Microstructure and mechanical properties of materials obtained by spark plasma sintering of Ni3Al-Ni powder mixtures

In this work, Ni3Al-Ni composite materials were obtained by spark plasma sintering (SPS) of commercial nickel aluminide Ni3Al and metallic nickel powder mixtures at 1100 degrees C. The effect of the nickel content on the structure and mechanical properties of the sintered composites was investigated. Nickel filled the gaps between particles of brittle nickel aluminide and acted as a binder, which led to increased ductility of the composite materials relative to the intermetallic sintered without nickel additions. The introduction of nickel had a positive effect on the particle conjugation and the relative density of the sintered materials. Attractive mechanical properties were found in the composite sintered from a mixture containing 30 wt% of metallic nickel. This composite showed a tensile strength of 590 MPa, while its deformation at fracture was similar to 20%. The bending strength of this composite (1900 MPa) was twice as high as that of the material, to which no nickel was added. In this composite, Ni3Al intermetallic (gamma'-phase) in the form of cubic particles 0.5-2.2 gm in size and a solid solution of aluminum in nickel (gamma-phase) formed between the particles of the starting intermetallic powder. These microstructural features made the composite fracture in the mixed mode.