VC被覆鋼の疲労強度に及ぼす平均応力の影響

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The effect of mean stress on the endurance limit of thin hard coatings has been studied by utilizing bending fatigue tests on SCM440 and ASP30, and axial loadling fatigue tests on SKD11 and SKD61. The fatigue tests have been made on the specimens VC-coated by the thermo-reactive deposition and diffusion method, namely the molten salt bath immersion method, and the quenched-and-tempered specimens for reference. The experimental results indicated that the endurance limit σ_ωwas predicted by treating the mean stress σ_m and the substrate residual stress σ_r in equivalence. The endurance limit was not influenced by the existence of a coating layer, even when the coating layer was cracked by high compressive stress under the first cyclic loading. This can be explained by the fact that the cracks, formed on the coating layer by compressive stress, do not play the role of trigger in the fracture of substrate because they have an obtuse angle (>120°). The equations, obtained over the Vickers hardness of substate Hv 300, are as follows: Atσ_m+σ_r≥0, σ_ω={(Hv/10)+20}×9.8-(1.04Hv/1000)×(σ_m+σ_r ) Hv:Substrate Vickers hardness (kgf/mm^2), σ_ω, σ_m, σ_r :(MPa) However, in the case of steels containing a large inclusion, σ_ω=1.56×(Hv+120)/√<area>^<1/6>-(1.04Hv/1000)×(σ_m+σ_r ) area:Projected inclusion area(μm^2) Atσ_m+σ_r <0, irrespective of the existence of inclusion, σ_ω={(Hv/10)+20}×9.8×{1-(σ_m+σ_r )/σ_r } σ_r:True strength of fracture(MPa)
社団法人日本材料学会の論文
1995-05-15

VC被覆鋼の疲労強度に及ぼす平均応力の影響

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