Solution-treated Specimens Research Articles

Effect of initial state and processing temperature on structure and properties under hot torsion of AA5754 alloy

The effect of initial state and processing temperature of AA5754 alloy during hot torsion tests is presented. This deformation scheme allows simulating complex strain-stressed conditions. The tests were conducted on specimens solution heat treated in water and for specimens after extrusion and homogenizing treatment, respectively. It was determined that in the investigated range of deformation parameters, the solution treatment process has no effect on the plasticity of the alloy under investigation, but does have an influence on its hardness, microhardness distribution and grain size. In particular, the specimens deformed in the initial state behave according to the deformation pattern i. e. the maximum values of hardening and grain refinement occur on the deformed specimen surface, while the minimum values, inside the specimen. The same effect of deformation was observed for solution-treated specimens deformed at 250°C. While deformation in the extruded and homogenized state, the most uniform hardness distribution and the maximum deformation were exhibited by specimens deformed at 250°C.Thus, a successful attempt to incorporate knowledge obtained from severe plastic deformations (SPD) into the AA5XXX series aluminum alloys treatment has been made. The incorporation of SPD advantages allowed revealing age hardenable mechanism in non-age-hardenable alloy AA5XXX. All side investigation of structure and properties was made.

Effect of δ-ferrite on susceptibility to hydrogen embrittlement of 304 austenitic stainless steel in high-pressure hydrogen atmosphere

Purpose The purpose of this paper is to demonstrate the effect of δ-ferrite on the susceptibility to hydrogen embrittlement of type 304 stainless steel in hydrogen gas environment. Design/methodology/approach The mechanical properties of as-received and solution-treated specimens were investigated by the test of tensile and fatigue crack growth (FCG) in 5 MPa argon and hydrogen. Findings The presence of δ-ferrite reduced the relative elongation and the relative reduction area (H2/Ar) of 304 stainless steel, indicating that δ-ferrite increased the susceptibility of hydrogen embrittlement in 304 stainless steel. Moreover, δ-ferrite promoted the fatigue crack initiation and propagation at the interface between δ-ferrite and austenite. The FCG tests were used to investigate the effect of δ-ferrite on the FCG rate in hydrogen gas environment, and it was found that δ-ferrite accelerated the FCG rate, which was attributed to rapid diffusion and accumulation of hydrogen around the fatigue crack tip through δ-ferrite in high-pressure hydrogen gas environment. Originality/value The dependence of the susceptibility to hydrogen embrittlement on δ-ferrite was first investigated in type 304 steel in hydrogen environment with high pressures, which provided the basis for the design and development of a high strength, hydrogen embrittle-resistant austenitic stainless steel.

Yttrium's Effect on the Hot Cracking and Creep Properties of a Ni-Based Superalloy Built Up by Additive Manufacturing.

We studied the effects of the rare earth element yttrium (Y) on the hot cracking and creep properties of Hastelloy-X processed by selective laser melting. We used two different alloys to study hot cracking in Hastelloy-X: one with 0.12 mass% yttrium added and one with no yttrium. Y-free Hastelloy-X exhibited less cracks, mainly due to the segregation of Si, W, and C resulting in SiC- and W6C-type carbides at the grain boundary and interdendritic regions. On the other hand, more cracks formed in the Y-added Hastelloy-X specimen because of segregation of Y, resulting in the formation of yttrium-rich carbide (YC). Post-heat treatment was conducted at 1177 °C for 2 h, followed by air cooling, to obtain good creep properties. We carried out a creep test along the vertical and horizontal directions. Despite having more cracks, the Y-added as-built Hastelloy-X specimen showed longer creep life and ductility than the Hastelloy-X specimen. This was mainly because of the formation of Y2O3 and SiO2 inside the grains. After solution treatment, the Y-added specimen’s creep life was eight times longer than that of the Y-free solution-treated specimen. This was mainly because of the maintenance of the columnar grain morphology even after solution treatment. In addition, the formation of M6C carbides, Y2O3, and SiO2 improved creep life. To summarize the effect of Y, Y addition promoted the formation of cracks, which brought about creep anisotropy; however, it improved creep properties through the stabilization of oxygen and the promotion of discrete carbide precipitation, which prohibited the migration and sliding of grain boundary.

