Towards revealing key factors in mechanical instability of bioabsorbable Zn-based alloys for intended vascular stenting
Towards revealing key factors in mechanical instability of bioabsorbable Zn-based alloys for intended vascular stenting
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DOI：
10.1016/j.actbio.2020.01.028
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发表时间：
2020-03-15
影响因子：
9.7
通讯作者：
Drelich, Jaroslaw W.
中科院分区：
文献类型：
--
作者：
Mostaed, Ehsan;Sikora-Jasinska, Malgorzata;Drelich, Jaroslaw W.
与镁相比，锌基合金具有良好的生物相容性和可降解性，因此被认为是有前途的心血管支架生物吸收材料。然而，低强度和由强应变率敏感性和应变软化行为引起的内在机械不稳定性使得Zn合金的开发对支架应用具有挑战性。在本研究中，我们开发了二元Zn-4.0Ag和三元Zn-4.0Ag- xmn合金（x = 0.2-0.6wt%）。设计了一种对挤压合金进行冷加工后再进行热处理的实验方法，通过该方法可以深入研究晶粒尺寸和析出物的影响。显微组织观察表明，在拉丝过程中，Zn-4.0Ag和Zn-4.0Ag-0.6 mn的晶粒发生了明显的细化，形成了尺寸分别为700 nm和200 nm的超细晶（UFG）组织。Mn促进了动态再结晶，表现出较强的晶粒细化作用。此外，冷加工导致AgZn3颗粒的动态析出，分布在整个Zn基体中。这些析出物通过激活Zn/AgZn3边界滑动引发机械降解，使Zn-4.0 ag和Zn-4.0 ag -0.6 mn的抗拉强度分别降低74%和57%。在冷拔合金中，析出软化引起了较强的应变速率敏感性。短时间退火通过降低AgZn3分数显著减轻了机械不稳定性。由于富锰颗粒在晶界上的钉住作用，三元合金丝的显微组织稳定性优于无锰合金丝。最后，在热处理后，观察到腐蚀状态从局部转变为更均匀，主要是由于AgZn3析出物的溶解。由于具有良好的生物可降解性，锌已被认为是一种潜在的生物可降解支架材料。然而，锌的低强度和内在的机械不稳定性促使研究人员寻找具有改善机械性能的锌合金。尽管已经进行了大量的研究来满足上述担忧，但尚未有稳定力学性能的锌基合金的报道。本文系统地评价了锌银基合金的力学性能和稳定性，并将其作为微观组织特征的函数。研究发现，锌合金的微观组织设计不仅可以有效地提高合金的强度，抑制合金的力学不稳定性，而且可以通过提高合金的腐蚀均匀性来减少合金的损伤。(C) 2020材料学报Elsevier Ltd.出版。版权所有。
Zn-based alloys are recognized as promising bioabsorbable materials for cardiovascular stents, due to their biocompatibility and favorable degradability as compared to Mg. However, both low strength and intrinsic mechanical instability arising from a strong strain rate sensitivity and strain softening behavior make development of Zn alloys challenging for stent applications. In this study, we developed binary Zn-4.0Ag and ternary Zn-4.0Ag-xMn (where x = 0.2-0.6wt%) alloys. An experimental methodology was designed by cold working followed by a thermal treatment on extruded alloys, through which the effects of the grain size and precipitates could be thoroughly investigated. Microstructural observations revealed a significant grain refinement during wire drawing, leading to an ultrafine-grained (UFG) structure with a size of 700 nm and 200 nm for the Zn-4.0Ag and Zn-4.0Ag-0.6Mn, respectively. Mn showed a powerful grain refining effect, as it promoted the dynamic recrystallization. Furthermore, cold working resulted in dynamic precipitation of AgZn3 particles, distributing throughout the Zn matrix. Such precipitates triggered mechanical degradation through an activation of Zn/AgZn3 boundary sliding, reducing the tensile strength by 74% and 57% for Zn-4.0Ag and Zn-4.0Ag-0.6Mn, respectively. The observed precipitation softening caused a strong strain rate sensitivity in cold drawn alloys. Short-time annealing significantly mitigated the mechanical instability by reducing the AgZn3 fraction. The ternary alloy wire showed superior microstructural stability relative to its Mn-free counterpart due to the pinning effect of Mn-rich particles on the grain boundaries. Eventually, a shift of the corrosion regime from localized to more uniform was observed after the heat treatment, mainly due to the dissolution of AgZn3 precipitates.Statement of SignificanceOwing to its promising biodegradability, zinc has been recognized as a potential biodegradable material for stenting applications. However, Zn's poor strength alongside intrinsic mechanical instability have propelled researchers to search for Zn alloys with improved mechanical properties. Although extensive researches have been conducted to satisfy the mentioned concerns, no Zn-based alloys with stabilized mechanical properties have yet been reported. In this work, the mechanical properties and stability of the Zn-Ag-based alloys were systematically evaluated as a function of microstructural features. We found that the microstructure design in Zn alloys can be used to find an effective strategy to not only improve the strength and suppress the mechanical instability but also to minimize any damage by augmenting the corrosion uniformity. (C) 2020 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.