Development of Ni-base Rought Alloy for Nuclear Heat Exchanger, Excellent in Phase Stability at High Temperature

高温相稳定性优异的核热交换器用镍基粗合金的开发

基本信息

批准号：
62850133
负责人：
KIKUCHI Makoto
金额：
$ 4.61万
依托单位：
TOKYO INSTITUTE OF TECHNOLOGY
依托单位国家：
日本
项目类别：
Grant-in-Aid for Developmental Scientific Research
财政年份：
1987
资助国家：
日本
起止时间：
1987 至 1989
项目状态：
已结题

项目摘要

Creep properties and microstructure of Ni-2OCr-Nb-W alloys containing variable amounts of niobium and tungsten were investigated at 900 and 1,000ﾟC, focusing on a role of grain boundary precipitates. The alloys with higher niobium content. In which the Widmanstatten type beta-Ni_3Nb phase precipitates after its precipitation at grain boundaries, showed a relatively small minimum creep rate at 900ﾟC, accompanied by the degradation of rupture elongation. The effect of time lag between the in-grain and grain boundary precipitations of the beta-phase on creep resistance of the alloy was evaluated by observing their creep rate-time curves. When the tungsten content of a Ni-2OCr-3Nb-l3W alloy increased up to 17 wt%, marked improvement of creep properties was found under lower stress levels and it is strongly correlated to the grain boundary precipitation of the alpha_2 W-phase which occurs after that of the beta-phase. It is concluded that the grain boundary precipitation strengthening effect due to such dual phases as beta and alpha_2, is one of the most effective methods for improving the creep strength.In order to make the high temperature creep strength of Ni-Cr-Nb-W type alloys higher, the effects of boron and zirconium on creep properties in high-purity Ni-2OCr alloys were investigated. By the boron and zirconium addition, creep resistance, rupture life and rupture elongation of a Ni-20Cr alloy were improved. The longer rupture life and larger rupture elongation with the addition of boron or zirconium would be caused by the formation of subgrains and dynamic recrystallization which retard the initiation and propagation of grain boundary aracks.The possibility of the development of a new alloy for nuclear heat exchanger with far higher creep rupture strength than several candidate alloys ( Ni-Cr-W type alloys ) was suggested.

研究了含不同量铌和钨的 Ni-2OCr-Nb-W 合金在 900 和 1,000°C 时的蠕变性能和显微组织，重点研究了铌含量较高的魏氏组织合金。 β-Ni_3Nb 相在晶界析出后析出，在900℃时，伴随着断裂伸长率的降低，通过观察其蠕变速率-时间曲线来评价β相晶内和晶界析出之间的时间滞后对合金的抗蠕变性能的影响。 Ni-2OCr-3Nb-l3W 合金的钨含量增加至 17 wt%，在较低应力水平下发现蠕变性能显着改善，并且与合金的晶界析出密切相关。 α_2 W相是在β相之后出现的，由此可见，β和α_2双相的晶界析出强化效应是提高蠕变强度的最有效方法之一。为了使Ni-Cr-Nb-W型合金的高温蠕变强度更高，研究了硼和锆对高纯Ni-2OCr合金蠕变性能的影响。添加硼或锆可提高Ni-20Cr合金的断裂寿命和断裂伸长率，这是由于亚晶粒的形成和动态再结晶阻碍了晶界裂纹的萌生和扩展。 .开发用于核热交换器的新型合金的可能性，其蠕变断裂强度远高于几种候选合金（Ni-Cr-W型合金））被建议。