Age-hardened Conditions Research Articles

Combinatorial Alloy Design and Microstructure Evolution in Laser-cladded Al–Co–Cr–Fe–Ni–Ti Compositionally Complex Alloys

In this work, we propose a strategy for high-throughput design and development of compositionally complex alloys combining theoretical and experimental alloy screening. This methodology was applied for the exploration of the (Co2CrFeNi2)1-x-yTixAly subsystem of so-called high entropy superalloys in the Al–Co–Cr–Fe–Ni–Ti alloy system. Alloy design was guided by thermodynamic calculations based on the CALPHAD approach. The evolution of the microstructure with increasing Al and Ti content was analyzed in the as-built, homogenized and age-hardened conditions by means of scanning electron microscopy, energy-dispersive X-ray spectroscopy and electron backscattered diffraction. Additionally, the evolution of the sample hardness with increasing Al and Ti contents was determined for all conditions. Based on the experimental results, the reliability of the CALPHAD calculations was assessed. Generally, a good agreement between calculations and experiments is achieved in the homogenized state. In the aged conditions, the CALPHAD predictions of the precipitation processes are partly inaccurate and need improvement. Optimal Al and Ti concentrations are derived for age hardening through L12 and combined L12 + B2 precipitations.

Dissimilar Welding of Cast Alloy 706 with Different Prior Heat Treatment Conditions and Austenitic Stainless Steel 321

Abstract The welding of dissimilar joints is most common in the aerospace applications, especially, cast nickel-based superalloys are welded with austenitic stainless steel for high-temperature service conditions. It is well known that heat-affected zone (HAZ) cracking is a common phenomenon while welding age-hardened alloy 706. In this study, an alloy equivalent to cast alloy 706 subjected to three different heat treatment cycles and was welded with annealed austenitic stainless steel 321. The HAZ on the alloy 706 was investigated, and it was found that the HAZ of alloy 706 that underwent stabilization heat treatment was free from microfissures. The fusion zone microstructures were also investigated. The mechanical properties were evaluated, and it was found that the alloy 706 welded in stabilized and age-hardened condition furnished better mechanical properties than in both room temperature and elevated temperature.

The effect of SiC content in aluminum-based metal matrix composites on the microstructure and mechanical properties of welded joints

Aluminum metal matrix composites of the varying percentage of SiC reinforcement were welded using the tungsten inert gas welding technique. For all the conditions of the specimen, the welding parameters were kept identical. The welded composites were thermally aged to peak age-hardening conditions. Significant differences in microstructure exist between aged and non-age hardened composites in terms of misorientation, grain boundary fractions and stored energy. These differences in microstructure were seen through identical changes in the mechanical behavior of the welded composites. After aging, microstructure showed refinement in grain size and preferential orientation. Hardness and tensile strength increased at different rates with increase in SiC content indicating that hardness was a clear function of stored energy and strength had a dependence on the misorientation. EBSD measured suggests that due to age hardening, a rearrangement in dislocation substructures occurred with precipitation of Mg2Si or increasing SiC content followed by dynamic recovery of the weld metal region which leads to enhancement of hardness. The increase in tensile strength with decreased misorientation was a clear indication that the effect of annihilation of dislocations as a result of recovery was less pronounced and precipitation strengthening was dominant. The present study aims to address the role of SiC addition in aluminum metal matrix composites on the welded microstructure and finally relating the microstructural changes to the observed mechanical behavior of the welded joints. The study reveals that strength not only depends on the average value of misorientation but also on the distribution of misorientation in the microstructure.