Origin of the O phase and its effect on the mechanical properties of rolled Ti-22Al-25Nb alloy sheets

ABSTRACT The microstructure and mechanical properties of a hot-rolled Ti-22Al-25Nb (at%) alloy sheet after aging and solution-aging treatment were studied. A typical core-shell structure formed in the as-received specimens upon aging at 650 °C to 950 °C for 6 h. O phases precipitated around the grain boundaries or in the B2 matrix for the solution-treated specimens upon aging at 650 °C to 950 °C. The combined effect of the precipitation and solution strengthening led to a decrease in microhardness while aging from 650 °C to 900 °C and an increase in microhardness while aging from 900 °C to 1000 °C for both the as-received and solution-treated specimens after the aging treatment. Finer O phases contributed to the increase in yield strength and elongation and were more beneficial to the improvement of high temperature strength than of room temperature strength.

Texture evolution associated with the preferential recrystallization during annealing process in a hot-rolled near β titanium alloy

Texture evolution associated with the recrystallization behavior during solution treatment was investigated in a hot-rolled Ti-7333 by virtue of Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM), X-ray Diffraction (XRD) and Electron Backscatter Diffraction (EBSD). The results show that the microstructure of the rolled specimens consists of a large number of elongated β grains and a small amount of equiaxed β grains. The dominant texture components are confirmed to be {111}<110> and {100}<001>. With the progressing of the solution treatment, the recrystallization occurs and the orientations of {111}<110> and {001}<100> hold the preferred orientations to act as the nuclei for the recrystallized grains. It is found that the recrystallized grains are mainly located on the bulged boundaries or within the deformed grains, and the mechanism of the strain-induced boundary migration (SIBM) mainly accounts for the formation of the recrystallized grains nucleated on the bulged boundaries, which eventually leads to the texture of the solution-treated specimens inheriting the previous orientation of <110> parallel to the rolling direction. The results of the present work provide a valuable reference for understanding the relationship between the texture evolution and the recrystallization behavior during the annealing process in near β titanium alloys.

Effects of Heat Treatment on the Microstructure and Mechanical Properties of Selective Laser Melting 316L Stainless Steel

316L stainless steel materials are widely used in impact‐resistant structures. Heat treatments could affect the mechanical properties of 316L stainless steel parts formed by selective laser melting (SLM), which is vital for ensuring service safety. This study aimed to analyze the mechanical behavior of SLM 316L stainless steel under different heat treatment methods. Therefore, test specimens were prepared using the SLM technique and then annealed at 400°C for 1 h. The solution was treated at 1050°C for 20 min. The dynamic compressive mechanical properties of the deposited, annealed, and solution‐treated specimens were tested at high strain rates by using a split Hopkinson pressure bar (SHPB) experimental apparatus. Moreover, the microstructures of the previously mentioned samples were analyzed by optical microscopy and scanning electron microscopy. The experimental results showed that the three‐state samples exhibited strain rate sensitivity in the dynamic mechanical tests and that solution treatment could alter their mechanical properties significantly. In addition, the microstructure of the deposited specimens presented cylindrical cellular crystal features, which have a higher dislocation density. Hence, the yield strength of deposited specimens is higher than that of the solution‐treated ones. After annealing, the microstructures of the samples did not change obviously, and their dynamic yield strength remained almost unchanged. After solution treatment, its cellular crystal disappeared and dislocation density dropped dramatically, resulting in a sharp decrease in yield strength. Finally, this research can provide a theoretical reference for broadening the practical application of SLM 316L material parts.

