纳米晶Ni-Ag合金在600-700℃的空气氧化

OXIDATION BEHAVIOR OF NANOCRYSTALLINE Ni-Ag ALLOYS AT 600-700℃ IN AIR

利用球磨和热压致密化过程 ,得到富Ag和富Ni相均匀分布的纳米晶Ni-Ag双相合金 .研究了含Ni分别为 50at%和 75at%的Ni- 50Ag和Ni- 2 5Ag合金在 60 0～ 70 0℃空气中的氧化 .Ni- 50Ag合金形成了Ni内氧化结构 ,最外层为连续Ag层 ,其氧化速率大于纯Ni.相反 ,Ni- 2 5Ag合金则形成了连续的NiO外氧化层且最外层为不连续的Ag层 .Ni- 2 5Ag合金氧化初期服从抛物线速率常数关系 ,随后氧化速率显著减小甚至小于纯Ni.合金的双相结构特性以及合金中极小的晶粒尺寸导致了上述结果的产生 .

Two Ni-Ag alloys, containing Ni of 50 at% and 75 at%, denoted as Ni-50Ag and Ni-25Ag were consolidated with hot pressing (HP) processing after mechanical alloying (MA) for 80 hr. The nanocrystalline alloys have been oxidized in air at 600-700 ℃ for 24 hr. Ni-50Ag alloy undergoes an internal oxidation of nickel associated with the formation of a continuous outermost layer of silver metal and has oxidation rates larger than those of pure nickel. On the contrary, Ni-25Ag alloy forms a continuous NiO layer surmounted by a discontinuous silver layer, while the internal oxidation is suppressed. These results are interpreted on the basis of the two-phase nature of the alloys and of their particularly small grain size.