Peak-aged Condition Research Articles

Synergistic effects of cold rolling and age hardening on the hardness and tensile characteristics of AA6061 hybrid composites

The present study involves the fabrication of aluminium alloy 6061 matrix hybrid composites with varying weight fractions of silica sand and copper particles by employing the conventional stir casting method. The combined influence of age hardening (AH) and low temperature thermomechanical treatment (LTMT) on the hardness and tensile properties of AA6061 hybrid composites was investigated. The uniform dispersion of the particles in the matrix was confirmed by microstructure analysis and the improvement of Brinell hardness values. The composites exhibited higher tensile strength and hardness than the base alloy. Both AH and LTMT enhanced the properties of the hybrid composites and a comparison between them revealed the best results for LTMT hybrid composites. The LTMT hybrid composite with 3 wt% silica sand and 3 wt% copper (3S3C) subjected to 12% rolling deformation and aged at 100 °C had the highest hardness and tensile strength of 144.26 HV and 290 MPa respectively. The hardness and tensile strength of AA6061-3S3C hybrid composite subjected to LTMT in peak aged condition showed an improvement of 125 and 97% respectively when compared with those of AA6061 alloy. Fracture surface analysis of the thermomechanical treated composites in peak aged condition showed a mixed mode of failure dominant with the ductile fracture.

Dry sliding wear behavior of sinter forged micrometric and nanometric yttrium oxide reinforced AA-7075 matrix composites

This study aims to investigate the dry sliding wear behaviour of AA-7075 based metal matrix composites developed by powder metallurgy route. AA-7075 metal matrix composites have been developed with 1–15 vol% micrometric yttrium oxide particulate reinforcement and 0.1–3 vol% nanometric yttrium oxide particulate reinforcement by sinter forging.The matrix and reinforcing powders were blended together to obtain a homogeneous composite powder mixture which was cold compacted and further sintered under pure nitrogen atmosphere. The sintered compacts were forged in a closed die to attain full density. The hot forged samples were further artificially age hardened to peak hardness. Wear behavior of AA-7075 and its composites at peak aged condition were investigated at various loads and sliding speeds. The coefficient of friction and wear rate were determined with respect to different volume fractions of micrometric and nanometric yttrium oxide additions to AA-7075 alloy matrix. The overall wear at a constant volume fraction was found to be lower for the compositions having nanometric Y2O3 as compared to micrometric Y2O3. Further the basic wear mechanism of pure aluminum 7075 alloy and reinforced composites consisted of adhesive wear with plastic deformation followed by abrasive wear (due to hard reinforcement particles).Material strengthening by precipitation hardening and reinforcement addition and the role of the forging operation and yttria reinforcements in the removal and uniform distribution of oxide layers present on the AA-7075 powder particles were accountable for the improvement in the wear resistance of the composites.

Section dimension induced microstructure and mechanical properties variations of sequential solidified sand–cast Mg–10Gd–0.2La–0.1Zn–0.4Zr (wt%) alloy

Casting dimension significantly influences the quality and performance of finished products when employing a sequential solidification process. Tapered cylinder Mg–10Gd–0.2La–0.1Zn–0.4Zr (wt%) castings with variable section dimensions were fabricated by sand–cast process, and the role of section dimension on the solidification behavior, microstructures and mechanical properties under different thermal conditions were systematically investigated. Increasing section dimension from Φ23 mm to Φ32 mm, the average cooling rate during solidification decreases from 1.70 °C/s to 0.86 °C/s, and the actual chemical composition of Gd element descends from 10.39 ± 0.11 wt% to 10.05 ± 0.06 wt%. Meanwhile, the primary α–Mg grains are coarsened in size from 29 ± 2 μm to 39 ± 3 μm, and the area ratio of the secondary phase degrades from 1.87 ± 0.19 % to 1.14 ± 0.31 %. With a solution treatment of 500 °C × 8 h, the area ratio of the residual secondary phase rises from 0.55 ± 0.06 % to 0.75 ± 0.12 %, accompanied by the decrease of Gd solubility with a grand value of 0.33 wt%. The decline of Gd solubility is unfavorable for the precipitation of strengthening phases during the ageing treatment and leads to a reduction of ∼13.5% in the area number density of the β′ precipitates. The strength and ductility at ambient temperature simultaneously worsen with increasing section dimension, in which the yield strength, ultimate tensile strength and elongation respectively descend from 230 ± 7 MPa, 364 ± 7 MPa and 8.5 ± 1.1 % to 219 ± 6 MPa, 336 ± 5 MPa and 5.5 ± 0.9 % in the peak–aged condition. The strength debasement is due to the grain coarsening and lower number density of the β’ precipitates, while the reduced ductility is attributed to the coarser grains and higher content of the residual secondary phase with larger size. Casting dimensions should be meticulously designed when developing high–performance Mg alloys by sequential solidification processes.

