密度ρ=7.0g/cm^3を有する焼結材料の疲労強度に及ぼす気孔寸法と硬さの重要性

概要

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In order to investigate the importance of pore size and hardness on the fatigue strength of a pre-alloyed powder metal (Fe-3.0 Cr-0.5 Mo-0.5 C mass%) with the density of ρ=7.0g/cm^3, ultrasonic fatigue tests were conducted at a test frequency of 20kHz in air at room temperature. The fatigue limit of the powder metal was the maximum critical stress under which fatigue cracks initiating from the pore stop propagating. Therefore, the fatigue limit was accurately predicted by the √<area> parameter model, σ'_ω=1.43(HV+120)/(√<area>)^<1/6>, for the surface defect. Here, as √<area> was employed the effective maximum pore size,√<area_<eff, max>>, in the control volume of the ultrasonic fatigue specimen which was estimated from the statistics of extremes distribution of the pore sizes at the polished surface. As HV was employed Vickers hardness, HV_<98.1N>, of the microstructure which included both the matrix and pores. The usage of √<area_<eff, max>> and HV_<98.1N> in the √<area> parameter model is practical use and useful for predicting the fatigue limit of the powder metal. In addition, the usage of √<area_<eff, max>> indicates that the dominating cause of fatigue strength for the powder metal is the maximum pore size rather than the porosity or density.
社団法人日本機械学会の論文
2009-02-25