Extreme creep resistance in a microstructurally stable nanocrystalline alloy
Extreme creep resistance in a microstructurally stable nanocrystalline alloy
复制标题
DOI：
10.1038/nature19313
复制
发表时间：
2016-09-15
期刊：
影响因子：
64.8
通讯作者：
Solanki, K. N.
中科院分区：
文献类型：
--
作者：
Darling, K. A.;Rajagopalan, M.;Solanki, K. N.
纳米晶金属的平均晶粒尺寸小于100纳米，其室温强度高于粗晶粒金属，部分原因是晶粒尺寸大幅减小（1）。然而，这种高强度通常伴随着其他机械性能的大量损失，例如抗蠕变性，这限制了它们的实际用途;例如，纳米晶铜的蠕变速率比典型的粗晶铜高约四个数量级（2，3）。纳米晶材料抗蠕变性的下降部分是由于晶界体积分数的增加，而晶界缺乏长程晶序，并导致扩散蠕变、滑动和旋转等过程（3）。在这里，我们表明，纳米晶铜钽合金具有前所未有的性能组合：高强度结合极高的高温抗蠕变性，同时保持机械和热稳定性。关于这一系列不混溶合金的前期工作先前已经强调了它们的热机械稳定性和强度（4，5），这促使它们在更极端的条件下进行研究，例如蠕变。我们发现，在0.50 ~ 0.64倍于基体熔化温度（1,356开尔文）的各种温度下，外加应力为剪切模量的0.85%~ 1.2%时，稳态蠕变速率小于每秒10（-6），比大多数纳米晶金属低6 ~ 8个数量级。我们的纳米晶合金中不寻常的特性组合是通过一种加工路线实现的，该路线产生了独特的纳米原子团簇，这些原子团簇在合金中固定了晶界。这种钉扎通过增加晶界滑动和旋转的能垒以及通过在极长期蠕变条件下抑制晶粒粗化来提高晶粒的动力学稳定性。我们的加工方法应该能够开发出具有高强度和抗蠕变性的微观结构稳定的结构合金，用于各种高温应用，包括航空航天，海军，民用基础设施和能源部门。
Nanocrystalline metals, with a mean grain size of less than 100 nanometres, have greater room-temperature strength than their coarse-grained equivalents, in part owing to a large reduction in grain size(1). However, this high strength generally comes with substantial losses in other mechanical properties, such as creep resistance, which limits their practical utility; for example, creep rates in nanocrystalline copper are about four orders of magnitude higher than those in typical coarse-grained copper(2,3). The degradation of creep resistance in nanocrystalline materials is in part due to an increase in the volume fraction of grain boundaries, which lack long-range crystalline order and lead to processes such as diffusional creep, sliding and rotation(3). Here we show that nanocrystalline copper-tantalum alloys possess an unprecedented combination of properties: high strength combined with extremely high-temperature creep resistance, while maintaining mechanical and thermal stability. Precursory work on this family of immiscible alloys has previously highlighted their thermo-mechanical stability and strength(4,5), which has motivated their study under more extreme conditions, such as creep. We find a steady-state creep rate of less than 10(-6) per second-six to eight orders of magnitude lower than most nanocrystalline metals-at various temperatures between 0.5 and 0.64 times the melting temperature of the matrix (1,356 kelvin) under an applied stress ranging from 0.85 per cent to 1.2 per cent of the shear modulus. The unusual combination of properties in our nanocrystalline alloy is achieved via a processing route that creates distinct nanoclusters of atoms that pin grain boundaries within the alloy. This pinning improves the kinetic stability of the grains by increasing the energy barrier for grain-boundary sliding and rotation and by inhibiting grain coarsening, under extremely long-term creep conditions. Our processing approach should enable the development of microstructurally stable structural alloys with high strength and creep resistance for various high-temperature applications, including in the aerospace, naval, civilian infrastructure and energy sectors.