Search Results (91)

This study investigates the effects of Hot Isostatic Pressing (HIP) treatment on the microstructural evolution and mechanical properties of Laser Powder Bed Fusion (LPBF)-manufactured Hastelloy H. This research evaluates the trade-offs between defect elimination, anisotropy reduction, and strength retention in well-optimized LPBF components. Specimens were manufactured using optimized LPBF parameters, achieving 99.85% density, and then subjected to HIP treatment at 1160 °C/100 MPa for 4 h. The analysis includes porosity analysis, grain size measurement, crystallographic texture evaluation, and tensile tests in two principal orientations. The results show that HIP treatment provides minimal benefits for defect elimination in already high-quality LPBF material, reducing porosity from 0.15% to <0.01%—a negligible improvement that does not translate to proportional mechanical enhancement. Tensile tests show that as-built specimens exhibited orientation-dependent strength, with XY-oriented samples reaching a yield strength (YS) of 682 MPa, ultimate tensile strength (UTS) of 864 MPa, and elongation of 17%, while XZ-oriented samples showed lower strength (YS = 621 MPa, UTS = 653 MPa) but superior ductility (elongation = 47%). After HIP treatment, anisotropy was largely removed, with both XY and XZ orientations showing comparable strength (YS ≈ 315–317 MPa, UTS ≈ 682–691 MPa) and elongation (38–41%). This indicates that HIP significantly improves ductility and isotropy at the cost of reduced strength. HIP treatment effectively eliminates the anisotropy of LPBF components, achieving uniform hardness across all orientations while reducing crystallographic texture intensity from 12.3× to 3.2× random orientation. This isotropy improvement occurs through grain-coarsening mechanisms that increase the average grain size from 7.5 μm to 13.5 μm, eliminating cellular–dendritic strengthening structures and reducing hardness by 32% (254 HV2 to 170 HV2) following Hall–Petch relationships. The conducted research confirms that HIP treatment allows for modification of the microstructure of Hastelloy X alloy, which may lead to the improvement of its mechanical properties in high-temperature applications and a significant increase in the isotropy of the material. Full article

FeAl intermetallic compounds exhibit high application potential in high-voltage transmission lines to withstand external forces such as powerlines’ own gravity and wind force. The ordered crystal structure in FeAl intermetallic compounds endows materials with high strength, but the remarkable brittleness at room temperature restricts engineering applications. This contradiction is essentially closely related to the deformation mechanism at the nanoscale. Here, we performed molecular dynamics simulations to reveal anomalous grain size effects and deformation mechanisms in nanocrystalline FeAl intermetallic material. Models with grain sizes ranging from 6.2 to 17.4 nm were systematically investigated under uniaxial tensile stress. The study uncovers a distinctive inverse Hall-Petch relationship governing flow stress within the nanoscale regime. This behavior stems from high-density grain boundaries promoting dislocation annihilation over pile-up. Crucially, the material exhibits anomalous ductility at ultra-high strain rates due to stress-induced phase transformation dominating the plastic deformation. The nascent FCC phase accommodates strain through enhanced slip systems and inherent low stacking fault energy with the increasing phase fraction paralleling the stress plateau. Nanoconfinement suppresses the propagation of macroscopic defects while simultaneously suppressing room-temperature brittle fracture and inhibiting the rapid phase transformation pathways at extreme strain rates. These findings provide new theoretical foundations for designing high-strength and high-toughness intermetallic nanocompounds. Full article

This article presents the results of studies of the degradation of the structure and mechanical properties of the core materials BN-350 fast neutron and research WWR-K reactors required to justify the service life extension of early-generation power and research reactors. Extending the service life of nuclear reactors is a modern problem, since most operating reactors are early-generation reactors that have exhausted their design lifespan. The possibility of extending the service life is largely determined by the condition of the structural materials of the nuclear facility, i.e., their residual resources must ensure safe operation of the reactor. For the SAV-1 alloy, the structural material of the WWR-K reactor, studies were conducted on witness samples which were in the active zone during its operation for 56 years. It was found that yield strength and tensile strength of the irradiated SAV-1 alloy decreased by 24–48%, and relative elongation decreased by ~2% compared to the unirradiated alloy. Inside the grains and along their boundaries, there were particles of secondary phases enriched with silicon, which is typical for aged aluminum alloys. For irradiated structural steels of power reactors, studied at 350–450 C, hardening and a damping nature of creep were revealed, caused by dispersion hardening and the Hall–Petch effect. Full article

