Subsequent Aging Treatment Research Articles

Improving strength and elongation combination of Cu–9Ni–6Sn-(0.2Nb) alloys by pre-annealing and aging treatment

Basing on the concept of processing rote design and the compositional design, a good combination of strength and ductility in a Cu–9Ni–6Sn-0.2Nb alloy was successfully achieved by the combination of Nb addition, pre-annealing and the subsequent aging treatment. The microstructure evolution, mechanical properties and electrical conductivity on the Cu–9Ni–6Sn alloys with Nb addition were investigated in details. The results indicated that NbNi3 particles efficiently suppressed the growth of recrystallized grains in the Cu–9Ni–6Sn-0.2Nb alloy and fined grains were achieved during pre-annealing treatment, the grain size being refined from ∼49.5 μm to ∼2.5 μm. After aging treatment, an optimal combination of ultimate tensile strength 1000 MPa, yield strength 825 MPa, elongation 13%, Vickers hardness 300 HV and electrical conductivity 13.1 %IACS were attained in the Cu–9Ni–6Sn-0.2Nb alloy by 80% cold-rolling, pre-annealing at 850 °C for 3 min and aging at 350 °C for 10 h. Especially a good strength with excellent elongation was firstly achieved in Cu–Ni–Sn alloys via the combination of Nb addition, pre-annealing and aging treatment in this study. Strengthening mechanism has been quantitatively established, indicating that the grain boundary and precipitation strengthening play important roles in enhancing the yield strength of the alloy with Nb addition. This study aims to provide a new insight into improving the comprehensive properties of Cu–Ni–Sn alloys, and supplies basis for the microstructure and mechanical property control of the materials.

Correlation between microstructure and shape memory properties in an Fe-9.5Ni-6.5Mn dual phase steel developed by intercritical annealing and subsequent ageing

Research was conducted to investigate the shape memory properties related to the microstructure in an Fe-9.5Ni-6.5Mn (wt.%) dual phase steel developed by intercritical annealing and subsequent ageing. Electron back scattering diffraction (EBSD) analysis and high resolution transmission electron microscope (HRTEM) images revealed that the microstructure of the initial steel in the solution-annealed condition was a typical lath α′-martensite with a high density of dislocations. During the intercritical annealing treatment of the solution-annealed steel at 590 °C in the ferritic-austenitic (α+γ) two-phase region for various annealing times, a part of α′-martensite transformed to the reversed γ-austenite with a difusionless shear nature, resulting in the development of a dual-phase (α′+γ) steel. Also, subsequent ageing treatment of the intercritically annealed steel at 480 °C for 3.6 ks led to formation of the nanoscale θ-NiMn precipitates in the dual-phase microstructure. The experimental results indicated a maximum shape recovery of ∼55% at 1% pre-strain for the intercritically annealed steel for 1.8 ks, followed by subsequent ageing. The presence of austenite phase reinforced by precipitates in the dual-phase steel was the main reason for appearance the shape recovery. In addition, the existence of isolated stacking faults in the reversed austenite region after straining confirmed that the occurrence of the austenite to ε-martensite transformation (γ→ε) under loading and the reverse transformation (ε→γ) upon heating are the main causes of the shape memory effect in the studied steel.

Effect of Rolling Temperature on Microstructure and Properties of Al-Mg-Li Alloy.

In this study, the effects of hot-rolled processes at different temperatures (420 °C, 450 °C, and 480 °C) and subsequent solid solution and aging treatments on the microstructure, mechanical properties, and corrosion properties of Al-Mg-Li alloys with trace Sc and Zr addition were investigated. The aging treatment of rolled sheets after solid solution treatment could obtain Al3Li particles and Al3(Sc, Zr)/Al3Li core-shell particles to improve the mechanical properties of Al-Mg-Li alloy products effectively. The results showed that, as the rolling temperatures increased from 420 °C to 480 °C, the alloy's ultimate tensile strengths and yield strengths increased, while the corrosion resistance decreased. The increase in rolling temperature increased the precipitation-free zone (PFZ) width of the alloy, which undermined the corrosion resistance of the alloy. Moreover, elevating the hot rolling temperature changes the texture strength of the alloy. Particularly in the 480 °C hot-rolled sample, the decrease in the Brass texture strength and the increase in the S texture and Copper texture strength led to an increase in the Taylor factor (M). The increase in rolling temperature also raised the number density of the Al3(Sc, Zr)/Al3Li core-shell particles. The presence of such particles not only inhibits grain growth but also changes the strength mechanism from dislocation cutting to Orowan bypassing. Due to the combination effect of grain morphology, texture evolution, and precipitation behavior, the 480 °C hot-rolled sample had the highest properties.