Effect of addition of SiC particles on the Microstructure and Hardness of Al-SiC composite

This work aims to investigate the effect of the addition of silicon carbide particles on the microstructure and the hardness of the Al-SiC metal matrix composites. The said composite is prepared using the stir casting technique for different weight percentages of the SiC particles. The higher composition of the reinforcement causes the clustering of the particles in the matrix. Thus, research has to be carried out on the aluminum-silicon carbide composites with the reinforcement 3wt%, 6wt%, 9wt%, and 12wt% of SiC particles to obtain the optimized composition. In order to study the microstructure and the reinforcement distribution in the matrix, a scanning electron microscope is utilized. The hardness testing has been carried out using the Vickers’ indentation technique for the as-cast and age hardening conditions. From the microstructural study, it is observed that the microstructure of the said composite exhibits the uniform distribution of the reinforcement. The EDX results show the presence of the reinforcing elements in the Al-SiC composite. From the results obtained from the hardness testing, it is observed that the presence of the carbide element in the composite increases the hardness of the Al-SiC particulate composites.

Effect of a T6 aging treatment on the corrosion behaviour of in-situ AlxNiy reinforced AA6061 composite

Abstract In-situ AlxNiy reinforced aluminium matrix composites (AMCs) were produced by stir-casting route by adding 5, 10 and 15 wt% (wt. %) Ni to AA6061 alloy. The as-cast samples were subjected to a T6 ageing treatment at 180 °C for 4 h after solutionizing treatment at 535 °C for 1 h. The density, porosity, microstructure, hardness, and corrosion behaviour of the as-cast and heat treated AA6061 and the AMCs were evaluated. All the castings were found to be sound with low porosity. Porosity in heat treated samples was lower than the porosity in the as-cast samples. This trend was reversed only in AMC containing 15 wt% Ni. Optical microscopy studies revealed that in-situ formed AlxNiy was distributed along the dendritic arms, both in the as-cast as well as in the heat treated AMCs. The distribution became non-homogeneous and coarse with increase in Ni content and with age hardening. Hardness increased with increase in Ni addition till 10 wt% Ni beyond which it decreased due to the coarse distribution of AlxNiy in the matrix. The artificially aged castings showed higher hardness compared to their as-cast counterparts. The corrosion current (icorr) increased while the polarization resistance (Rp) decreased with the increase in Ni addition in the AMC, in the as-cast as well as in the age-hardened condition. The age-hardened samples showed poor corrosion resistance than the as-cast composites. This indicates that the coarse non-homogeneous distribution of in-situ AlxNiy had a detrimental effect on the corrosion performance of the AMCs.

Evaluation of Stress Corrosion Cracking, Sulfide Stress Cracking, Galvanic-Induced Hydrogen Stress Cracking, and Hydrogen Embrittlement Resistance of Aged UNS N06625 Forged Bars

UNS N06625 is a nickel-based superalloy used for oil and gas applications and commonly produced according to NACE MR0175 in the annealed/solution annealed condition. The annealing/solution annealing treatment makes the material corrosion resistant in the most challenging environments, in the presence of sulfides and chlorides at high pressure and temperature. However, thanks to its chemical composition, UNS N06625 can also be considered as an age-hardenable material whose mechanical strength can be improved by promoting the metastable second phase γ′′ precipitation into the γ matrix. However, the corrosion behavior of the aged alloy has never been investigated in NACE environments. This paper aims to understand the suitability of the age-hardened condition of UNS N06625 for oil and gas applications through the evaluation of the material corrosion performance in NACE level VII environments by using NACE TM0177 tests. Three heats of UNS N06625 have been produced and forged in different bar diameters: 152 mm (6 in), 203.2 mm (8 in), and 254 mm (10 in). Afterward, the bars have been annealed and age-hardened according to optimized time-temperature parameters and finally tested to assess their mechanical properties and resistance to stress corrosion cracking, sulfide stress cracking, galvanic-induced hydrogen stress cracking, and hydrogen embrittlement.

CARTECH CUSTOM AGE 725

Abstract CarTech Custom Age 725 is a precipitation hardenable nickel-chromium-molybdenum-niobium alloy that displays outstanding corrosion resistance, similar to that of alloy 625 and superior to that of alloy 718, along with high strength in the age-hardened condition. This datasheet provides information on composition, physical properties, and tensile properties. It also includes information on corrosion resistance as well as forming. Filing Code: Ni-757. Producer or source: Carpenter Technology Corporation.

