Composition formulas of Ti alloys derived by interpreting Ti-6Al-4V

• Published in: Science China. Technological sciences 2021-08, Vol.64 (8), p.1732-1740
• Main Authors: Liu, TianYu, Zhang, Shuang, Wang, Qing, Min, XiaoHua, Dong, Chuang
• Format: Article
• Language: English
• Subjects: Aluminum; Atomic structure; Beta phase; Chemical composition; Clusters; Engineering; Heat resistant alloys; High strength alloys; High temperature; Titanium alloys; Titanium base alloys
• ISSN: 1674-7321; 1869-1900
• DOI: 10.1007/s11431-020-1812-9

Titanium alloys are composed of α and β phases and are classified as near α, dual-phase α+β, and β types. This study attempts to derive their general composition formulas within the cluster-plus-glue-atom model by interpreting Ti-6Al-4V and other popular dual-phase α+β Ti alloys with well-established chemical compositions. Our model identified a molecule-like structural unit that covers only a nearest-neighbor cluster along with a few next-neighbor glue atoms, which can be represented as “[cluster](glue atoms) x ”. The structural units of the α and β phases in Ti-6Al-4V, α-[Al-Ti 12 ](AlTi 2 ), and β-[Al-Ti 14 ](V 2 Ti), were derived first and were in an unusual unit ratio of about 2.33:1. To obtain an alloy composition formula that satisfied this unit ratio, the two clusters were treated as hard spheres of different radii and packed according to the cluster-plus-glue-atom model. Our calculations determined that the Ti-6Al-4V alloy unit is composed of 12 α-[Al-Ti 12 ](AlTi 2 ) and 5 β-[Al-Ti 14 ](V 2 Ti) units (Ti-6.05Al-3.94V wt.%), with the fractional volume of the β phase being 32.5 vol.%, which is in agreement with experimental data. Finally, we describe how the chemical formulas of the α and β phases explain the high temperature near-α alloys (such as Ti-1100, [Al-(Ti 0.97 Zr 0.03 ) 12 ](Al 0.67 Si 0.12 Sn 0.18 Mo 0.03 ) 1.01 Ti 1.99 ) and high-strength β-Ti alloys (such as Ti-5553, [Al-Ti 14 ](Al 0.24 Fe 0.03 Cr 0.20 -Mo 0.18 V 0.35 ) 2.45 Ti 0.55 ), respectively.