The extensive use of copper in thermal and electrical systems calls for constant performance enhancement by means of innovative material treatments. The effects on the microstructural, mechanical, and electrical characteristics of copper in deep cryogenic treatment (DCT) and deep cryogenic treatment followed by heat treatment (DCT + HT) are investigated in this work. Copper samples were treated for various soaking durations ranging from 6 to 24 h. Mechanical properties such as tensile strength, hardness, and wear rate were analyzed. In the DCT-treated samples, tensile strength increased, reaching a peak of 343 MPa at 18 h, alongside increased hardness (128 HV) and a refined grain size of 9.58 µm, primarily due to elevated dislocation density and microstrain. At 18 h of soaking, DCT + HT resulted in improved structural stability, high hardness (149 HV), a fine grain size (7.42 µm), and the lowest wear rate (7.73 × 10⁻¹⁰ mm³/Nm), consistent with Hall–Petch strengthening. Electrical measurements revealed improved electron mobility (52.08 cm²/V·s) for samples soaked for 24 h in DCT + HT, attributed to increased crystallite size (39.9 nm), reduced lattice strain, and higher (111) texture intensity. SEM–EBSD analysis showed a substantial increase in low-angle grain boundaries (LAGBs) in DCT + HT-treated samples, correlating with enhanced electrical conductivity. Overall, an 18 h soaking duration was found to be optimal for both treatments. However, the strengthening mechanism in DCT + HT is influenced by grain boundary stabilization and thermal recovery and is different to DCT, which is strain-induced enhancement. Full article

This study examines the microstructural evolution, mechanical properties, and wear behavior of medium-carbon dual-phase steel (AISI 1040) processed via Multi-Axis Compression (MAC). The DP steel was produced through inter-critical annealing at 745 °C, followed by MAC at 500 °C, resulting in a refined grain microstructure. Optical micrographs confirmed the presence of ferrite and martensite phases after annealing, with significant grain refinement observed following MAC. The average grain size decreased from 66 ± 4 μm to 18 ± 1 μm after nine MAC passes. Mechanical testing revealed substantial improvements in hardness (from 145 ± 9 HV to 298 ± 18 HV) and ultimate tensile strength (from 557 ± 33 MPa to 738 ± 44 MPa), attributed to strain hardening and the Hall–Petch effect. Fractographic analysis revealed a ductile failure mode in the annealed sample, while DP0 and DP9 exhibited a mixed fracture mode. Both DP0 and DP9 samples demonstrated superior wear resistance compared to the annealed sample. However, the DP9 sample exhibited slightly lower wear resistance than DP0, likely due to the fragmentation of martensite induced by high accumulated strain, which could act as crack initiation sites during sliding wear. Furthermore, wear resistance was significantly enhanced due to the combined effects of the DP structure and Severe Plastic Deformation (SPD). These findings highlight the potential of MAC processing for developing high-performance steels suitable for lightweight automotive applications. Full article

In this study, lanthanum (La), a rare earth element, was added at concentrations of 0.25 wt.%, 0.5 wt.%, and 0.75 wt.% to an Al–10%Si–2%Cu-based alloy prepared by die casting. The effects of solution and aging heat treatment conditions on the mechanical properties and corrosion resistance were investigated. Microstructural changes, hardness, and corrosion behavior were analyzed as functions of La content and heat treatment parameters. The optimal hardness was achieved at a solution treatment temperature of 500 °C or higher and an aging time of 2 h. In particular, the addition of 0.5 wt.% La led to significant refinement of the α-Al grains, enhancing hardness through the Hall–Petch strengthening mechanism. Furthermore, the combined effects of aging treatment and La addition promoted the formation of a fine, uniform microstructure and stable dispersion of precipitates, resulting in improved mechanical performance. Electrochemical polarization tests revealed that the alloy containing 0.5 wt.% La exhibited the best corrosion resistance. This enhancement was attributed to the formation of the LaCu₂Al₄Si intermetallic compound, which has a lower electrochemical potential than the Al₂Cu phase, thereby reducing corrosion susceptibility within the microstructure. Full article