The combined effects of hydrogen and aging condition on the deformation and fracture behavior of a precipitation-hardened nickel-base superalloy

The effect of hydrogen (H) on the deformation behavior of Monel K-500 in various isothermal heat treatment conditions (non-aged, under-aged, peak-aged, and over-aged) was assessed via uniaxial mechanical testing. H-charged and non-charged specimens were strained to failure to facilitate a comparison of ductility, fracture surface morphology, strength, and work hardening behavior. For all examined heat treatment conditions, H charging leads to a significant reduction in ductility, which is accompanied by a consistent change in fracture surface morphology from ductile microvoid coalescence to brittle intergranular fracture. While H charging led to a systematic enhancement in the yield strength of all heat treatments, the three age-hardened conditions exhibited a more than 2-fold increase relative to the non-aged heat treatment. This suggests that H modifies the dislocation–precipitate interactions, which also manifest themselves through changes in work hardening metrics related to the dislocation storage and recovery rates. In particular, the H-charged peak-aged specimen exhibited a significant increase in initial hardening (dislocation storage) rate relative to the H-charged under-aged specimen. Transmission electron microscopy of these samples revealed the onset of widespread dislocation looping in the H-charged peak-aged sample, in addition to the planar slip bands characteristic of the non-charged condition. This result suggests that hydrogen induces the particle shearing-to-looping transition at smaller particle sizes. Possible mechanistic explanations for this observed behavior are presented.

Study on the electrochemical behaviour of 22k gold (Au-5.8wt.%Cu-2.5wt.%Ag) and Ti containing 22k gold (Au-5.8wt.%Cu-2.0wt.%Ag-0.5wt.%Ti)

The electrochemical corrosion behaviour of 22k gold (Au-5.8wt.%Cu-2.5wt.%Ag) and Ti containing 22k (Ti-22k) gold (Au-5.8wt.%Cu-2.0wt.%Ag-0.5wt.%Ti) was studied. Elemental Ti was added as the quaternary element to 22k gold by replacing Ag, resulting in the formation of secondary phase precipitates during age hardening treatment, thereby improving the hardness of the alloy. Anodic polarization tests were conducted for both 22k and Ti-22k samples in their as-cast annealed, cold-rolled annealed and age-hardened conditions using 0.9% sodium chloride and 1% lactic acid as medium. The as-cast and annealed 22k samples showed better corrosion resistance in both corrosion media whereas the 22k samples in the cold-rolled, annealed condition and Ti-22k samples in the as-cast, annealed condition showed poor corrosion resistance. After age-hardening treatment, cold-rolled Ti-22k samples showed better corrosion resistance due to the formation of passive layer (of TiO2) on the surface. However, corrosion gets initiated in the age-hardened Ti-22k due to the breaking and decomposition of the passive layer (TiO2) at a potential > 1.3 V.

Generation of mechanically mixed layer during wear in hybrid aluminum MMC under as-cast and age hardened conditions

In the present investigations, dry sliding wear test is conducted using a pin on disc tribometer at room temperature for both the as-cast and age hardening conditions. Al7075 has chosen as the matrix material. The reinforcement used are particles of silicon carbide and alumina with 5 wt%, 10 wt%, and 15 wt%. Hybrid aluminum metal matrix composites are produced utilizing stir casting route for enhancing the wear behavior. In the aluminum matrix, micro-structural characterization reveals the homogeneous mixing of reinforcements. From the investigation, it is observed that composites containing 10% by weight of silicon carbide and aluminum oxide reinforcements with ageing exhibited superior tribological properties. From the micro-structural study, it has been observed that the generation of the mechanically mixed layer in the hybrid aluminum metal matrix composites will lead to a reduction in wear rate.

