Wrought Form Research Articles

Impact behaviour of Al 2014 wrought alloy using Split-Hopkinson pressure bar (SHPB): Its influence on mechanical and microstructural properties

The deformation behaviour of Al 2014 alloy under high strain rate dynamic load experienced in the actual service condition of aero-structural components is scarce in the literature. Therefore, Split Hopkinson Pressure Bar (SHPB) based high strain rate compressive behaviour (dynamic loading) of Al 2014 is investigated in this work. The wrought (WAR) form of Al 2014 alloy has been chosen to examine its deformation behaviour with varying high strain rate compressive loading, generated through 4 different pressure ranges (1 bar, 1.5 bar, 1.75 bar, and 2 bar) at striker bar end in SHPB technique. These pressure ranges induced high strain rates 5536/s, 6236/s, 6576/s, and 7783/s in separate WAR specimen, correspondingly, which were recorded as flow stress curves. Also, the WAR Al 2014 alloy was heat treated with standard Tempered-6 (T6) condition to homogenize its microstructure. The T6 condition was exposed further with the same pressure values, which induced high strain rates 5303/s, 6139/s, 6977/s, and 7861/s in T6 specimens. The SHPB-based flow stress responses for both WAR and T6 conditions were compared to understand high strain rate deformation behaviours. The WAR specimen exposed at 7783/s strain rate has shown superior Peak Stress (P.S., ∼765 MPa) and %contractionP.S. (∼15%) compared to its T6 counterpart (at 7861/s). Prior to the dynamic studies, the quasi-static responses were also explored through tensile, compressive and hardness measurements (with WAR and T6) to realize the overall materials' behaviour. These dynamic responses under high strain rate compressive loading were correlated with in-process microstructural evolution, explored through SEM and XRD techniques. Exhaustive EBSD analysis quantified the excellent peak stress and % contraction in WAR conditions due to presence of huge amount of low angle grain boundaries (∼85%), ultrafine grains, relatively textured microstructure ({111} 〈100〉, {101} 〈001〉, etc), and significant strain hardening phenomena, whereas large amount of high angle grain boundary (∼88%), equiaxed and uniform microstructure contributed for higher hardness (∼22%) and tensile strength (∼2%) in T6 conditions.

Wire Based Directed Energy Deposition of JBK-75

Applications and adoption of metal additive manufacturing (AM) are increasing for fabrication of low volume, complex components with novel materials, as well as replacement parts. While the use of powder bed fusion-based processes have been widely used to build complex components with fine feature resolution, there is a volume limitation. Expanding the application of metal AM will rely on other processes that remove this build size constraint. These processes are referred to as Directed Energy Deposition (DED) and can use either powder or wire feedstock. Wire based DED provides the highest deposition rates which shortens the fabrication time making it attractive for fabrication of large parts replacing traditional wrought billets or castings. In this study, an iron-based austenitic superalloy (JBK-75) was deposited using an arc-based, wire-fed (AW)-DED process. The material was metallographically characterized and quasi-static mechanical properties were obtained. The resulting microstructure and mechanical properties are compared with conventional wrought and cast forms of JBK-75 subjected to the same heat treatments. As compared to wrought material, the AW-DED grain size was larger after the heat treatment, although the strengths were similar. Improved homogenization was observed after heat treatment in the AW-DED specimens as compared to the cast specimens.

Tribo-corrosion and titanium particles: A conducive factor for implant complication

In dentistry, titanium and its alloys are utilized for implants due to their unique blend of chemical, physical, and biological properties. These alloys are employed in both cast and wrought forms. The fractures of the alloy-abutment interface, abutment, or implant body are caused by the long-term presence of corrosion reaction products and ongoing corrosion. Implant failure results from the combined effects of stress, corrosion, and bacteria.