Effect of Natural Ageing on Subsequent Artificial Ageing of AA7075 Aluminum Alloy

The effects of natural ageing treatment prior to artificial ageing treatment on the microstructures and mechanical properties of AA7075 Al-5.7Zn-2.6Mg-1.5Cu-0.18Cr-0.08Mn-0.05Si-0.17Fe (wt.%) aluminum alloy have been investigated. The hardness of solution-treated samples (91.0 HV) profoundly increased to 146.8 HV after 7 days of natural ageing. The purpose of the present work was to examine the kinetic hardening evolution in subsequent artificial ageing treatments of samples naturally aged for 7 days and their counterparts without natural ageing. The former were labelled as NA-7d samples, and the latter, NA-0d samples. After artificial ageing at 120 °C for 2 h, the hardness of NA-0d samples increased rapidly to 148.2 HV, which was approximately the same as that of the specimens with natural ageing for 7 days, compensating for the prior state of lower hardness without natural ageing. After being treated at 120 °C for 16 h, the ultimate tensile strength (UTS) and yield strength (YS) of NA-7d reached the highest value, respectively, 601 MPa and 539 MPa, followed by a slight decrement of UTS when aged to 24 h. On the other hand, NA-0d specimens aged at 120 °C for 16 and 24 h showed nearly the same UTS (598 MPa); the former possessed YS of 538 MPa, and the latter, 545 MPa. The results presumably reveal that the peak ageing condition for NA-0d samples can be achieved under 24 h ageing at 120 °C. Under the same treatment at 120 °C for 24 h, the size of η’ phase in NA-7d sample (with a length of 4.96 nm) coarsened and grew larger than that in NA-0d sample (with a length of 3.46 nm). In addition, some η’ phase in the NA-7d sample was found to be transformed into the η2 phase. The results indicated that the naturally aged specimens (NA-7d) reached the peak ageing condition earlier, but did not significantly enhance the UTS in AA7075 aluminum alloy, as compared to the samples without prior natural ageing (NA-0d).

Edge-crack free and high mechanical properties of AA7075 sheets by using cryorolling and subsequent aging

In this study, AA7075 sheets were processed by cryorolling and room-temperature rolling respectively, and subsequent aging. The microstructure evolution and mechanical properties of AA7075 sheets were investigated by hardness measurements, tensile tests, X-ray diffraction, scanning electron microscopy and transmission electron microscopy. Results show that with the rolling reduction ratio of 80%, the room-temperature rolled samples had massive edge cracks, while the cryorolled samples were in good shape and without any cracks. The improved ductility of materials in cryogenic environments, the reduced precipitation and the absence of shear bands in sheets during cryorolling contributed to the reduced edge cracks. Compared to solution treated samples, the yield strength and ultimate tensile strength of cryorolled samples were increased by 155% and 44%, respectively, and the elongation decreased as a loss, which is obviously better than that of room-temperature rolled samples. After the subsequent aging treatment, the strength and ductility of the rolled samples were simultaneously improved, the yield strength of cryorolled + peak-aged sample was increased by 44 MPa and the elongation was increased by 68% compared with those of the cryorolled samples. Compared with room-temperature rolled + peak-aged samples, the strength of cryorolled + peak-aged sample was higher, and the elongation to failure and uniform elongation were increased by 58% and 72%, respectively. Numerous nanosized GP zones and η' phases were precipitated after aging, and the precipitation strengthening is the main contributor to the strength enhancement of the samples after aging. The improved ductility of cryorolled + peak-aged samples is mainly due to the combined effect of dislocation annihilation, uniform deformation and fine precipitates in them.

