Wrought Conditions Research Articles

Comparative analysis of microstructural, compositional, and grazing incidence characteristics of oxide scale on 316L steel: SLM vs. wrought conditions

The aim of this research is to compare the oxidation behavior and characteristics of oxide scale of 316L steel produced by two methods: selective laser melting (SLM) and conventional casting and forming (wrought). To this end, the initial composition and microstructure of samples produced by those methods were first studied. Thermogravimetric analysis (TGA) and long-term isothermal oxidation tests were carried out on the samples and the oxidation kinetics were compared. The oxidized samples were then examined by scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS) and grazing incidence X-ray diffraction (GIXRD). The results indicated that in the temperature range of 600 °C–900 °C, the oxidation resistance of the SLM alloy is lower than that of the wrought alloy, especially at 800 °C. This is attributed to the combined effect of: i) smaller grain size due to the rapid solidification in the SLM alloy that increases the paths of oxygen penetration, ii) lower presence of chromium and manganese elements in the oxide layer and iii) preferential growth of iron oxide in the form of hillocks on the surface. Surface and cross-section analysis of the oxide layers show that iron oxide is dominant on the surface of the SLM sample at temperatures of 600 °C and 800 °C, and at 800 °C its extended hilly growth leads to significant spallation of the oxide scale and an exponential increase in the oxidation rate. However, at 900 °C, with the formation of a continuous oxide layer containing Fe2MnO4 and CrMnO4, the oxidation rate significantly decreases in both alloys.

Room- and elevated-temperature mechanical property of selective laser melting-fabricated Hastelloy X with different heat treatments

Superalloy alloy Hastelloy X was fabricated by selective laser melting (SLM), and heat treatments have been designed to optimize microstructures for better mechanical property at high temperature. Specimens of as-printed, aging treatment (AT), solution treatment (ST), and wrought conditions are of interests to this study, and their grains, dislocations, grain boundaries, precipitates, twins and defects have been characterized. Compared to the wrought specimens, the as-printed specimens showed sub-micron cellular microstructure, while M23C6-type carbides and Fe2Mo phases were found after AT condition with partial recrystallization. The ST treatment introduced a large number of high angle grain boundaries (HAGBs) and a high twin boundary ratio due to recrystallization. With this, their post-mortem microstructures at both room temperature (RT) and elevated temperature (ET) of 850 °C were easily correlated to the mechanical performance. AT yielded the highest ultimate tensile strength (UTS) of ∼1067 MPa, while ST gave the highest ductility of ∼51% at RT. At ET, the as-printed, AT, and ST SLM specimens showed improved UTS over the wrought counterparts, all with a reduced ductility. With these observations, a comprehensive heat treatment roadmap has been proposed to summarize their microstructure-property relationship, which rigorously included the traditional ST + AT heat treatment and proved SLM-fabricated Hastelloy X's incompatibility. This research not only deepens our understanding of its mechanical behavior after possible heat treatments, but also semi-quantitatively guides its feasible processing even for high-temperature applications.

Microstructural and mechanical characteristics of hot worked homogenized AA7068 using 3D processing map and DEFORM-3D

AA7068 is classified as high strength aluminum alloy and is primarily utilized in wrought conditions which can be achieved with hot deformation. The process of hot deformation is a competent way of optimizing material properties; thus, understanding its deformation behavior in the wide range (250–450 °C, 10−3–100 s−1) is vital in processing a high-performance product. The true stress-true strain trend indicated its dependence on thermomechanical variables and precipitate size. The constitutive calculations accurately predicted the flow stress behavior. The kinetic rate calculations demonstrated that glide dislocation motion (with a value of n = 6.3) was observed during hot deformation. 3-dimensional processing map (PM) has revealed a progressive rise in efficiency (η) with increase in true strain. The PM analysis has successfully identified both stable and unstable working regions. Within the stable working region, a peak efficiency (η) of 54% was observed in the range of 347–359 °C and 10−3 s−1, 0.69 true strain. In, the stable working region, the microstructural characteristics demonstrated a notable increase in the dynamic softening depending on the process time and deformation temperature. At lower temperatures, the dynamic softening in the deformed specimens predominantly occurred through dynamic recovery (DRV), whereas at high temperatures, it facilitated by dynamic recrystallization (DRX). The DRX during deformation was observed to occur through continuous dynamic recrystallization (CDRX) and particle stimulated nucleation (PSN) mechanism. Hot forging finite element modeling (FEM) exhibited an uneven material flow with the peak effective strain occurring in the core of the specimen. Open forging in the optimum working conditions resulted in the highest tensile strength of 340 MPa, observed at a temperature of 450 °C and strain rate of 10−3 s−1.

