添加 Si 及 Nd 元素對於 CoCrNi 中熵合金薄膜 顯微結構與機械性質之影響

Abstract

本研究利用三個靶材共鍍的磁控濺鍍系統，藉由改變類金屬元素矽及稀土元素釹的成分比例，成功製備一系列的(CoCrNi)100–x–ySixNdy 中熵合金薄膜。第一部分是固定矽元素的含量在大約 0.7 at.%，改變釹元素的含量。隨著釹元素的添加量增加，可以在 X 光繞射儀及穿透式電子顯微鏡選區繞射的圖譜中觀察到材料的結構從單一的 FCC 相逐漸轉變為 FCC CoCrNi 相、HCP CoCrNi 相及 HCP NdNi5 相共同存在，且可以在掃描式電子顯微鏡及穿透式電子顯微鏡的圖片中觀察到細化的柱狀晶結構。在 Si0.58Nd5.14 的薄膜中，因為固溶強化、晶粒細化以及析出強化的效果，材料的硬度及壓縮降伏強度會分別到達 10.29 及 4.27 GPa 的最大值。第二部分是固定釹元素的含量在大約 2.6 at.%，改變矽元素的含量。隨著矽元素的添加量增加，可以在 X 光繞射儀及穿透式電子顯微鏡選區繞射的圖譜中觀察到材料的結構從完全的結晶相逐漸轉變為結晶相被包圍在非晶相中，且可以在掃描式電子顯微鏡及穿透式電子顯微鏡的圖片中觀察到柱狀晶結構消失。在Si0.76Nd2.91 的薄膜中，因為間隙型固溶強化的效果，材料的硬度及壓縮降伏強度會分別些微提升至9.75 及 4.10 GPa 的最大值。將兩部分的(CoCrNi)100–x–ySixNdy 中熵合金薄膜進行綜合討論，發現在Si0.58Nd5.14 的薄膜中具有最佳化的機械性質，表示析出強化及晶粒細化可以成為(CoCrNi)100–x–ySixNdy 中熵合金薄膜中主要的強化機制。

A series of (CoCrNi)100–x–ySixNdy medium entropy alloy films (MEAFs) with manipulated metalloid element, Si, and rare earth element, Nd, was synthesized using magnetron three-target co-sputtering. A transformation from single FCC CoCrNi phase to the coexistence of FCC CoCrNi, HCP CoCrNi and HCP NdNi5 phases was observed in X-ray diffraction (XRD) and transmission electron microscopy (TEM) diffraction patterns with the increasing Nd content for Si content of ~0.7 at.%, and the scanning electron microscope (SEM) and TEM images presented the refined columnar grains. The hardness and compressive yield strength reached the maxima of 10.29 and 4.27 GPa, respectively, in Si0.58Nd5.14 film owing to the solid solution strengthening, grain refinement and precipitation strengthening. The films exhibited a transition from fully crystalline to crystalline within the amorphous matrix in XRD and TEM results with the increasing Si content for Nd content of ~2.6 at.%, and the columnar structure disappeared in the SEM and TEM images. The hardness and yield strength increased slightly to the maxima of 9.75 and 4.10 GPa, respectively, in Si0.76Nd2.91 film attributed mainly to the interstitial solid solution strengthening. Comprehensive discussion of (CoCrNi)100–x–ySixNdy MEAFs showed the optimized mechanical properties in Si0.58Nd5.14 film, indicating the precipitation strengthening and grain refinement strengthening would be the major strengthening mechanisms in this system.