Microstructural Evolution and Mechanical Properties of Constrained Groove-Pressed 304 Austenitic Stainless Steel

The present work investigates the influence of constrained groove pressing (CGP) on the microstructural evolution and mechanical properties of 304 austenitic stainless steel. CGP shows a significant improvement in mechanical properties such as tensile strength and micro-hardness. XRD analysis shows the transformation of austenite phase into deformation-induced martensite phase which is also confirmed by vibrating sample magnetometer. Finite element analysis employing Deform 3D software shows the average induced strain of 2.29, after two passes of CGP. Rietveld refinements on XRD patterns affirm the decrease in crystallite size, increase in microstrain and dislocation density. EBSD also shows the formation of substructures due to CGP. The ultimate tensile strength of solution-treated specimens enhances from 729 to 1058 MPa, and the value of micro-hardness increases from 238 to 477 VHN after two passes of CGP. The augmentation in mechanical properties is attributed to the synergic effect of increased dislocation density, martensitic transformation, substructure formation and reduced crystallite size.

A comparative study of a solid solution hardening in carbon-alloyed FeMnCrNiCo0.95C0.05 high-entropy alloy subjected to different thermal–mechanical treatments

Different thermal–mechanical processing regimes were used to provide a precipitate-free austenitic structure in interstitial FeMnCrNiCo0.95C0.05 high-entropy alloy containing 1.07 at. % of carbon. Relative to interstitial-free FeMnCrNiCo alloy (a = 0.3599 nm), an expanded FCC crystal lattice (a = 0.3602–0.3603 nm) is typical of as-cast and solution-treated specimens, but grain-boundary carbides are also observed in them. Near complete carbon dissolution in austenite of FeMnCrNiCo0.95C0.05 high-entropy alloy was achieved utilizing two multistage thermal–mechanical processing regimes, which included the combinations of (i) a high-temperature anneal (25 h total), hot forging and cold rolling, and (ii) cold rolling with intermediate high-temperature anneals (6 h total). Despite the fact that both processing regimes provided high solid-solution hardening of austenite (a = 0.3611 nm) and complete dissolution of grain-boundary precipitates, some individual coarse carbides were identified in microstructure of the alloy. Both processing regimes enhanced the mechanical properties of the alloy.

Effects of Initial Precipitate on Shear Deformation during Asymmetric Rolling of Al-Mg-Si Alloy: Texture and Formability

Al-Mg-Si alloy was rolled asymmetrically at several temperatures to apply shear deformation, and the effects of the initial precipitate on shear deformation, texture evolution, formability, and plastic anisotropy were studied. Texture was analyzed using a EBSD, and the formability and plastic anisotropy of the specimen were evaluated using the value and value calculated from the plastic strain ratio (r-value) which was determined from the change in the length of the specimen during tensile deformation. Asymmetric rolling induces a larger equivalent strain than symmetric rolling, and the equivalent strain increases as the asymmetric rolling temperature increases. When a specimen with peak-aged initial precipitates was asymmetrically rolled, less shear deformation occurred at room temperature than in a solution-treated specimen without initial precipitates. In contrast, a larger shear deformation occurred at high temperatures (500°C). With asymmetric rolling at room temperature, the specimens without initial precipitates had higher formability and lower plasticity, while for asymmetric rolling at high temperature, the specimens with initial precipitates had higher formability and lower plastic anisotropy. This is due to the &lt;111&gt;//ND texture, such as {111}&lt;110&gt; and {111}&lt;112&gt; orientation that has similar and high r-values at 0°, 45°, and 90° to the rolling direction, developed by the shear deformation that occurred during asymmetric rolling.

Effect of thermo-mechanical treatment on microstructural evolution and mechanical properties of a superelastic Ti–Zr-based shape memory alloy

Achieving a combination of good superelastic performance and high strength in the bio-functional nickel-free Ti-based shape memory alloys is always required for the superelastic biomedical devices. For achieving this combination, in this paper, the thermo-mechanical treatment's influence on the microstructural development, mechanical performance and superelastic behavior of a Ti–45Zr–8Nb–2Sn (at.%) shape memory alloy was studied by using X-ray diffraction (XRD), transmission electron microscope (TEM), and tensile tests. 773 K and 823 K annealed specimens after cold rolling showed (β+α) two-phase microstructure. The grain size increased from 0.11 μm in 773 K annealed specimen to 125 μm in 1173 K solution-treated specimen. A maximum recovery strain of 5.4% was achieved at room temperature in the 1073 K annealed specimen due to some extent of the favorable recrystallization texture together with reasonable grain size but the tensile strength was 830 MPa. A combination of a large recovery strain of 5.0%, a high tensile strength of 1030 MPa and good ductility with fracture strain of 13.2% was achieved at room temperature in the 823 K annealed specimen due to the fine β grains of 0.74 μm, which can be beneficial for biomedical applications.

