Effect of B on the microstructure and mechanical properties of mechanically milled TiAl alloys (original) (raw)
Related papers
Microstructure and mechanical properties of high Nb containing TiAl alloys by reactive hot pressing
Journal of Alloys and Compounds, 2008
Microstructure and mechanical properties of Ti–45Al–8.5 Nb–(W, B)(at.%) alloys fabricated by elemental powder metallurgy (EPM) were investigated. The results showed that microstructure hot pressed at 1300° C is inhomogeneous for a few Nb particles are dispersed in Ti–Al matrix. With the increase of hot pressing temperature and sintering time, microstructure becomes more homogeneous. However, the diffusion of Nb is inhomogeneous at 1400° C/0.5 h, and fully lamellar (FL) microstructure happens coarse at ...
Materials Today: Proceedings, 2021
Titanium aluminides are considered the choice material for next generation propulsion systems due to their high specific strength and high temperature performance coupled with good oxidation resistance. They are considered best materials for specific applications in the aerospace and automobile industry. Their production process, however, determines the final phase in the alloy, which greatly affects their mechanical properties. The effect of the milling parameters on the particle size and the formation of phases were studied on mechanically alloyed Ti-Al powder. A high-energy ball mill (HEBM) was used to mill a mixture of CP Ti and Al to produce titanium aluminide. The alloy was produced at a fixed ball-to-powder weight ratio of 10:1 whilst varying the milling speed and milling time. The mechanically produced powders were analysed using SEM with EDX and XRD to investigate the chemical homogeneity and the formation of phases after the mechanical alloying technique. The analysis of the mechanically alloyed powders from the mill are reported in terms of the morphology evolution during different milling speed, milling time, elemental composition and the phases formed. Alloys milled at a speed of 500 rpm for a milling time range of 5-20 h revealed the formation of Ti alpha (a-Ti) and gamma phase (c-TiAl).
Journal of Alloys and Compounds, 2009
An ultrafine grained TiAl based alloy with a composition of Ti-45Al-2Cr-2Nb-1B-0.5Ta (at%) was synthesized by a combination of subzero temperature (ST) (−140 to −5 • C) milling of a mixture of elemental powders and hot isostatic pressing (HIP). The size, morphology and microstructure of the Ti/Al based composite powder particles produced by ST milling and room temperature milling, respectively, were also compared, and it is demonstrated that ST milling significantly enhances the effectiveness of milling in forming and refining the composite structure. The bulk ultrafine grained TiAl based alloy samples produced using the ST milled Ti/Al composite powder exhibited a near-gamma two-phase microstructure with grain sizes in the ranges of 50-200 and 100-400 nm corresponding to HIP temperature of 800 and 1000 • C respectively. These samples showed relatively low tensile strength at room temperature and 800 • C but high tensile elongation of 70-130% at 800 • C. The reasons for the effect of ST milling and the mechanical behaviour of the consolidated samples are discussed.
Structure of Ti–Al–Nb intermetallics produced by mechanical alloying and hot-pressing techniques
Materials Chemistry and Physics, 2003
Mechanical alloying and hot-pressing consolidation were applied for the manufacturing of γ-TiAl alloys with additions of 5, 10 and 15at.% Nb. The microstructure shows numerous twins within the γ-TiAl phase in the hot-pressed alloys. The grain size (about 0.5μm) is much smaller than in the cast alloys. Local chemical analysis indicates that Ti is preferentially replaced by Nb in all
JOM, 2019
The hot deformation response of third-generation titanium aluminides with compositions Ti-45Al-5Nb-0.2B-0.2C and Ti-45Al-10Nb-0.2B-0.2C (hereafter referred to as Ti-45-5 and Ti-45-10, respectively) has been investigated through isothermal compression tests. The tests have been carried out in the ða 2 þ cÞ and ða þ cÞ phase regions for both alloys. The flow response, kinetics and microstructural evolution during hot deformation have been analysed in detail, and the outcome of the investigation has been used to predict the processing window for the two alloys. The optimum processing domain for the Ti-45-10 alloy is situated 50°C higher than that of the Ti-45-5 alloy. The postmortem analyses of the microstructures revealed that deformation in the ða 2 þ cÞ phase field leads to dynamic recrystallisation of all the phases resulting in a distribution of very fine grains. Microstructural features of both alloys depict kinking and breaking of the lamellae for the equivalent temperatures. The higher strength of the Ti-45-10 alloy has been attributed to shifting of the order-disorder transition toward the higher temperature side. In the ða þ cÞ region, the fraction of a phase increases more for the Ti-45-10 alloy compared with the Ti-45-5 alloy. JOM
Additive Manufacturing
This paper clarified a novel strategy to improve the tensile properties of the Ti-48Al-2Cr-2Nb alloys fabricated by electron beam melting (EBM), via the finding of the development of unique layered microstructure composed of duplex-like fine grains layers and coarser ␥ grains layers. It was clarified that the mechanical properties of the alloy fabricated by EBM can be controlled by varying an angle  between EBM-building directions and stress loading direction. At room temperature, the yield strength exhibits high values more than 550 MPa at all the loading orientations investigated ( = 0, 45 and 90 •). In addition, the elongation at  = 45 • was surprisingly larger than 2%, owing to the development of this unique layered microstructure. The anisotropy of the yield strength decreased with increasing temperature. All the examined alloys exhibited a brittle-ductile transition temperature of approximately 750 • C and the yield strength and tensile elongation at 800 • C were over 350 MPa and 40%, respectively. By the detailed observation of the microstructure, the formation mechanism of the unique layered microstructure was found to be closely related to the repeated local heat treatment effect during the EBM process, and thus its control is further possible by the tuning-up of the process parameters. The results demonstrate that the EBM process enables not only the fabrication of TiAl products with complex shape but also the control of the tensile properties associated with the peculiar microstructure formed during the process.
