Improving the Mechanical Properties of Ti-6554 Alloy by Tailoring Dislocation Density and Multi-Morphologic Αs Phase Via Magnetic Field

Abstract

Metastable β titanium alloys are mainly strengthened by precipitation strengthening of secondary α (αs) phases during aging, but the ductility is not as expected. Surprisingly, the alloy shows a magnetoplastic effect after the magnetic field treatment, with a significant increase in ductility. In this work, we combined the above two methods, i.e. magnetic field coupled aging process, to improve the mechanical properties of Ti-65554 alloy by tailoring the dislocation density and αs phase. The magnetic field provides energy to promote the transformation of β to α phases and the precipitation of the αs phase. After the magnetic field, the alloy precipitates the multi-morphologic and multi-scale αs phase, with the volume fraction of these α phases increasing to ~14.3%. In addition, the dislocation density in the β matrix increases from ~5.18×1014 m-2 to ~7.34×1014 m-2 due to the magnetic field altering the spin state of the radical pair to accelerate the dislocation movement. The strength of the Ti-6554 alloy dramatically increased from ~801.0 MPa to ~1034.1 MPa, while the uniform elongation also improved to ~7.4% after magnetic field treatment. This significant strengthening and ductility improvement is attributed to the increased dislocation density and multi-morphologic αs phase precipitation. The precipitation of the αs phase increases the number of α/β phase interfaces, which not only hinders dislocation movement and strengthens the alloy, but also enhances strain compatibility and strain hardening ability, thereby improving deformation coordination.

Keywords: Metastable β titanium alloys, Magnetic field, Aging, Multi-morphologic αs phase, Dislocation, strength