Novel method for fast neutron irradiation of materials via positron emission tomography isotope producing cyclotron

A proof-of-principle experiment for the irradiation testing of candidate reactor materials utilizing fast neutrons from a cyclotron as it produces clinical Positron Emission Tomography (PET) isotopes is presented. The reaction 18O(p, n)18F results in 18F for use in the radio-pharmaceutical fluorodeoxyglucose, as well as a significant flux of by-product fast neutrons. In this work, wrought forms of alloy Inconel 625 and its additively manufactured counterpart were placed in near proximity to the 18F producing cyclotron targets. The microhardness values were tracked periodically for over 25 weeks as the samples acquired fast neutron dose; up to approximately 9 × 1015 1-MeV-equivalent n/cm2. Hardness values for the wrought sample evolved with dose, by as much as ∼15% throughout the experiment. However, the additively manufactured samples remained relatively unchanged under identical dose. These results demonstrate the promising feasibility of using this irradiation method to explore mechanical property changes in nuclear-relevant alloys under low-dose conditions.

Effect of Heat-to-Heat Variability on Long-Term Creep Rupture Lifetime Predictions of Single Step Aged Wrought Haynes 282 Alloy

Abstract The impact of a weaker heat of the wrought form of Haynes 282 nickel superalloy on predicted 100,000 h creep rupture strength (CRS) and hence maximum allowable working stress (MAWS) was determined by correlating the creep rupture data of the two stronger heats of material that were used (along with the third weaker heat) to develop the ASME Code Case for this alloy. In comparison with the established MAWS values, estimated MAWS values were 3–7% higher in the temperature range of 700–800 °C and up to 30% higher above 800 °C when the weaker heat was removed from the data analysis. These results show the importance of minimizing heat to heat variability of properties that affect high temperature creep strength, including grain size, which can be affected by parameters that might not be included in the alloy specification. For nickel superalloys, such as Haynes 282, design optimization and manufacturing control of grain size, in addition to chemical composition and gamma prime content and size, can provide measurable improvements in MAWS values established by ASME in the time-dependent region, where these alloys are usually employed.

Diagnostic Technique Characterizing Neutron Irradiation Effects on Additively Manufactured Inconel 625 Eliminating the Need for Remote Handling

Experimentally characterizing radioactive materials can be time consuming and expensive. This is mainly due to the size requirements of inspected specimens. Due to the growing interest in using additively manufactured components in next-generation reactors, there is an urgent need to develop new accelerated testing techniques with regard to characterizing radiation damage. This will ensure a more timely certification of the unique material structures inherent to additively manufactured parts. In this study, we investigate a means to reduce the time investment, and thus the human exposure to radioactive specimens in need of experimental characterization. We determine the feasibility of using ultra-small specimens in lieu of much larger specimens to characterize bulk material properties before and after irradiation. Experiments were conducted to investigate this technique and compare it to conventional bulk irradiations and characterization activities. It was found that discernable radiation damage existed in the ultra-small specimens even after relatively short neutron irradiation times. The results also demonstrate decreased radiation hardening in additive manufactured Inconel 625 material relative to its wrought forms.

A Comparative Tribo-Mechanical Behavior Analysis of Laser Cladded Nitronic 60 Coating Against Wrought Nitronic 60 Alloy

In this study the tribological and mechanical behavior of a laser cladded Nitronic 60 coating on maraging steel is compared to that of a wrought Nitronic 60 alloy. A multi-layer Nitronic 60 coating was deposited using laser directed energy deposition, and its microstructure, porosity, and microhardness were characterized. The microhardness of the coated region in the laser cladded Nitronic 60 varied between 270-300 HV whereas that for wrought form was 230 HV. Controlled tribological tests under motor oil lubricated conditions were conducted at both room and elevated temperatures. The laser cladded Nitronic coating exhibited poorer wear resistance at room temperature but higher wear resistance at elevated temperature as compared to the wrought Nitronic alloy. Severe plastic deformation and fracture was observed on the laser cladded coating after the wear tests at both temperatures. Wear mechanisms were investigated based on the morphological and compositional characterization of the wear tracks.

Evolution of Fe-Rich Phases in Thermally Processed Aluminum 6061 Powders for AM Applications.

