The creep crack growth(CCG)and the time to carck initiation and rupture of specimen (t_(rc)and t_r)were measured by means of electrical potential method on single edge notched specimens at 700℃.The field near the cra...The creep crack growth(CCG)and the time to carck initiation and rupture of specimen (t_(rc)and t_r)were measured by means of electrical potential method on single edge notched specimens at 700℃.The field near the crack tip under steady-state creep was represented by energy rate integral(C~*),and the CCG rate as a function of C~* has been obtained.The agreement between the predicted and observed t_(rc)values is quite good.It was found that the addition of small amount of Mg and Zr in the alloys causes t_(rc)and t_r of the specimens to in- crease significantly.展开更多
Alloy 718 is a precipitation strengthened nickel-based superalloy based on the precipitation of γ″-Ni3Nb (DO22 structure) and γ′-Ni3(Al,Ti) (L12 structure) phases. Creep crack growth rate (CCGR) was investigated a...Alloy 718 is a precipitation strengthened nickel-based superalloy based on the precipitation of γ″-Ni3Nb (DO22 structure) and γ′-Ni3(Al,Ti) (L12 structure) phases. Creep crack growth rate (CCGR) was investigated after high temperature exposure at 593, 650 and 677℃ for 2000h in Alloy 718. In addition to the coalescence of γ′/ γ″ and the amount increasing of δ phase, the existence of a bcc chromium enriched α-Cr phase was observed by SEM, and the weight fraction of α-Cr and other phases were determined by chemical phase analysis methods. The CCGR behavior and regulation have been analyzed by means of strength and structure analysis approaches. The experimental results show higher the exposure temperature and longer the exposure time, lower the CCGR. This is probably attributed to the interaction of material softening and brittling due to complex structure changes during high temperature exposure. Therefore, despite α-Cr phase formation and amount enhancement were run in this test range. It seems to us a small amount of α-Cr will be not harmful for creep crack propagation resistance, which is critical for disk application in aircraft and land-based gas turbine.展开更多
为准确描述疲劳-蠕变裂纹的扩展行为,选取材料在一个循环周次内吸收的应变能密度增量为材料的损伤变量。将加、卸载阶段的裂纹扩展量与保载期的裂纹扩展量叠加,导出了基于有效应变能密度的疲劳-蠕变裂纹扩展速率表达式。该表达式不仅与...为准确描述疲劳-蠕变裂纹的扩展行为,选取材料在一个循环周次内吸收的应变能密度增量为材料的损伤变量。将加、卸载阶段的裂纹扩展量与保载期的裂纹扩展量叠加,导出了基于有效应变能密度的疲劳-蠕变裂纹扩展速率表达式。该表达式不仅与载荷的循环周次相关,而且还与材料的疲劳-蠕变速率相关。将1Cro10Mo Ni VNb N合金在600梯形应力波加载下的裂纹扩展速率实验值与该表达式的计算值相比较,结果基本吻合。该公式合理解释了某些合金材料的疲劳-蠕变裂纹扩展的部分行为特征。展开更多
文摘The creep crack growth(CCG)and the time to carck initiation and rupture of specimen (t_(rc)and t_r)were measured by means of electrical potential method on single edge notched specimens at 700℃.The field near the crack tip under steady-state creep was represented by energy rate integral(C~*),and the CCG rate as a function of C~* has been obtained.The agreement between the predicted and observed t_(rc)values is quite good.It was found that the addition of small amount of Mg and Zr in the alloys causes t_(rc)and t_r of the specimens to in- crease significantly.
基金The authors thank Ladish Co.,Inc.to support the test samples for this analysis.And this work was supported by the National Natural Science Foundation of China(No.50171005)the Teaching and Research Award Program for Outstanding Young Teachers in Higher Education Institutions of MOE to support it.
文摘Alloy 718 is a precipitation strengthened nickel-based superalloy based on the precipitation of γ″-Ni3Nb (DO22 structure) and γ′-Ni3(Al,Ti) (L12 structure) phases. Creep crack growth rate (CCGR) was investigated after high temperature exposure at 593, 650 and 677℃ for 2000h in Alloy 718. In addition to the coalescence of γ′/ γ″ and the amount increasing of δ phase, the existence of a bcc chromium enriched α-Cr phase was observed by SEM, and the weight fraction of α-Cr and other phases were determined by chemical phase analysis methods. The CCGR behavior and regulation have been analyzed by means of strength and structure analysis approaches. The experimental results show higher the exposure temperature and longer the exposure time, lower the CCGR. This is probably attributed to the interaction of material softening and brittling due to complex structure changes during high temperature exposure. Therefore, despite α-Cr phase formation and amount enhancement were run in this test range. It seems to us a small amount of α-Cr will be not harmful for creep crack propagation resistance, which is critical for disk application in aircraft and land-based gas turbine.
文摘为准确描述疲劳-蠕变裂纹的扩展行为,选取材料在一个循环周次内吸收的应变能密度增量为材料的损伤变量。将加、卸载阶段的裂纹扩展量与保载期的裂纹扩展量叠加,导出了基于有效应变能密度的疲劳-蠕变裂纹扩展速率表达式。该表达式不仅与载荷的循环周次相关,而且还与材料的疲劳-蠕变速率相关。将1Cro10Mo Ni VNb N合金在600梯形应力波加载下的裂纹扩展速率实验值与该表达式的计算值相比较,结果基本吻合。该公式合理解释了某些合金材料的疲劳-蠕变裂纹扩展的部分行为特征。