A large compressive recoverable strain induced by heterogeneous microstructure in a Ni50.6Ti49.4 shape memory alloy via laser powder bed fusion and subsequent aging treatment

Laser induced highly metastable microstructure provides the possibility for the tunable precipitation behavior and mechanical/functional properties via direct aging treatment. In this paper, Ni-rich NiTi-based samples were fabricated by laser powder bed fusion (LPBF) and then were directly aged for different aging times that spanning three time-scales (10 min-100 h). The results showed that through the aging treatment, a heterogeneous microstructure consisting of Ti 4 Ni 2 O x nanoparticles, nanoscale Ni-rich precipitates, dislocation structures, and martensitic twin variants formed in the matrix. Due to the change in the elastic strain field, the short time aging treatment tended to induce (001) compound twins, while the long time aging assisted in the formation of< 011 > type II twins. The temperature-induced and deformation-induced phase transformation behavior were further studied. With the progress of precipitates, it was found that a rapid evolution from a single-stage phase transformation to a multi-stage one occurred. During the cyclic compression, the sample aged for 1 h showed the most excellent superelasticity with initial recoverable strain of 0.089 and steady recoverable strain of 0.087, as well as good cyclic stability. • Microstructure evolution of LPBF-ed Ni-rich NiTi SMA with the aging time was disclosed. • Effects of aged microstructure on transformation behavior and pseudoelasticity were elaborated. • A large compressive recoverable strain and its good cyclic stability were achieved via the proper aging treatment.

Effect of intercritical annealing and subsequent ageing on the microstructure and mechanical properties of a medium Ni–Mn low carbon steel

The aim of this research was to develop a medium Ni–Mn dual phase steel with a combination of relatively high strength and good formability for industrial applications. Accordingly, this research was conducted to examine the effects of intercritical annealing and subsequent ageing treatments on the microstructure and mechanical properties of an Fe-9.5Ni-6.5Mn (wt.%) low carbon martensitic steel. Electron back scattering diffraction (EBSD) analysis revealed that intercritical annealing treatment at 610 °C in the ferrite + austenite (α+γ) dual phase region for various holding times led to formation of the reversed austenite phase in the martensite matrix, producing a medium Ni–Mn dual phase steel. It was resulted that the volume fraction of austenite and its grain size were significantly increased with increasing the holding time. Also, high resolution transmission electron microscope (HRTEM) images illustrated the formation of nano-sized θ-NiMn precipitates within the martensite phase after subsequent ageing at 450 °C for 7.2 ks. Intercritical annealing followed by ageing yielded a good combination of an ultimate tensile strength (∼1160 MPa) and fracture strain (∼11.5%) in the developed dual phase steel compared to the initial martensitic steel. The high strength and good ductility of the developed dual phase steel were respectively attributed to the presence of θ-NiMn precipitates with a hard character and reversely formed austenite with a ductile nature in the microstructure. Furthermore, the fully brittle fracture mode in the aged initial steel changed to a mixture of brittle and ductile behavior in the dual phase steel produced by intercritical annealing and subsequent ageing.

Laser powder bed fusion of high-strength maraging steel with concurrently enhanced strength and ductility after heat treatments

Laser powder bed fusion (LPBF) has been demonstrated as a metal additive manufacturing technique that can manufacture high-performance metal components with complex shapes directly from raw powder materials. Although 18Ni-300 maraging steel has been extensively employed in this process, a significant trade-off has always existed between strength and ductility when using traditional solution and ageing heat treatments. This study addresses this problem by introducing a heat treatment combination that includes hot isostatic pressing (HIP) before the conventional ageing treatment. The experimental results demonstrated an enhancement of the relative density from 99.6% in the as-built conditions to 99.96% after HIP, although a small number of residual gas pores remained. The subsequent ageing treatment after HIP had a negligible effect on the reopening of these closed defects. Microstructure observations revealed that a fully martensitic structure can be obtained after HIP, and austenite reversion was less sensitive with the HIP + ageing treatment (HAT) compared to direct ageing treatment (DAT). Grain growth and alloying homogenisation also occurred during HIP. Massive nanoscale precipitations were formed both after DAT and HAT; quantitative analysis based on TEM observation indicated that the size of these precipitates was larger after subjecting to HAT. The room-temperature ultimate tensile strength and elongation to failure after HAT were approximately 6% and 100% higher than DAT, confirming the simultaneous enhancement of the strength and ductility after HAT. The findings of the present study offer insights into heat treatment approaches that can overcome the strength-ductility trade-off of LPBF-manufactured 18Ni-300 maraging steel, while also providing an alternative strategy for obtaining the simultaneous improvement of strength and ductility through heat treatments.