Journal of Materials Research
Hot deformation and softening response for the titanium aluminide Ti-48Al-2V-0.2B has been investigated. The deformation response to softening mechanisms has been examined. Deformation experiments were carried out in the strain rate range 0.01-10 s −1 keeping the temperature constant at 1200°C and in the temperature range 1000-1200°C at the strain rate 1 s −1. With an increase in strain rate, the microstructural changes associated with the softening mechanism include breaking of the lamellae, spheroidization of the broken laths and dynamic recrystallization. For the strain rate 1 s −1 , deformation in the (α 2 +γ) phase field leads to fine recrystallized grains, remnant lamellae and cavitation along the grain boundaries (for temperatures 1000 and 1100°C). Deformation in the (α +γ) phase field leads to dynamic recrystallization at the shear bands, within the lamellae, breaking and rotation of the α phase during the continuous increase in the deformation strain. Nitish Bibhanshu received his bachelor's degree in Metallurgy and Materials Engineering from National Institute of Foundry and Forge Technology, and master and doctoral degrees in Materials Engineering from the Indian Institute of Science Bangalore, India. During the education, he did investigation on processing of several alloys of γ-titanium aluminides and stablished the relationships between microstructure, texture, mechanical properties. He has also investigated microstructure-mechanical property relations in high entropy alloys, steels, magnesium, and titanium alloys. He was Institute Postdoctoral Research Associate for 6 months at the Indian Institute of Science Bangalore before joining Oak Ridge National Laboratory as a Postdoctoral Research Associate, where he is doing in situ experiments to study the mechanical properties of materials.
Cold-pressing and vacuum arc melting of γ-TiAl based alloys
Advanced Powder Technology, 2019
Beta (b) solidifying c-TiAl intermetallic alloys of nominal composition Ti-48Al, Ti-48Al-2Nb, Ti-48Al-2Nb-0.7Cr alloys have been cold pressed and vacuum arc melted. The Al loss was due to compaction method used prior to the melting technique, since it was evident after compaction that Al particles migrated to the surface in contact with the die facets after cold pressing. Electron backscatter diffraction (EBSD)orientation mapping demonstrated that the a-precipitation from the parent b-phase follows the Blackburn orientation relationship (BOR). Microstructural characterization of the alloys was studied by scanning electron microscopy (SEM) equipped with energy dispersion spectroscopy (EDS) for microanalysis. X-ray diffraction (XRD) technique was used to detect phase compositions.
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2013
Hot extrusion was performed on a Ti-42Al-9V-0.3Y alloy at 1200-1325 1C to explore effects on mechanical properties and hot workability. The microstructure after hot extrusion was analyzed, tensile tests were conducted, and hot workability was assessed. Three types of microstructures resulted from extrusion at increasing temperature, including a dual-phase microstructure (DPM), a bi-lamellar microstructure with retained gamma phase (BLMG), and a bi-lamellar microstructure (BLM). Hot extrusion of the TiAl alloy in the range of 1275-1325 1C produced the BLM microstructure, yielding superior comprehensive properties. The predominant fracture mode was transgranular cleavage fracture in the DPM, translamellar cleavage and delamination in BLM, and mixed fracture in BLMG. Aggregation of the YAl 2 phase accelerated the fracture of the as-extruded alloy. As-extruded Ti-42Al-9V-0.3Y alloy exhibited excellent high-temperature mechanical properties and hot workability, demonstrating the feasibility of precision forming TiAl alloy components by conventional hot forging with nickel-based alloy dies.