Effect of Heat Treatment on Gradient Microstructure of AlSi10Mg Lattice Structure Manufactured by Laser Powder Bed Fusion

The present study addressed the effect of heat treatment process on microstructure of an AlSi10Mg lattice structure with a body-centered cubic unit cell manufactured via laser powder bed fusion (LPBF). The as-manufactured lattice specimen exhibited a unique cellular structure composing of primary α-Al phases bounded by α-Al/Si eutectic microstructure. A gradient microstructure (continuous microstructural changes) was found in the node and strut portions composed of the lattice specimen. The microstructure appears more equiaxed and coarser with approaching the bottom surface of both portions. The continuous microstructural changes contributed to a variation in hardness measured at different locations in the as-manufactured lattice specimen. Si particles finely precipitate in the primary α-Al phases, and eutectic Si particle coarsening occurs at an elevated temperature of 300 °C. The microstructural coarsening is more pronounced at a higher temperature. A number of significantly coarsened Si particles and a stable Fe-containing intermetallic phase (β-AlFeSi) were observed at all locations in 530 °C solution-treated specimen. The homogenous microstructure results in a constant hardness value independent of the location in the lattice specimen. These results provide new insights to control the compressive properties of the AlSi10Mg lattice structure manufactured via LPBF by subsequent heat treatment processes.

Effect of heat treatment on microstructural evolution and creep behaviors of a conventionally cast nickel-based superalloy

The evolution of microstructures caused by heat treatment on Ni-based superalloy CM 247 LC was examined, and the creep behaviors were analyzed at various temperature and stress conditions. Secondary γ′ hardly precipitated in aged specimens subjected to solution treatment, but secondary γ′ precipitated in specimen subjected to two-step aging at 1080 °C and 871 °C without solution treatment, because the size and volume fraction of precipitated γ′ particles and the width of the γ channel depend on the heat-treatment path. The creep properties of the specimen subjected to two-step aging without solution heat treatment under low temperature and high stress was the best, owing to the uniform deformation and damage-relieving effect of the fine secondary γ′ particles in the γ channel and the eutectic γ/γ′ phase. At and above 871 °C, the effect of γ′ rafting on the creep properties was very important, and the creep lifetimes of the solution-treated specimens with better rafting were longer than those of the aged specimens.

Effects of Testing Temperature on the Serration Behavior of an Al–Zn–Mg–Cu Alloy with Natural and Artificial Aging in Sharp Indentation

Serration phenomena, in which stress fluctuates in a saw-tooth shape, occur when a uniaxial test is performed on an aluminum alloy containing a solid solution of solute atoms. The appearance of the serrations is affected by the strain rate and temperature. Indentation tests enable the evaluation of a wide range of strain rates in a single test and are a convenient test method for evaluating serration phenomena. Previously, the serrations caused by indentation at room temperature were clarified using strain rate as an index. In this study, we considered ambient temperature as another possible influential factor. We clarify, through experimentation, the effect of temperature on the serration phenomenon caused by indentation. An Al–Zn–Mg–Cu alloy (7075 aluminum alloy) was used as the specimen. The aging phenomenon was controlled by varying the testing temperature of the solution-treated specimen. Furthermore, the material properties obtained by indentation were evaluated. By varying the testing temperature, the presence and amount of precipitation were controlled and the number of solute atoms was varied. Additionally, the diffusion of solute atoms was controlled by maintaining the displacement during indentations, and a favorable environment for the occurrence of serrations was induced. The obtained results reveal that the variations in the serrations formed in the loading curvature obtained via indentation are attributed to the extent of interaction between the solute atoms and the dislocations.