Study on the microstructure and mechanical properties of VW73B alloy at high extrusion ratio

The microstructure and mechanical characteristics of VW73B prepared by a high extrusion ratio (70:1) were studied. High-strength plastic VW73B alloy containing long-period structural phase (LPSO) was obtained by extrusion process. OM, SEM, TEM, and EBSD were used to investigate the relationship between microstructure and mechanical characteristics of VW73B. The findings indicate that VW73B presents complete dynamic recrystallization after deformation, and there are 14H-LPSO phases, SFs, and a large amount of β´ phase, which are precipitated after aging treatment. The UTS, YS, and EL of VW73B in peak aging state are 406 MPa, 339 MPa, and 9%, respectively. The β´ phase, LPSO phase, poor texture, and fine grain strengthening of VW73B contribute to its exceptional characteristics.

On the influence of crystallographic texture on cyclic hardening of an AlMgSi alloy

The influence of crystallographic texture on hardening achieved by cyclic loading at room temperature, was tested by comparing samples from an axisymmetric round bar and a flat profile, both made of non-recrystallized, extruded profiles of similar AlMgSi alloys (AA6082). It was found that the plastic strain accumulated during the cyclic loading was significantly (nine times) larger for the flat profile. Tensile testes of the cyclically hardened samples revealed that in spite of the large accumulated plastic strain during cyclic hardening of the flat sample, the local tensile strain at fracture in the necking region was similar to the peak aged conditions obtained by artificial aging.

Elucidating the tensile work hardening behaviour of precipitate containing Al0.3Co1.5CrFeNi1.5Ti0.2 high entropy alloy

A significant amount of work has been performed, since the last decade, on designing novel high entropy alloy (HEA) compositions. However, the effort on concluding a universal mechanism on the strain hardening behavior of these alloys with precipitates is limited. The current study is designed with an aim to comprehend the mechanical behavior of Al0.3Co1.5CrFeNi1.5Ti0.2 HEA in solution treated and aged conditions. The results show that the peak aged condition of sample contains two types of precipitates – B2 and L12 (γ′) of approximately 800 nm and 40 nm size, respectively. They are found to be responsible for a significant increase in strength in aged samples than solution treated ones. Deformation was found to occur mainly by planar slip on the {111} primary slip planes. Noticeable strain hardening behavior was attributed to the formation of stacking faults (SFs) and Lomer-Cottrell (LC) locks, inhibiting the dislocation motion. Numerous paired dislocations formed due to inhibition of slip by the ordered γ′ precipitates, coexist with a few Orowan loops in the peak-aged alloy after deformation. However, the primary strengthening mechanism was found to be the shearing of γ′ precipitates by partial dislocations. Shearing of nanosized γ′ precipitates by partial dislocations is energetically favourable for the system than shearing by full dislocations. Overall, this study enhances the understanding of the precipitation strengthening and strain hardening mechanisms in high entropy alloys.

