Elimination of oxygen sensitivity in \u03b1-titanium by substitutional alloying with Al

Yan Chong,J W Morris,Andrew M Minor,Mohammad S Hooshmand,Shiteng Zhao,Ruopeng Zhang,Daryl C Chrzan,Mark Asta

doi:10.1038/s41467-021-26374-w

Abstract

Individually, increasing the concentration of either oxygen or aluminum has a deleterious effect on the ductility of titanium alloys. For example, extremely small amounts of interstitial oxygen can severely deteriorate the tensile ductility of titanium, particularly at cryogenic temperatures. Likewise, substitutional aluminum will decrease the ductility of titanium at low-oxygen concentrations. Here, we demonstrate that, counter-intuitively, significant additions of both Al and O substantially improves both strength and ductility, with a 6-fold increase in ductility for a Ti-6Al-0.3 O alloy as compared to a Ti-0.3 O alloy. The Al and O solutes act together to increase and sustain a high strain-hardening rate by modifying the planar slip that predominates into a delocalized, three-dimensional dislocation pattern. The mechanism can be attributed to decreasing stacking fault energy by Al, modification of the “shuffle” mechanism of oxygen-dislocation interaction by the repulsive Al-O interaction in Ti, and micro-segregation of Al and O by the same cause.

Highlights

Increasing the concentration of either oxygen or aluminum has a deleterious effect on the ductility of titanium alloys
We experimentally demonstrate that the synergy of 6 wt.% Al and 0.3 wt.% O does produce an excellent combination of high strength (~1.3 GPa) and good ductility (~25%) at cryogenic temperature
The findings presented here enable the development of low-cost titanium alloys by lifting the rigorous processing required to control interstitial impurities, broadening the spectrum of the materials’ engineering applications

Summary

Introduction

Increasing the concentration of either oxygen or aluminum has a deleterious effect on the ductility of titanium alloys. Despite the successful application of solid solution strengthening in a wide range of metal alloys, anomalous alloying sensitivity can occur when intense chemical interactions exist among the solute atoms and the matrix atoms[2,3,4,5] Such interactions lead to extreme sensitivity to solute concentrations that can decrease instead of increase both strength and ductility of the alloys[4,6,7,8]. Pure α-Ti deforms in tension through a combination of deformation twinning and dislocation glide[9,10] It has excellent ductility at cryogenic temperatures as low as 77 K, but rather low strength[11] and, is usually alloyed to achieve desirable mechanical properties. This possibility is intriguing given recent work by Gunda, et al.[21], whose

Methods

Results

Conclusion