DESIGN AND CHARATERIZATION OF BETA PHASE TRANSFORMATION TOUGHENING OF GAMMA ALLOY

Due to their light weight, relatively good high-temperature mechanical properties and oxidation resistance, gamma-TiAl based alloy are among the candidate materials for advanced engine application. However, a wide scale application of these materials is current hampered by their limited tensile ductility and fracture toughness at temperature below ~600 C.

A comprehensive experimental investigation of the materials microstructure (using optical, scanning and transmission electron microscope), the crystal structure of the constinent phases (using X-ray and selected area electron diffraction) and fracture toughness (using three-point bending tests) has been carried out in a (Ti-40Al-32V-2Fe, wt%) two-phase gamma TiAl-based alloy containing second-phase particles of a b.c.c. phase and in a (Ti-44Al-27V-0.6Fe, wt%) single-phase gamma TiAl alloy.

Experimental characterization of the alloys microstructure and fracture toughness showed that a deformation-induced beta to alpha'' martensitic transformation take place within the beta phase, and that due to the orthorhombic crystal structure of the alpha'' martensite the transformation is accompanied by a ~2.8% increase in volume. In addtion, the occurrent of the martensitic transformation and the accompanied crack-tip shielding effect is found to give rise to increase in the fracture toughness relative to that of the single-phase gamma-TiAl alloy, in which no martensitic transformation takes place.

• Design the Single-Phase Gamma and Two-Phase Gamma+Beta Alloys
• Three-Point Bending Test Result of Fracture Toughness
• Characterization of Microstructures
  • Microstructures in Two-Phase Alloy Before Fracture (Optical, SEM/EDS)
  • Microstructures in Two-Phase Alloy After Fracture (Optical)
  • Fracture Surfaces in a) Two-Phase and b) Single-Phase Alloys (SEM)
  • Phases and Structures in Two-Phase Alloy After Fracture (X-Ray)
  • Martensite and Other Phases in Two-Phase Alloy After Fracture (TEM)
  • Phase Orientation Relations in Two-Phase Alloy After Fracture (TEM/SED)
  • Beta Phase Stability Respect to Stress (Deformation) and Temperature

PUBLICATIONS

1. M. Grujicic and P. Dang, "Dispersed Ti-base B.C.C. Beta Phase Transformation Toughening of Gamma-Titanium Aluminide Intermetallics", Materials Science and Engineering A, 187-199, 224 (1997).

2. P. Dang and M. Grujicic, "The Effect of Crack-tip Materials Evolution on Fracture Toughness-An Atomistic Simulation Study of the Ti-V alloy System", Acta Metallurgica et Materialia, 75-87, 45 (1997).

3. M. Grujicic and P. Dang, "A Molecular Dynamics Study of Transformation Toughening in the Gamma TiAl/Beta Ti-V System", Materials Science and Engineering A, 219 (1996) 109-125.

4. P. Dang and M. Grujicic, "A study of Crystal Defects Effect on the Martensitic Transformation in Ti-V B.C.C. Beta Alloy", Modeling and Simulation in Materials Science and Engineering , 123-136, 4 (1996).

5. P. Dang and M. Grujicic, "Atomic Simulation of Crack-tip Transformation in Ti-V beta Alloy", Scripta Metallurgica et Materialia, 59-64, 35 (1996).

6. M. Grujicic and P. Dang, "Atomic-Scale Analysis of Martensitic Transformation in Titanium Alloyed with Vanadium -- Part I: Verification of the EAM Model", Materials Science and Engineering A, , 139-152, 205 (1996).

7. M. Grujicic and P. Dang, "Atomic-Scale Analysis of Martensitic Transformation in Titanium Alloyed with Vanadium -- Part II: Molecular Dynamics Study", Materials Science and Engineering A, , 153-156, 205 (1996).

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