Properties and fast low-temperature consolidation of nanocrystalline Ni–ZrO2 composites by high-frequency induction heated sintering

Nanopowders of Ni and ZrO2 (11 nm and 90 nm, respectively) were synthesized from NiO and Zr by high energy ball milling. A highly dense nanostructured 2Ni–ZrO2 composite was consolidated at low temperature by high-frequency induction heat sintering within 2 min of the mechanical synthesis of the powders (Ni–ZrO2) with horizontal milled NiO + Zr powders under 500 MPa pressure. This process allows very quick densification to near theoretical density and prohibits grain growth in nano-structured materials. The grain sizes of Ni and ZrO2 in the composite were calculated. Finally, the average hardness and fracture toughness values of nanostructured 2Ni–ZrO2 composites were investigated.

Research highlights▶ Nanopowders of ZrO2 and Ni were synthesized from Zr and NiO by high energy ball milling. The powder sizes of Ni and ZrO2 were 31 nm and 12 nm, respectively. Using the high-frequency induction heated sintering method, the densification of nanostructured Ni–ZrO2 composite was accomplished using mechanically synthesized powders and horizontal milled powders within 2 min of synthesis. The average grain sizes of Ni and ZrO2 prepared by HFIHS were lower than 100 nm. The average hardness and fracture toughness values obtained from mechanically synthesized powders and horizontal milled powders were 760 and 650 kg/mm2 and 10 and 9 MPa m1/2, respectively. The fracture toughness of the Ni–ZrO2 composite is higher than that of monolithic ZrO2.