“Effect of Zn content and aging temperature on the in-vitro properties of heat-treated and Ca/P ceramic-coated Mg-0.5%Ca-x%Zn alloys”

While potentially strong enough for load-bearing skeletal reconstruction applications, the corrosion (biodegradation) rate of biocompatible Mg-Zn-Ca-based alloys still presents. The present work reports on the use of heat treatment (strengthening and resorption delaying) and micro arc oxidation (MAO) coating (corrosion delaying) processes which were developed to induce desirable corrosion rates which are essential to maintaining the mechanical integrity of Mg-Zn-Ca-based alloys during the bone healing period. Three Mg-x%Zn-0.5%Ca (wt%) alloys with different levels of Zn content (1.2, 1.6 and 5 wt%) were prepared and heat-treated at different age hardening temperatures (100, 150, 200 and 250 °C). In order to further decrease the corrosion rate and improve the bioactivity, samples of the heat-treated Alloy I (Mg-1.2wt%Zn-0.5wt%Ca) at the optimized age-hardening conditions were successfully coated with a biocompatible composite coating without and with HA/β-TCP nanoparticles by using an MAO process. The microstructure, morphology and the composition of the heat-treated and coated materials were characterized by scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), and x-ray diffraction (XRD). Hardness and compression tests were conducted, while a corrosion investigation of heat-treated and coated samples was performed using potentiodynamic polarization (PDP) and a mechanical integrity immersion test. The results confirmed that Zn content and age hardening temperature have significant effects on the mechanical and corrosion properties of heat-treated Mg-Zn-Ca-based alloys. Alloy I, which has 1.2 wt% Zn content and was aged at 200 °C, showed the best combination of corrosion (slowest) and mechanical (highest) properties. The MAO (HA/β-TCP) composite coating significantly improved corrosion resistance compared to the uncoated heat-treated alloy, with only 11.3% reduction in the compressive strength after 8 weeks of immersion.

A study of the dynamic impact behaviour of IN 718 and ATI 718Plus® superalloys

ABSTRACTThe dynamic impact response of IN 718 and ATI 718Plus®, in both the solution heat treated and age-hardened conditions, were investigated at different deformation temperatures and strain rates using a direct impact Hopkinson pressure bar. Analyses of the results provide a vital but previously not reported information that the ATI 718Plus® offers a higher resistance to damage during high strain rate ballistic impact deformation compared to the most widely used Iron-nickel based superalloy, Inconel 718. ATI 718Plus® showed higher strain hardening and strain rate sensitivity, in both heat treatment conditions, than IN 718. The difference in the deformation behaviour of both alloys, in the annealed condition, is attributable to the compositional modification in ATI 718Plus® which has been reported to lower its stacking fault energy and increases the tendency for deformation twinning. However, in the age-hardened condition, the difference is believed to be related to the disparity in the operative strengthening mechanism, of the precipitates present in both alloys. Furthermore, a higher susceptibility to strain location and the formation of adiabatic shear band, in aged IN 718, is attributable to the stronger temperature-softening characteristics observed in the alloy and to the limited strain hardening tendency under dynamic impact loading.

Liquid-Phase Sintering and Properties of PIMed 10-20 vol.% SiCp-Reinforced Aluminium Composites

Liquid-phase sintering and properties of powder injection moulded aluminium composite reinforced with SiCp has been investigated via thermal-phase analyses and hardness property. Mixing of 10 and 20 vol.% SiCp and aluminium powder was done via ball milling prior to feedstock preparation at 55% solid loading. Powder injection moulding was carried out at 170°C, followed by solvent and thermal debinding. The brown samples were sintered in a nitrogen atmosphere at 650–660°C, prior to age-hardening. Experimental result shows relatively high % linear shrinkage of 9.9–21.9 % and high % volumetric shrinkage of 34.5–46.5%. Thermal analysis indicates the formation of the liquid around 632 °C, facilitating liquid phase sintering. The composite microstructures consists of uniformly distributed SiCp throughout the densified aluminium matrix. SiCp addition scales up SiCp clustering, accompanying with gap porosity. The composite reinforced with 10 vol.% SiCp possesses higher sintered density at 2.63 g/cm3, yielding 93.1% theoretical. However the maximum macro Vickers hardness was measured at 164.2 Hv for 20 vol.% SiCp – reinforced aluminium composite in the age-hardened condition. Liquid phase sintering was found effective for the microstructure evolution of the PIMed composite, rendering densification. Hardening is influenced by SiCp addition and the roles of AlN, Al2Cu and Mg2Si precipitates.

