Hung Pham Tran, Kawasaki Megumi, Szabó Ábel, Lábár János L, Hegedűs Zoltán, Gubicza Jenő
Department of Materials Physics, Eötvös Loránd University, P.O.B. 32, 1518 Budapest, Hungary.
School of Mechanical, Industrial and Manufacturing Engineering, Oregon State University, Corvallis, OR 97331, USA.
Nanomaterials (Basel). 2022 Sep 27;12(19):3371. doi: 10.3390/nano12193371.
Severe plastic deformation (SPD) is an effective route for the nanocrystallization of multi-principal element alloys (MPEAs). The stability of the refined microstructure is important, considering the high temperature applications of these materials. In the present study, the effect of SPD on the stability of a body-centered cubic (bcc) HfNbTiZr MPEA was investigated. SPD was performed using a high-pressure torsion (HPT) technique by varying the number of turns between ½ and 10. The evolution of phase composition and microstructure was studied near the disk centers and edges where the imposed strain values were the lowest and highest, respectively. Thus, the shear strain caused by HPT varies between 3 (½ turn, near the center) and 340 (10 turns, near the edge). It was found that during annealing up to 1000 K, the bcc HfNbTiZr alloy decomposed into two bcc phases with different lattice constants at 740 K. In addition, at high strains a hexagonal close packed (hcp) phase was formed above 890 K. An inhomogeneous elemental distribution was developed at temperatures higher than 890 K due to the phase decomposition. The scale of the chemical heterogeneities decreased from about 10 µm to 30 nm where the shear strain increased from 3 to 340, which is similar to the magnitude of grain refinement. Anneal-induced hardening was observed in the MPEA after HPT for both low and high strains at 740 K, i.e., the hardness of the HPT-processed samples increased due to heat treatment. At low strain, the hardness remained practically unchanged between 740 and 1000 K, while for the alloy receiving high strains there was a softening in this temperature range.
严重塑性变形（SPD）是实现多主元合金（MPEA）纳米晶化的有效途径。考虑到这些材料的高温应用，细化微观结构的稳定性至关重要。在本研究中，研究了SPD对体心立方（bcc）HfNbTiZr MPEA稳定性的影响。采用高压扭转（HPT）技术进行SPD，扭转圈数在1/2至10之间变化。研究了在盘中心和边缘附近相组成和微观结构的演变，其中施加的应变值分别为最低和最高。因此，HPT引起的剪切应变在3（1/2圈，靠近中心）和340（10圈，靠近边缘）之间变化。研究发现，在高达1000 K的退火过程中，bcc HfNbTiZr合金在740 K时分解为两个具有不同晶格常数的bcc相。此外，在高应变下，890 K以上形成了六方密排（hcp）相。由于相分解，在高于890 K的温度下出现了不均匀的元素分布。化学不均匀性的尺度从约10 µm减小到30 nm，此时剪切应变从3增加到340，这与晶粒细化的幅度相似。在740 K下，对经过HPT处理的低应变和高应变MPEA均观察到退火诱导硬化，即HPT处理样品的硬度因热处理而增加。在低应变下，硬度在740至1000 K之间基本保持不变，而对于接受高应变的合金，在此温度范围内出现软化。
