New Tough Ductile Nano Titanium Aluminide Alloys Forged by German Metals Physicists at GKSS for Lightweight Construction and High Temperature Applications

FIG. 1A is an electron photomicrograph of a nano titanium aluminide alloy developed at GKSS

GKSS-Research Center (Geesthacht, DE) scientists developed nano titanium aluminide (TiAI) alloys.  The alloys are characterized by an extremely high rigidity and creep resistance with simultaneously high ductility and fracture toughness.

GKSS Metals Physicists Dr. Fritz Appel,  Dr. Jonathan Paul and Dr. Michael Oehring created titanium aluminide alloys with a  morphology in the nanometer range. Titanium aluminide components can form a homogeneous alloy.

It has been shown that in some alloys or intermetallic connections have composite lamella structures structures in the nanometer size. The lamella structures include modulated lamellas made of the crystallographically different, and alternatingly formed, B19 phase and .beta. phase. The created composite lamella structures are largely surrounded by .gamma.-TiAI,  according to  the inventors in U.S. Patent Application 20100000635.

Without wishing to be bound by any one particular theory, the invention is based on the idea of using lattice transformations through shear conversion for an additional refining of the microstructure of the titanium aluminide alloys. This type of process is not previously known for titanium aluminide alloys in scientific literature. In the case of the alloys as described herein, the formation of brittle phases like .omega., .omega.' and .omega.'', which are extremely disadvantageous for the mechanical material properties, are also avoided, due to shear conversions. 

 

GKSS nano titanium aluminide alloys are characterized by a low density, a high rigidity and good corrosion resistance. In the fixed state, they have domains with hexagonal (.alpha.), two-phase structures (.alpha.+.beta.) and cubically body-centered .beta. phase and/or .gamma. phase.

For industrial practice, alloys based on an intermetallic phase .gamma. (TiAl) with a tetragonal structure and containing minority shares of intermetallic phase .alpha₂(Ti₃Al) with hexagonal structure in addition to the majority phase .gamma. (TiAl) are particularly interesting.

These .gamma. titanium aluminide alloys are characterized by properties like low density (3.85-4.2 g/cm³), high elastic modulus, high rigidity and creep resistance up to 700.degree. C., which make them attractive as lightweight construction materials for high-temperature applications. Examples of such applications include turbine buckets in aircraft engines and in stationary gas turbines, and valves for engines and hot gas ventilators. 

These types of composite lamella structures can be established in alloys using known production technologies, i.e. through casting, reshaping and powder technologies.  FIG. 1B is an electron photomicrograph providing a detailed view of selected lamella structures T of FIG. 1A

FIG. 1C is an electron photomicrograph of an alloy. FIG. 1C shows a cast structure of the same alloy, i.e., an alloy containing titanium, 42 at % aluminum, and 8.5 at % niobium, in which a composite lamella structure (indicated in the Figure by the reference letter T) is also formed, which is surrounding by the .gamma. phase.

FIG. 2B is an electron photomicrograph providing a still more detailed view of a lamella structure T of FIG. 1A.