Characterization of rapidly consolidated γ-TiAl

Kothari, Kunal; Radhakrishnan, R.; Sudarshan, T. S.; Wereley, Norman M.

doi:10.12989/amr.2012.1.1.051

Cited by 4 publications

(6 citation statements)

References 27 publications

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“…The microstructure that eventually settles down in the dual phase TiAl compositions ultimately depends on the processing conditions, mainly the temperature. For instance, elemental powders having composition (48% Al-2% Cr-2% Nb) similar to the present work, when consolidated by the powder metallurgy route at a temperature of 1400˝C resulted in a fully lamellar microstructure, while at a lesser temperature of 1200˝C, the same powder resulted in a duplex structure [24]. Likewise, in the current study, a higher beam current produced a microstructure dominated by coarse lamellar structure with few equiaxed grains (Figure 13), but when the current was lowered, more equiaxed regions started to emerge (Figure 13 right).…”

Section: Effect Of Beam Currentsupporting

confidence: 74%

“…As was discussed above (Section 3.2), modified scan strategy resulted in a duplex microstructure, whereas the standard scan strategy produced a lamellar microstructure. A duplex microstructure is better as far as stress and ductility are concerned [24]. Thus, the appropriate microstructure could be said to have contributed to better compression properties.…”

Section: Compression Testmentioning

confidence: 99%

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Porous γ-TiAl Structures Fabricated by Electron Beam Melting Process

Mohammad

Al‐Ahmari

Moiduddin

et al. 2016

Metals

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Porous metal structures have many benefits over fully dense structures for use in bio-implants. The designs of porous structures can be made more sophisticated by altering their pore volume and strut orientation. Porous structures made from biocompatible materials such as titanium and its alloys can be produced using electron-beam melting, and recent reports have shown the biocompatibility of titanium aluminide (γ-TiAl). In the present work, we produced porous γ-TiAl structures by electron-beam melting, incorporating varying pore volumes. To achieve this, the individual pore dimensions were kept constant, and only the strut thickness was altered. Thus, for the highest pore volume of~77%, the struts had to be as thin as half a millimeter. To accomplish such fine struts, we used various beam currents and scan strategies. Microscopy showed that selecting a proper scan strategy was most important in producing these fine struts. Microcomputed tomography revealed no major gaps in the struts, and the fine struts displayed compressive stiffness similar to that of natural bone. The characteristics of these highly-porous structures suggest their promise for use in bio-implants.

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Section: Effect Of Beam Currentsupporting

confidence: 74%

Section: Compression Testmentioning

confidence: 99%

Porous γ-TiAl Structures Fabricated by Electron Beam Melting Process

Mohammad

Al‐Ahmari

Moiduddin

et al. 2016

Metals

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“…γ-TiAl powders with composition similar to our study were consolidated using a rapid consolidation process called Plasma Pressure Compaction [ 18 ]. Similar results to our study were reported; that is, higher consolidation temperature resulted in a fully lamellar microstructure, whereas lower temperature produced a duplex structure.…”

Section: Resultsmentioning

confidence: 99%

Effect of Energy Input on Microstructure and Mechanical Properties of Titanium Aluminide Alloy Fabricated by the Additive Manufacturing Process of Electron Beam Melting

et al. 2017

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Titanium aluminides qualify adequately for advanced aero-engine applications in place of conventional nickel based superalloys. The combination of high temperature properties and lower density gives an edge to the titanium aluminide alloys. Nevertheless, challenges remain on how to process these essentially intermetallic alloys in to an actual product. Electron Beam Melting (EBM), an Additive Manufacturing Method, can build complex shaped solid parts from a given feedstock powder, thus overcoming the shortcomings of the conventional processing techniques such as machining and forging. The amount of energy supplied by the electron beam has considerable influence on the final build quality in the EBM process. Energy input is decided by the beam voltage, beam scan speed, beam current, and track offset distance. In the current work, beam current and track offset were varied to reflect three levels of energy input. Microstructural and mechanical properties were evaluated for these samples. The microstructure gradually coarsened from top to bottom along the build direction. Whereas higher energy favored lath microstructure, lower energy tended toward equiaxed grains. Computed tomography analysis revealed a greater amount of porosity in low energy samples. In addition, the lack of bonding defects led to premature failure in the tension test of low energy samples. Increase in energy to a medium level largely cancelled out the porosity, thereby increasing the strength. However, this trend did not continue with the high energy samples. Electron microscopy and X-ray diffraction investigations were carried out to understand this non-linear behavior of the strength in the three samples. Overall, the results of this work suggest that the input energy should be considered primarily whenever any new alloy system has to be processed through the EBM route.

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“…However, it has been observed that the final microstructure was dominated by α 2 phase, while the γ phase scarcely existed [ 11 ]. This was attributed to the rapid cooling that does not allow the γ phase to sufficiently decompose [ 20 ]. The dominance of the α 2 phase increases the alloy strength at the expense of the ductility [ 21 ].…”

Section: Introductionmentioning

confidence: 99%

Influence of Combined Heat Treatment and Hot Isostatic Pressure (HT-HIP) on Titanium Aluminide Processed by L-PBF

Soliman

Pineault²,

Elbestawi

2023

Materials

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Postprocessing is essential for improving titanium aluminide (TiAl) microstructure and part quality after using the laser powder bed fusion (L-PBF) method. It has been reported that Ti-48Al-2Cr-2Nb (%at) processed by L-PBF has internal defects and low fracture toughness. Microstructure control by heat treatment (HT) showed a significant improvement in the ductility of the material. Alternatively, hot isostatic pressing (HIPing) could be applied to reduce the residual stresses and internal defects formed during the L-PBF. Combining the benefits of these two subsequent processes into a single predetermined process is appealing for Ti-48Al-2Cr-2Nb (%at) to minimize cost. This work presents a novel strategy to postprocess L-PBF TiAl by applying combined heat treatment and hot isostatic pressing in one process, namely HT-HIP. The process includes three cycles with different conditions (i.e., temperature, time, and pressure). These conditions were determined to achieve improved part quality and microstructure. The results show that the tensile residual stresses decreased from a peak of 249 MPa in the as-built sample to compressive stresses that peaked at −90 MPa after the HT-HIP process. The number and size of internal defects could be greatly reduced. The defects were transformed into a regular spherical shape, which is good in terms of fatigue strength. Additionally, a duplex microstructure with lamellar α2/γ colonies could be introduced for better ductility. Different levels of duplex microstructure could be achieved along with the process cycles. The grain structure using EBSD analysis showed refined equiaxed grains, which demonstrate better strength after the HT-HIP process. Twinning boundaries were also observed in the HT-HIP sample. The grain orientation tendency to the build direction significantly reduced after the HT-HIP process. The nanoindentation test was applied to evaluate the nanohardness of the as-built and HT-HIP samples. It could be demonstrated that the nanohardness is dependent on the formed phases and lamellar density inside the grains. The mean hardness value was 8.19 GPa for the as-built sample, while it was 5.48 GPa for the HT-HIP sample.

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Characterization of rapidly consolidated γ-TiAl

Cited by 4 publications

References 27 publications

Porous γ-TiAl Structures Fabricated by Electron Beam Melting Process

Porous γ-TiAl Structures Fabricated by Electron Beam Melting Process

Effect of Energy Input on Microstructure and Mechanical Properties of Titanium Aluminide Alloy Fabricated by the Additive Manufacturing Process of Electron Beam Melting

Influence of Combined Heat Treatment and Hot Isostatic Pressure (HT-HIP) on Titanium Aluminide Processed by L-PBF

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