| Summary: | The lattice square degree, denoted by the c/a value, is a crucial factor that influences the slip mode of α-Ti alloys and thereby affects their plasticity. However, the relationship between the c/a value and the plasticity of α-Ti alloys has not been fully clarified. In this study, the powder metallurgy method (PM) was used to prepare Ti alloys with different square degrees by introducing interstitial O and substitutional Si solutes into α-Ti crystal. Then the mechanical properties, particularly plasticity, and lattice parameters of the resulted alloys were measured. By combining first-principles calculation with experimental studying, a plastic criterion based on the square degree was established. Subsequently, the mechanism of strength and plasticity was investigated by means of the density of states and charge density difference. Finally, the composition of α-Ti alloys with both O and Si solution atoms was designed, whose c/a values were calculated by the first-principles calculation and accorded with the proposed square degree criterion, and then the reliability of this criterion was verified by the experimental results. As a result, a high strength and plasticity α-Ti alloy with tensile strength 1106 MPa and elongation 23.2 % was successfully prepared. The findings of this research offer new insights into the alloying design of α-Ti alloys with high strength and moderate plasticity.
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