Gas-atomized powders are frequently used in metal additive manufacturing (MAM) processes. During consolidation, certain properties and microstructural features of the feedstock can be retained. Such features include porosity, secondary phases, and oxides. Of particular importance to alloys such as Al 6061, secondary phases found in the feedstock powder can be directly related to those of the final consolidated form, especially for solid-state additive manufacturing. Al 6061 is a heat-treatable alloy that is commonly available in powder form. While heat treatments of 6061 have been widely studied in wrought form, little work has been performed to study the process in powders. This work investigates the evolution of the Fe-containing precipitates in gas-atomized Al 6061 powder through the use of scanning and transmission electron microscopy (SEM and TEM) and energy dispersive X-ray spectroscopy (EDS). The use of coupled EDS and thermodynamic modeling suggests that the as-atomized powders contain Al13Fe4 at the microstructure boundaries in addition to Mg2Si. After one hour of thermal treatment at 530 °C, it appears that the dissolution of Mg2Si and Al13Fe4 occurs concurrently with the formation of Al15Si2M4, as suggested by thermodynamic models.

Examining the Relationship Between Post-Build Microstructure and the Corrosion Resistance of Additively Manufactured 17-4PH Stainless Steel

The performance of wrought and post-build heat treated, additively manufactured SS17-4PH stainless steel was evaluated to determine whether additive processing can produce material with a similar corrosion resistance to the alloy in wrought form, and to establish whether the additive manufacturing (AM) processing conditions alter the electrochemical conditions required for corrosion attack. Samples built by laser powder bed fusion (LPBF) from nitrogen-atomized and argon-atomized powder were heat treated to achieve a homogenized, solutionized martensitic microstructure. A wrought sample was also solutionized to minimize the influence of Cu precipitates. Multicomponent E-pH diagrams were constructed for the three compositions in a chloride containing environment using equilibrium thermodynamic data to elucidate the chemical reactions that can occur in the SS17-4PH alloy and to indicate the regions where variations in passivity would occur. Electrochemical measurements compared the behaviors under free corrosion conditions and the pitting resistances of the three compositions in chloride environments with differing solution pH levels. The results revealed that the nitrogen retained from atomization does enhance the corrosion resistance of additively-processed SS17-4PH and that the benefit was strongest in a neutral pH environment. The results also revealed that the dissolution of the nitrogen containing matrix suppressed the activity of CuCl3−2 in the solution and enhanced the activity of NH+4 ions at electrode potentials near Epit. This signifies that the ionic phases at the surface of the electrode are influenced by both the alloy composition and the processing conditions.

Comparing Stress Corrosion Cracking Behavior of Additively Manufactured and Wrought 17-4PH Stainless Steel

As a high-strength corrosion-resistant alloy, stress corrosion cracking (SCC) behavior is a key consideration for the conventional, wrought form of 17-4PH stainless steel. With the increasing popularity of the additively manufactured (AM) form of 17-4PH, understanding the SCC behavior of AM 17-4PH will be similarly critical for its presumed, future applications. The current study quantifies and compares the SCC behavior of both the wrought form, as a baseline, and AM form of 17-4PH at peak-aged (∼1,200 MPa) and overaged (∼1,050 MPa) strength levels. The laser powder bed fusion technique followed by post-process hot isostatic press (HIP), solution annealing, and aging heat treatments is used to produce AM 17-4PH with similar microstructures and strength levels to wrought 17-4PH and facilitate the comparison. SCC behavior is quantified using fracture mechanics-based rising (dK/dt = 2 MPa√m/h) and constant (dK/dt = 0 MPa√m/h) stress intensity tests in neutral 0.6 M NaCl at various applied potentials. Limited SCC susceptibility was observed at open-circuit and anodic potentials for both forms of 17-4PH. At cathodic applied potentials, AM consistently underperforms wrought with up to 5-fold faster crack growth rates and 200 mV to 400 mV wider SCC susceptibility ranges. These results are interrogated through microstructural and fractographic analysis and interpreted through a decohesion-based hydrogen-assisted crack model. Initial analyses show that (1) increased oxygen content, (2) porosity induced by argon processing, and (3) slow cooling (310°C/h) during conventional HIP processing might contribute to degraded SCC performance in AM 17-4PH.

