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Superelasticity and shape memory effect in zirconia nanoparticles
Extreme Mechanics Letters ( IF 4.7 ) Pub Date : 2021-04-01 , DOI: 10.1016/j.eml.2021.101301
Ning Zhang , Mohsen Asle Zaeem

Superelasticity and shape memory effect are two key properties of zirconia-based ceramics which are mediated by the reversible tetragonal to monoclinic phase transformation. Although experimental studies discovered that the shape memory behavior of ceramics can be improved by reducing the grain boundary density, degradation in shape memory response still happens after a few cycles of loading-unloading-heating-cooling. In this work, superelastic and shape memory properties of single crystalline and polycrystalline yttria stabilized tetragonal zirconia (YSTZ) nanoparticles are studied by atomistic simulations. Fully recoverable superelastic strain (8.3%) is observed in a single crystalline nanoparticle by merely removing the compressive load. However, the shape memory behavior degrades with the increase of loading-unloading-heating-cooling cycles. In other words, a higher temperature is required for an additional strain recovery, but some residual displacement may still remain after few cyclic loadings. Amorphous phase formation and its accumulation around the applied load contact area, as well as an increase in surface roughness are responsible for the observed degradation of shape memory response. In a polycrystalline YSTZ nanoparticle, besides the regular reverse transformation at the end of cyclic loading, some amorphous phase regions transfer back to the original tetragonal structure. However, some monoclinic phase is restrained by the permanent amorphous phase and grain boundaries at the end of cyclic loading, causing degradation of shape memory behavior.



中文翻译:

氧化锆纳米粒子的超弹性和形状记忆效应

超弹性和形状记忆效应是氧化锆基陶瓷的两个关键特性,这些特性是由可逆的四方相向单斜相转变介导的。尽管实验研究发现可以通过降低晶界密度来改善陶瓷的形状记忆性能,但是在经过几次装卸-加热-冷却循环之后,形状记忆响应仍会下降。在这项工作中,通过原子模拟研究了单晶和多晶氧化钇稳定的四方氧化锆(YSTZ)纳米粒子的超弹性和形状记忆特性。仅除去压缩载荷,就可以在单晶纳米颗粒中观察到完全可恢复的超弹性应变(8.3%)。然而,形状记忆行为随着装卸-加热-冷却循环的增加而降低。换句话说,需要更高的温度以恢复额外的应变,但是在几次循环加载后仍可能残留一些残余位移。非晶相的形成及其在所施加的载荷接触区域周围的积累,以及表面粗糙度的增加,是观察到的形状记忆响应下降的原因。在多晶YSTZ纳米粒子中,除了在循环加载结束时进行规则的逆向转换外,一些非晶相区域还转换回原始的四方结构。但是,某些单斜晶相在循环载荷结束时会受到永久性非晶相和晶界的限制,从而导致形状记忆性能下降。但经过几次循环载荷后,仍可能残留一些残余位移。非晶相的形成及其在所施加的载荷接触区域周围的积累,以及表面粗糙度的增加,是观察到的形状记忆响应下降的原因。在多晶YSTZ纳米粒子中,除了在循环加载结束时进行规则的逆向转换外,一些非晶相区域还转换回原始的四方结构。但是,某些单斜晶相在循环载荷结束时会受到永久性非晶相和晶界的限制,从而导致形状记忆性能下降。但经过几次循环载荷后,仍可能残留一些残余位移。非晶相的形成及其在所施加的载荷接触区域周围的积累,以及表面粗糙度的增加,是观察到的形状记忆响应下降的原因。在多晶YSTZ纳米粒子中,除了在循环加载结束时进行规则的逆向转换外,一些非晶相区域还转换回原始的四方结构。但是,某些单斜晶相在循环载荷结束时受到永久性非晶相和晶界的约束,从而导致形状记忆性能下降。以及表面粗糙度的增加是所观察到的形状记忆响应降低的原因。在多晶YSTZ纳米粒子中,除了在循环加载结束时进行规则的逆向转换外,一些非晶相区域还转换回原始的四方结构。但是,某些单斜晶相在循环载荷结束时会受到永久性非晶相和晶界的限制,从而导致形状记忆性能下降。以及表面粗糙度的增加是所观察到的形状记忆响应降低的原因。在多晶YSTZ纳米粒子中,除了在循环加载结束时进行规则的逆向转换外,一些非晶相区域还转换回原始的四方结构。但是,某些单斜晶相在循环载荷结束时受到永久性非晶相和晶界的约束,从而导致形状记忆性能下降。

更新日期:2021-04-01
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