Unified Interpretations of Two Kinds of Needle-Shaped Precipitates Using Transmission Electron Microscopy and Small-Angle Neutron Scattering in Aged Al-Mg2Si(-Cu) Alloys.

This study investigates the nanostructural properties of pseudo-binary Al-1.0Mg2Si (mass%) alloys with and without 0.5Cu using transmission electron microscopy (TEM) and small-angle neutron scattering (SANS). The TEM results show that both alloys exhibit extra electron diffraction spots related to MgSiMg second clusters at peak-aged conditions. High-resolution TEM images have revealed that the second cluster exists as a needle-shaped precipitate that is shorter and thicker than the β″ phase. We found that the second cluster, which we referred to as the R phase in this paper, is more likely to form partially along the longitudinal axis of a random-type precipitate. Thus, the atomic arrangement in the random-type precipitate is not completely random. SANS is used to quantify the size and volume fraction of the observed needle-shaped precipitates since the R phase is difficult to observe with TEM. The R phase forms even in the Cu-free alloy, but the volume fraction is low, and the growth and formation are retarded near the peak-aged conditions. Undoubtedly, the Cu addition has the effect of stabilizing the growth of the R phase and also promoting its formation. Therefore, the R phase also contributes to the increase in hardness at both under- and peak-aged conditions in the Cu-containing alloy in addition to the strengthening β″ phases.

Effects of aging temperature on microstructure and mechanical properties of PH 13-8Mo stainless steel

Precipitation hardening stainless steel (PHSS) possesses high strength, impact resistance, and corrosion resistance, making it extensively employed in aerospace, nuclear power equipment, and petrochemical industries. The precipitates and reversed austenite (RA) generated during heat treatment significantly influence the properties of PHSS. This study investigates the impact of aging temperature (480–620 °C) on PH 13-8Mo stainless steel. As the aging temperature increased from 480 °C to 620 °C, the yield strength (YS) and ultimate tensile strength (UTS) initially increased and then decreased, while the impact energy initially decreased and then increased. At an aging temperature of 510 °C, the strength and hardness reach their maximum values, indicating peak aging conditions. The microstructure after aging treatment is lath martensite, RA and NiAl. With increasing aging temperature, the size of NiAl precipitates increases, accompanied by a rise in RA content. The quantitative analysis assessed the contributions of various strengthening mechanisms (precipitation strengthening, solid solution strengthening, grain refinement strengthening, dislocation strengthening, etc.) to YS. Quantitative calculations revealed that the precipitation strengthening effect was most pronounced at an aging temperature of 510 °C.

Effect of filler materials on the tensile properties and fracture toughness of laser beam welded AA2198 joints under different ageing conditions

The influence of different filler materials on the microstructure, tensile mechanical properties, and fracture toughness of laser beam welded AA2198 alloy as well as the effect of different artificial ageing heat treatments were investigated in this contribution. The welded joints were produced when exploited either, Al-Si (AA4047) or Al-Cu (AA2319) filler wires. It was shown that the Al-Si filler wire gave higher hardness values in the fusion zone when compared to the Al-Cu filler wire. The post heat treatment of the welded specimens increased by approximately +100 % the yield stress and by +20 % the ultimate tensile strength with increasing ageing time, in a similar way to the non-welded material. Elongation at fracture decreased in an inverse proportional manner to yield stress. Artificial ageing before welding gave improved elongation at fracture for the over-aged condition only. The quality index concept showed that the artificial ageing before the welding did not succeed in giving a higher quality of the welded joints, for both filler materials investigated. The opposite was shown on the post heat treatment, where the peak-aged condition increased substantially the ‘quality’ of the welded joints with both filler materials. The critical stress intensity factor was increased by +25 % for the under-aged condition for the post-welded condition and both investigated filler wires as a result of the balance between medium values in strength and ductility, respectively.