Hot deformation constitutive analysis and processing maps of the as-cast and wrought Mg–2.5Gd–0.5Zr alloy

Hot deformation behavior and constitutive analysis of the as-cast and extruded Mg–2.5Gd–0.5Zr alloy were compared, using the shear punch testing (SPT) method in the temperature range of 623–723 K and shear strain rate range of 2.8 × 10–3–2.2 × 10–2 s–1. The respective hyperbolic-sine exponents of 2.67 and 2.59 as well as activation energies of 183 and 275 kJ mol–1 obtained for the as-cast and extruded alloy suggested grain boundary sliding as the prevailing deformation mechanism. Surprisingly, regardless of the instability domains, the efficiency of power dissipation exceeded 30% in most areas in the processing maps of both cast and wrought conditions. The safe and instability domains were rather similar in both processing maps. The relatively high potential of the as-cast alloy for hot deformation, despite its initial coarse grain size of about 150 µm, can be ascribed to the severe dynamic recrystallization (DRX) during hot deformation caused by Zr. This could be economically advantageous, as there would be no need for homogenization of the as-cast material before deformation processing. The most noticeable optimum window occurred in the temperature range of 673–723 K for both as-cast and extruded conditions with a vaster strain-rate range for the extruded one (5.6 × 10–3–1.4 × 10–2 s–1), owing to its initial finer grain size. The instability domains, however, took place for both conditions in the temperature range of 648–673 K and strain rates of about 5.6 × 10–3 s–1, manifested by cracking in the deformed zone, and also at temperatures higher than 673 K and medium to high strain rates.

An innovative constitutive material model for predicting high temperature flow behaviour of inconel 625 alloy

Inconel 625 nickel alloy with its attractive high-temperature strength, excellent corrosion and oxidation resistance is mainly used for critical applications in demanding environments, in both as-cast and wrought conditions. Hot processing of this alloy is crucial for achieving its tailored mechanical properties due to the significant variation in microstructural changes with varying process parameters like temperature, strain, and strain rate. In this study, isothermal hot compression tests were carried out at temperatures ranging from 900 to 1100 °C, and under strain rates ranging from 0.01 to 1 s−1. The flow curves revealed three stages of deformation, including a substantial work-hardening stage followed by dynamic recovery and flow softening. Microstructural observations showed the occurrence of discontinuous dynamic recrystallisation (DDRX) as the dominant recrystallisation mechanism during the flow softening. Microstructural analysis suggested that the DRX was more sensitive to the test temperature as compared to the strain rate. An innovative material's constitutive model was developed, by combining Johnson–Cook (JC) and Avrami approaches, to predict work-hardening, dynamic recovery, and flow softening stages of deformation. The predicted flow behavior was in a good agreement with the experimentally measured data. The developed material model was integrated into DEFORM® 3D finite element (FE) simulation software as a user subroutine for the prediction of deformation behaviour in a double truncated cone (DTC) sample. Comparison between the experimentally measured data and the results of FE simulation on the DTC sample showed a very good convergence, indicating the suitability of the proposed material’s constitutive model for large scale simulations.Graphical

Influence of punch diameter on impression creep behaviour of AZ91 magnesium alloy

The influence of punch diameter on impression creep behaviour of the AZ91 alloy in the cast and wrought conditions was studied. The stress exponents of 5.3–7.8 and 1.8–2.6 were found, respectively, for the cast and wrought alloy, and the activation energy is close to the lattice diffusion of magnesium for both conditions. The punch diameter has no influence on the deformation mechanisms and the obtained creep data introduce lattice diffusion-controlled dislocation climb and grain boundary sliding, which are the dominant deformation mechanisms during creep of the cast and wrought alloys, respectively. The punch diameter affected the impression creep behaviour of the alloys so that with an increase in the punch diameter, the steady-state impression rate in both deformation mechanisms was increased exponentially.

