Details

Autor(en) / Beteiligte

• Zhang, Bowen
• Wu, Xiaogang
• Zhang, Deliang

Titel

Effect of silicon addition on microstructure and mechanical properties of a high strength Ti-4Al-4Mo-4Sn alloy prepared by powder metallurgy

Ist Teil von

• Journal of alloys and compounds, 2022-02, Vol.893, p.162267, Article 162267

Ort / Verlag

Lausanne: Elsevier B.V

Erscheinungsjahr

2022

Link zum Volltext

Quelle

Elsevier ScienceDirect Journals Complete

Beschreibungen/Notizen

• •With an addition of 0.2 wt%Si, the Si atoms are equally in α and β phases.•Si solute atoms retard the growth of α phase, causing refinement of the α/βt lamellar structure.•Si atoms enhance solid solution strengthening and Si atoms enhanced α/βt interface strengthening.•Increasing the Si content to 0.5 wt% cause a further increase of the yield strength by 50 MPa.•With a high strength, the tensile ductility deteriorates, due to the premature fracture of grain boundary α layers. Ti-4Al-4Mo-4Sn-xSi (wt%) (x = 0, 0.2, 0.5) alloys were fabricated by hot extrusion of compacts of blends of TiH2, AlMo60 master alloy and other required elemental powders followed by heat treatments involving vacuum annealing, solution treatment, air cooling and aging. The microstructure of the alloys consists of α plates, lamellae of α and transformed β structure (βt), βt blocks as well as grain boundary α layers. With the addition of 0.2 wt%Si, the Si atoms exist in equal concentration in both α and βt regions as solute atoms, and they retard the growth of α phase, causing a decrease of the average thickness of α plates and lamellae and slight increase of the volume fraction of βt lamellae and blocks. The solid solution strengthening and enhanced α/β interface hardening brought by the 0.2 wt%Si cause the yield strength of the Ti-4Al-4Mo-4Sn alloy to increase significantly from 1030 to 1130 MPa with a slight decrease of the tensile ductility (7.4% vs 6.8%) and without changing the fracture behavior. With the addition of 0.5 wt%Si, the extra Si causes nanometer sized silicide (Ti5Si3) precipitates to form in both α and βt regions and further microstructural refinement. The additional α/β interface hardening and precipitation hardening cause the yield strength of the alloy to increase further to 1177 MPa, but the tensile ductility deteriorates clearly with the elongation to fracture decreasing to 4.9%. The main reason for this ductility decrease is the premature fracture of grain boundary α layers caused by the higher flow stress which can induce more strain localization at the grain boundary α layers.