Revealing a correlation between microstructure, stoichiometry, coherency strains and mechanical behavior of bulk polycrystalline oxide-based age hardened/toughened ceramic alloys

The processing challenges and microstructural inhomogeneity associated with ceramic (nano)composites render it important to develop hardened/toughened oxide-oxide ceramic alloys, possessing good mechanical properties, via a facile solid-state precipitation-based approach. However, detailed understanding of processing-microstructure-property correlations in age-hardened/toughened polycrystalline ceramics is still lacking. The present research, therefore, focuses on understanding the possible effects of variation of dimension/stoichiometry of coherent second-phase precipitate particles in such ceramic alloys on the coherency strains, associated residual stresses and mechanical properties. Polycrystalline MgO-based ceramic alloys have been developed via controlled aging treatments of partially supersaturated Fe(oxide)-containing MgO solid solution. Air-quenching post sintering-cum-solution treatment results in the formation of ultra-fine (∼5–20 nm) coherent intragranular Mg-ferrite precipitates; with subsequent aging treatments causing increases in their size and amount. The intragranular precipitate particles remain coherent with the MgO matrix even upon aging at 1000 °C for 20 h, despite coarsening to ∼130 nm. Detailed compositional analysis using EDS (with HAADF-STEM) and 3D APT reveal progressive increment in Fe-content of the precipitates with aging duration, such that the ultra-fine particles obtained right after solution treatment correspond to non-stoichiometric Fe-deficient Mg-ferrite (with ∼6 at.% Fe), whereas the relatively coarser particles obtained after 20 h of aging correspond to near-stoichiometric MgFe2O4 (with ∼27 at.% Fe). Such increment in Fe-content results in increase in lattice misfit/coherency strains, which dominates the hardening response and improves the hardness despite loss of solution hardening. Furthermore, increase in compressive residual stress in the matrix due to increment in misfit/coherency strains results in improved resistance to crack propagation.

A new β-Ti alloy with good tensile properties by the mixed microstructure characteristics of α phase

In this study, the mechanical properties, microstructural characteristics and deformation behavior of a novel high-strength metastable β alloy Ti-6.5Cr-4.5Sn-4.5Mo (wt %) were investigated. By obtaining α phase mixed microstructure with different size, morphology and orientation combinations in β matrix, a good combination of tensile strength σb~1305 MPa and total elongation ɛf~13.4 % was achieved. The microstructural characteristics of α phase consisting of discontinuous thin grain boundary α phase (αGB), lamellar α colonies and acicular αs precipitates were obtained by the solution treatment above β transus for a short time plus subsequent aging treatment after the heavy cold rolling. Detailed TEM analysis shows that it is difficult to deform for acicular αs precipitates due to their fine-scale, leading to a large number of α/β interfaces acting as dislocation barriers, which may ultimately result in an improvement on strength of the alloy. Compared with αs, the αGB and lamellar α colonies are soft, which could produce the large enough deformation and allow dislocations to generate and accumulate within them, so that it is beneficial to improve the mechanical properties of the alloy. Stress-relaxation experiments show that the sample with a uniform and finer distribution of α precipitate has a larger value of mobile dislocation ρm/ρm0 after relaxation, implying that most of the mobile dislocations remains in the sample, which results in the ultrahigh strength meanwhile accepted ductility in the specimen.

Effects of cryorolling, room temperature rolling and aging treatment on mechanical and corrosion properties of 7050 aluminum alloy

In this study, effects of cryorolling (CR), room temperature rolling (RTR) and subsequent aging treatment on mechanical and corrosion properties of 7050 aluminum alloy (AA7050) were investigated. After the severe rolling deformation, the ultrafine-grained structure and high-density dislocations are produced in CR and RTR AA7050 alloys. CR AA7050 exhibits higher volume fraction of UFGs and dislocation density compared to RTR AA7050. Both CR and RTR AA7050 alloys follow the precipitation procedure of nucleation, growth and coarsening, while the DSC test shows that CR AA7050 has stronger response to aging treatment and age-hardening effect. CR AA7050 presents higher micro-hardness (253 HV), yield strength (650 MPa) and ultimate tensile strength (685 MPa), while the elongation (2.2%) is less than RTR AA7050 (245 HV, 573 MPa, 613 MPa, 3.5%). The aging treatment can improve the elongation of rolled samples, while the other mechanical properties are gradually decreased with the increasing in aging time. CR and RTR AA7050 sheets show a low corrosion resistance, while CR are beneficial to improving the corrosion resistance of the aged samples.

