Electroless Nickel Plating and Spark Plasma Sintering of nano ZrO2 for Mechanical Property Enhancement

A new approach of combined electroless nickel plating (ENP) and spark plasma sintering (SPS) was used to determine the feasibility of fracture toughness improvement of ZrO2. Nano-grained yttria stabilized zirconia (YSZ) particles of 100nm average diameter were coated with about 1-5 nm of nickel coating by ENP. To reduce nano particle agglomeration throughout the ENP process; vigorous agitation with an ultrasonic horn was used. The coated powder was characterized using Scanning Electron Microscopy (SEM), Energy-dispersive X-ray spectroscopy (EDX) and Transmission electron microscopy (TEM) to study the microstructure and coating characteristics. The coating was identified to be predominantly nickel and of 1 to 5 nm thickness. The plated powder was dried and consolidated by Spark plasma sintering (SPS) with sintering times significantly lower than used in conventional sintering processes. The solid compact was evaluated for mechanical properties. Hardness values were obtained from Vickers micro hardness indentations; fracture toughness was calculated by indentation-crack-length measurement and three-point bend test of notched samples; flexural strength was measured by 3-point bend tests. The measured hardness is comparable to the results found in the literatures. The coated and uncoated zirconia show significantly higher average fracture toughness compare to existing values