Commercial Alloys Research Articles

Influence of surface condition on the high-temperature corrosion of 12Cr1MoVG, T91, and TP347H steels in waste-to-energy boilers

High-temperature corrosion of superheater and reheater is a major obstacle for improving steam parameter of waste-fired boiler. In the present study, three commercial alloys (12Cr1MoVG, T91 and TP347H) were investigated under a simulated atmosphere. The anti-corrosion performance of Inconel 625 overlay weld coating on 12Cr1MoVG was also investigated in a real waste-to-energy (WtE) plant. The experiments were carried out by a two-zone lab-scale tube furnace where the gas temperature was 600℃ and the sample temperature was 380℃. Different sample surface conditions of the corrosion test specimens were set up includes clean surface, NaCl/KCl deposition, and ash deposition. Corrosion kinetics were plotted on the basis of specimens weight gain. The results showed that chloride salts are the main corrosive species in ash deposit. The corrosion rate of different deposits and clean surface was in the following order: KCl/NaCl > ash deposit > clean surface. The corrosion products were Fe2O3, Cr2O3, Fe3O4, NiO, (Fe, Ni)Cr2O4, FeCl2, and FeCl3. The presence of chromium was beneficial for high-temperature corrosion resistance. The anti-corrosion performance of the three alloys in descending order was TP347H > T91 > 12Cr1MoVG. This is consistent with the chromium and nickel content in the alloys. The engineering investigation showed that Inconel 625 overlay weld coating can effectively protect base material from the attack of corrosion species includes ash deposit and MSW incineration atmosphere, for long-term in real WtE plant.

Effect of CaO Addition on Microstructural Evolution Due to the Annealing of AZ31 Alloys Processed by Equal-Channel Angular Pressing (ECAP)

This study demonstrated the application of equal-channel angular processing (ECAP), which was performed via the BC route, to determine the effect of the addition of CaO on the microstructural evolution of an AZ31 alloy due to annealing. Compression tests were performed to evaluate the mechanical properties of the alloy, and the corresponding microstructures were observed to elucidate the flow behavior. Ca-bearing second-phase particles were fragmented with the increase in the number of ECAP passes. The increase in the yield strength and flow stress with the addition of CaO was attributed to the dispersion of the Ca-bearing second-phase particles. When the CaO-added AZ31 and commercial AZ31 alloys were subjected to annealing, their flow stress decreased owing to the grain growth. However, the extent of the decrease in the flow stress for the CaO-added AZ31 alloy was lower than that for the commercial AZ31 alloy.

Biodegradable Magnesium Alloys for Personalised Temporary Implants.

The objective of this experimental work was to examine and characterise the route for obtaining demonstrative temporary biodegradable personalised implants from the Mg alloy Mg-10Zn-0.5Zr-0.8Ca (wt.%). This studied Mg alloy was obtained in its powder state using the mechanical alloying method, with shape and size characteristics suitable for ensuing 3D additive manufacturing using the SLM (selective laser melting) procedure. The SLM procedure was applied to various processing parameters. All obtained samples were characterised microstructurally (using XRD-X-ray diffraction, and SEM-scanning electron microscopy); mechanically, by applying a compression test; and, finally, from a corrosion resistance viewpoint. Using the optimal test processing parameters, a few demonstrative temporary implants of small dimensions were made via the SLM method. Our conclusion is that mechanical alloying combined with SLM processing has good potential to manage 3D additive manufacturing for personalised temporary biodegradable implants of magnesium alloys. The compression tests show results closer to those of human bones compared to other potential metallic alloys. The applied corrosion test shows result comparable with that of the commercial magnesium alloy ZK60.

The effect of heat treatment on the structure and properties of a heat-resistant nickel alloy based on Ni–Fe–Co–Nb–Ti–Ta

The effect of heat treatment on the structure and properties of a new weldable heat-resistant alloy based on Ni–Fe–Co–Nb–Ti–Тa with a low coefficient of thermal expansion for parts of gas turbine engines was studied. The stability of the intermetallic globular phase, the features of precipitation of lamellar particles during annealing after quenching were studied. It is shown that the structure formed during heat treatment with nanosized cuboid and rounded particles of the γ′-phase, as well as with a small amount of lamellar η-phase precipitates along the grain boundaries, provides a high set of properties and excellence heat-resistance in comparison with iron-nickel commercial alloys of a similar purpose. With uniform precipitation of the γ′-phase higher tensile strength are achieved.