Влияние наводороживания на механические свойства и механизмы разрушения высокоазотистых хромомарганцевых сталей, подвергнутых дисперсионному твердению

Currently, many technical problems require a comprehensive study of the properties of materials operating in hydrogen-containing environments. The authors investigated the effect of age-hardening on the hydrogen embrittlement and fracture micromechanisms of high-nitrogen austenitic Fe-23Cr-17Mn-0.1C-0.6N (wt. %) steel. For this purpose, using heat treatments, the authors formed in specimens of Fe-23Cr-17Mn-0.1C-0.6N steel the structural phase states characterized by different distribution and content of dispersed phases. The experiment determined that the accumulation of hydrogen atoms occurs predominantly in the grains in solution-treated specimens without dispersed phases. This causes the effects of solid solution hardening and leads to a change in the micromechanism of steel fracture from a ductile dimple fracture in the absence of hydrogen to a transgranular fracture by the quasi-cleavage mechanism in hydrogen-charged specimens. It was established that the discontinuous decomposition of austenite with the formation of Cr 2 N cells and austenite depleted in nitrogen, predominantly along the grain boundaries causes the formation of a large fraction of interphase (austenite/Cr 2 N particles) boundaries. Cells of discontinuous decomposition promote hydrogen accumulation along the grain boundaries and cause brittle intergranular fracture of hydrogen-charged specimens during plastic deformation. The study showed that in specimens with the discontinuous decomposition of austenite both along the grain boundaries and spreading into the grain body, plenty of intragranular interphase boundaries (Cr 2 N plates in austenite) are formed, which causes the formation of a transgranular brittle fracture in the hydrogen-charged specimens.

Combustion behaviour and mechanism of a Cu-Ni-Mn alloy in an oxygen enriched atmosphere

The combustion behaviour and underlying mechanism of a Cu-Ni-Mn alloy solution treated at 880 ℃ and aged at 450 ℃ for different time are studied. The oxidation of elements is found to follow the sequence of Mn→Ni→Cu. The remaining length of solution-treated specimens is found to increase under higher oxygen pressures, whereas that of aged specimens show no distinct dependency on oxygen pressures. The different combustion behaviors are attributed to diffusion pathways of Mn and O atoms, i.e., continuous diffusion of Mn atoms in the solution-treated samples and diffusion from the precipitates in aged ones.

Self-healing behavior of Inconel 617B superalloy

In the present study, the self-healing behavior of Inconel 617B superalloy (617B), used as a high-temperature material, was investigated through both preliminary test consisting of room-temperature tension and annealing and creep rupture test. Micro-cracks in the solution-treated specimen, which had been fractured at room temperature, were filled in by the precipitation of M23C6 and the segregation of B, C, and S after annealing at 800 °C for 16 h. Due to this healing effect and dislocation recovery, a 33% pre-strained and annealed specimen exhibited the longer total elongation, compared to the specimen strained until fracture without annealing after 33% pre-strain. Finally, creep rupture tests revealed that the creep strength of 617B is higher than Inconel 617 superalloy (617) due to the self-healing effect by the high-temperature precipitation of M23C6 and the segregation of B, C, and S as well as grain boundary strengthening of B and C.

Tailoring the microstructure and mechanical properties of metastable Ti–29Nb–13Ta-4.6Zr alloy for self-expansible stent applications

In this paper, thin-struts of β-type titanium alloy (Ti–29Nb–13Ta-4.6Zr, wt%) were successfully fabricated by cold rolling, and their elastic behavior and mechanical properties are discussed for different processing conditions. Before cold rolling, the extremely low yield and ultimate tensile strength of the as-cast and solution-treated specimens, result of a notable “double yielding” behavior, make them inadequate to be applied as structural devices. However, after cold rolling plus short time aging, a nonlinear elasticity with a substantial recoverable strain, considered as the intermediate stage between “double yielding” and normal linear elasticity, is obtained and ascribed to a moderate precipitation of nanometer-sized secondary phases. These precipitates strengthen the material by hindering the motion of dislocations while the β-matrix with relatively low content of β-stabilizers can give rise to a low elastic modulus. The ultimate tensile strength, yield strength, Young's modulus and elastic recoverable strain of the cold rolled plus aged specimens were measured as being between 967 and 1192 MPa, 920–1180 MPa, 48–83 GPa and 1.5–2.0%, respectively. As such, the alloy is anticipated to be promising metallic self-expansible stent material by virtue of the unique combination of extraordinarily high elastic strain, high mechanical strength, and excellent biocompatibility [1, 2].

