Ni基合金におけるスモールパンチクリープ試験の荷重/応力換算係数に及ぼす延性の影響

Abstract

Remaining-life assessment of high temperature components using the small punch (SP) creep testing technique necessitates the evaluation of SP load (F)/uniaxial stress (σ) conversion coefficient, F/σ, obtained by comparing the SP and uniaxial creep test results. In the present study, the SP creep tests were carried out at 850°C on various Ni-base alloys having different rupture elongations in the range of 0.06-0.63 to investigate the influence of ductility on the value of F/σ. The F/σ value was determined for each alloy by correlating SP creep rupture data with corresponding uniaxial creep ones. The experimental results revealed that the F/σ value increased with increasing rupture elongation up to 0.45 and remained almost constant at around 2 with further increase of rupture elongation. This result indicated that the SP creep rupture test result could be converted to that of uniaxial one if the ductility on a given material was available. Moreover, the correlation between the F/σ and the equivalent fracture strain in SP creep test specimen were also analyzed to establish a procedure for estimating the stress equivalent to the SP load from the SP creep test result alone. As the result, the variation of F/σ with the equivalent fracture strain was similar to its variation with the rupture elongation.