Liquidlike sintering behavior of nanometric Fe and Cu powders: Experimental approach

Nanometric Fe and Cu powders were sintered in vacuum, He, and H(2) atmospheres after uniaxial cold pressing. The shrinkage behavior of samples was studied using three different dilatometric techniques: constant heating rate, isothermal annealing, and the Dorn method. Density greater than 90 pet was obtained at sintering temperatures of 900 degrees C. In nanometric powders, densification and grain coarsening occurred in a narrow temperature interval. Despite the low oxide content in the starting powders (1.5 to 4 wt pet), the reducing atmosphere plays a relevant role in the sintering process. The self-diffusion activation energies obtained for nanometric Fe were 116 and 60 kJ/mole in vacuum and H(2), and those obtained for nanometric Cu were 70 and 43 kJ/mole in He and H(2). According to the present results, the activation energies obtained from both nanometric powders in H(2) could be associated with those for self-diffusion in liquid Fe (65 kJ/mole) and Cu (41 kJ/mole).