Effects of mechanical constraint on thermally induced reverse martensitic transformation in granular shape memory ceramic packings
Effects of mechanical constraint on thermally induced reverse martensitic transformation in granular shape memory ceramic packings
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DOI：
10.1063/5.0035041
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发表时间：
2020-12
影响因子：
3.2
通讯作者：
H. Rauch;Hang Z. Yu
中科院分区：
文献类型：
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作者：
H. Rauch;Hang Z. Yu
氧化锆基陶瓷表现出形状记忆和超弹性效应，其基础是四方和单斜晶系结构之间的可逆马氏体相变。这些形状记忆陶瓷以颗粒填充的形式存在，尽管其固有的脆性，但仍可扩大到大批量应用，同时显示出与单块对应物截然不同的转变特征。在这里，我们提供了一个比较研究，以了解热诱导逆马氏体相变在颗粒堆积和机械约束的影响。本研究采用相同成分但机械约束程度不同的ZrO2-CeO2形状记忆陶瓷。探索的材料形式包括松散和堵塞的颗粒填料，它们本身由多晶或单晶颗粒组成，以及烧结体多晶体。除后者外，在逆变过程的热流测量中没有观察到吸热峰。研究表明，这种反常行为源于颗粒间较弱的力学约束和单个颗粒之间的相变不均匀，而不是应力松弛或颗粒重排。相比之下，明显的吸热峰只出现在强机械约束下的爆裂型相变中。对于颗粒堆积，颗粒内的机械约束不会影响热回复过程中任何吸热峰的存在，但会影响奥氏体的起始温度。
Zirconia-based ceramics exhibit shape memory and superelastic effects based on the reversible martensitic transformation between tetragonal and monoclinic crystal structures. In the form of granular packings, these shape memory ceramics can be scaled up for bulk applications despite their intrinsic brittleness, while displaying drastically different transformation characteristics than the monolithic counterparts. Here, we present a comparative study to understand the thermally induced reverse martensitic transformation in granular packings and the influence of mechanical constraints. This study employs ZrO2–CeO2 shape memory ceramics of the same composition but with different degrees of mechanical constraints. The explored material forms include loose and jammed granular packings, themselves consisting of polycrystalline or single crystal particles, as well as sintered bulk polycrystals. Except for the latter, no endothermic peak is observed in the heat flow measurement of the reverse transformation process. This unusual behavior is shown to stem from the weak inter-particle mechanical constraint and the transformation heterogeneity among individual particles, rather than stress relaxation or particle rearrangement. To compare, conspicuous endothermic peaks only appear in bursting-type transformations under a strong mechanical constraint. For granular packings, the intra-particle mechanical constraint does not affect the presence of any endothermic peaks in thermal reversion but can influence the austenite start temperature.