| Summary: | In this work, the hot deformation characteristics of a near-<inline-formula><math display="inline"><semantics><mi>α</mi></semantics></math></inline-formula> Ti-Al-2SnZr-2Mo alloy (Ti6242 alloy) with a Fine-Grained (FG) microstructure (<inline-formula><math display="inline"><semantics><msub><mi>d</mi><mi>α</mi></msub></semantics></math></inline-formula> = 2.86 <inline-formula><math display="inline"><semantics><mi mathvariant="sans-serif">μ</mi></semantics></math></inline-formula>m) were investigated at two levels of temperature, <i>T</i> = 730 <inline-formula><math display="inline"><semantics><msup><mrow></mrow><mo>∘</mo></msup></semantics></math></inline-formula>C and <i>T</i> = 840 <inline-formula><math display="inline"><semantics><msup><mrow></mrow><mo>∘</mo></msup></semantics></math></inline-formula>C. The initial microstructure consists of equiaxed nodules of the <inline-formula><math display="inline"><semantics><mi>α</mi></semantics></math></inline-formula> phase as well as some <inline-formula><math display="inline"><semantics><mi>α</mi></semantics></math></inline-formula> lamellae sparsely distributed and separated by thin layers of the BCC <inline-formula><math display="inline"><semantics><mi>β</mi></semantics></math></inline-formula> phase. For both temperatures, three strain rates (<inline-formula><math display="inline"><semantics><mrow><msup><mn>10</mn><mrow><mo>−</mo><mn>4</mn></mrow></msup><mo>,</mo><msup><mn>10</mn><mrow><mo>−</mo><mn>3</mn></mrow></msup><mo>,</mo><msup><mn>10</mn><mrow><mo>−</mo><mn>2</mn></mrow></msup><mspace width="4pt"></mspace><msup><mi mathvariant="normal">s</mi><mrow><mo>−</mo><mn>1</mn></mrow></msup></mrow></semantics></math></inline-formula>) were analysed during loading. Moreover, the microstructural evolution (<inline-formula><math display="inline"><semantics><mi>α</mi></semantics></math></inline-formula> size and morphology) was also evaluated by conducting interrupted tensile tests. The different tensile testing conditions greatly influence the stress-strain response of the material as well as the microstructure evolution. Indeed, various phenomena can take place such as elongation of the grain structure, globularization, dynamic recrystallization and grain growth of the equiaxed areas depending on the temperature, the strain rate and the strain level. The FG Ti6242 alloy exhibits interesting superplastic ductility at <i>T</i> = 840 <inline-formula><math display="inline"><semantics><msup><mrow></mrow><mo>∘</mo></msup></semantics></math></inline-formula>C. At this temperature either a very gradual flow softening (at higher strain rate) or flow hardening (at lower strain rate) can be observed and are related respectively to one or more of the following mechanisms: lamellae globularization, DRX and grain growth. At the intermediate strain rate, both mechanisms, strain hardening and softening, coexist. At <i>T</i> = 730 <inline-formula><math display="inline"><semantics><msup><mrow></mrow><mo>∘</mo></msup></semantics></math></inline-formula>C, the onset of the <inline-formula><math display="inline"><semantics><mi>α</mi></semantics></math></inline-formula> lamellae globularization was only promoted at low strain rate. A mechanical behavior model was developed in the temperature range of 730–840 <inline-formula><math display="inline"><semantics><msup><mrow></mrow><mo>∘</mo></msup></semantics></math></inline-formula>C, which was able to take into account all the observed phenomena: viscosity, softened behavior and strain hardening. Constitutive equations were calibrated from the stress-strain responses and microstructural observations, and the computed results were in good agreement with the experiments.
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