Fabrication and mechanical properties of homogeneous and gradient nanocomposites by two-step sintering.

Homogeneous and functional gradient nanocomposites were prepared using a two-step sintering process at a pressure of 30 MPa. The effects of macro –micro fracture morphologies and element distributions on the mechanical properties of the composites were studied. The results showed that the fracture toughness of the inner layers of the gradient material was almost the same as that of the corresponding homogeneous material. The composition content difference between the gradient layers had a significant influence on the bending strength and hardness. There was little Ni and Mo diffusion in the gradient nanocomposites because of the relatively low contents and suitable processing parameters. A gradient distribution of the metals was ensured. The surface layer thickness had little influence on the flexural strength of the gradient nanocomposite, but it had an obvious influence on the hardness and fracture toughness of the surface. The five-layered gradient composite with a surface layer thickness of 85 μm exhibited the best mechanical properties, including a flexural strength of 1021 ± 35 MPa, fracture toughness of 7.60 ± 0.21 MPa m1/2 and surface hardness of 19.26 ± 0.62 GPa. [ABSTRACT FROM AUTHOR]