The microstructure and hardness of Ni-Co-Al-Ti-Cr quinary alloys

The effects of Ni:Co and Al:Ti ratios on the room temperature microstructure, hardness and lattice parameter of twenty-seven quinary Ni-Co-Al-Ti-Cr alloys have been evaluated. All of the alloys exhibited a uniform gamma-gamma' microstructure. Differential scanning calorimetry (DSC) showed that the liquidus and solidus temperatures of the alloys increased with greater Al: Ti ratios, decreased with Cr concentration and remained largely unchanged with respect to the Ni:Co ratio. Neutron diffraction measurements of the gamma and gamma' lattice parameters revealed that the lattice misfit in all of the alloys was positive and increased with Ti concentration (i.e. lower Al:Ti ratio) regardless of the concentration of Cr, or the ratio of Ni: Co. Importantly, alloys with a Ni:Co ratio of 1:1, were found to have consistently greater lattice misfits than alloys with Ni:Co ratios of either 1:3 or 3:1. The measured lattice misfits were found to be strongly correlated with the Vickers hardness of the alloys, suggesting that lattice misfit plays a key role in the strengthening of gamma-gamma' alloys of this type. (C) 2016 Elsevier B.V. All rights reserved.