On the preparation of TiAl alloy by direct reduction of the oxide mixtures in calcium chloride melt
In recent years, TiAl-based intermetallic alloys are being increasingly considered for application in areas such as (i) automobile/transport sector (passenger cars, trucks and ships) (ii) aerospace industry (jet engines and High Speed Civil Transport propulsion system) and (iii) industrial gas turbines. These materials offer excellent (i) high temperature properties (at higher than 6000C) (ii) mechanical strength and (iii) resistance to corrosion and as a result have raised renewed interest. The combination of these properties make them possible replacement materials for traditional nickel-based super-alloys, which are nearly as twice as dense (than TiAl based alloys). Since the microstructures of these intermetallic alloys affect, to a significant extent, their ultimate performance, further improvements (by way of alteration/modification of these microstructures), have been the subject matter of intense research investigations. It has now been established that the presence of alloy additives, such as niobium, tantalum, manganese, boron, chromium, silicon, nickel and yttrium etc, in specific quantities, impart marked improvement to the properties, viz. fatigue strength, fracture toughness, oxidation resistance and room temperature ductility, of these alloys. From a number of possible alloy compositions, {gamma}-TiAl and Ti-Al-Nb-Cr have, of late, emerged as two promising engineering alloys/materials. . The conventional fabrication process of these alloys include steps such as melting, forging and heat treatment/annealing of the alloy compositions. However, an electrochemical process offers an attractive proposition to prepare these alloys, directly from the mixture of the respective oxides, in just one step. The experimental approach, in this new process, was, therefore, to try to electrochemically reduce the (mixed) oxide pellet to an alloy phase. The removal of oxygen, from the (mixed) oxide pellet, was effected by polarizing the oxide pellet against a graphite electrode in a pool of molten calcium chloride at a temperature of 9000C. The dominant mechanism of the oxygen removal was the ionization of oxygen followed by its subsequent discharge, as CO2/CO, at the anode surface. The removal of oxygen from the oxide mixture helped form the alloy in situ. The presentation shall cover the detailed experimental results pertaining to the preparation, evaluation and characterization of Ti-47Al-2Nb-2Cr (atom%) alloy.
- Research Organization:
- Idaho National Lab. (INL), Idaho Falls, ID (United States)
- Sponsoring Organization:
- USDOE
- DOE Contract Number:
- DE-AC07-05ID14517
- OSTI ID:
- 1042346
- Report Number(s):
- INL/CON-10-20068; TRN: US201212%%752
- Resource Relation:
- Conference: Fray International Symposium,Cancun, Mexico,11/27/2011,12/01/2011
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
ADDITIVES
ALLOYS
ALUMINIUM ALLOYS
ANODES
BORON
CALCIUM CHLORIDES
CHROMIUM
CORROSION RESISTANCE
DUCTILITY
ELECTRODES
FABRICATION
FATIGUE
FORGING
FRACTURE PROPERTIES
GRAPHITE
HEAT
INTERMETALLIC COMPOUNDS
IONIZATION
MANGANESE
MECHANICAL PROPERTIES
MELTING
MIXTURES
NICKEL
NIOBIUM
OXIDATION
OXIDES
OXYGEN
PELLETS
PERFORMANCE
REDUCTION
REMOVAL
SILICON
TANTALUM
TEMPERATURE RANGE 0400-1000 K
USES
VELOCITY
YTTRIUM
aluminum
electrochemical
molten salt
oxide reduction
TiAl alloy
titanium