Heterostructures enhance simultaneously strength and ductility of a commercial titanium alloy

Enhancing both strength and ductility simultaneously in commercial alloys at an industrial scale remains a challenging task. In this study, we have demonstrated a simple heat treatment method to achieve a heterostructure with coarse and ultra-fine lamellar α precipitates in a common titanium alloy, Ti-5Al-5Mo-5V-3Cr-1Zr. Guided by computer simulations, we successfully attained microscale concentration modulations in the β-phase matrix using up-quenching of a duplex microstructure consisting of a globular primary α phase (αp) and β matrix to dissolve the αp phase rapidly and leave residual concentrations. We subsequently applied aging treatments to create finely dispersed regions of coarse and ultra-fine α precipitates embedded in the β matrix by activating different phase transformation mechanisms. Compared to the commercial alloy that has a homogeneous lamellar structure, the heterostructured alloy we produced exhibits a 6% increase in ultimate tensile strength and a remarkable 130% increase in elongation. The outstanding ductility of the heterostructured alloy is attributable to its unique microstructure design, which prevents strain localization and allows full activation of dislocation and twin deformations in the coarse and ultra-fine α regions. Meanwhile, the high strength of the alloy can be attributed to the enhanced back stress effect induced by strain partitioning of the heterostructure. Our study demonstrates a simple and effective method for creating bulk heterostructures in precipitation-hardened alloys at an industrial scale, leading to substantially improved strength and ductility.

Carbon‐Coated Porous Hollow Silicon Microspheres for High‐Capacity and Durable Lithium Storage

AbstractSilicon‐based materials are promising lithium‐ion battery (LIB) anodes owing to their natural abundance and high capacity. However, their practical application is restricted by the poor electrical conductivity and large volume expansion. Herein, we successfully construct carbon coated porous hollow silicon microspheres (Si‐40@C) as LIB anode materials, which are derived from the acid etching of commercial AlSi alloy with subsequent chemical vapor deposition carbon coating. The porous hollow structure of Si‐40@C buffers the volume variation and promotes the transportation of Li+; the carbon coating enhances the overall conductivity as well as structural stability. The as‐prepared Si‐40@C porous hollow microspheres deliver a high reversible capacity (2029 mAh g−1 at 0.2 A g−1), good cyclability (1668 mAh g−1 after 100 cycles at 0.2 A g−1), and an ideal rate capability (1200 mAh g−1 at 10 A g−1).

Feasibility of 3D-Printed Locking Compression Plates with Polyether Ether Ketone (PEEK) in Tibial Comminuted Diaphyseal Fractures.

The applicability of a polyether ether ketone locking compression plate (PEEK LCP) fabricated using FDM (fused deposition modeling)-based 3D printing to treat actual patients was studied. Three different tests-bending, axial compression, and axial torsion-were conducted on tibial non-osteoporotic comminuted diaphyseal fracture samples fixed with the commercial titanium alloy LCP and 3D-printed PEEK LCP. Comparing the outcomes of these tests revealed that the commercial titanium alloy LCP underwent plastic deformation in the bending and axial torsion tests, though the LCP did not fail even when an external force greater than the maximum allowable load of the tibia fixture of the LCP was applied. Elastic deformation occurred in the 3D-printed PEEK LCP in the bending and axial torsion tests. However, deformation occurred even under a small external force, and its stiffness was 10% compared to commercial titanium alloy LCP. Thus, 3D-printed PEEK LCP can be applied to the fracture conditions in non-weight-bearing regions. The experimental results reveal detailed insights into the treatment of actual patients by considering the stiffness and high toughness of 3D-printed PEEK LCP.

Processing and microstructure–property relations of Al-Mg-Si-Fe crossover alloys

This study introduces new alloys, which combine the age-hardening capability of Al-Mg-Si alloys with the microstructure-controlling effect on processing of primary Fe-rich intermetallic phases used in foil stock. In detail, the processing and microstructure–property relations in new crossover aluminum alloys derived from 6xxx and 8xxx foil stock alloys, is shown. A highly Fe-rich intermetallic phase content was deployed to conceptually mimic high scrap content. Fast and slow solidification rates were applied to represent thin strip and direct chill casting, respectively. The effects of adding Fe and Mn to alloy 6016 were examined, while the Si consumed in primary phases was partly adjusted to maintain age-hardening potential. It was shown that upon thermomechanical processing, primary intermetallic phases in the new alloys are finely fragmented and well dispersed, resulting in strong grain refinement and a uniform texture. Attractive combinations of strength and ductility were revealed, also in material processed under direct chill casting conditions. The new alloys’ high elongation values of up to 30%, and their age-hardening response, were similar to those seen in commercial alloy 6016, while their strain hardening capacity was significantly greater. This can be attributed mainly to the formation of geometrically necessary dislocations near primary Fe-rich intermetallic phases. The study discusses microstructure refinement on the basis of particle stimulated nucleation. It uses a simple model to describe the individual contributions to yield strength, including the effect of primary phases. It also models the effect of these particles on increased strain hardening and ductility.

