The influence of hydrogen permeation properties on notch tensile strength of IN718 superalloy in hydrogen-containing environment

• Main Author: 林素嫻
• Other Authors: 蔡履文
• Format: Others
• Language: zh-TW
• Published: 2002
• Online Access: http://ndltd.ncl.edu.tw/handle/12803285625477842683

碩士 === 國立海洋大學 === 材料工程研究所 === 90 === Solution-annealed specimens after 704oC/20 hr aging treatment comprise of predominantly intragranular precipitation ofγ"(Ni3Nb) with a less amount of γ''[Ni3 (Al,Ti)]. Solution-annealed specimen consists of an equiaxed grain with annealing twins inside, and is free of any fine precipitates except for some randomly distributed, blocky carbides. Two precipitatesγ"(Ni3Nb) and γ''(Ni3Ti) after aging treatments were found, which had been confirmed through X-ray diffraction. For smooth tensile specimens, the results of tensile tests indicated that aged specimens had an obviously higher strength and lower ductility than that of the solution-annealed specimens, which could be attributed to the precipitation of strengthening particles within the matrix . Notched tensile strength (NTS) of various specimens tested in air, gaseous hydrogen and saturated H2S solution. The aged and laser-treated specimens had nearly same NTS, and far greater than that of the solution-annealed one. The solution-annealed specimen still provide a higher plastic deformation before fracture than other specimens. Both aged and laser-treated specimens behaved the same trend during loading. It indicated that the Deff of the solution-annealed specimen was about four times greater than that of the aged specimen, and the difference in permeation flux between them was limited. Both specimens showed an extremely high hydrogen solubility, especially for the aged specimen as high as 17500 mole H/m3 . The relatively low diffusivity and high solubility of the aged specimen could be attributed to the presence of fine precipitates ( reversible trapping sites ) absorbed and retarded the hydrogen diffusion inward.