By introducing heterogeneous interfaces: Improved fatigue crack growth resistance of a metastable β titanium alloy

We present a method for the improvement of the fatigue crack growth (FCG) resistance of a metastable β titanium alloy with uncompromised high strength and ductility by introducing more heterogeneous interfaces produced by diffusion bonding. FCG behavior and tensile properties of this bonded alloy were measured at room temperature. The detailed features of α grains precipitated at the laminated interface and substate during furnace cooling and subsequent aging treatment were characterized. Dense α grains, grain boundary α (αWG) layer-free, and residual stress due to compression strain at the laminated interface can hinder FCG, resulting in an increase of FCG life of 9.4% in the high-layers laminated structure (HLS) sample compared with the low-layers laminated structure (LLS) sample. This available method can be also extended to other near and metastable β titanium alloys as a reference for designing enhanced FCG resistance with uncompromised tensile performance.

Microstructural evolution and mechanical performance after precipitation hardening of PH 13-8Mo martensitic stainless steel fabricated by wire arc additive manufacturing

In the present study, wire arc additive manufactured precipitation hardening (PH) 13-8Mo martensitic stainless steel was subjected to various solution and aging treatments to eliminate the columnar structure, non-equilibrium phases (e.g., δ-ferrite), inhomogeneous microstructure, and anisotropic ductility, detected in the as-printed part. The microstructural characterizations showed that 1050 °C was the optimum solutionizing temperature to remove the columnar grain structure and deleterious δ-ferrite phases, leading to a fully martensitic microstructure with a slightly higher hardness as compared to the as-printed part. The subsequent aging treatment at 450 and 500 °C led to the formation of nanometric and coherent β-NiAl precipitates inside the martensite laths, resulting in a substantial microhardness and tensile strength improvement. Higher temperature aging at 550 and 600 °C caused the formation of other secondary phases, i.e., Cr-rich carbides and reverted austenite, respectively, contributing to enhanced ductility at the expense of reduced tensile strength of the material. The implemented post-printing heat treatment was found to be efficient in suppressing the observed anisotropic ductility in the as-printed part, primarily dictated by the texture weakening that occurred during solution treatment.

Effect of aging treatment on the microstructure, fracture toughness and fracture behavior of the extruded Mg-7Gd-2Y–1Zn-0.5Zr alloy

A commercial scale Mg-7Gd-2Y–1Zn-0.5Zr alloy extrusion rod with synergetic high yield strength of 350 MPa and fracture toughness KIC of 22.4 MPa m1/2 was fabricated by direct-chill casting, hot extrusion and subsequent aging treatment at 200 °C for 108 h. The microstructures and mechanical properties of the as-extruded and peak-aged alloys were investigated, and the fracture toughness and fracture mechanisms before and after aging treatment were also analyzed. The results showed that the as-extruded alloy consisted of long period stacking ordered (LPSO) phase and bimodal matrix microstructure composed of fine dynamic recrystallized (DRXed) grains and coarse deformed grains. Microstructural analysis near fracture surfaces indicted that twinning was activated in the coarse deformed grains during fracture toughness test, which may be conducive to the improvement of the fracture toughness of the alloys. The lamellar-shaped LPSO phases enhanced the fracture toughness since the formation of secondary cracks parallel to the lamellar LPSO can cause significant energy dissipation and deflection of main crack. The micro-cracks were initiated and propagated in the bulk LPSO phases, which may deteriorate the fracture toughness. Large amount of nano β' phase precipitated in the T5 peak-aged alloy significantly improved the strength of the alloy. Fractography analysis indicated that fracture mechanism changed from ductile fracture of the as-extruded alloy to quasi-cleavage fracture of the peak-aged alloy. The precipitation of β' would suppress twin growth and induce the microcracks initiated at the DRXed grain boundaries and in the deformed grains, which led to slight decrease of KIC.

