On the hot deformation behavior of Ti-6Al-4V made by additive manufacturing (original) (raw)
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The origins of heterogeneous deformation during primary hot working of Ti–6Al–4V
International Journal of Plasticity, 2002
A Ti-6Al-4V cylindrical specimen with a large grain colony microstructure was upset forged to 35% reduction at 815 C at a nominal strain rate of 0.1 s À1 . An orientation imaging microscopy (OIM) analysis was conducted in two representative areas, near the center with an estimated von Mises strain of 1.6, and 0.8 about midway from the center to the outer edge. The process of physically breaking up the lamellar microstructure (globularization) was examined, focusing on how the globularization efficiency was affected by the initial colony orientation. Microstructural maps based upon the electron backscattered pattern quality, crystal orientation, and an estimated Taylor factor (using a continuum assumption) were used to identify and quantify heterogeneous deformation phenomena. These analyses show that in regions where both prism and basal slip systems were not operational, macro shear bands developed, leading to kinked lamellar microstructural features. The shear bands concentrated shear in localized regions that were able to flow easily around remaining hard regions, leaving remnants of the hard regions intact. Also, development of large misorientations of 50-90 from the parent grain arising from a transformation from b to a are quantified and related to the globularization efficiency. #
Integrating Materials and Manufacturing Innovation
In this paper, phenomenological relationships are presented that permit the prediction of the plastic regime of stress–strain curves using a limited number of parameters. These relationships were obtained from both conventional (wrought + β annealed) and additively manufactured (i.e., “3D printed”) Ti-6Al-4V. Three different methods of additive manufacturing have been exploited to produce the materials, including large-volume electron beam additive manufacturing, large-volume laser hot wire additive manufacturing, and small-volume selective laser melting. The general fundamental expressions are independent not only of the additive manufacturing process, but also of a wide variety of post-deposition heat treatments, however the coefficients are specific to material states. Thus, this work demonstrates that it is possible to predict not only the ultimate tensile strength, but also the full true stress, true strain curves, if certain parameters of the material are known. In general, th...
Materials Research Letters
To improve the mechanical properties of additively manufactured parts, specific heat treatments must be developed. Annealing of electron beam-melted Ti-6Al-4V was performed at sub-transus temperatures and followed by water quenching. Such treatments generate an α + α dual-phase microstructure. Microstructural and mechanical characterizations revealed that the heat-treated specimens show a broad range of tensile properties, depending on the fraction of martensite. The specimens treated between 850°C and 920°C exhibit an increase in strength and ductility, which is related to a remarkable hardening behavior. Work-hardening is attributed to kinematic hardening arising from the mechanical contrast between the α and α phases. IMPACT STATEMENT Innovative heat treatments leading to α + α dual-phase microstructures are developed on Ti-6Al-4V parts produced by additive manufacturing. They lead to unprecedented work-hardening capabilities for this alloy.
Journal of Alloys and Compounds, 2018
Wire þ Arc Additive Manufacturing (WAAM) is a promising manufacturing process for producing large aerospace components. Based on welding technology, the process is highly affordable, has a very high deposition rate and is not limited by chamber size. Ti-6Al-4V is a promising candidate material for this technology given that it is extensively used in aerospace applications and some large, high buy-fly ratio components can be more efficiently produced by WAAM than via the conventional machining from billet approach. There is currently limited knowledge about whether additional post processes including heat treatments and hot isostatic pressing are necessary to unlock the optimal mechanical properties of Ti-6Al-4V components produced by WAAM. This work explores a range of different post process treatments and the effects on the microstructure and tensile properties of Ti-6Al-4V components produced by WAAM. The relatively slow cooling rate (10-20Ks À1) during the b-a transformation produced Wid-manst€ atten-a and offered an optimal balance between strength and ductility. Hot Isostatic Pressing (HIPing) removed gas porosity but was not effective in improving strength or ductility. Residual tensile stresses in as-built components severely impair ductility and should be removed through stress relief treatments.
Dynamic mechanical response of additive manufactured Ti-6Al-4V
Nucleation and Atmospheric Aerosols, 2018
The dynamic mechanical response of additive manufactured (AM) Ti-6Al-4V has been investigated via Split-Hopkinson Pressure Bar (SHPB) and single-stage gas gun plate-impact experiments. Rods of Ti-6Al-4V were manufactured from Arcam and Renishaw electron beam melting (EBM) and laser melting deposition (LMD) powder bed systems, respectively. Horizontal and vertical build directions were produced for plate impacts to determine any effect of build layers on dynamic tensile strength. The as-received microstructures were characterized via optical microscopy and electron backscatter diffraction (EBSD). Johnson-Cook constitutive model parameters were found for the EBM condition via SHPB experiments. Plate impacts producing nominal peak shock stresses near the theoretical tensile strength of the material (3-5 GPa) were conducted to study incipient spall damage conditions as a function of AM material condition.
