Effects of Ni content on the shape memory properties and microstructure of Ni-rich NiTi-20Hf alloys
Effects of Ni content on the shape memory properties and microstructure of Ni-rich NiTi-20Hf alloys
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DOI：
10.1088/0964-1726/25/9/095029
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发表时间：
2016-09-01
影响因子：
4.1
通讯作者：
Noebe, R. D.
中科院分区：
文献类型：
--
作者：
Saghaian, S. M.;Karaca, H. E.;Noebe, R. D.
四种富镍NiTiHf合金（Ni50.3Ti29.7Hf20、Ni50.7Ti29.3Hf20、Ni51.2Ti28.8Hf20和Ni 52 Ti 28 Hf 20（at.%））的形状记忆性能和显微组织在炉冷条件下进行了系统的表征。在炉冷过程中形成的H相沉淀物中的组合物大于50.3Ni和成核的驱动力与Ni含量增加。随着Ni含量的增加，合金强度增加，而可恢复应变降低，这是由于析出物特性的变化。当析出物很小（类似于5-15 nm）时，它们容易被马氏体板吸收，这导致Ni50.7Ti29.3Hf20中的最大可恢复应变为2%。随着Ni含量的增加，析出相的尺寸（>100 nm）和体积分数增加，当Ni含量大于50.7at.%时，马氏体片的生长被限制在析出相之间。在Ni 52 Ti 28 Hf 20合金中，在高达2GPa的应力水平下观察到几乎完美的尺寸稳定性，可忽略不计的不可恢复应变，尽管可恢复应变相当小。在一般情况下，强烈的局部应力场产生在沉淀物/基体界面，这导致高存储的弹性能在马氏体相变。
Shape memory properties and microstructure of four Ni-rich NiTiHf alloys (Ni50.3Ti29.7Hf20, Ni50.7Ti29.3Hf20, Ni51.2Ti28.8Hf20, and Ni52Ti28Hf20 (at.%)) were systematically characterized in the furnace cooled condition. H-phase precipitates were formed during furnace cooling in compositions with greater than 50.3Ni and the driving force for nucleation increased with Ni content. Alloy strength increased while recoverable strain decreased with increasing Ni content due to changes in precipitate characteristics. When the precipitates were small (similar to 5-15 nm), they were readily absorbed by martensite plates, which resulted in maximum recoverable strain of 2% in Ni50.7Ti29.3Hf20. With increasing Ni content, the size (>100 nm) and volume fraction of precipitates increased and the growth of martensite plates was constrained between the precipitates when the Ni concentration was greater than 50.7 at.%. Near perfect dimensional stability with negligible irrecoverable strain was observed at stress levels as high as 2 GPa in the Ni52Ti28Hf20 alloy, though the recoverable strain was rather small. In general, strong local stress fields were created at precipitate/matrix interphases, which lead to high stored elastic energy during the martensitic transformation.