Synergistic enhancement of strength and ductility of Ti2AlC/TiAl through Mn solid solution and interface manipulation

Abstract

Introducing Ti2AlC particles into TiAl alloys can effectively improve their strength, but this can also lead to stress concentration at the interface, resulting in the reduction of ductility. Therefore, Mn is adopted to synergistically improve the strength and ductility of the Ti2AlC/TiAl composite through solid solution and interface manipulation. The first-principles calculation shows the Ti–Mn bonds are formed at the Ti2AlC/TiAl interface after Mn doping, characterized primarily by metallic bonds with some covalent bonding. This combination preserves strength while enhancing ductility. Then, Ti2AlC/TiAl–Mn composite is prepared. The Ti2AlC, with an average size of 1.6 μm, is uniformly distributed within the TiAl matrix. Mn doping reduces the lamellar colony size and lamellar thickness by 25.1% and 27.4%, respectively. A small quantity of Mn accumulates at the boundaries of the lamellar colonies. The Mn content must be controlled to avoid segregation, which may negatively impact performance. The yield stress, ultimate compressive stress, fracture strain, and product of strength and plasticity of the Ti2AlC/TiAl–Mn composite have been increased by 5.5%, 11.5%, 10.4%, and 23.0%, respectively, compared to those of the Ti2AlC/TiAl composite. The enhancement in strength is due to the combined effects of grain refinement, solid solution of Mn, and twinning strengthening. Grain refinement and twin strengthening also can reduce stress concentration and improve ductility. In addition, at the electronic level, the Ti–Mn bond formed at the interface is contributed to the improvement of ductility.

1. Introduction

With the rapid development of aerospace and related fields, the requirements for high-temperature structural materials are constantly increasing. TiAl alloys, recognized for their low density, superior specific strength, and exceptional resistance to oxidation and creep, have attracted extensive attention [1–5]. At present, TiAl alloys have been successfully utilized in the low-pressure turbine blades of aerospace engines [6–8]. Nonetheless, due to the limited ductility of TiAl alloys at room temperature and insufficient strength at high temperatures, their application scope is significantly limited. Therefore, further research and development are necessary to overcome these limitations [9–10].

The mechanical properties of TiAl alloys can be effectively enhanced through solid solution of alloying elements [11–14]. TiAl alloys reinforced with Nb and Mo were prepared by Feng et al. [14], resulting in improvements in microhardness, compressive strength, and fracture strain. Solid solution strengthening played a significant role in these enhancements. Pan et al. [11] prepared TiAl alloys with excellent mechanical properties by adding Sn. Due to the optimized microstructure and the solid solution of Sn, the compressive strength and yield strength improved by 5.6% and 15.1%, respectively. Moreover, reinforcing TiAl alloys with ceramic particles is also an effective method for fabricating high-performance TiAl composites. This approach merges the benefits of both the ceramic particle reinforcements and the TiAl matrix. Currently, TiAl composites reinforced with ceramic particles, including TiB2 [15], Ti2AlC [16], and Ti5Si3 [17], have been successfully fabricated. Notably, the reinforcement of Ti2AlC with the ternary layered structure not only exhibits the exceptional properties of both metal and ceramic, but also its density and thermal expansion coefficient match well with the TiAl matrix [18]. In research conducted by Zhou et al. [19], graphene was introduced into the Ti–47Al–2Cr–4Nb–0.3W alloy, resulting in the in-situ formation of Ti2AlC particles and a notable refinement of the grain structure. Upon incorporating 0.8at% graphene, a marked enhancement in mechanical properties of the TiAl alloy was observed. Specifically, the yield strength and fracture strength were elevated from 478 and 2001 to 772 MPa and 2347 MPa, respectively. In the pursuit of improving the mechanical properties of TiAl alloys, Wang et al. [20] employed a pre-alloyed powder of Ti–48Al–2Nb–2Cr and multi-walled carbon nanotubes (CNTs) to fabricate Ti2AlC/TiAl composite reinforced with dual-scale Ti2AlC particles. The TiAl composite exhibited exceptional comprehensive mechanical performance. However, due to a deformation mismatch between ceramic particles and the TiAl matrix at the interface during the deformation process, stress concentration is prone to occur, which consequently reduces the ductility of composites [21]. Therefore, gaining a comprehensive insight into the interfacial structure between ceramic particles and TiAl matrix is of great importance for the fabrication of TiAl composite with excellent strength and ductility.