Additive manufacturing and postprocessing of Ti-6Al-4V for superior mechanical properties
MRS Bulletin
The capabilities of metal additive manufacturing (AM) are evolving rapidly thanks to both increasing industry demand and improved scientifi c understanding of the process. This article provides an overview of AM of the Ti-6Al-4V alloy, which has essentially been used as a yardstick to gauge the capability of each metal AM process developed to date. It begins by summarizing the metal AM processes existing today. This is followed by a discussion of the macro-and microstructural characteristics, defects, and tensile and fatigue properties of AM Ti-6Al-4V by selective laser melting, laser metal deposition (both powder and wire), and selective electron-beam melting compared to non-AM Ti-6Al-4V. The tensile and fatigue properties of as-built AM Ti-6Al-4V (with machined or polished surfaces) can be made comparable, or even superior, to those of Ti-6Al-4V in the most commonly used millannealed condition. However, these properties can exhibit a large degree of scatter and are often anisotropic, affected by AM build orientations. Post-AM surface treatments or both the post-AM surface and heat treatments are necessary to ensure the minimum required properties and performance consistency. Future directions to further unlock the potential of AM of Ti-6Al-4V for superior and consistent mechanical properties are also discussed.
Deformation Mechanisms of Ti-6Al-4V During Tensile Behavior at Low Strain Rate
Journal of Materials Engineering and Performance, 2007
A superplastic Ti-6Al-4V grade has been deformed at a strain rate of 5 · 10 )4 s )1 and at temperatures up to 1050°C. Structural mechanisms like grain boundary sliding, dynamic recrystallization, and dynamic grain growth, occurring during deformation, have been investigated and mechanical properties such as flow stress, strain hardening, and strain at rupture have been determined. Dynamic recrystallization (DRX) brings on a decrease in the grain size. This could be of great interest because a smaller grain size allows a decrease in temperature for superplastic forming. For DRX, the driving force present in the deformed microstructure must be high enough. This means the temperature must be sufficiently low to ensure storing of enough dislocation energy but must also be high enough to provide the activation energy needed for DRX and to allow superplastic deformation. The best compromise for the temperature was found to be situated at about 800°C; this is quite a bit lower than the 925°C referenced in the literature as the optimum for the superplastic deformation. At this medium temperature the engineering strain that could be reached exceeds 400%, a value high enough to ensure the industrial production of complex parts by the way of the superplastic forming. Microstructural, EBSD, and mechanical investigations were used to describe the observed mechanisms, some of which are concurrent.
MATEC Web of Conferences
The most commonly used technology among the additive manufacturing is Direct Metal Laser Sintering (DMLS). This process is based on selective laser sintering (SLS). The method gained its popularity due to the possibility of producing metal parts of any geometry, which would be difficult or impossible to obtain by the use of conventional manufacturing techniques. Materials used in the elements manufacturing process are: titanium alloys (e.g. Ti6Al4V), aluminium alloy AlSi10Mg, etc. Elements printed from Ti6Al4V titanium alloy find their application in many industries. Details produced by additive technology are often used in medicine as skeletal, and dental implants. Another example of the DMLS elements use is the aerospace industry. In this area, the additive manufacturing technology produces, i.a. parts of turbines. In addition to the aerospace and medical industries, DMLS technology is also used in motorsport for exhaust pipes or the gearbox parts. The research objects are samples...
Local deformation of Ti6Al4V modified 1wt% B and 0.1wt% C
Materials Science and Engineering: A, 2010
Ti-6Al-4V-1B-0.1C is a modification of the mostly used titanium alloy Ti-6Al-4V (Ti64). TiB whiskers (around 5 vol%) precipitate in the Ti64 matrix in two size classes during the solidification of the powders mixture and before consolidation. The hot deformation of this material is studied between 850 and 1100 • C and at strain rates 0.001-10 s −1 using compression tests. The processing maps using the modified dynamic mechanical model are applied to correlate the flow behaviour with the dissipated energy. At low strain rates the large values of efficiency of energy dissipation are related to superplasticity, which is also observed in the microstructure of a sample deformed at 950 • C up to 1 of true strain. The low values of dissipation efficiency at high strain rates and the flow instabilities are related to cracking and debonding of the fraction of larger TiB at low temperatures, and to porosity evolving at the triple grain boundaries at temperatures above 1000 • C. A method to correlate the microstructure with the local deformation parameters is developed using finite elements methods. The parameters of the constitutive equations can be correlated with the processing maps and the microstructures verifying the different deformation mechanisms in the studied range.