Towards strength-ductility synergy through an optimized two-stage solution treatment in Al–7Si–3Cu-0.5Mg alloys

In order to obtain superior mechanical properties, the incipient melting and maximum dissolution of Cu-containing phases, spheroidization and coarsening of eutectic Si phase in Al–Si–Cu–Mg alloy are important factors that should be considered during solution treatment. However, the conventional single-stage solution treatment was difficult to meet this requirement. In this study, an optimized two-stage solution treatment (495 °C/8 h + 515 °C/4 h) was established for Al–7Si–3Cu-0.5 Mg casting alloys through systematically investigating the microstructure evolution at different solution temperatures (470 °C, 495 °C, 515 °C and 525 °C). The first stage (495 °C/8 h) was applied to dissolve most Cu-containing phases and avoid incipient melting, while the employ of the second one (515 °C/4 h) was to promote fast spheroidization of eutectic Si phase and prevent severe overheating. Two modified quality indexes evaluated the synergy of strength and ductility indicated that the optimized two-stage solution treatment and the subsequent aging treatment (175 °C/8 h) gave rise to an optimization (QIU = 537.1 MPa, QIT = 0.47) on the strength and ductility of Al–7Si–3Cu-0.5 Mg alloys, as compared with the alloys (QIU = 527.4 MPa, QIT = 0.46) under the conventional heat treatment including a single-stage solution treatment (515 °C/16 h). The strength-ductility synergy was arisen from the fuller dissolution of Cu-containing phases, the finer eutectic Si phase, the depletion in number density of micropores and the precipitation of nano-sized Q′ and θ′ particles. 0.3 wt% Zr addition further increased the modified quality indexes (QIU = 549.5 MPa, QIT = 0.50), which was attributed to the grain refinement and the formation of nanoscale Al–Si–Zr precipitates. Furthermore, the fracture mechanism of the obtained alloys was also discussed.

Effects of Ni/Cu replacement on improvement of tensile and hydrogen-embrittlement properties in austenitic stainless steels

Effects of Ni/Cu replacement and subsequent aging treatment on tensile and hydrogen embrittlement (HE) properties were investigated in Fe-Cr-Ni austenitic stainless steels. With the Ni/Cu replacement, tensile strength and ductility were reduced in the as-annealed state by the increased stacking fault energy (SFE), whereas they were enhanced in the aged state due to the consumption of Cu in the matrix by the precipitation and resultantly lowed SFE. After the electrochemical H-charging, the H permeation depth decreased in the aged Cu-containing steels, indicating that Cu-rich precipitates effectively interfered the diffusion of H to increase the HE resistance. However, the excessive formation of Cu-rich precipitates destabilized the austenite phase, and induced the martensitic transformation. This α’-martensite preferably formed inside or at intersections of deformation twins, along with austenite grain boundaries, thereby providing H-induced crack propagation paths. These cracks caused the earlier brittle fracture and severe HE as a consequence. This result would suggest that the formation of Cu-rich precipitates by replacing expensive Ni could enhance both tensile properties and HE resistance, but a delicate control of SFE should be required to overcome the trade-off relationship of strength and HE resistance.

A good balance between mechanical properties and electromagnetic shielding effectiveness in Mg-9Li-3Al-1Zn alloy

It is still a challenge to develop MgLi alloy with a good balance of strength, plasticity and electromagnetic shielding effectiveness. Herein, a reasonable combination strategy for it was put forward through the processing steps: 1) dissolve the excess phase in the matrix by solid solution treatment, 2) promote the dynamic precipitation of the second phase and the formation of fine recrystallization by rolling, and 3) obtain the subgrain and more hard MgLi2Al and soft AlLi particles by subsequent aging treatment. Finally, the comprehensive improvement in strength, plasticity and electromagnetic shielding effectiveness of Mg-9Li-3Al-1Zn alloy was achieved. The ultimate tensile strength was increased by 34% compared to the as-cast alloy. The plasticity of the as-aged alloy was improved from 9.2% to 24.6% through the combination of the soft AlLi phase and subgrains, meanwhile, the electromagnetic shielding effectiveness at 1500 MHz was increased from 87 dB to 91 dB.

Microstructural Evolution, Mechanical Properties, and Preosteoblast Cell Response of a Post-Processing-Treated TNT5Zr β Ti Alloy Manufactured via Selective Laser Melting.

