通过表面机械加工调控Zr52.5Cu17.9Ni14.6Al10Ti5非晶合金的结构和韧性

作为一种新型结构材料, 非晶态合金的韧性需要进一步提高. 提高非晶态合金韧性的方法有引入枝晶相、调整其成分改变其泊松比影响其剪切带衍生、裂纹扩展等.本文通过表面机械加工的方法来调控非晶态合金的微观结构及韧性. 我们采用真空电弧熔炼、亚稳态薄板离心浇铸系统制备了Zr_52.5Cu_17.9Ni_14.6Al₁₀Ti₅ (原子百分比) (Vit105)非晶合金板,并用表面机械研磨处理方法(surface mechanical attrition treatment, SMAT), 在Vit105板上形成纳米尺度局域类晶体序结构. 基于差示扫描量热分析、纳米压痕实验, 我们发现SMAT处理后的Vit105合金板表面附近弛豫焓更低, 微观结构更加均匀、稳定. 通过显微维氏硬度计测试, 发现SMAT处理后样品的表面附近硬度增大,硬度值分布也更均匀. 通过三点弯断裂实验, 可得到SMAT处理后合金板缺口韧度值从70.7 ± 4.7 MPa·m1/2提高到112.8 ± 3.7 MPa·m1/2. SMAT处理后合金板断裂后, 缺口前端剪切带密度比未处理的更大. Vit105合金板韧性的提高源于SMAT处理对剪切带萌生的促进作用. 该研究表明,表面机械加工可以在非晶态合金中形成局域类晶体有序结构, 影响其结构均匀性, 增大其硬度, 促进剪切带萌生, 提高其韧性. 表面机械加工作为一种新型的改变材料性能的手段, 具有广阔的应用前景. 

STRUCTURE AND TOUGHNESS MODULATION OF A Zr$_{52.5}$Cu$_{17.9}$Ni$_{14.6}$Al$_{10}$Ti$_{5}$ METALLIC GLASS BY SURFACE MECHANICAL ATTRITION TREATMENT 1)

As a new type of structural material, the toughness of metallic glasses (MGs) needs to be further improved. The methods of improving the toughness of MGs include introducing dendrite phase, tuning their compositions to change the Poisson's ratios in order to affect the formation and spread of shear bands and cracks, {etc}. In this paper, we use the method of surface mechanical treatment to alter the microstructure and toughness of MGs. A Zr$_{52.5}$Cu$_{17.9}$Ni$_{14.6}$Al$_{10}$Ti$_{5}$ (at. %) MG (Vit105) plate was prepared by arc melting in vacuum and centrifugal casting system for thin plates in the metastable state. Surface mechanical attrition treatment (SMAT) is introduced to form nanoscale local crystal-like ordered structure in Vit105. Through differential scanning calorimetry and nano-indentation experiments, we find that the relaxation enthalpy near the surface of the SMAT-treated Vit105 plate is reduced, and its microstructure is more homogenous and stable The analysis by Vickers hardness tester shows that the hardness of the regions near the surface is increased and the hardness values distribute more narrowly after the SMAT treatment. Three-point bending fracture experiment reveals that notch toughness of the plate is also improved by SMAT. By SMAT treatment, the notch toughness increases from $70.7\pm 4.7$ MPa$\cdot $m$^{1/2}$ to $112.8\pm 3.7$ MPa$\cdot $m$^{1/2}$. Meanwhile, the density of shear bands becomes larger near the fracture surface as compared to the untreated sample. The enhancement of the toughness of Vit105 plate treated by SMAT originates from the promotion of the formation of shear bands. Our studies show that surface mechanical treatment leads to the formation of local crystal-like ordered structure in MGs with the enhancement of structural homogeneity. The hardness and toughness of MGs are improved, being associated with the formation of profusive shear bands. As a novel approach of improving the properties of materials, surface mechanical treatment has a broad application prospect in future.