Low cycle fatigue of additively manufactured thin-walled stainless steel 316L

To ensure the robust design freedom of metallic additive manufacturing, the fatigue properties and the dimensional limitation of as-built components by laser powder bed fusion (PBF-LB) are investigated. Fully reversed and strain-controlled fatigue tests were carried out on tubular specimens with different wall thicknesses, 1 mm and 2 mm, for the purpose of studying the thin-wall effect without having risk of buckling problem during compression. Two wrought conditions are also enclosed as a comparison, which are the cold worked (CW) and solution annealed condition (SA). In the as-built PBF-LB tubular specimens, deformed microstructure and deformation twins are discovered close to the surface region, together with a higher roughness of the inner surface due to the heat accumulation. The surface roughness is evaluated as micro-notches, and a higher fatigue notch factor, Kf, at lower applied strain range is revealed. The factors influencing Kf include, the non-conductive inclusions serving as crack initiation sites at the surface region, and the deformation twins formed by the local stress concentration. The strain-life of PBF-LB samples is comparable with the wrought samples. However, the fatigue strength of the responding mid-life stress shows greater difference and is in the following order, CW wrought > PBF-LB > SA wrought. Secondary cyclic hardening owing to deformation induced martensitic transformation is found in both of the wrought samples. Yet, only cyclic softening exhibits in the PBF-LB samples, which is the result of the suppressed martensitic transformation and the dislocation unpinning from the cell boundaries.

On the Fatigue Performance of Friction-Stir Welded Aluminum Alloys.

This work was undertaken in an attempt to ascertain the generic characteristics of fatigue behavior of friction-stir welded aluminum alloys. To this end, different alloy grades belonging to both the heat-treatable and non-heat-treatable types in both the cast and wrought conditions were studied. The analysis was based on the premise that the fatigue endurance of sound welds (in which internal flaws and surface quality are not the major issues) is governed by residual stress and microstructure. Considering the relatively low magnitude of the residual stresses but drastic grain refinement attributable to friction-stir welding, the fatigue performance at relatively low cyclic stress was deduced to be dictated by the microstructural factor. Accordingly, the fatigue crack typically nucleated in relatively coarse-grained base material zone; thus, the fatigue strength of the welded joints was comparable to that of the parent metal. At relatively high fatigue stress, the summary (i.e., the cyclic-plus residual-) stress may exceed the material yield strength; thus, the fatigue cracking should result from the preceding macro-scale plastic deformation. Accordingly, the fatigue failure should occur in the softest microstructural region; thus; the fatigue strength of the welded joint may be inferior to that of the original material.

Mechanical properties of Mg-Al-Mn magnesium alloys with low Al content in the as-cast and extruded conditions

The reported works on the Mg-Al-Mn (AM) alloys with low Al contents are scant. As a result, in the present work, the microstructure and mechanical properties of AM20 (Mg-2Al-0.5Mn) and AM21 (Mg-2Al-1Mn) alloys in the as-cast and wrought conditions were studied. Intermetallics of Al8Mn5 and Al2Mn3 were characterized in the former and the latter, respectively. Grain refinement due to aluminum and manganese addition and applying hot extrusion process were discussed. Besides the as-cast condition, the addition of 0.5 wt% Mn was found to be in favor of obtaining a finer grain size in the extruded condition. The enhancements of tensile properties with respect to the observed grain refinement were discussed and a Hall-Petch slope of 290 MPa/μm0.5 was obtained, which revealed the remarkable effect of Mn.