Effect of grain size and precipitates on hydrogen embrittlement susceptibility of nickel alloy 718

The present work reports on the effect of grain size and its combined effect with precipitation on hydrogen uptake and hydrogen embrittlement (HE) susceptibility of alloy 718. HE susceptibility of fine-grained microstructure obtained by friction-stir processing (FSP) is compared with standard heat-treated conditions. Melt extraction measurements on hydrogen pre-charged samples reveal that fine-grained FSP condition compared to solution-treated (ST) condition contains increased hydrogen content, indicating that higher vol% of grain boundaries and density of dislocations promote trapping. The presence of γ’ and γ” phases reduces hydrogen uptake in both fine-grained and aged (FSP-A) and peak-aged (PA) conditions, indicating a lack of affinity of these phases to hydrogen. Under tensile loading, for identical pre-charging conditions, the FSP (with fine grains) and ST (with coarse grains) conditions display similar susceptibility to HE. However, the FSP-A condition with refined grains and precipitates showed substantially reduced HE susceptibility than coarse grained PA condition, measured through % reduction in area. The finding that fine-grained microstructures absorb more hydrogen than larger grained microstructures yet have similar or reduced susceptibility to HE, demonstrates the inherent HE resistant character of fine-grained microstructures.

A Yield Stress and Work Hardening Model of Al-Mg-Si Alloy Considering the Strengthening Effect of β" and β' Precipitates.

Precipitates are the primary source of strength for the Al-Mg-Si alloy. Aluminum alloy in the peak-aged state mainly contains β" and β' precipitates. Most of the literature has only considered the strengthening effect of β". Here, we develop a single-crystal intensity model including both precipitate enhancement effects for the first time. This model was subsequently implemented into a crystal plastic finite-element method to model the uniaxial tensile process of a polycrystalline aggregate model of Al-Mg-Si alloy. The simulation results for uniaxial stretching are in good agreement with the experimental results, confirming that the constitutive parameters used for the single-crystal strength model with two precipitates are based on realistic physical implications. Furthermore, by comparing the uniaxial tensile simulation results of a peak-aged alloy considering the actual precipitated phase composition of the alloy with those assuming that the precipitated phase is only the β" phase, the predicted tensile strength of the former is around 5.65% lower than that of the latter, suggesting that the two kinds of precipitation should be separately considered when simulating the mechanical response of Al-Mg-Si alloy. It is highly expected that the present simulation strategy is not limited to Al-Mg-Si alloys, and it can be equally applied to the other age-enhanced alloys.

Effect of microstructure on the effectiveness of hybridization on additively manufactured Inconel718 lattices

This work aims to investigate the effect of the material microstructure on the effectiveness of hybridization in additively manufactured Inconel718strut-based lattices. Two microstructures, namely the as-built solid solution and a peak aged condition, are coupled with three hybrid architectures formed by alternating face centred cubic (matrix) and octet-truss (reinforcement) domains containing 1, 8, and 64 unit cells. Digital image correlation is utilized to map the local strain distribution during compression, and finite element analysis is utilized to map stress localization. It is shown that in the as-built condition the mechanical behavior of all the hybrid lattices was very similar to that of the single-oriented components, irrespective of the reinforcement size. In the peak-aged lattices, on the contrary, including octet-truss reinforcements of sufficiently small size resulted in an increase inmechanical stability, damage tolerance, and absorbed energy, as interphase boundaries act as obstacles to shear band propagation. It is also shown that effect of hybridization is a function of the size of the reinforcements. In particular, below a critical size, the lattice behaves as a reinforced “single-phase” structure, rather than a two-phase architecture. This work defines guidelines for the design of robust lattices manufactured by laser powder bed fusion.