Effects of Electrode Combinations on RSW of 5182-O/AlSi10MnMg Aluminum

Aluminum is a key lightweight material for reducing vehicle weight and improving fuel efficiency and is used in wrought, extruded, and cast forms. There is little research on resistance spot welding (RSW) of wrought-to-cast dissimilar aluminum alloys. For this paper, two types of electrodes were developed, and 2.3-mm 5182-O wrought and 4-mm AlSi10MnMg die cast sheets were welded by RSW with different electrode combinations. The results demonstrate that electrode geometry significantly influences the weld nugget morphology, weld performance, and failure mode. The proprietary Newton ring electrode produces the largest weld nugget size and consistent weld performance. Through the optimized electrode combination, severe weld nugget migration problems can be addressed for RSW of dissimilar aluminum alloys. Furthermore, the fracture crack under the tensile shear load always starts from the AlSi10MnMg side but not on the 5182-O side due to work hardening and concentration of stress regardless of whether the welds failed in the interfacial failure or pullout failure modes.

Laser free-form fabrication of dual phase DP600 steel using water atomized feedstock powder

Wrought dual-phase (DP) steels are exploited extensively within the automotive sector in the manufacture of components critical to occupant safety. Despite the widespread deployment of these alloys in wrought form, there exists an acute lack of knowledge on their performance/applicability in the context of additive manufacturing (AM). To address this knowledge gap, a preliminary study into the feasibility of utilizing laser directed energy deposition as a means to fabricate prototype structural components from a water atomized dual-phase (DP600) steel powder was completed. A statistical design of experiments approach was used to parametrically model the effects of laser power, traverse rate, hatch spacing, z-step size and powder feed rate on the density, tensile properties, microstructure, and impurity content (O-H-N) of the deposited products produced from each powder. Using optimized parameters, specimen with densities of up to 7.867 g/cm 3 (were obtained while maintaining an equiaxed ferritic microstructure. Intercritical heat treatment developed the requisite dual phase microstructure and elevated tensile properties to effectively match wrought DP600. The prototyping capability of this material and system were then demonstrated through the fabrication of large format tubular specimen coupled with quasi-static axial compression tests.

Thermal Analysis and Phase Transformation of Ti6Al4V Alloy Fabricated by Direct Metal Laser Sintering

Titanium alloys including Ti6Al4V have been used in cast or wrought form in the aerospace, biomedical and automotive industries for more than six decades. Recently, additive manufacturing techniques have been employed for the production of parts directly from a powder metal precursor with a chemical composition and mechanical properties suitable for various applications. In the present work, we investigate temperature changes and phase transformation of body crystal centered (bcc) structure into hexagonal close packed (hcp) structure laser powder bed fusion process. The finite element model was used to determine temperature of multi-layer deposition of Ti6AI4V. The obtained results can be used in the optimization of technological parameters.

The Evolution of Oxygen-Based Inclusions in an Additively Manufactured Super-Duplex Stainless Steel

Super-duplex stainless steel powder feedstocks specified for use in directed energy deposition additive manufacturing processes can have an oxygen composition nearly five times higher than that present in comparable wrought forms. A combination of computational thermodynamic calculations and experimental validation showed that high levels of oxygen promoted the formation of oxygen-rich inclusions during directed energy deposition additive manufacturing. These inclusions play an important role in microstructural evolution during the rapid heating and cooling cycles prevalent in additive manufacturing and impact mechanical and corrosion properties. Inclusions observed across the powder feedstock and additively manufactured and post-processed materials exhibited complex structures with a combination of amorphous, metastable, and stable phases. The powder feedstock, which experiences rapid cooling rates during the gas atomization process, yielded amorphous inclusions that were rich in manganese, chromium, silicon, and oxygen surrounded by small crystalline MnS particles. After additive manufacturing, inclusions transformed to a combination of rhodonite (MnSiO3) and spinel (MnCr2O4) with amorphous regions around the exterior. Post-process hot isostatic pressing treatments, which replicate conditions most similar to equilibrium, resulted in the formation of a stable spinel oxide with MnS particles around the exterior, matching the results predicted by thermodynamic equilibrium calculations.

