Room temperature tensile ductility is an important property of titanium (Ti) and titanium alloys for structural applications This article reviews the dependency of tensile ductility on oxygen for α-Ti, (α+β)-Ti and β-Ti alloys fabricated via traditional ingot metallurgy (IM), powder metallurgy (PM) and additive manufacturing (AM) or three-dimensional printing methods and recent advances in understanding the effect of oxygen on ductility Seven mechanisms have been discussed based on case studies of individual titanium materials reported in literature The dependency of ductility on oxygen is determined by both the composition and microstructure of the titanium alloy For Ti–6Al–4V (wt-%), as sintered Ti–6Al–4V shows a critical oxygen level of about 0·33 wt-% while additively manufactured Ti–6Al–4V exhibits different critical levels ranging from about 0·22% to well above 0·4% depending on microstructure Rare earth (RE) elements are effective scavengers of oxygen in titanium materials even just wi

Review of effect of oxygen on room temperature ductility of titanium and titanium alloys

High performance aerospace alloys via rapid solidification processing

The effect of cooling conditions, giving estimated cooling rates in the range 104 °C per second to 107 °C per second, on the microstructure of Ti-6Al-4V has been evaluated. The microstructures of as-solidified particulates were martensitic, with the martensite lath length decreasing with beta grain size,L, which in turn decreased with increasing cooling rate. For material alpha + beta heat-treated or vacuum hot pressed, the alpha morphology was dependent on the prior cooling rate. For materials cooled at 5 × 105 °C per second developed an equiaxed alpha morphology. This change in morphology was explained in terms of high dislocation density or grain size refinement, both of which result from the high cooling rate. When the beta grain size (L) was plottedvs section thickness (z), and estimated cooling rate (T), power law relationships analogous to those reported for secondary dendrite arm spacing were found:L = 1.3 ± 0.4z089±006 (thin, chill-substrate quenched),L = 0.17 ± 0.05z0.86±0.01(thick, convection-cooled material), andL = 3.1 × 106 T−0.93±0.12 (all material), whereL and z are in μm andT is in K/s. The last relationship is in agreement with the 0.9 exponent predicted using a model developed for the effect of grain size on cooling rate assuming classical homogeneous nucleation and isotropic linear growth during solidification. The first two relationships were rationalized by assuming that the two materials cooled under near-Newtonian conditions.

The Effect of Cooling Conditions on the Microstructure of Rapidly Solidified Ti-6Al-4V

A fibre coating process has been used to produce continuously reinforced advanced metal-matrix composites with up to 8% volume fraction of SiC fibre. Matrix materials were an α/β titanium alloy (Ti-Al-V), a dispersion-strengthened titanium alloy (Ti-Al-V-Y), a rapid solidification processed aluminium alloy (Al-4.3Cr-0.3Fe), and intermetallic compounds Ti3Al and TiAl. Thick metal coatings are shown to adhere well to the fibres, no evidence is found for chemical reaction between the coating and the fibre during the coating process, and the coated fibres can be handled and bent without damage. Tensile test data for Ti-Al-V alloy reinforced with 21% SiC fibre show a modulus near to a theoretical prediction, but tensile strength significantly below prediction. Loss of strength is attributed to the formation of a brittle reaction product during hot consolidation. The advantages and potential of the coated-fibre route for MMC production are discussed.

A fibre coating process for advanced metal-matrix composites

The characteristics of microstructures and second-phase particles in yttrium (0.1 mass%) bearing Ti-1100 high temperature titanium alloy were investigated at different conditions. The results show that the prior β grain and α platelets in Ti-1100 alloy with yttrium are remarkably refined compared to Ti-1100 alloy without yttrium, and that the coarsening rate of the refined microstructure in Ti-1100 alloy with yttrium is slow at higher annealing temperature and slower cooling rate. The reason is attributed to the formation of small size and stable Y 2 O 3 particles which delays the coarsening of the microstructure. The special precipitation features of silicide and α 2 phase in yttrium-bearing Ti-1100 alloy are also discussed.

Characteristics of microstructures and second-phase particles in Y-bearing Ti-1100 alloy

The feasibility of developing dispersion-strengthened powder metallurgy Ti alloys was determined in Ti-RE (RE = Ce, Dy, Er, Gd, La, Nd, or Y) alloys prepared by rapid solidification processing. The alloys were produced by electron-beam melting and splat quenching. Dispersoid precipitation and growth were studied as functions of annealing temperature, 700 to 1000 °C, for annealing times between 5 and 50,000 minutes. Dispersoid diameters, spacings, compositions, and crystal structures were characterized by transmission and scanning electron microscopy, X-ray and electron diffraction, energy-dispersive X-ray analysis, and scanning Auger microscopy. Two classes of dispersoid coarsening behavior at temperatures below theβ-transus were identified. In Ti-Ce, Ti-Gd, and Ti-Nd alloys, equilibrium rare earth sesquioxide (RE2O3) dispersoids form early in the annealing process and coarsen rapidly to > 1 μm diameter. The Ti-Nd alloys additionally contain large volume fractions of small (< 100 nm diameter) dispersoids. In the other Ti-RE alloys, dispersoids identified as Ti-RE-O-C compounds coarsen relatively slowly. Ti-Er is the most promising of the investigated systems for application in a multicomponent dispersion-strengthened alloy because long-time annealing at 700 to 800 °C produces stable dispersoids of 50 to 150 nm average diameter and 300 to 600 nm inter-particle spacing.

Structure and properties of rapidly solidified dispersion-strengthened titanium alloys: Part I. Characterization of dispersoid distribution, structure, and chemistry

J. E. O’neal

Papers

Structure and properties of rapidly solidified dispersion-strengthened titanium alloys: Part I. Characterization of dispersoid distribution, structure, and chemistry