Stamping an AA5754 Train Window Panel with High Dent Resistance Using Locally Annealed Blanks

The warm stamping of an AA5754-H32 window panel for railway vehicles applications has been proposed in the present work. The adoption of increased working temperatures can be surely considered the most effective solution for this alloy to overcome the limited material formability at room temperature [Palumbo et al. “Warm Forming of an AA5754 Component for Railway Vehicle Applications”, Procedia Engineering, Vol. 183, 2017, Pages 351-356] but, in order to improve the overall dent resistance of the component, the initial wrought conditions have been chosen in the present work. The manufacturing of the window panel was thus subdivided into a preliminary local heat treatment (assumed to be performed by laser) to anneal the material and a subsequent warm stamping step using heated tools. The best combination of temperature and holding time able to produce the annealing of the investigated alloy was determined using the physical simulator Gleeble 3180. On the contrary, the warm forming step was designed by means of thermo-mechanical simulations: in order to model the AA5754-H32 blank with annealed regions, an extensive experimental campaign (tensile and formability tests) was conducted using specimens in the annealed (H111) and in the wrought (H32) conditions. Through the numerical approach it was thus possible define: (i) the extent of the annealed regions; (ii) the punch speed to get a sound component.

Hot workability of cast and wrought Ni–42Cu alloy through hot tensile and compression tests

In order to analyze the flow behavior and workability of Ni–42Cu in cast and wrought conditions, hot deformation tests were performed at temperatures and strain rates within the ranges of 900–1150 °C and 0.001–1 s−1, respectively. Tensile tests showed a “hot ductility trough” at 950 °C for both alloys. The drop in hot ductility was more considerable in the cast alloy because of the sluggish dynamic recrystallization. The hot ductility drop and grain boundary cracking, particularly in the cast alloy, were attributed to the segregation of detrimental atoms to the boundaries. It was shown that the hot ductility of the wrought alloy could be improved with increasing strain rate. It was associated with increasing the fraction of dynamic recrystallization at higher strain rates. This finding corroborated the change in the mechanism of dynamic recrystallization with strain rate. The strain rate sensitivity and instability parameters calculated for the wrought alloy showed that the material is prone to strain localization at low temperatures, i.e., 950–1050 °C, and high strain rates of 0.1 and 1 s−1. Based on the tensile and compression tests, the best temperature range for a desirable hot workability was introduced as 1050–1150 °C.

Hot ductility behavior of Incoloy901 superalloy in the cast and wrought conditions

Abstract Hot ductility was investigated in Incoloy901 using hot tensile testing over a temperature range of 900 to 1 200 °C and at strain rates of 0.01 to 1 s−1, in the cast and wrought conditions. Maximum ductility was detected in the cast and wrought conditions at temperature ranges of 1 000 to 1 050 °C and 1 000 to 1 100 °C, respectively. More voids were seen at the fracture surface of the wrought specimens compared to the cast ones. At 950 °C, the formation of large and non-homogeneous voids at the fracture surface, as well as the appearance of transgranular and intergranular cracks in the wrought specimen, support moderate ductility of the alloy. Microstructural analysis does not support the occurrence of dynamic recrystallization in the cast specimens. In contrast, dynamic recrystallization in the wrought specimens at the region of maximum hot ductility promoted diffusion, leading to ductile fracture. At temperatures higher than the maximum ductility range, the formation of intergranular cracks resulted in a remarkable decline in ductility.

New insights into hard phases of CoCrMo metal-on-metal hip replacements

The microstructural and mechanical properties of the hard phases in CoCrMo prosthetic alloys in both cast and wrought conditions were examined using transmission electron microscopy and nanoindentation. Besides the known carbides of M23C6-type (M=Cr, Mo, Co) and M6C-type which are formed by either eutectic solidification or precipitation, a new mixed-phase hard constituent has been found in the cast alloys, which is composed of ∼100 nm fine grains. The nanosized grains were identified to be mostly of M23C6 type using nano-beam precession electron diffraction, and the chemical composition varied from grain to grain being either Cr- or Co-rich. In contrast, the carbides within the wrought alloy having the same M23C6 structure were homogeneous, which can be attributed to the repeated heating and deformation steps. Nanoindentation measurements showed that the hardness of the hard phase mixture in the cast specimen was ∼15.7 GPa, while the M23C6 carbides in the wrought alloy were twice as hard (∼30.7 GPa). The origin of the nanostructured hard phase mixture was found to be related to slow cooling during casting. Mixed hard phases were produced at a cooling rate of 0.2°C/s, whereas single phase carbides were formed at a cooling rate of 50 °C/s. This is consistent with sluggish kinetics and rationalizes different and partly conflicting microstructural results in the literature, and could be a source of variations in the performance of prosthetic devices in-vivo.

