Strength and Deformation Mechanisms is Titanium Aluminides alloyed with Vanadium containing γ+β Dual Phase Microstructures

2005 Fiscal Year Final Research Report Summary

• Project/Area Number: 16560606
• Research Category: Grant-in-Aid for Scientific Research (C)
• Allocation Type: Single-year Grants
• Section: 一般
• Research Field: Structural/Functional materials
• Research Institution: National University Corporation Tokyo University of Agriculture and Technology
• Principal Investigator: TAKAHASHI Tohru National University Corporation Tokyo University of Agriculture and Technology, Institute of Symbiotic Science and Tchnology, Department of Mechanical Systems Engineering, Professor, 大学院・共生科学技術研究部, 教授 (80188028)
• Project Period (FY): 2004 – 2005
• Keywords: Intermetallice / Titanium Aluminide / Light-weight Heat-resisting Metals / Microstructure / Strength and Deformation / Vanadium / Alloying Effects / Creep Characteristics

Research Abstract

Strength and deformation characteristics of aluminum-titanium-vanadium ternary alloys with γ+β microduplex structure have been investigated in this 2-years research project. A wide range of experimental results have been obtained, and the summary is presented below. The original findings will be reported in journals with some complementary data to be gained in the continuing effort that is still under way.
(1) Microstructure Characterization of the γ phase (L1_0 tetragonal structure) and β phase (body centered cubic structure)
Microduplex structure containing fine grains of γ and β phases were obtained in the aluminum-titanium-vanadium ternary alloys with 40 mol% aluminum compositions ; the rest 60 mol% were shared by titanium and aluminum. The average grain diameters ranged from 2 to 5 microns, and the volume fractions of both phases were around 50:50.
(2) Strength and its temperature dependence in aluminum-titanium-vanadium ternary alloys under compression tests
The above microduplex all oys showed considerably high strength around 800MPa in the temperature range from room temperature to 900K. Their strength, however, rapidly decreased with increasing temperature above 900K. The materials with higher vanadium content showed larger softening in elevated temperatures. The temperature above which the strength fell was lower in the materials with higher vanadium content, which can be explained by the softening behavior of the β phase.
(3) Creep characteristics as obtained in the compressive creep tests
Compressive creep tests were carried out at temperatures ranging from 1000 to 1200K in vacuum. In accordance with the above mentioned high-temperature strength of the materials, the materials with higher vanadium content showed higher creep rates. Stress dependence of the creep rate in one material containing 20 mol% vanadium revealed a stress exponent of about 2, which can be in close relationship with the deformation mechanism controlled by grain boundary sliding.
(4) Characterization of the deformed microstructures
In the higher temperature range where the β phase grains became softer than the γ phase grains, the specimen surface became wavy on the scale corresponding to the grain size. Agglomeration of the γ grains was observed in the specimens heavily deformed to about 50% compression, which is similar to the particle rafting in the crept nickel-base superalloys.