Abstract
Specimens containing 2 wt.-% alumina as a disperse phase and whose matrices consisted of either pure nickel or nickel + 1 wt.-% iron have been produced by powder-metallurgy techniques and subsequently worked to form thin sheets. The sheets were annealed in the range 1380–1420°C, under oxygen partial pressures in the range 5 × 10–11 to 10–18 atm, for times between 15 and 1200 min.
Metallographic examination shows that the particles do not grow in size but that they move to fill the grain boundaries and eventually to form large clumps at grain-boundary corners. The particle movement is suppressed by the control of oxygen partial pressure and/or the addition of iron to the matrix. A tentative mechanism to explain this movement has been put forward, based on the flow of nickel atoms round the particles, resulting in particle movement in the contrary direction.
Further experiments, on wires of nickel matrix containing 1 wt.-% additions of iron, cobalt, chromium, or copper, but without the disperse phase, have shed further light on the way in which nickel atoms can move in these environmental conditions.
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