粉末超合金MERL76の高温疲労特性におよぼす欠陥と組織の影響

概要

論文の詳細を見る
Elevated temperature fatigue tests were conducted on P/M HIP'ed superalloy, MERL 76. The defects, such as preciptitates on the prior particle boundaries(PPBs), gas-porosities and nonmentallic inclusions, were found at fatigue origins. The relation between defect size, a_i, and fatigue life, N_f, was independent of deect types and was formulated as N_f・Δσ^m_<eq>=h・a^<1-m/2>_i Δσ_<eq>=Δσ√<1+(2Eg(n))/(n+1)・(Δε_p)/(Δσ)> when m : exponent in crack propagation law, da/dN=C△K^m, h : a material constant, E : Young's modulus, g(n) : a function of cyclic strain hardening exponent, n, and Δε_p : plastic strain range. The relation between threshold stress,Δσ_<th>, and defect size, a_i, was also expressed as ΔK_<th>=2/π・Δσ_<th>√<π(a_i+a_0) where ΔK_<th> : threshold stress intensity factor for long cracks. The value, a_0, was about 0.1 mm, which coincided with the size estimated by an experimental relationship between grain size and a_0 on steels. The usage of Ar-treated powders and the hot-work after HIP'ing improved fatigue life since they prevented PPB failure. Furthermore, the usage of fine powders is preferable because it can reduce the size of pores and inclusions.
社団法人日本材料学会の論文
1990-02-15