Precipitation kinetics of gamma double prime phase during direct aging treatment of Inconel 718 superalloy additively manufactured by selective laser melting

While direct aging of Inconel 718 nickel-based superalloy from the as-built state is known as a promising practice to tune the mechanical properties, the precipitation kinetics of γ″ phase, as the main precipitating phase, has received less attention. Accordingly, in the present work, post-processing in the form of the direct aging treatment of Inconel 718 superalloy manufactured by the laser powder bed fusion additive manufacturing, also known as selective laser melting (SLM), was systematically investigated by microstructural analysis and hardness measurements. It was revealed that the peak aged condition for direct aging can be achieved at much shorter holding times compared to aging after homogenization/solutionizing heat treatment. Moreover, the Johnson–Mehl–Avrami–Kolmogorov (JMAK) analysis based on both hardness measurements and microstructural analysis were applied to unravel the γ″ precipitation kinetics, which respectively led to the precipitation activation energies of 160 and 157 kJ/mol, which are consistent with the activation energy for the diffusion of Nb in IN718 superalloy manufactured by SLM. Moreover, the Lifshitz–Slyozov–Wagner (LSW) diffusion-controlled growth theory was modified to become applicable for investigating the precipitation kinetics during the evolution of the volume fraction of the precipitating phase, which also led to the activation energy of 157 kJ/mol. These results can also shed light on the procedures used for investigating the kinetics of phase transformations during aging of additively manufactured Inconel 718 superalloy.

Yield strength modelling via precipitation/recovery kinetics in rapidly solidified thin-strip cast AA6005 AlMgSi sheets subjected to cold rolling and direct aging

A comprehensive and experimentally verified yield strength model of AA6005 Al–Mg–Si sheets rapidly solidified via a novel Thin Strip (TS) casting route is developed and presented. The cast sheets were cold-rolled and directly aged via a heat-treatment process (termed TSH) that effectively utilizes the increased solute supersaturation of matrix due to the high casting cooling rates experienced. The TSH conditions were optimized based on the hardness and tensile data, with the peak aging conditions found to be 160°C-4 hrs, 180°C-1 hr and 200°C-15 min. The TEM analysis revealed that, due to the presence of prior cold work, β′ precipitates formed during TSH, i.e., as opposed to the β" precipitates that form upon a typical T6 aging treatment. Also, while the total precipitate volume fraction was comparable among the three peak aging conditions, the sample aged at 200 °C exhibited a lower peak aging strength (300 MPa vs. ∼315 MPa in the other two conditions), i.e., due to a higher dislocation recovery rate and therefore a lower strengthening contribution from the remaining cold work. Interestingly, at each temperature, aging beyond the peak aging time still resulted in an increase in the precipitate volume fraction. The concurrent drop in the yield strength could be explained by the offsetting effect of the recovery of the remaining cold work. Therefore, thanks to the sufficiently high solute supersaturation of the matrix during TSH, together with the remaining cold work (as well as the formation of β′), peak aging at 180 °C is achieved after only 30 min to 1 h, i.e., as opposed to generally 4–6 h of aging needed for a traditional T6 aging. This gives the low-cost, less energy-intensive TS-cast sheets also a significantly faster response to the paint-baking process (typically performed at near 180 °C for around 30 min), thus allowing for a higher strength achieved via a typical automotive body fabrication route. Finally, a robust model of precipitation/recovery kinetics, incorporating precipitate aspect ratio evolution, was developed to simulate the yield strength during TSH. The model predicts a peak-aging time of ∼100 min, aligning well with the observed 60–120 min interval measured from the tensile test results.

Accelerating the precipitation kinetics of nano-sized T1 and S’ phases in Al-Cu-Li alloys by hot-deformation and creep-aging

