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

• Published in: Journal of alloys and compounds Vol. 688; pp. 542 - 552
• Main Authors: Christofidou, K.A., Jones, N.G., Pickering, E.J., Flacau, R., Hardy, M.C., Stone, H.J.
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 15.12.2016
• Subjects: High-temperature alloys; Metallography; Metals and alloys; Microstructure; Neutron diffraction; High-temperature alloys; Metallography; Metals and alloys; Microstructure; Neutron diffraction
• ISSN: 0925-8388; 1873-4669
• DOI: 10.1016/j.jallcom.2016.07.159

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 γ-γ′ 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 γ and γ′ 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 γ-γ′ alloys of this type. •27 alloys in the Ni-Co-Al-Ti-Cr system assessed using neutron diffraction.•Lattice parameters of both the γ and γ′ phases increase with Ti and Cr.•No significant variation of lattice parameters with the Ni:Co ratio.•Strong correlation observed between room temperature hardness and lattice misfit.