Forming behavior and microstructural evolution during single point incremental forming process of AA-6061 aluminum alloy sheet

AA-6061 aluminum alloy is extensively used in automobile and aerospace industries due to its high strength-to-weight ratio. However, this material shows limited formability in age-hardened condition at room temperature. Therefore, a new forming method known as single point incremental forming (SPIF) to deform the sheet was adopted. The SPIF experiments and finite element method (FEM) simulation were performed to form the sheet into the desired conical shape. Digital image correlation (DIC) method was used to measure the major and minor strains post deformation experimentally, and results were compared with FEM results. Detailed microstructural study was performed to understand the deformation behavior of AA-6061 aluminum alloy sheets during SPIF. It is observed that plastic anisotropy has strong effect on microstructure and texture development in different directions of AA-6061 alloy sheet during SPIF. It is also observed that volume fraction of goss and S texture components remains stable, whereas volume fraction of cube and brass texture changes significantly.

Mechanical Properties of As-Exposed Al-SiC<sub>p</sub> Composite Fabricated by Powder Injection Moulding

This research investigated mechanical degradation of powder injection moulded SiCp-reinforced aluminium composite subjected to moderate temperature exposures. Aluminium composite of 20 vol.% SiCp reinforcement was produced by powder injection moulding and sintering at 680°C, followed by 500°C solution treatment plus 150°C for 6 hours artificial aging, and subsequent exposures at 100, 200 and 300°C for 10 and 100 hours. It was found that short-term exposure for 10 hours provided increasing hardness with increasing exposure temperature, while long-term exposure for 100 hours led to an opposite result. The maximum micro Vickers hardness was obtained at 182.2 Hv for Al-SiCp composite exposed at 300°C for 10 hours. Tensile strength was however found deleterious with increasing both exposure temperature and time. The maximum tensile strength was achieved at 191.2 MPa for Al-SiCp composite exposed at 100°C for 100 hours. The formations of AlN, Mg2Si and Al2Cu were observed in both age-hardened and as-exposed conditions. Furthermore, the highest temperature exposure at 300°C and extended exposure time at 100 hours resulted in the lowest hardness and tensile properties due possibly to the loss of coherency of precipitates. SiCp clusters were the main cause of the tensile failure.

Effect of plastic anisotropy on forming behavior of AA-6061 aluminum alloy sheet

AA-6061 (T6) aluminum alloy sheet is used extensively for structural applications in various automotive and aerospace industries due to its excellent mechanical and physical properties. Due to lower formability of this material in age-hardened (T6) condition, forming of complex-shaped components is a major challenge. Forming behavior of the sheet was studied in T6 condition using limit dome height tests by experiment and finite element method for three different sheet directions (rolling direction, inclined direction (ID) and transverse direction). Strain path diagrams were obtained from the experimental limit dome height tests and finite element method simulations from drawing to stretching region, and the results were compared for all the sheet directions. Forming limit diagrams were plotted using strain localization and fracture criteria from experimental and simulated strain path curves. Effect of plastic anisotropy on crack propagation direction was studied using finite element method, and it has been found that the direction of crack propagation was strongly dependent on plastic anisotropy ratio (“r” value) of the sheet in biaxial strain paths.

Структура и свойства упрочненных нержавеющих сталей с эффектом памяти формы

A possibility of obtaining the shape memory effect has been investigated as a result of γ→e→γ transformations in stainless steels hardened by VC carbides. Age hardening conditions at 650 and 720 °C for stainless steels containing (in mass %) 0.20 – 0.35 C, 1 V, 3 – 4 Si, 9 and 13 – 14 Cr are presented. The values of reversible strain e determined after heating to 400 °C in specimens preliminarily deformed by 3.5 – 4 % vary from 0.15 to 2.7 % depending on the composition of the steels and the conditions of stabilizing and destabilizing aging.

