Presentation on theme: "ASTP MMR MOTIVATION Development of next generation space exploration vehicles and space structures require high temperature materials with Low density."— Presentation transcript:
1ASTP MMRMOTIVATIONDevelopment of next generation space exploration vehicles and space structures require high temperature materials withLow densityHigh strength and ductilityOxidation resistanceGood creep propertiesMetal Matrix Composites based on intermetallics such as gamma-titanium aluminides (-TiAl) have been identified as material of choice for aerospace applications in the temperature range of 600oC to 900oC.-TiAl have been identified as possible replacement for superalloys in engine components and nozzles due to their high specific strength and oxidation resistance at high temperatures.
2STATE OF THE ART IN TITANIUM ALUMINIDES ASTP MMRSTATE OF THE ART IN TITANIUM ALUMINIDESCurrent state of the art manufacturing techniques have produced -TiAl based alloys withStrength of 1 GPaDensity of 3.8 gm/cm3Thus, they have posed a stiff competition for superalloys which haveStrength of ~1.2 GPaDensity of ~8 gm/cm3In order to capitalize on these advancements on -TiAl, further work is needed in the areas ofNear-net shape manufacturingLow cost material productionMaterials property databaseTi-45Al-X(Nb, B, C)Draper et al, 2003Example of advanced concept for TiAlBartolotta, et al 1999
3Hexagonal Closed Packed ASTP MMRINTERMETALLICSHigh strength compounds of metals whose crystal structures are different from the constituent metals.They form because the strength of bonding between unlike atoms is greater than that between like atoms.Examples are TiAl, Ti3Al, TiAl3, Ni3Al, Co3Ti.AlTiTiAlFace Centered CubicStructureTi3AlHexagonal Closed PackedStructure
4PHASES OF TITANIUM ALUMINIDES ASTP MMRPHASES OF TITANIUM ALUMINIDES-TiAl can exist in two different phasesPure -TiAl phaseMixture of -TiAl and 2-TiAlPure -TiAl has high strength and oxidation resistance, but it shows almost no ductility. Thus, not much research has been done on pure -TiAl.Mixture of -TiAl and 2-TiAl has high strength and good ductility, but does not show good oxidation resistance.But the properties of this phase can be improved byControl of its microstructureSmall additions of TiB2, Nb, and Cr.A lot of research has been concentrated on this phase of TiAl.Phase diagram -Titanium Aluminide
5-TiAl MICROSTRUCTURES ASTP MMR-TiAl MICROSTRUCTURESLamellar MicrostructureDuplex MicrostructureTwo main characteristic microstructures possible in -TiAl.Duplex Microstructure: Exhibits good strength and ductility.Lamellar Microstructure: Has good creep properties.These microstructures can be produced with appropriate heat-treatments.Refinement and control of grain size of these microstructures have shown improved mechanical properties.
6MANUFACTURING TECHNIQUES ASTP MMRMANUFACTURING TECHNIQUESThe state of the art manufacturing techniques of -TiAl involve ingot metallurgy and extrusion processes, which are often time consuming and expensive.Other methods follow the powder metallurgy route such asSinteringHot PressingHot Isostatic pressingPowder consolidation methods usually have the advantage of yielding near-net shape parts.But the methods mentioned above require exposure to high temperatures for long time to achieve full densification.Such extended exposure at high temperatures leads to grain growth and deterioration in mechanical properties. Controlling or minimizing grain growth has long been known to increase strength and ductility of materials.Rapid consolidation can be a potential solution since it generally reduces segregation, refines microstructure and thus produces a more homogeneous material.
7PLASMA PRESSURE COMPACTION (P2C) ASTP MMRPLASMA PRESSURE COMPACTION (P2C)Developed by Materials Modification, Inc., P2C is designed for rapid consolidation of nanocrystalline and micron-sized powders.The powder is loaded into a graphite die.An electrical discharge between the particle surfaces provides electrical resistance and surface heating.Before applying high temperatures and pressures, a plasma activation stage removes all adsorbed surface oxides and contaminants.The P2C process has the following advantagesRapid consolidation of powders (minutes vs hours).No sintering additive required.Near-net shape processing.Fewer impurities.Lower oxygen content in consolidated part compared to starting powders.