Influence of laser-directed energy deposition process parameters and thermal post-treatments on Nb-rich secondary phases in single-track Alloy 718 specimens

In this article, process parameters such as laser power, deposition speed, and powder feed rate are varied at three levels, and their effect on geometrical characteristics and microstructural features of laser-direct energy deposited single-track Alloy 718 specimens is analyzed. Furthermore, the influence of standard heat treatments recommended for wrought form of Alloy 718 is investigated on as-built deposits. The main aim of the research is to curtail the amount of secondary Nb-rich precipitates such as Laves and NbCs either during the process or by subsequent heat treatments. The volume fraction analysis of Nb-rich phases shows that processing at high laser power conditions is ideal for minimizing segregation. Upon subjecting as-built deposits to (i) solution treatment, (ii) solution treatment and aging, and (iii) direct aging, a difference in volume fraction of Nb-rich phases is noticed compared to the as-built condition. Characterization of size, morphology, phase constitution through volume fraction estimation, and elemental concentrations employing electron dispersive spectroscopy analysis indicates dissolution of Nb-rich phases when subjected to heat treatments. The delta phase precipitation preferentially occurs in the top and bottom regions and sparsely in the middle region of the specimens subjected to solution heat treatment. In case of specimens subjected to direct aging (718 °C/8 h and 621 °C/8 h), delta phase is not discernable, indicating that a higher temperature (>900 °C) treatment may be necessary for delta precipitation and growth.

Correlative statistical microstructural assessment of precipitates and their distribution, with simultaneous electron backscatter diffraction and energy dispersive X-ray spectroscopy

Modern engineering alloys have bespoke microstructures, where features such as precipitates are used to control properties. In many Ni-based alloys, carbo-nitride precipitates are introduced to strengthen and improve performance. These precipitates can be distributed throughout the microstructure and niobium rich carbides are often found at grain boundaries. In this work, we used combined energy dispersive X-ray spectroscopy (EDS) and electron backscatter diffraction (EBSD) to characterise the population of these precipitates. Processing of the EDS signal is used to label the Mo/Nb-rich precipitates, and their size and location are measured from maps using a circular Hough transform. This label map is combined with the grain boundary network (from EBSD analysis). Statistical analysis, using ANOVA testing, reveals differences in chemistry between carbides found in Ni-rich matrix grain interiors, on random high angle boundaries and on special boundaries (Σ3 and Σ9). These results are compared between wrought and power metallurgy product forms. These distributions are discussed in the context of their performance within demanding environments, such as reactor core internals.

A full-field crystal plasticity model including the effects of precipitates: Application to monotonic, load reversal, and low-cycle fatigue behavior of Inconel 718

This work advances a recently developed high-performance, full-field elasto-viscoplastic fast Fourier transform (MPI-ACC-EVPCUFFT) formulation to model large plastic deformation and low-cycle fatigue behavior of Inconel 718 (IN718). Specifically, the recently developed model of Eghtesad et al., 2020 [1] incorporating a strain rate, temperature, and strain-path sensitive hardening law based on the evolution of dislocation density and a slip system-level back-stress law influencing the resolved shear stress is advanced in several aspects. First, strengthening effects due to grain size and shape, solid solution, shearing of small precipitates, and Orowan looping around larger precipitates are incorporated into the initial slip resistance, which evolves with the hardening law including the latent hardening. Second, the resolved shear stress on the slip plane in the direction of slip is altered by accounting for the two orthogonal shear stress components and the three normal stress components, in addition to the slip system-level kinematic effects. The model is used to interpret the complex mechanical behavior and microstructural data for samples of alloy IN718 in additively manufactured (AM) forms before and after hot isostatic pressing (HIP) and in a wrought form. Voxel-based microstructural cells consistent with the characterization data are synthetically constructed to initialize the model setups for predicting simple compression, tension, load reversal, and low cycle fatigue behavior of the alloy. Variation in the microstructural features such as the distribution of grain size and shape, crystallographic texture, content of annealing twins, and precipitates among the samples facilitated reliable calibration and validation of the model parameters. Predicted anisotropy, tension/compression asymmetry, non-linear unloading upon the load reversal, the Bauschinger effect, reverse hardening, texture evolution as well as cyclic hardening/softening along with the mean stress relaxation during low-cycle fatigue are in good agreement with the corresponding experimental data for the alloy. Furthermore, the simulations based on the high-resolution microstructural cells facilitated the discussion of the mechanical fields induced by microstructure, and especially annealing twins.

