The effect of zirconium addition on sintering behaviour, microstructure and creep resistance of the powder metallurgy processed alloy Ti–45Al–5Nb–0.2B–0.2C

• The effect of zirconium addition to Ti–45Al–5Nb–0.2B–0.2C was evaluated.
• Zirconium additions were conducted by using elemental powders.
• The melting point and the sintering temperature were significantly decreased.
• The presence of Zr-enriched γ phase at the colony boundaries was found.
• The creep resistance was improved almost threefold.

Since the presence of retained β phase might be detrimental for the creep properties of titanium aluminides, elements that stabilize the β phase, e.g. Nb and Mo, can only be used within a limited range. In this work, additions of the neutral element Zr to the alloy Ti–45Al–5Nb–0.2B–0.2C (in at.%) through elemental powder metallurgy were investigated. A powder-metallurgical processing route has been selected for this study, as it appears attractive with respect to microstructural homogeneity and manufacturing costs of complex parts. Different alloys with Zr content varying from 1 to 5 at.% were prepared by uniaxial pressing of a mix of elemental and pre-alloyed powders together with a binder system. The mechanical properties were evaluated by hardness and compression creep tests. The results indicate that Zr significantly decreases the melting point of the base alloy, which directly influences the sintering behaviour and with increasing Zr content the optimum sintering temperature decreases. The creep resistance showed a general improvement with increasing Zr content. The Zr additions resulted in the formation of γ phase enriched with Zr at the colony boundaries, the implications of which are discussed in the paper.

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