利用XRD、SEM研究球磨时间对Ag-Zn合金粉末显微组织和内氧化性能的影响.结果表明:球磨初期,晶粒尺寸迅速减小,微观应变急剧增加,球磨25 h后,变化趋于平缓,球磨100 h后,晶粒尺寸和微观应变分别为20 nm和0.55%.Ag-Zn合金粉末在机械球磨过程中经历了片层化、片层结构破裂细化、破裂和冷焊的平衡阶段以及片层组织焊合成团4个阶段.Ag-Zn合金粉末的内氧化速度随球磨时间延长而增加,球磨100 h的粉末在0.5 h内即达到最大氧化程度,与未球磨粉末相比提高了25%.Ag-Zn合金粉末在内氧化过程中,未球磨粉末样品中ZnO呈针状和片状形成于表面且尺寸较大;粉末经机械球磨后氧化,ZnO则主要以针状形式存在于基体中,尺寸较小.生成ZnO产生的体积膨胀,在内氧化区形成压应力,导致银原子向粉末表面扩散形成银球.
Influence of ball-milling time on the microstructure and internal oxidation properties of Ag-Zn alloy powder was investigated by XRD and SEM. The results show that the grain size decreased rapidly while the microstrain increased sharply at the initial stage of ball milling. After ball-milling for 25 h, the change became gentle. After 100 h, the grain size and microstrain were 20 nm and 0.55%, respectively. The milling process may be divided into four stages, i.e. flattening, breaking & refining, balancing of breakage and cold welding, and welded conglomerations. The internal oxidation velocity of Ag-Zn alloy powder increased with the milling time prolonging. The oxidation ratio of Ag-Zn powder milled for 100 h reached the maximum in 0.5 h, which increased by 25% compared with that of the milling-free powders. During internal oxidation, ZnO were grown as spicule and flake with big sizes on the surface of the milling-free powders, while on the surface of milled powders ZnO was shaped mainly as spicule with small sizes. Nodules of virtually pure silver atoms formed on the surface of powder during internal oxidation, which is attributed to the compressive stress caused by the expansion of ZnO in the silver-matrix during internal oxidation.
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