Thermal property measurements of metal injection moulded Inconel 625 and Inconel 718 using combined thermal analysis techniques

ABSTRACT The high-temperature thermal properties of powder metallurgy derived superalloys have not been reported in the literature. In this study, the coefficient of thermal expansion (CTE), specific heat and thermal diffusivity of metal injection moulded (MIM) Inconel 625 and Inconel 718 were measured. Measurements of wrought Nickel 200 were also made to verify the methods. These thermal property measurements were made in the range of room temperature to 1000–1200°C using dilatometry, differential scanning calorimetry and laser flash analysis. Thermal conductivity of all three materials was calculated using the measured diffusivity, specific heat and CTE. All the MIM results were compared to published data for the wrought form of these alloys and found to be in close agreement outside of phase transition regions.

Computational Study of Fatigue in Sub-grain Microstructure of Additively Manufactured Alloys

Additively manufactured (AM) materials experience shorter fatigue lives compared to their wrought form. Shorter fatigue life can be related to different effects like defects, residual stresses, surface finish, geometry, size, layer orientation, and heat treatment. One of the main contributors to the shorter fatigue life of AM alloys is their unique and complex microstructure. In this paper, we study this challenge from a novel perspective in which the interaction between the microstructure and fatigue life is explored. Among different microstructural features in the AM alloys, here we focus on the cells which form inside the grains during fabrication. While this microstructural feature is not always the prominent site for the fatigue initiation, it always has a significant role in the fatigue failure, particularly in high cycle fatigue because it occupies a high percentage of the volume in the material. A fatigue damage model is developed and verified to predict the life of cellular microstructures present in the AM metal microstructure. It is shown that the life of a cellular microstructure, which is composed of an arrangement of cells and cell boundaries is lower than a single-phase material without such an arrangement. We investigate how the arrangement if cells can govern the fatigue life, and analyze different cellular geometries to find the best performing cellular microstructure. By changing the geometrical parameters, the considerable variation in life can be as high as 95% in some strain amplitudes. Since the microstructure of cells in AM alloys can be tailored by changing the processing parameters, our results can be used as a guide to additively manufacture alloys with improved fatigue-resistance.

A parametric investigation on friction stir welding of Al-Li 2099

ABSTRACT Aluminum-lithium alloys have lower density compared to other traditional aluminum alloys and as such, are being used in lightweighting applications. However, while the microstructure and mechanical behavior of the wrought form of aluminum-lithium alloy 2099 are well characterized, the effect of process variability in friction stir welding (FSW) of this alloy is not well understood. As such, a parametric investigation was performed to examine the effects of tool rotational rates and transverse speeds during FSW on the corresponding microstructure and tensile strength of aluminum-lithium alloy 2099. In general, a strong correlation between tool translation speed and tensile strength and ductility was found. Specifically, the elongation to failure and ultimate tensile strength increased as the transverse speeds increased due to a direct decrease in the heat input. However, elongation to failure and ultimate tensile strength were less dependent on the rotational rate since adequate material mixing was achieved and strain rate sensitivity is negligible at these strain rates. Postmortem analysis revealed a greater presence of micro void and coalescence on the fracture surface for the more ductile specimens as opposed to a higher occurrence cleavage fracture due to the coarsening of intermetallics.