At elevated temperature, creep failures of polycrystalline metals after long-term constant loading are often caused by the nucleation, growth and coalescence of creep voids on the grain boundaries. Void h＇action is a...At elevated temperature, creep failures of polycrystalline metals after long-term constant loading are often caused by the nucleation, growth and coalescence of creep voids on the grain boundaries. Void h＇action is an important parameter for the evaluation of creep damage level of structural materials operating at high temperature. In this paper, a 2-D numerical simulation method was developed for analyzing the void fraction evolution during the process of creep, based on some hypothesis from experiments. The model was implemented and then was used to predict the evolution of void fraction in the 2.25Cr-1Mo steel of uniaxial creep experiment at 570 ℃, in which the simulation results showed good agreement with the experimental results.展开更多
11Cr-0.4Mo-2W-CuVNb steel （ASME Gr.122） is used for boiler components in ultra- supercritical （USC） thermal power plants. The creep strength of high-Cr steel welds decreases due to the formation of Type IV creep d...11Cr-0.4Mo-2W-CuVNb steel （ASME Gr.122） is used for boiler components in ultra- supercritical （USC） thermal power plants. The creep strength of high-Cr steel welds decreases due to the formation of Type IV creep damage in the heat-affected zone （HAZ） during long-term use at high temperatures. In the present study, the processes and mechanisms of Type Ⅳ creep damage were elucidated by investigating the long-term creep strength, microstructure and damage behavior of Gr.122 steel welds. Creep tests using thick welded joints were interrupted at several time steps, and the initiation, evolution and distribution of creep damage were measured. It was found that the formation and growth of creep damage was suppressed during the steady- state stage; creep voids formed at 0.5 of life, and coalesced to form a crack after 0.9 of life. Type IV creep damage was mostly observed in the area about 30% below the surface of the plate. Differences in creep damage behavior between Gr.122 and Gr.91 steel welds were examined. Experimental creep damage distribution was compared with computed versions using the finite element method and damage mechanics.展开更多
The cleavage rupture behaviour of the Ti alloy TC11 with various microstructures,i.e., equiaxed,duplex and interweaving,has been studied under fatigue-creep interaction at 520℃.It was found to be not only related to ...The cleavage rupture behaviour of the Ti alloy TC11 with various microstructures,i.e., equiaxed,duplex and interweaving,has been studied under fatigue-creep interaction at 520℃.It was found to be not only related to the rate of creep void initiating,but also control- led by the creep strain accumulation on holding under tension test and stress state at crack-tip.This seem to be combinably offected by both value of critic void initiating strain and parameter,V_(GC),of critic void growth.展开更多
基金supported by National Natural Science Foundation of China(No.51071094) and the IHI-Tsinghua Joint Research Center
文摘At elevated temperature, creep failures of polycrystalline metals after long-term constant loading are often caused by the nucleation, growth and coalescence of creep voids on the grain boundaries. Void h＇action is an important parameter for the evaluation of creep damage level of structural materials operating at high temperature. In this paper, a 2-D numerical simulation method was developed for analyzing the void fraction evolution during the process of creep, based on some hypothesis from experiments. The model was implemented and then was used to predict the evolution of void fraction in the 2.25Cr-1Mo steel of uniaxial creep experiment at 570 ℃, in which the simulation results showed good agreement with the experimental results.
文摘11Cr-0.4Mo-2W-CuVNb steel （ASME Gr.122） is used for boiler components in ultra- supercritical （USC） thermal power plants. The creep strength of high-Cr steel welds decreases due to the formation of Type IV creep damage in the heat-affected zone （HAZ） during long-term use at high temperatures. In the present study, the processes and mechanisms of Type Ⅳ creep damage were elucidated by investigating the long-term creep strength, microstructure and damage behavior of Gr.122 steel welds. Creep tests using thick welded joints were interrupted at several time steps, and the initiation, evolution and distribution of creep damage were measured. It was found that the formation and growth of creep damage was suppressed during the steady- state stage; creep voids formed at 0.5 of life, and coalesced to form a crack after 0.9 of life. Type IV creep damage was mostly observed in the area about 30% below the surface of the plate. Differences in creep damage behavior between Gr.122 and Gr.91 steel welds were examined. Experimental creep damage distribution was compared with computed versions using the finite element method and damage mechanics.
文摘The cleavage rupture behaviour of the Ti alloy TC11 with various microstructures,i.e., equiaxed,duplex and interweaving,has been studied under fatigue-creep interaction at 520℃.It was found to be not only related to the rate of creep void initiating,but also control- led by the creep strain accumulation on holding under tension test and stress state at crack-tip.This seem to be combinably offected by both value of critic void initiating strain and parameter,V_(GC),of critic void growth.
文摘针对钠冷快中子增殖反应堆(简称快堆)燃料元件包壳材料316以及15-15Ti奥氏体不锈钢,讨论了通过晶界工程(grain boundary engineering,GBE)技术进一步提高材料抗辐照肿胀以及抗蠕变性能的可行性.通过GBE技术能够大幅增加材料中与孪晶相关的低Σ重合位置点阵(coincidence site lattice,CSL)晶界比例.快堆燃料元件包壳在固溶退火处理后还要经过20%左右的冷加工变形,目的是在显微组织中引入大量位错,吸收由辐照产生的点缺陷,并增加吸收裂变产物的陷阱.如果在这样的冷加工变形前大幅提高材料的低ΣCSL晶界比例,使冷加工变形时的位错滑移在具有特殊取向关系的晶粒间的传播以及位错在特殊结构晶界处的堆积排列发生变化,那么就有可能使冷加工后位错的分布状态有利于吸收更多的由辐照产生的点缺陷,提高材料抗辐照肿胀的能力.