Grain Refinement of Co-Cr-Mo-C Through Plastic Deformation Followed by Reversion of Lamellar Eutectoid Structure

Small plastic straining was combined with a two-step heat treatment to obtain grain refinement of the Co-28Cr-6Mo-0.33C alloy. The solution-treated specimens were furnace cooled to room temperature, obtaining partially transformed pearlite at grain boundaries. Afterward, the specimens were compressed up to 10% of engineering strain, followed by aging at 850 °C that contributed to the decomposition of the austenite phase into a lamellar eutectoid structure (α + M23C6). The full lamellar structure was then reverse-treated at temperatures from 1000 to 1237 °C, where the austenite phase was stable. The reversion treatment led to the nucleation of a fine-grained austenitic structure (with average size of 48.23 ± 21.30 μm—i.e., about 1/10 of its initial average size) at the lamellar eutectoid structure. Compression tests carried out on reverse-transformed samples showed better mechanical properties compared to those of the samples tested before reversing transformation.

The states of hydrogen and hydrogen embrittlement susceptibility of precipitation hardened SUS630 stainless steel

To elucidate the influence of precipitates on the states of hydrogen and hydrogen embrittlement susceptibility of SUS630, solution treatment, sub-aging (410 °C, 1 h), peak-aging (470 °C, 1 h), and over-aging (550 °C, 1 h) methods were used to prepare specimens. States of hydrogen were analyzed by thermal desorption analysis (TDA). Hydrogen embrittlement susceptibility was evaluated using tensile tests. Specimens were electrochemically precharged with hydrogen and then tensile tests were carried out simultaneously with hydrogen charging under the same conditions as those after precharging. Susceptibility was evaluated as the elongation ratio with/without hydrogen. The solution-treated and sub-aged specimens displayed a single peak near 100 °C, whereas peak- and over-aged specimens displayed two peaks, one near 100 °C and the other near 200 °C. The peak near 100 °C corresponded to hydrogen desorbed from the matrix and the peak near 200 °C corresponded to hydrogen desorbed from Cu precipitates. Ductility of peak- and over-aged specimens with hydrogen did not decrease, however, that of solution-treated and sub-aged specimens with hydrogen did. These findings indicate that specimens containing hydrogen with a higher temperature peak associated with Cu precipitates showed less hydrogen embrittlement susceptibility than those containing hydrogen with only a lower temperature peak.

Mechanical and corrosion properties of CoCrFeNiTi-based high-entropy alloy additive manufactured using selective laser melting

The effectiveness of applying selective laser melting (SLM) to a CoCrFeNiTi-based high-entropy alloy was compared with that of using electron beam melting (EBM). The higher solidification rate during SLM promoted a fine uniform microstructure with no visible segregation, which led to superior tensile properties (yield strength: 773.0 ± 4.2 MPa, ultimate tensile strength: 1178.0 MPa, elongation: 25.8 ± 0.6%) and a higher pitting potential (0.88 ± 0.03 V versus Ag/AgCl in a 3.5% NaCl solution at 353 K) in comparison to the EBM specimens (743.4 ± 11.6, 932.2 ± 4.8 MPa, 4.0 ± 0.2%, and 0.50 ± 0.04 V versus Ag/AgCl, respectively). The effect of a solution treatment on the tensile properties and pitting-corrosion resistance of the SLM specimens was then examined. The effect of the solution treatment on these properties depended on the cooling method used during the treatment. In particular, the tensile properties and pitting-corrosion resistance improved as a result of water quenching. On the other hand, the properties of the solution-treated specimens depended on the size and volume fraction of very fine-ordered particles, with diameters of tens of nanometers that contained Ni and Ti. The as-built and solution-treated SLM specimens exhibited excellent tensile strength and exceptional pitting-corrosion resistance; they had higher tensile strength and pitting-corrosion resistance than the conventional high-corrosion-resistant alloys.