Tensile properties of an AlCrCuNiFeCo high-entropy alloy in as-cast and wrought conditions

Abstract Extensive multistep forging at 950 °C was applied to the cast AlCuCrFeNiCo high-entropy alloy to transform the cast coarse dendritic structure into a fine equiaxed duplex structure consisting of the mixture of BCC and FCC phases, with the average grain/particle size of ∼1.5 ± 0.9 μm. Tensile properties of the alloy in the as-cast and forged conditions were determined in the temperature range of 20–1000 °C. The hot forged alloy was stronger and more ductile during testing at room temperature, than the as-cast alloy. The yield stress (YS), ultimate tensile strength (UTS), and tensile ductility ( δ ) of the forged condition were 1040 MPa, 1170 MPa, and 1%, respectively, against 790 MPa, 790 MPa and 0.2% for the as-cast condition. In both conditions, the alloy showed brittle to ductile transition (BDT), with a noticeable increase in the tensile ductility within a narrow temperature range. In the as-cast condition, this transition occurred between 700 and 800 °C, while in the forged condition, it was observed between 600 and 700 °C. With an increase in the testing temperature above the BDT, a continuous decrease in tensile flow stress and an increase in tensile ductility were observed. In the temperature range of 800–1000 °C, the forged alloy showed superplastic behavior. The tensile elongation was above 400% and reached 860% at 1000 °C.

Hot Deformation Microstructure and Mechanical Properties of Mg-Zn-Nd-Cd-Zr Alloy

Hot compression tests of the homogenized Mg-Zn-Nd-Cd-Zr magnesium alloy were performed on Gleeble-1500 at temperatures between 300 °Cand 420 °C and at strain rates ranging from 0.001 to 1 s-1 with maximum strain of 0.8. The microstructure of the experimental alloy in the hot-compression procedure at elevated temperatures was observed by OM (optical microscope) and TEM (transmission electron microscope). The results provide the experimental basis for selecting hot wrought conditions of the alloy. The peak flow stress becomes larger with the increasing strain rate at constant temperature, and gets smaller with the increasing deformation temperature at constant strain rate. The deformation activation energy increases greatly in the range of higher than 420°C, and no more change in the range of 340-380°C. The alloy can be extruded successfully at 360°C with of δb 310 Mpa, δ2 of 290Mpa, and δof 16%。

Hot ductility of a Fe–Ni–Co alloy in cast and wrought conditions

The hot ductility of Fe–29Ni–17Co alloy was studied in both cast and wrought conditions by hot tensile tests over temperature range of 900–1250 °C and at strain rates of 0.001–1 s −1. Over the studied temperature range, the wrought alloy represented higher elongation and reduction in area as compared to the cast alloy. Dynamic recrystallization was found responsible for the higher hot ductility of the wrought alloy and the improvement of hot ductility of the cast alloy at high temperatures. At temperature range of 1000–1150 °C the wrought alloy exhibited a hot ductility drop while a similar trough was not observed in case of the cast alloy. It was also found that at temperatures of 1150–1250 °C the best hot ductility is achieved in both cases of cast and wrought alloy. The experimental data of flow stress were constitutively analyzed and the apparent activation energy of deformation was estimated to be 344 kJ/mol.

