Preperation And Performance Of Ni-Cu Alloy Nano-Powders

Pure Ni, pure Cu, and Ni-Cu alloy nanopowders were prepared by the directcurrent arc plasma evaporation method. The effects of process parameters on the grainsize and yield of the three nanopowders were studied by an orthogonal experiment,and the optimal process conditions were determined. The growth mechanism of Ni-Cualloy nanopowders into Ni-Cu bulk alloys during the course of preparing and sinteringwas described. The mechanical properties and strengthening mechanism of Ni-Cualloy nanopowders consolidated by spark plasma sintering were studied. Comparedwith pure Ni and pure Cu nanopowders, the catalytic properties and catalyticmechanism of Ni-Cu alloy nanopowders on ammonium perchlorate (AP) were studiedby differential scanning calorimetry.The optimal process conditions of Ni-Cu nanopowders were determined atcurrent of300A,1:1ratio of hydrogen to argon, and total gas pressure of0.06MPawhen the effect of the yield was evaluated. A current of300A, ratio,1:1ratio ofhydrogen and argon, and total gas pressure of0.07MPa were used when the effect ofthe grain size was evaluated. The optimal process conditions for both pure Ni and pureCu nanopowders were determined to be a current of300A,1:1ratio of hydrogen toargon, and total gas pressure of0.06MPa. Based on the classical nucleation theory,the growth driving force of Ni-Cu alloy nanopowders was studied according to theexperimental results.We studied the phase composition, texture evolution, and grain morphologies ofNi-Cu bulk alloys sintered at different temperatures (773,823,873,923, and973K).The Ni-Cu bulk alloys had a single face-centered cubic phase. However, the peakintensity ratio of face (111) to face (200) I(111)/I(200)differed, indicating that the textureof the bulk materials evolved during sintering. FESEM photos showed that the particleshape gradually varied from spherical to polygonal. Based on TEM photos, thequantities of twins, dislocations, and pores were the primary reasons for the differentmechanical properties of the materials. The growth mechanism during the sintering of Ni-Cu alloy nanoparticles was discussed according to the crystal dynamic growththeory. The dynamic growth index and grain growth activation energy weredetermined.The hardness values of Ni-Cu bulk alloys sintered at different temperatures wereseparately measured using a nanoindentation mechanical test machine and the Vickershardness test. The tensile strength, yield strength, and elongation were determined bytensile tests.The strength mechanism of the Ni-Cu bulk alloys was discussed according to themechanism of deformation and fracture. The mechanical properties of the Ni-Cu bulkalloys was discussed based on the fine grain strengthening theory, which states that themechanical properties of Ni-Cu bulk alloys are superior to those of Ni-Cu bulk rawingots. However, the relationship between the strength and grain size did not obey theHall-Petch rule. The primary strength mechanism of the Ni-Cu bulk alloys was twinsstrength; their good mechanical properties mainly resulted from deformation twins,which prevented dislocation slip.The catalytic properties of the three nanopowders were evaluated based on threeaspects, including exothermic peak at high temperatures, apparent decomposition heat,and apparent activation energy. The following trend was observed: Ni-Cu nanopowders>Ni nanopowders> Cu nanopowders. The catalytic mechanism of Ni and Cunanopowders on AP was investigated according to the valence bond and energy bandtheories. The catalytic mechanism of Ni-Cu alloy nanopowders on AP was studiedaccording to the multiplet theory, which states that various factors such as latticedistortion, defects (e.g., twins and pores), and non-uniform surface promote theformation of surface catalytic activity centers.