ABSTRACT It is well known that a Cu/Li ratio over 4.0 leads to significant precipitation hardening in the third generation of Al–Li alloys, which have been widely used in aerospace and aeronautic industries. However, increasing Cu levels not only cancels some gains in weight reduction but also results in reductions in ductility when the traditional age-hardening process is adopted. In this study, we show that higher strength and ductility can be achieved simultaneously by replacing traditional artificial aging with new creep aging and tailoring the entire process from casting to age hardening without changing any nominal chemical compositions. Surprisingly, the precipitation kinetics of AA2060 alloy is significantly enhanced through the combination of hot extrusion, creep aging, and pre-strain compared to traditional artificial aging. For example, at 160°C, it follows the transformation path of supersaturated solid solution (SSSS)→GP zones + δ′+T1 precursors which will further transform into T1 +S’; at 200°C, SSS→ GP zones, and they transform into T1 + S’ immediately. The precipitation of θ′ and δ′ phases is significantly inhibited at elevated temperatures due to the competing relationship with T1 and S’ phases at a peak-aged state. Contrary to traditional knowledge in Al–Li alloys, we have found that the greater extrusion ratio at 33.0 and higher aging temperature at 200°C can give a much higher peak aging strength with average ultimate tensile strength 659 MPa.

Direct ageing of LPBF Al-1Fe-1Zr for high conductivity and mechanical performance

The novel Al-1Fe-1Zr alloy leverages the non-equilibrium solidification conditions characteristic of the laser powder bed fusion (LPBF) process, namely a high thermal gradient (G) and solidification front velocity (R). The multiscale characterization of its microstructure in as-built and peak-aged conditions by SEM, TEM with EDS and automated crystal orientation mapping (ACOM), brings new insights on alloy design for LPBF. The solidification conditions permit the solute supersaturation of Fe and Zr, with the latter precipitating as L12-Al3Zr nanoparticles following ageing, bringing a high strengthening contribution. In conventional Al alloy ingots, Fe tends to create coarse particles which are detrimental to ductility. Here the Fe particles show a fine globular morphology in the as-built condition, and fine faceted Fe-rich intermetallics are obtained upon ageing. Nanoindentation and in situ tensile tests in the SEM coupled with microscale strain measurements shed light on the relation between microstructural and strain heterogeneities in the as-built condition. Our characterization results for this new Al-1Fe-1Zr grade are synthesized into a simple model for its solidification upon LPBF. In particular, the origin of melt pool boundaries is revealed. These are associated with Fe depletion caused by an early planar growth front, and the evolution of these zones upon ageing is presented. With a high potential for industrial applications, the novel alloy with the two elements Zr and Fe exhibiting low solubility at equilibrium and diffusivity in the Al matrix permit to achieve high conductivity (27 MS/m) and yield strength (330MPa) after a simple direct ageing step at 400°C/4h.

Effect of pre-stretching on the precipitation evolution and mechanical properties of GW63K magnesium alloy

The regulation of precipitates remains a critical issue in the advancement of high-strength magnesium-rare earth (Mg-RE) alloys. An effective method to manipulate the precipitates in Mg-RE alloy is through cold deformation before ageing. In this work, we investigated the impact of pre-deformation before artificial ageing on the microstructures and mechanical properties of GW63K alloy. The results reveal that, pre-stretching introduces <a> type dislocations which facilitate uniform nucleation in the matrix of 200 °C-aged alloys and non-uniform nucleation on the dislocations of 225 °C-aged alloys. Compared with the undeformed alloy after peak ageing treatment, pre-deformation increases the number density of β' precipitates with reduced average size. Semi-quantitative estimations show that precipitation strengthening and solid solution strengthening are the dominant contributors to strengthening in peak-aged alloys at temperatures of 200 and 225 °C respectively. Furthermore, pre-deformation not only introduces the dislocation strengthening of approximately 25 and 26 MPa, but also enhances the precipitation strengthening by 23 and 17 MPa at 200 and 225 °C peak-aged conditions, respectively.

Research on hydrogen embrittlement behavior of L-PBF 18Ni(300) maraging steel by experiments and numerical simulations

Affected by complex microstructural evolution, dominant factors in hydrogen embrittlement (HE) of maraging steels in different aging states were not clear. This fundamental issue was clarified systematically by experiments and numerical simulations in this work. In under-aged and peak-aged states, diffuse coherent ω/matrix interfaces and sharp semi-coherent η-Ni3Ti/matrix interfaces acted as reversible traps, respectively. Their different interfacial properties determined the differences in trap density in the two states. The lowest trap density led to the fastest hydrogen diffusion and the highest hydrogen content in lattice, causing the worst HE in under-aged state. In peak-aged state, the situation was relieved by the highest trap density. In over-aged state, the newly formed Laves-Fe2Mo/matrix interfaces acted as slightly deeper traps compared with the η-Ni3Ti/matrix interfaces, but the reduction in interfacial area decreased trap density and accelerated hydrogen diffusion instead. Even so, the improvement in ductility by reverted austenite further relieved HE susceptibility in this state.

