Creep behavior of TiAl alloys with enhanced high-temperature capability

Abstract

For high-temperature applications, creep strength is of major concern, in addition to oxidation and corrosion resistance, and determines the application range of titanium aluminide alloys in competition with other structural materials. Thus, this work was aimed at identifying mechanisms of creep deformation and microstructural degradation and at developing alloying concepts with respect to an enhanced high-temperature capability. The analysis shows that dislocation climb controls deformation in the range of the intended operation temperatures. Further, complex processes of phase transformations, recrystallization, and microstructural coarsening were observed, which contribute to microstructural degradation and limit component life in long-term service. By alloying with high contents of Nb, both room-and high-temperature strength properties can be improved as Nb increases the activation energy of diffusion and increases the propensity for twinning at ambient temperature. For alloys with enhanced hightemperature capability, microalloying with carbon is also of particular use, because carbide precipitates effectively hinder dislocation motion and are thought to increase microstructural stability.

High temperature tribological performance of CrAlYN/CrN nanoscale multilayer coatings deposited on γ-TiAl

“…Such potential has already been demonstrated by the use of this material as exhaust values and turbocharger wheels [4,5], however further expansion into this and other markets, such as aerospace, has been somewhat limited by environmental and tribological degradation at elevated temperatures [5]. Efforts to improve both the low temperature ductility as well as high temperature environmental resistance of γ-TiAl initially centred 2 on processing and microstructural control [3,6], however in recent years the use of novel coatings deposited by physical vapour deposition (PVD) have emerged as an alternative means of protecting this alloy [7,8].…”

Grain Refinement in Cast Ti‐46Al‐8Nb AND Ti‐46Al‐8Ta Alloys via Massive Transformation

“…However, this way is very laborious taking into account very high extrusion/forging temperatures. [1,2] Two approaches are now considered in the literature to refine the microstructures in cast TiAl alloys without involving any hot working: it is through solidification (during freezing and cooling) and through various heat treatments. The first approach can include: i) adding strong b-stabilizers (such as Re) and boron, [3,4] ii) adding boron in a level of about 1 at%, [4,5] iii) the use of b-solidifying alloys doped with b-stabilizing elements (such as Nb, Mo) and small boron additions.…”

Creep Behavior of Ti–40Al–16Nb Intermetallic Alloy and Strengthening Effects of Minor Sc

“…25) Moreover, similar work on TiAl alloy with a high Nb content shows that a stress exponent of about four under a creep condition of 988-1078 K/150-225 MPa is a creep behavior governed by dislocation climb. 14,26) Consequently, the controlling mechanism for creep behavior of Ti40Al-16Nb and Ti-40Al-16Nb-0.4Sc alloys under test conditions herein is dislocation climb.…”

“…The literature demonstrates that adding a small amount of Si, N, or C improves creep resistance by impeding of particles to dislocation motion. [12][13][14] Base on the strengthening effects of precipitates at high temperature, the Ti-40Al-16Nb alloy with the addition of a little of a quaternary element, such as Sc, is used to elucidate the properties of the specified alloy at high temperature. Accordingly, the object of this study is to investigate the creep behavior of Ti-40Al-16Nb alloy, with high Nb content, as well as the precipitation hardening by a small amount of Sc element added.…”