Influence of Rare-Earth Additions on Properties of Titanium Alloys Microstructures and Room-Temperature Tensile Properties of Ti-6A1-4V with Yttrium, Erbium, and Mischmetal Additions.
Abstract
The influence of different concentrations of metallic yttrium, erbium, and mischmetal (MM) on the microstructure and room-temperature mechanical properties of Ti-6Al-4V was studied. Alloy ingots containing 0.02-0.3 wt% Y, 0.1-2.0 wt% Er, and 0.01-0.2 wt% MM were cast, forged, hot-rolled, and mill-annealed in the alpha-beta and beta fields. The metallic rare-earth additions produce a uniform dispersion of small (< 70 nm diam) second-phase precipitates in the Ti-6Al-4V matrix. Both Y and Er effect grain refinement and microstructural homogeneity and ratard grain growth; Mischmetal is less effective than Y or Er. Yttrium and erbium act slightly as beta-phase stabilizers and mischmetal is an alpha-phase stabilizer. The roller pressures required for hot-rolling are less for rare-earth-modified Ti-6Al-4V, and edge-cracking during rolling is reduced for Y concentrations < or = 0.05 wt% and Er concentrations < or = 0.1 wt%. The transverse and longitudinal elastic modulus, yield stress, and ultimate tensile stress are not adversely affected by Y and Er concentrations < or = 0.1 wt%, and the room-temperature ductility is increased. Mischmetal in 0.01-0.2 wt% concentrations degrades the tensile properties. Rare-earth second-pahse precipitation-strengthening is a factor in the room-temperature tensile properties for only alpha-beta annealed Ti-6Al-4V in which the volume fraction of equiaxed alpha is significant. Slight (< 5%) reductions of yield stress observed for Y- and Er-containing Ti-6Al-4V are likely due to scavenging of interstitial oxygen by the rare-earth precipitates.
Document Details
- Document Type
- Technical Report
- Publication Date
- May 31, 1977
- Accession Number
- ADA044235
Entities
People
- Charles R. Whitsett
- James E. O'neal
- Richard J. Lederich
- Shankar M. L. Sastry