8CONSOLIDATION OF TITANIUM ALUMINIDE ASTP MMRCONSOLIDATION OF TITANIUM ALUMINIDETwo different compositions of Titanium Aluminides powders were consolidatedCommercially available micron sized powders of composition Ti-50Al (at%) were procured from CERAC, Milwauke, WI, and ESPI, Inc., OR.Specialized micron sized powders of composition Ti-46Al-2Cr-2Nb (at%) were procured from Oak Ridge National Laboratories, Infrared Processing Center, Department of Energy, Oak Ridge, TN.P2CSEM of micron-sized titanium aluminide powder,average particle size ~ 10 µm3 inch x 2.25 inch x 0.25 inch TiAl tile
9P2C CONSOLIDATION PARAMETERS FOR TiAL ASTP MMRP2C CONSOLIDATION PARAMETERS FOR TiALP2CSampleConsolidationTimeTemperature(Celsius)Pressure(MPa)CERAC Disc20 mins1000100ESPI Disc 110 mins54ESPI Disc 21200DOE Tile 130DOE Tile 2
10MICROSTRUCTURE TiAl TiAl-Nb-Cr ASTP MMRMICROSTRUCTUREOptical and Scanning Electron Microscopy showed duplex microstructure10 mTiAlTiAl-Nb-CrAverage measured grain size ~ 5 to 10 µmAverage powder particle size ~ 5 to 10 µmMicrographs showed no grain growth.
11TiAl Sample Annealed at 1400oC ASTP MMRMICROSTRUCTUREScanning Electron Microscopy of TiAl samples annealed at 1400oC showed fully lamellar grainsTiAl Sample Annealed at 1400oC
12MICROSTRUCTURAL CHARACTERIZATION ASTP MMRMICROSTRUCTURAL CHARACTERIZATIONEnergy Dispersive Spectroscopy (EDS) of the scanning electron micrographs (SEM) showed presence of both γ-TiAl and α2-Ti3Al.O, Ti and AlTi3Al (alpha phase)ElementAtomic %O61.77Al32.39Ti5.83ElementAtomic %Al32.92Ti67.07TiAl (gamma phase)ElementAtomic %Al43.49Ti56.50Scanning Electron Micrograph of Consolidated TiAl Sample
13CHEMICAL COMPOSITION Phase Diagram ASTP MMRCHEMICAL COMPOSITIONChemical composition analyses of the CERAC/ESPI powders and consolidated samples revealed the chemical composition as Ti-49.5(at%)Al.Presence of alpha2 phase is very less in this composition.In order increase alpha2 composition, the aluminum must be decreased up to 46% to 48%New powders were procured from Oakridge National Laboratories with 46% Al and additions of Nb and Cr.Phase Diagram
14Density (gm/cm3) TiAl Sample DENSITY ASTP MMRDENSITYDensity (gm/cm3)TiAl SampleThe average density of the consolidated samples was found to be ~ 3.9 gm/cm3.The density of the gamma phase is 3.76 gm/cm3, while that of the alpha2 phase is 4.2 gm/cm3.The theoretical density of the samples will be determined by calculating the amount of alpha2 phase present in the sample.From the micrographs and the density data, the consolidated samples seem fully dense.
15ASTP MMRMECHANICAL TESTINGMechanical testing was conducted via four-point bending tests in a self-aligning silicon carbide fixtureThe test was conducted as per ASTM 1161 and 1421 specifications.The test specimen was mounted with a strain gage for tests conducted at room temperatureThe four-point bending tests revealed flexure strength and Young’s modulus and fracture toughness.
16MECHANICAL PROPERTIES OF TiAl ASTP MMRMECHANICAL PROPERTIES OF TiAlStress (MPa)% StrainFour-point Bend Test Results for Various TiAl Samples
17HIGH TEMPERATURES TEST RESULTS ASTP MMRHIGH TEMPERATURES TEST RESULTSFlexure Strength (MPa)Temperature (Celsius)High Temperature Tests for Ti-50Al (at%)
18HIGH TEMPERATURES TEST RESULTS ASTP MMRHIGH TEMPERATURES TEST RESULTSMaximum sustainedstressFlexure Strength (MPa)Temperature (Celsius)High Temperature Tests for Ti-46Al-2Al-2Cr (at%)
19HIGH TEMPERATURES TEST RESULTS ASTP MMRHIGH TEMPERATURES TEST RESULTSStress v. Displacement Plot forTiAl-Nb-Cr at 950oCTiAl and TiAl-Nb-Cr Samples Testedat 950oC in Air
20COMPARISON WITH STATE OF THE ART ASTP MMRCOMPARISON WITH STATE OF THE ARTStrength (MPa)P2C consolidatedDraper, et al 2003Temperature (Celsius)TemperatureP2C consolidated(flexure Strength)As-extruded(tensile strength)400oC1600 MPa1100 MPa800oC1000 MPa700 MPa950oC800 MPa500 MPaHigh temperature mechanical properties of P2C consolidated TiAl were comparable to that of TiAl produced by extrusion process by Draper et al, 2003.