A Ti–34Nb–13Ta–5Zr (TNT5Zr) β Ti alloy with a high strength-to-modulus ratio has been developed, showing its potential to become another candidate material in load-bearing implant applications. This work mainly investigates the microstructural evolution, mechanical properties, and biocompatibility of a post-processing-treated TNT5Zr alloy manufactured via selective laser melting (SLM). Transmission electron microscopy observation shows the existence of the single beta grain matrix and alpha precipitates along the grain boundary in the SLM + HIP manufactured TNT5Zr alloy (TNT5Zr-AF + HIP), and ellipsoidal nano-sized intragranular α″ precipitates (approx. 5–10 nm) were introduced after the subsequent low-temperature aging treatment. The precipitation strengthening enables the SLM + HIP + aging manufactured TNT5Zr (TNT5Zr-AF + HIPA) alloy to show a comparable ultimate tensile strength (853 ± 9 MPa) to that of the reference material (Ti64-AF + HIP, 926 ± 23 MPa). Including the inferior notch-like surface of the test pieces, the slip-band cracking that occurs in this ductile TNT5Zr-AF + HIPA alloy is regarded as the main factor in determining its fatigue strength (170 MPa). In vitro short-term biocompatibility evaluation reveals almost no significant difference in the preosteoblast viability, differentiation, and mineralization between TNT5Zr-AF + HIPA and the reference biomaterial (Ti64-AF + HIP).

Enhanced electrical, mechanical and tribological properties of Cu-Cr-Zr alloys by continuous extrusion forming and subsequent aging treatment

• A high performance Cu-1Cr-0.1Zr alloy was obtained by continuous extrusion forming and subsequent aging treatment. • The strengthening contributions of the grain refinement, dislocation and precipitation were quantitatively calculated. • The wear behavior was studied by examining the evolution of wear surface morphology and subsurface microstructure. • The microhardness (H), H/E r ratio and H 3 /E r 2 ratio were considered to gage the wear resistance of Cu-Cr-Zr alloy. As a promising material for the new generation of high-speed railway contact wires, the comprehensive optimization of the electrical conductivity, strength, hardness and wear resistance of the Cu-Cr-Zr alloy has received extensive attention. In this paper, a high-performance Cu-1Cr-0.1Zr alloy with an ultimate tensile strength of 599.1 MPa, a uniform elongation of 8.6%, a microhardness of 195.7 HV 0.2 and an electrical conductivity of 80.07%IACS was achieved by the continuous extrusion forming (CEF) and subsequent peak-aging treatment. The grain refinement strengthening, dislocation strengthening and precipitation strengthening are identified to be responsible for the excellent electrical and mechanical properties of Cu-Cr-Zr alloy. The wear behavior of Cu-Cr-Zr alloy was investigated by examining the evolution of worn surface morphology and subsurface microstructure. The microhardness ( H ) and reduced elastic modulus ( E r ) of the subsurface below the worn surface measured by nanoindentation were calculated to gage the tribological performance of Cu-Cr-Zr alloy. Results show that the continuously extruded and subsequently peak-aged specimen has the best wear resistance, which indicates that the tribological properties of Cu-Cr-Zr alloy strongly depend on its strength and hardness. It can be concluded that the CEF and subsequent aging treatment process provides a new and high-efficiency procedure for the continuous preparation of Cu-Cr-Zr alloys.

Research of rolling-drawing coupled deformation on the microstructure-property evolution and strengthening mechanism of 6201 conductive tubes

To meet the major needs of national defense, transportation, aerospace, and other fields, aluminum alloys with excellent comprehensive performance are continually developed. To reduce the high cost of preparing high-performance aluminum alloys and alleviate the limitations of existing research, the effects of a rolling-drawing coupled deformation on the microstructure-property evolution and strengthening mechanism of 6201 conductive tubes developed by using two different processes were investigated. Subsequently, the evolution of grains, precipitates, texture, and dislocation were examined by performing optical microscopy, scanning electron microscopy, X-ray diffraction, and electron backscattered diffraction. The results showed that the main phases of the investigated tubes were the α-Al matrix, Mg2Si, and Al0.5Fe3Si0.5 second phase. The Al0.5Fe3Si0.5 phase with a face-centered cubic structure functioned as the inhomogeneous nucleation core of Mg2Si. In the rolling process, severe plastic-deformation-induced re-dissolution of the precipitated phases was observed, improving the effect of the subsequent solution treatment and aging treatment. An optimal ultimate tensile strength (UTS) of 341 MPa and electrical conductivity (EC) of 54.12% IACS were successfully obtained in the “extrusion-rolling-solution-aging-drawing” process. Compared with those of the initial tube, these values increased by 136.81% and 41.60%, respectively. However, after the order of rolling and solution treatments was reversed, the UTS and EC of the final tube decreased to 325 MPa and 52.91% IACS, respectively. The microstructure and performance evolution revealed that the uniformly distributed fine Mg2Si phase resulting from the good fit of the processes plays an important role in achieving a higher UTS and EC.