Preparation of Corrosion-Resistant Bulk Amorphous Alloys

采用铜模铸造法制备了直径为1 mm和2 mm的Ni-Cr-Nb-P-B、Ni-Cr-Ta-P-B和Ni-Cr-Me-P-B耐蚀块体合金。除含氘合金外，其它合金体系的玻璃形成能力与过冷液态稳定性之间存在良好的相关性。由此制备的大块非晶合金是自发钝化的，即使在非常积极的6 M和12 M HCl溶液在303 K下开放到空气中的大块非晶合金揭示了相同的阳极和阴极极化曲线作为相应的熔体快淬合金带，只要获得非晶单相合金。大块非晶合金中fcc结构Ni相的析出对合金的耐蚀性不利。然而，沉淀的影响强烈地依赖于沉淀物的尺寸。当在非晶基体中形成尺寸为20 nm的面心立方结构的Ni时，合金的钝化电流密度比单相非晶合金高两个数量级。相比之下，只有2-3 nm尺寸的fcc Ni沉淀导致钝化电流密度仅增加两倍。2 mm厚的大块非晶Ni-10 Cr-5 Nb-16 P-4 B合金板也通过在过冷液态下（即，708 K）通过护套轧制（sheath rolling）的气体雾化非晶合金粉末的固结来制备。发现由此制备的大块合金在303 K下在6 M HCl中显示出与相应的熔体快淬合金类似的极低腐蚀速率。然而，在12 M HCl溶液中，鞘辊合金显示出优先腐蚀攻击的气体雾化粉末的边界处，可能是由于在加热固结过程中的颗粒表面的氧化的影响。因此，进一步改进制备工艺，以获得高耐蚀性块体非晶合金。

Corrosion-resistant bulk Ni-Cr-Nb-P-B, Ni-Cr-Ta-P-B and Ni-Cr-Me-P-B alloys with cylindrical shape of 1 and 2 mm diameter are prepared by a copper mold casting method. A good correlation between the glass forming ability and stability of super-cooled liquid state has been found for these alloy systems except the molybdenum-containing alloy system. The bulk amorphous alloys thus prepared are spontaneously passive even in very aggressive 6M and 12M HCl solutions open to air at 303 K.The bulk amorphous alloys reveal the same anodic and cathodic polarization curves as the corresponding melt-spun alloy ribbons, as far as amorphous single phase alloys are obtained. Precipitation of fcc Ni phase in the bulk amorphous alloys is detrimental to the corrosion resistance of the alloys. The influence of the precipitation is, however, strongly dependent upon the size of the precipitates. When fcc Ni with size of 20〜nm is formed in the amorphous matrix, the alloys show about two orders of magnitude higher passive current density in comparison with the amorphous single phase alloys. In contrast, precipitation of fcc Ni with only 2-3 nm size results in the increase only twice in the passive current density. Bulk amorphous Ni-10Cr-5Nb-16P-4B alloy plates of 2 mm thickness are also prepared by consolidation of gas-atomized amorphous alloy powders by sheath rolling at a super-cooled liquid state, that is, 708 K.The bulk alloy thus prepared is found to reveal similar extremely low corrosion rate in 6M HCl at 303 K to the corresponding melt-spun alloy. However, in 12M HCl solution, the sheath-rolled alloy shows preferential corrosion attack at boundaries of the gas-atomized powders, possibly due to the influence of the oxidation of the particle surface during heating for consolidation. Thus, further improvement of the preparation processes to obtain highly corrosion-resistant bulk amorphous alloys using this method.