To achieve the desired material properties of automotive components made by friction welding, post-weld heat treatment is critical. The high temperatures encountered during the friction welding of steels can lead to changes in the microstructure, especially in the heat-affected zones. In the present work, a D3 tool steel and an AISI1010 structural steel are friction welded by varying the rotational speed, and this is followed by post-weld heat treatment. Microstructural evaluation was performed on the friction-welded joints and those produced after heat treatment. Micrographs taken by scanning electron microscope show the formation of distinct zones with ultrafine grains at the interface. Zone measurements at the interfaces of the joints provide information on the proportions of the various zones formed during friction welding. Depending on the rotation speed, the width of the heat-affected zone (HAZ) can range from 10.8 to 19.5 mm, and the width of the total deformed zone varies from 700 to 1070 µm. The width of the fully plasticized zone is between 48 and 380 microns. The region of the friction-welded joint at 1600 rpm shows fine ferrite grains with a width of 48 µm FPDZ, which increase the strength of the joint according to the Hall–Petch equation. Primary carbides are dissolved in the ferrite matrix, and secondary carbides are formed due to the effects of alloying elements such as chromium in particular. Although the formation of secondary carbides cannot be prevented, at higher speeds the primary carbides are dissolved and the tendency to form secondary carbides is reduced. Post-weld heat treatment helps to redistribute these phases and leads to a more homogeneous material structure. The results show that post-weld heat treatment greatly improved the corrosion resistance of dissimilar AISI 1010/D3 steel joints produced by means of friction welding. Coarse grains have been eliminated, and thus the galvanic corrosion at the weld interface is alleviated and reduced. Post-weld heat treatment reduces the corrosion rate and weight loss significantly, by 54.8% and 60%. Full article

This study developed a new heat treatment method, normalizing and stress relief (NSR), to increase productivity compared to spheroidizing annealing (SA). The influence of different microstructures resulting from these heat treatments was investigated in cold-forged steel. Despite a shorter heat treatment time, the mechanical properties of the NSR alloy were found to be similar to those of the SA alloy. The factors influencing the mechanical properties of the experimental alloys were analyzed using the Hall–Petch equation, and the predicted values closely matched the measured strength of hyper-eutectoid steels. The primary factors affecting mechanical properties were microstructure and dislocation density. In the case of the SA alloy, the microstructure was associated with lower strength due to the spherical cementite structure. In contrast, the NSR alloy had lower strength because of a reduced dislocation density. This was achieved via stress-relief heat treatment below the A₁ temperature after phase transformation. Based on the mechanical properties, cold forging simulations showed that the effective stress during cold forging of the NSR alloy was similar to that of the SA alloy. Full article

Nano- and microscale titanium and its alloys have potential applications in semiconductor-based micro-electromechanical systems due to their excellent mechanical properties. The uniaxial tensile mechanical properties and deformation mechanism of polycrystalline pure Ti with five different grain sizes measuring 6.74–19.69 nm were studied via molecular dynamics simulation using the embedded-atom potential function method. The Hall–Petch relationships and the critical grain size of the polycrystalline pure Ti are given. The dislocation migration of grain boundaries is the main deformation mechanism when the grain size exceeds 16.61 nm, which causes a direct Hall–Petch effect. When grain sizes are smaller than 16.61 nm, grain boundary sliding is the preferred deformation mechanism, which causes an inverse Hall–Petch effect. The polycrystalline pure Ti shows the highest tensile strength and average flow stress of 2.70 GPa and 2.15 GPa, respectively, at the 16.61 nm grain size, which is the critical grain size in the Hall–Petch relationships. The polycrystalline Ti is at its highest strength when its grain size ranges from 16 to 17 nm. The current research provides a theoretical basis for the use of pure titanium in emerging technologies at the nanoscale. Full article

