrittled by a high level of hydrogen content. The tensile elongation of pre-deformed and then hydrogen-charged Ni 3(Si,Ti) polycrystals increases with increasing pre-deformation although absorbed hydrogen content increases. It is suggested that residual hydrogen at ∼2 mass ppm is enough to embrittle the Ni 3(Si,Ti) alloys when the hydrogen is trapped at grain boundaries, but, ineffective when the hydrogen is distributed within the grain interior or trapped at dislocations. Also, it is suggested that boron competes for site occupation with the hydrogen, and/or directly enhances grain boundary cohesion, thereby resulting in the effect of suppressing hydrogen embrittlement.
Published Version
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