Mechanical properties of cryo-rolled aluminium alloy AA2219 at 300, 77 and 20 K

In the present work, AA2219-T87 plates (40 mm thickness) in two different pre-deformation conditions: without solution treatment (WST) and solution treatment (ST) are cryo rolled (at 77 K) into sheets (imparting reduction ratio of ∼97.2%) and rods (reduction ratios of 30, 50 and 70%). The mechanical performance and ageing kinetics of the cryo rolled sheets are compared with cold rolled sheets, to assess any beneficial effect. The as-rolled sheets and rods were subjected to duplex ageing at 175 °C/3 min + 125 °C/8 h, which reduces the effective ageing time by several hours compared to industrially practiced ageing time for peak aged tempers. The microstructures of the ST sheets and rods in as-rolled and peak aged conditions consist of very fine structure with high dislocation density in the form of tangles. Peak ageing treatment generated uniform distribution of semi-coherent θ′ precipitates with slight decrease in dislocation density due to partial recovery of the structure. Tensile properties are evaluated for the sheets and rods in as-rolled and peak aged conditions at ambient (300 K) and cryogenic (77 and 20 K) temperatures. Significant improvement in the strength and ductility values were observed in as-rolled and peak aged conditions for ST sheets and rods, whereas tensile properties in WST condition were significantly lower. The combined effect of suppression of dynamic recovery (DRV), grain size refinement, dislocation strengthening and precipitation hardening from the θ′ precipitates are responsible for achieving optimum strength and ductility balance at temperatures up to 20 K. Based on the outcomes of the present work, severe deformation through cold/cryo/caliber rolling of the ST sheets and rods followed by peak ageing is very effective in improving the cryogenic strength and ductility over conventional processed routes for AA2219 alloy.

Crystallography and diffraction patterns of the precipitates in Cu-3 wt% Ti alloy

Cu–Ti alloys are candidates for replacing Cu–Be alloys owing to their excellent mechanical properties, bending properties, and stress relaxation resistance. However, the precipitation behavior of Cu–Ti alloys remains poorly understood. In this study, diffraction patterns, orientations, and morphologies of continuous and discontinuous precipitates in a Cu–3 wt% Ti (Cu–3Ti) alloy are investigated by transmission electron microscopy (TEM) and high-resolution transmission electron microscopy (HRTEM). In the peak-aging condition, numerous rod-like nanosized continuous precipitates (CP) of β′-Cu4Ti are uniformly distributed in the Cu–3Ti alloy. The CP retain their tetragonal structure, and their orientation relationships with the matrix are determined as [001]Cu//[001]β' and (010)Cu//(310)β', exhibiting six variants. With increasing aging time, discontinuous precipitates (DP) of β-Cu4Ti grow at the grain boundaries, displaying an orthorhombic structure (a = 0.453 nm, b = 0.4342 nm, and c = 1.293 nm). The orientation relationships between the DP and the Cu-matrix are determined as (Laughlin and Cahn, 1975; Han et al., 2016; Datta and Soffa, 1976; Han et al., 2020; Huang et al., 2023; Soffa and Laughlin, 2004; Wang et al., 2021; Si et al., 2016; Markandeya et al., 2004; Nagarjuna et al., 2001) [1-10]Cu//[501]β and (111)Cu//(010)β. Typical diffraction pattern models of the CP and DP in different directions were simulated, and the simulations were in good agreement with the experimental data.