TB18 is a newly developed high-strength metastable β-titanium alloy, commonly used in aerospace structural materials, which demands high mechanical performance. By altering the alloy’s microstructure, heat treatment can affect its mechanical characteristics. The alloy was solution treated for one to four hours at 870 °C in order to examine the impact of solution treatment duration. Using X-ray diffraction (XRD) and scanning electron microscopy (SEM), the effects of solution treatment time on the β-phase grain size and its effect on stress distribution during tensile testing were examined. The findings showed that stress concentration during the tensile process was successfully decreased by refining the β-phase grain size. Sample solutions treated for two hours at 870 °C were then aged at various temperatures (510 °C, 520 °C, 530 °C, and 540 °C) to examine the impact of aging temperature. While the mass proportion of the α-phase first climbed and subsequently declined, reaching its maximum at 530 °C, the size of the α-phase increased monotonically as the aging temperature increased. The varies of mass fraction is associated with how the aging temperature affects α-phase nucleation. Tensile studies on TB18 alloy aged at various temperatures showed that while the alloy’s ductility reduced, its strength increased as the aging temperature rose. The Hall-Petch relationship explains this tendency. Full article

The trimodal grain-structured (TGS) carbon nanotube-reinforced aluminum matrix composites (CNT/Al) exhibit better strength–ductility synergy compared to bimodal grain-structured (BGS) composites. The addition of fine grain (FG) to the TGS composites effectively facilitates strain hardening and reduces strain/stress concentrations. In order to address the strain incompatibility in TGS composites, a significant accumulation of geometrically necessary dislocations (GNDs) occurs at the hetero-zone boundaries. This accumulation serves as the key factor in generating additional strengthening and work hardening. By utilizing a multi-mechanism strain gradient model, a quantitative analysis of the contributions made by Hall–Petch, Taylor, and back stress strengthening was conducted. Furthermore, effects of each domain volume fraction on the GND density at the boundaries between heterogeneous domains were carefully and extensively investigated and compared. It is found that the strengthening effect of back stress significantly surpasses that of the Hall–Petch and Taylor strengthening accounting. Compared to BGS composites, the TGS composites are more effective in facilitating strain hardening and reducing strain/stress concentrations, which may lead to a better balance between strength and ductility. Full article

Metal matrix composites (MMCs) reinforced with Copper Oxide (CuO) and Aluminum (Al) 6061 (Al6061) alloys are being studied to determine their mechanical, physical, and dry sliding wear properties. The liquid metallurgical stir casting method with ultrasonication was employed for fabricating Al6061-CuO microparticle-reinforced composite specimens by incorporating 2–6 weight percent (wt.%) CuO particles into the matrix. Physical, mechanical, and dry sliding wear properties were investigated in Al6061-CuO MMCs, adopting ASTM standards. The experimental results show that adding CuO to an Al6061 alloy increases its density by 7.54%, hardness by 45.78%, and tensile strength by 35.02%, reducing percentage elongation by 40.03%. Dry wear measurements on a pin-on-disc apparatus show that Al6061-CuO MMCs outperform the Al6061 alloy in wear resistance. Al6061-CuO MMCs’ strength has been predicted using many strengthening mechanism models and its elastic modulus through several models. The strengthening of Al6061-CuO MMCs is predominantly influenced by thermal mismatch, more so than by Hall–Petch, Orowan strengthening, and load transfer mechanisms. As the CuO content in the composite increases, the strengthening effects due to dislocation interactions between the matrix and reinforcement particles, the coefficient of thermal expansion (CTE) difference, grain refinement, and load transfer consistently improve. The Al6061-CuO MMCs were also examined using an optical microscope (OM), energy-dispersive spectroscopy (EDS), X-ray diffraction (XRD), and scanning electron microscopy (SEM) before and after fracture and wear tests. The investigation shows that an Al6061-CuO composite material with increased CuO reinforcement showed higher mechanical and tribological characteristics. Full article

