AbstractAn investigation has been made of the constitution of the titanium rich partial Ti–V–Fe–Al system in the composition range applicable to commercialα+βandβTi–V–Fe–Al alloys (e.g. Ti–10V–2Fe–3Al alloy) and at temperatures between 650 and 800°C. Partial Ti–V–Fe isothermal sections for alloys containing ~4 wt-%Al and V and Fe in a ratio≥1:1 show onlyαandβas the equilibrium phases for compositions up to 13 wt-%V and 4 wt-%Fe. The position of theα+β/βboundary is temperature dependent and its shape is affected by the amount of aluminium present in theβin equilibrium with a in the quaternary Ti–V–Fe–Al alloys. By contrast, theα/α+βboundary is independent of these parameters. Microstructural features relating to morphology and volume fractions ofαandβphases have been investigated and, together with the compositions ofαandβ, are discussed in the context of alloy properties and processing.MST/1323