研究鈮與釩摻雜對鈷鉻鎳中熵合金薄膜顯微結構與機械性質之影響

Abstract

本研究利用磁控濺鍍設備，藉由鈷鉻鎳靶、鈮靶和釩靶進行三靶共鍍，成功製備了一系列 (CoCrNi)100–2xNbxVx（標稱為NbxVx，x = 0, 1, 2, 2.5, 3, 4）中熵合金薄膜，目的在探討改變鈮和釩元素的添加對鈷鉻鎳中熵合金薄膜系統之顯微結構與機械性能的影響。隨著鈮和釩含量增加，掃描式電子顯微鏡影像展示薄膜的斷裂橫截面發生了延性—脆性的變化。X光繞射和穿透式電子顯微鏡圖譜呈現Nb2.5V2.5薄膜由單一面心立方CoCrNi固溶相轉變為面心立方晶相CoCrNi基地相和斜方晶相Ni3Nb析出相共存。Nb3V3薄膜開始出現奈米晶體，並且鈮和釩進一步的添加，Nb4V4薄膜將出現非晶區域。奈米壓痕和微柱壓縮測試的結果表明，Nb2.5V2.5薄膜在所有中熵合金薄膜中達到最佳的硬度（10.17 GPa）、降伏強度（5.45 GPa）和斷裂強度（7.58 GPa）。此外，高分辨率穿透式電子顯微鏡影像顯示，奈米晶體和非晶結構的形成可能與薄膜機械性能的下降相關。綜合上述實驗結果，可以推論固溶強化和析出強化為 (CoCrNi)100–2xNbxVx中熵合金薄膜的主要強化機制。

A series of (CoCrNi)100–2xNbxVx (denoted as nominal NbxVx, x = 0, 1, 2, 2.5, 3, 4) medium entropy alloy films (MEAFs) were successfully fabricated using magnetron sputtering with CoCrNi, Nb, and V targets via a three-target co-sputtering process. This study investigated the effects of niobium (Nb) and vanadium (V) additions on microstructures and mechanical properties of the CoCrNi MEAFs. With increasing Nb and V content, scanning electron microscopy (SEM) images revealed the ductile-to-brittle transition in the cross-section of the fractured films. X-ray diffraction (XRD) and transmission electron microscopy (TEM) patterns of Nb2.5V2.5 indicated a phase transformation from a single face-centered cubic (FCC) CoCrNi solid solution to the coexistence of an FCC CoCrNi matrix and orthorhombic Ni3Nb precipitates. The formation of nanocrystals was initially observed in Nb3V3, while the addition of further Nb and V led to the emergence of amorphous regions in Nb4V4. Nanoindentation and micropillar compression tests demonstrated that Nb2.5V2.5 film achieved the highest hardness (10.17 GPa), yield strength (5.45 GPa) and fracture strength (7.58 GPa), respectively, among all the MEAFs. Additionally, high-resolution transmission electron microscopy (HRTEM) images showed that the formation of nanocrystalline and amorphous structures was likely associated with the obvious decrease in mechanical behaviors. The experimental results suggested solid solution strengthening and precipitation hardening would be the primary strengthening mechanisms in the (CoCrNi)100–2xNbxVx MEAFs.