Solution and Precipitation Hardening in Carbon-Doped Two-Phase γ-Titanium Aluminides

Abstract

A two-phase titanium aluminide alloy was systematically doped with carbon to improve its high temperature strength. Solid solutions and precipitates of carbon were formed by different thermal treatments. A fine dispersion of perovskite precipitates was found to be very effective for improving the high temperature strength and creep resistance of the material. The strengthening mechanisms were characterized by flow stresses and activation parameters. The investigations were accompanied by electron microscope observation of the defect structure which was generated during deformation. Special attention was paid on the interaction mechanisms of perfect and twinning dislocations with the carbide precipitates.

High carbon solubility in a γ-TiAl-based Ti–45Al–5Nb–0.5C alloy and its effect on hardening

“…Earlier TEM studies [12,13,16,17] have revealed typical C-containing precipitates of 20 -100 nm in length and 3-6 nm in width, which form arrays with a spacing of about 50-100nm. If a similar distribution was present in our material, we would have detected several precipitates within our analysed APT volume as well as observing them in the TEM, e.g.…”

“…Typical agehardening behaviour is observed where the strength is increasing with the formation of precipitates [12,14,15]. It was shown that dislocations are effectively pinned by these precipitates [12,16,17]. In contrast, it was reported that C in solid-solution is a weak obstacle for dislocation gliding which can be easily overcome by thermal activation [16,17].…”

“…It was shown that dislocations are effectively pinned by these precipitates [12,16,17]. In contrast, it was reported that C in solid-solution is a weak obstacle for dislocation gliding which can be easily overcome by thermal activation [16,17]. These studies were restricted to binary TiAl alloys, and did not address whether other alloying elements such as Nb might modify the solid-solution strengthening behaviour of C.…”

Microstructure Design and Its Effect on Mechanical Properties in Gamma Titanium Aluminides

“…After a long time annealing or creep test, p − Ti 3 AlC carbide would nucleate at the α 2 /γ interface and grow into γ-lamella [62]. The perovskite carbide can effectively pin the perfect and twinning partial dislocation, but the C solid solution can only act as weak obstacles which can be overcome by the aid of thermal activation [61,63]. Therefore, the strengthening effect is more significant in precipitated carbide than in C solid solution [63].…”

Microstructure evolution and enhanced creep property of a high Nb containing TiAl alloy with carbon addition

“…Thus, the further enhancement of creep resistance can be obtained by microstructural optimization. It is reported that carbon addition can improve the creep properties of TiAl alloys via solid-solution and precipitation strengthening depending on the carbon content [14][15][16][17]. Klein et al claimed that the addition of carbon stabilized the α 2 phase and hindered the precipitation of γ and β o (ω o ) phases [18].…”