Room-temperature indentation creep of lead-free Sn–Bi solder alloys

Creep behavior of the lead-free Sn-5%Sb solder alloy was studied by long-time Vickers indentation testing at room temperature. Four different conditions of the material were examined. These were unhomogenized cast (UC), homogenized cast (HC), unhomogenized wrought (UW), and homogenized wrought (HW) conditions. Based on the steady-state power-law creep relationship, the stress exponents were determined through different methods of analysis, and in all cases, the calculated exponents were in good agreement. The stress exponent values of about 5 and 12, depending on the processing route of the material, are very close to those determined by room-temperature conventional creep testing of the same material reported in the literature. For the HW condition, the n value of about 5 together with a very fine grain size of 4.5 µm and a high volume fraction of second-phase particles of 8.6% may suggest that dislocation climb is the creep mechanism. For all other conditions with different grain sizes and second-phase volume fractions, however, the high n value of 12 implies that the operative creep mechanism is dislocation creep, which is independent of grain size.

Indentation creep study of lead-free Sn–5%Sb solder alloy

Creep behavior of the lead-free Sn–5%Sb solder alloy in the cast and wrought conditions was investigated by long time Vickers indentation testing under a constant load of 15 N and at temperatures in the range 298–405 K. Based on the steady-state power law creep relationship, the stress exponents were determined for the cast and wrought materials. These exponents, depending on the testing temperature, were in the range 4.8–2.9 and 13.7–6.0 for the wrought and cast conditions, respectively. The activation energy of 46.8 kJ mol −1 which is very close to the activation energy for grain boundary diffusion of β-Sn, together with a very fine grain size of 4.5 μm and a uniform distribution of fine SnSb particles, may suggest that the dominant creep mechanism in the wrought condition is grain boundary diffusion. However, for the cast material with a coarse grain size of 280 μm, the n-values of 13.7 to 6.0 and the activation energy of 66.5 kJ mol −1 are indicative of a dislocation creep mechanism over the whole temperature range investigated.

Impression creep behavior of lead-free Sn–5Sb solder alloy

Creep behavior of the lead-free Sn–5Sb solder alloy in the cast and wrought conditions was investigated by impression testing. The tests were carried out under constant stress in the range of 18–135 MPa and at temperatures in the range of 298–403 K. Assuming a power law relationship between the impression rate and the punching stress, stress exponents of 2.8 and activation energies of 41.3 kJ mol −1 were determined for the wrought material over the whole stress and temperature ranges studied. For the cast condition, however, stress exponents of 5.4 and 11.4 and activation energies of 53.8 and 75.8 kJ mol −1 were obtained at low and high stresses, respectively. The n value of 2.8 and the activation energy of 41.3 kJ mol −1, which is very close to the activation energy for grain boundary diffusion of β-Sn, together with a very fine grain size of 4.5 μm and a uniform distribution of fine SnSb particles, may suggest that grain boundary sliding is the dominant creep mechanism in the wrought condition. For the cast material with a coarse grain size of 280 μm, the low stress regime activation energy of 53.8 kJ mol −1, which is close to that of the self diffusion of pure Sn, and a stress exponent of 5.4 suggest that the operative creep mechanism is dislocation climb. This behavior is in contrast to the high stress regime in which, the n = 11.4 and Q = 75.8 kJ mol −1 are indicative of a dislocation creep mechanism.

Room-temperature indentation creep of lead-free Sn-5%Sb solder alloy

Creep behavior of the lead-free Sn-5%Sb solder alloy was studied by long-time Vickers indentation testing at room temperature. Four different conditions of the material were examined. These were unhomogenized cast (UC), homogenized cast (HC), unhomogenized wrought (UW), and homogenized wrought (HW) conditions. Based on the steady-state power-law creep relationship, the stress exponents were determined through different methods of analysis, and in all cases, the calculated exponents were in good agreement. The stress exponent values of about 5 and 12, depending on the processing route of the material, are very close to those determined by room-temperature conventional creep testing of the same material reported in the literature. For the HW condition, the n value of about 5 together with a very fine grain size of 4.5 µm and a high volume fraction of second-phase particles of 8.6% may suggest that dislocation climb is the creep mechanism. For all other conditions with different grain sizes and second-phase volume fractions, however, the high n value of 12 implies that the operative creep mechanism is dislocation creep, which is independent of grain size.