Formation of Amorphous ＆ Nanocrystalline Ni-W Alloys Produced by Electrodeposition and Their Mechanical Properties.

采用电沉积法制备了高强度纳米晶Ni-W合金。电沉积的镀液由硫酸镍、柠檬酸三钠、钨酸钠和氯化铵组成，在不同的镀液浓度和电解条件下运行。沉积过程中共沉积氢的夹杂对合金的塑性和抗拉强度有很大的影响。氢气脱气后，获得了平均晶粒度约为3 nm、W含量约为20.7at.%的高强度纳米晶Ni-W合金，抗拉强度约为2300 Mpa。这种合金还具有很高的延展性：可以弯曲180度角而不折断。然而，在不同温度下对这些材料进行退火热处理时，会发生晶粒长大，从而使其失去延性。为了估算纳米晶合金保持良好塑性所需的临界晶界尺寸，在纳米尺度的球形硬质颗粒被表示为密集堆积阵列的条件下，晶界滑移沿纳米晶颗粒的紧密堆积平面发生。

High-strength nanocrystalline Ni-W alloys were produced by electrodeoisition. The plating bath for the electrodeposition contained nickel sulfate, trisodium citrate, sodium tungstate and ammonium chloride, and was operated at various bath concentrations and conditions of electrolysis. The ductility and tensile strength of the deposited alloys are strongly influenced by inclusion of codeposited hydrogen during deposition process. After degassing the hydrogen, the high-strength nanocrystalline Ni-W alloy containing about 20.7 at.% W with an average grain size of about 3 nm has been obtained : the tensile strength attained to about 2300 MPa. The high ductility of this alloy was also observed : bending through an angle of 180 degree was possible without breaking. On annealing these materials at various temperatures, however, grain growth occurred and they lost their ductility. In order to estimate the critical grain size for keeping the good ductility in the nanocrystalline alloys, grain boundary sliding is considered to occur along the close-packed planes of the nanocrystalline grains under the condition where the nanoscaled spherical hard grains is represented as a densely packed array.