High-strength steels are widely used in various mechanical production and construction industries for their low cost, high strength and high toughness. Among these, bainitic steels have better comprehensive performance relative to martensite and ferrite. In this paper, from the point of view of its microscopic fine structure and mechanical properties, the high-carbon silicon-containing steel Fe-0.99C-1.37Si-0.44Mn-1.04Cr-0.03Ni was austenitized at high temperature after a brief isothermal treatment at 280 °C and is briefly reviewed. We have used EBSD, TEM and 3D-APT to observe a unique transformation in which high-carbon silicon-containing steels form nanostructured bainite with nanometer widths. Intriguingly, as the isothermal duration decreases, the beam bainite width becomes increasingly finer. When the beam bainite width falls below 50 nm, there is a sudden shift in defect type from the conventional edge-type dislocations to a defect characterized by the insertion of a semi-atomic surface in the opposite direction, which leads to different degrees of reduction in the micro- and macro-mechanical properties of high-carbon silicon-containing steels from 1754 MPa to 1667 MPa. This sudden change in the sub-structural properties is typical of the reverse Hall–Petch effect. Full article

In this study, the molecular dynamics (MD) method was used to study the tensile deformation of polycrystalline γ-TiAl with complex and random grain orientations. Firstly, the tensile deformation was simulated with different average grain sizes (8.60 nm, 6.18 nm, and 4.50 nm) and strain rates (1 × 10⁸ s⁻¹, 5 × 10⁸ s⁻¹, and 1 × 10⁹ s⁻¹). The results show that the peak stress increases with an increase in tensile strain rate, and the peak stress decreases as the grain size decreases, showing an inverse Hall–Petch effect. Upon observing atomic configuration evolution during tensile deformation, it is found that the grain boundary is seriously distorted, which indicates obvious grain boundary sliding occurring. With a further increase in the loading, some dislocations nucleate at the grain boundaries and propagate towards the interior of the grains along the grain boundaries, which demonstrates that dislocation motion is the primary coordination of the mechanical process of the grain boundaries. The dislocation density near the grain boundaries continues to increase, leading to the generation of micro-cracks and eventually causing material failure. Another interesting phenomenon is that the grains rotate, and the specific rotation angle values of each grain are quantitatively calculated. Grain rotation relaxes the stress concentration near the grain boundaries and plays a toughening role. Consequently, the plastic deformation behaviors of polycrystalline γ-TiAl are achieved through the grain boundary mechanical process, that is, grain boundary sliding and grain rotation. Full article

Single-pass-welding thermal cycles with different peak temperatures (T_p) were reproduced by a Gleeble 3800 to simulate the heat-affected zone (HAZ) of a Fe-24Mn-4Cr-0.4C-0.3Cu (wt.%) high manganese austenitic steel. Then, the effect of T_p on the microstructure and mechanical properties of the HAZ were investigated. The results indicate that recrystallization and grain growth play dominant roles. Based on this, the HAZ is proposed to categorize into three zones: the recrystallization heat-affected zone (RHAZ) with a T_p of 700~900 °C, the transition heat-affected zone (THAZ) with a T_p of 900~1000 °C, and the coarse grain heat-affected zone (CGHAZ) with a T_p of 1000~1300 °C. The recrystallization fraction was 29~44% in the RHAZ, rapidly increased to 87% in the THAZ, and exceeded 95% in the CGHAZ. The average grain size was 17~19 μm in the RHAZ, slightly increased to 22 μm in the THAZ, and ultimately increased to 37 μm in the CGHAZ. The yield strength in the RHAZ and THAZ was consistent with the change in recrystallization fraction, while in the CGHAZ, it satisfied the Hall–Petch relationship with grain size. In addition, compared with the base material, the Charpy impact absorbed energy at −196 °C decreased by 22% in the RHAZ, but slightly increased in the CGHAZ. This indicates that the theory of fine grain strengthening and toughening is not entirely applicable to the HAZ of the investigated high-Mn steel. Full article