Microstructures and hardness of ultrafine-grained Ni3Al |
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Affiliation: | 1. College of Mechanics and Materials, Hohai University, Nanjing 211100, China;2. Jiangsu Maritime Institute, Nanjing 211100, China;3. Suqian Institute, Hohai University, Suqian 223800, China |
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Abstract: | The microstructural evolution of the ultrafine-grained intermetallic compound Ni3Al is studied as a function of annealing at different temperatures. The ultrafine microstructure is produced by a high plastic torsional straining. Transmission electron microscopy, X-ray diffraction and differential scanning calorimetry are used to characterize the microstructural evolution and microhardness is used to determine mechanical behaviour. The as-deformed microstructure exhibits an almost fully disordered crystalline structure with coherent domain size of about 18 nm, a strong torsional texture and high internal elastic strains. On annealing the as-deformed samples at different temperatures, the recrystallization of the material into a granular type structure containing non-equilibrium grain boundaries is first observed. This is followed by the transformation from non-equilibrium grain boundaries with simultaneous grain growth. This transformation is correlated with an increase of hardness. A new concept of non-equilibrium grain boundaries transparency is presented to interpret this singular behaviour. The results are compared to those obtained on an ultrafine-grained Al-1.5% Mg alloy produced by the same technique and which exhibits the same mechanical behaviour. |
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