Growth and interconnection of pressurized pores in nickel and relation to stress rupture models

Swelling and gas release were studied using pure nickel as a model metallic system. 'Green' powder compacts were sintered in a high pressure argon atmosphere until pores closed and gas was entrapped. When the ambient high pressure was reduced, the compact swelled until pores interconnected and the gas was released. Gas release was detected by a quadrupole mass spectrometer system. Microstructure evolution during swelling and gas release was examined by scanning electron microscopy and quantitative microscopy. The pore size and form factor distributions were measured and pores were found to reside primarily at the grain boundaries. For pure nickel, the swelling driving force. DF = p - P - 2γ/r (where p is the internal pore pressure, P is the external pressure, γ is the surface energy and r is the pore radius) may be completely determined using this technique. For low driving forces and high density, a linear relationship was found between the swelling strain-rate and the driving force. At higher driving forces and lower density, a non-linear relationship was found