Through Thickness Microstructural and Texture Inhomogeneity Within Al Layers in ARB-Produced Al-Al(Sc) Layered Composite Sheets

Alternatively layered composite sheets of commercially pure (99.8 pct purity) aluminum and an Al-0.3wtpctSc alloy (either in the supersaturated solid solution or age-hardened conditions) were generated through accumulative roll bonding for up to 5 cycles. The transverse sections of the sheets were examined to investigate the microstructure and texture inhomogeneities developed during the rolling process. Electron backscatter diffraction and transmission electron microscopy was used for this investigation. It was found that an inhomogeneous microstructure and texture was developed through the aluminum layers of the sheet thickness. The nature of inhomogeneities changes as the ARB bonding progresses to higher cycles. Microstructural inhomogeneities remain prominent in the first ARB cycle and diminish during the subsequent cycles. Texture inhomogeneities appear in different forms as rolling progresses. High frictional shear forces in the surface and in-plane shear forces across bonding interfaces derive these inhomogeneities.

Effect of age hardening on the deformation behavior of an Mg–Y–Nd alloy: In-situ X-ray diffraction and crystal plasticity modeling

The present study investigates the deformation behavior of an extruded Mg–Y–Nd (WE54) alloy in as-extruded and aged conditions. Via age-hardening at 250°C for 16 and 500h or annealing treatments at 400°C for 24h, precipitates are formed within the grains or at the grain boundaries. To characterize microstructural changes with the age-hardening conditions, we employ electron-backscattered diffraction, transmission electron microscopy, and optical microscopy. In the as-extruded material, we observed an uncommonly low activity of {101¯2}〈101¯1¯〉 tension twinning in comparison with other Mg alloys. The tension twinning activity substantially increased after precipitation hardening and the accompanying reduction of alloying element concentration in solid solution. Consistent with the microstructural observations, the increase in twin activity clearly manifests in the compression flow curves. While the as-extruded and 16 h/250°C samples exhibited a classical decreasing hardening rate throughout straining associated with crystallographic slip, the 500 h/250°C and the 400°C annealed sample featured a characteristic increase in the hardening rate associated with twinning. In order to determine the impact of the different heat treatments on the individual slip and twinning modes, in-situ energy-dispersive X-ray synchrotron diffraction experiments during loading and elasto-plastic self-consistent modeling were conducted. We find that plate-shape precipitates on the {101¯0}α planes harden 〈a〉 basal slip more than the other slip systems, while the reduced solute concentration in the 500h 250°C and 24h 400°C samples results in a significant decrease in the critical resolved shear stress for {101¯2}〈101¯1¯〉 tension twinning.

Cyclic plasticity experiments and polycrystal plasticity modeling of three distinct Ti alloy microstructures

Cyclic deformation experiments have been performed on three titanium alloy microstructures to facilitate calibration of two distinct simplified polycrystal plasticity model frameworks. These microstructures include Ti–6Al–4V β-annealed, Ti-18 in a solution-treated, age-hardened (STA) condition (Fanning, 2011), and Ti-18 with a beta-annealed, slow-cooled, age-hardened (BASCA) treatment. Experimental results suggest that superior uniaxial yield strength, ultimate strength and tensile ductility are achieved through the STA processing for the Ti-18 material. This processing route produces a fine bi-modal microstructure. In contrast, corresponding measured properties of the Widmanstätten morphology generated via the BASCA heat treatment were lower. The constitutive frameworks for the two different simplified polycrystal plasticity models and associated flow rules have been outlined and the model parameters have been estimated for cyclic loading such that the simulated stress–strain response is consistent with experimental results for each of the titanium microstructures investigated. In view of envisioned application to fatigue, focus is placed on cyclic behavior after the initial loading cycle(s). Certain estimated parameters differ for each model among microstructures, mainly related to elasticity, threshold for slip system yielding, and work hardening; this suggests limits on a simplified model framework and the need for in situ studies of dislocation-interface reactions and the relative role of β-phase fraction.