Transition from earth mining toward urban mining: up-cycling post-consumer scraps to produce automotive grade aluminum extrusions

Aluminum extrusions encompass a range of structural components for managing crash energy. Currently automotive grade aluminum extrusions are made from primary aluminum of high carbon footprint. This study proposes a pathway to significantly reduce carbon footprint of automotive grade aluminum extrusions via using post-consumer scrap. Guided by thermodynamics-based simulations, 0.25 wt% was set as the iron tolerance limit for aluminum AA6082 alloy extrusion. This enables a scrap utilization ratio exceeding 70% in casting, which has been demonstrated in a production trial. Extrusions made from the low-carbon AA6082 alloy has a yield strength of 316.3 ± 3.5 MPa, an ultimate tensile strength of 343.9 ± 1.9 MPa, and a tensile elongation of 13.4 ± 1.2%, all of which are comparable to those of the commercial AA6082 extrusion made from 100% primary aluminum. Component-level 3-point bending test shows that front bumper beams made from low-carbon and commercial AA6082 alloys have the same performance. These results indicate that up-cycling post-consumer aluminum scrap to produce automotive grade extrusions is a promising route to help decarbonize vehicle manufacturing process.

Strengthening model development and effects of low diffusing solutes to coarsening resistance in aluminum alloys

A modified Orowan strengthening model is proposed to account for finite rod-shaped precipitates with hemispherical caps in aluminum alloy systems. A combined computational and experimental approach is used to study the influences of anisotropic Orowan looping and solute-dislocation interaction on temperature-dependent yield strength. The strengthening model is validated with a dataset containing 297 experimental precipitate geometries, chemistries, temperatures, and strength measurements, and achieves a strong predictive correlation of 0.8713 with experimentally measured yield strengths. Under conditions that are applicable to coarsening, constant particle volume fraction and aspect ratio, the model predicts that short rod precipitates provide far superior strengthening effects compared to plate precipitates. A cast Al-Si-Mg-Cu alloy with rod-shaped Q-phase (Al3Cu2Mg9Si7) precipitates was developed with a novel chemistry exploring the use of low-diffusivity elements (Mn, Ni, V, Zr) to limit precipitate coarsening. The thermodynamic behavior of Mn, Ni, V, and Zr across the Q-phase interface is examined using transmission electron microscopy (TEM), first-principles density-functional theory (DFT) calculations. and atom-probe tomography (APT). DFT calculations utilizing TEM identified Q-phase/Al-matrix interfaces show that Mn, Ni, V, and Zr preferentially segregate to the Q-phase precipitate boundaries which suggests inhibition of precipitate coarsening and higher strengths after temperature exposure. Atom-probe tomography confirms solute atom partitioning/segregation at the Q-phase/Al-matrix interface, found in the modified commercial AS7GU alloy (A356 +0.5%Cu), which supports these observations.

CALPHAD-assisted composition and processing design of high-strength and high-conductivity copper alloy

In this work, a Cu–Cr–Ag–Mg–Sn alloy was developed assisted by a CALPHAD technique, by which a suitable chemical composition (Cu-0.5Cr-0.1Ag-0.05Mg-0.05Sn) and processing parameters were efficiently designed. The achieved alloy exhibited yield strength and conductivity values of 642 MPa and 74.2% IACS, respectively, which greatly surpassed the commercial C18150 alloy. Transmission electron microscopy observation demonstrated that such a good comprehensive performance was attributed to numerous nano-scale Cr precipitates that possessed a strong coherent relationship with the Cu matrix. Further microstructure characterizations demonstrated that these beneficial Cr precipitates were associated with subgrain boundaries in the alloy introduced by a cold-rolling→short-time secondary solid solution. Atom probe tomography analysis demonstrated that Sn atoms that readily attached to the surfaces of Cr precipitates.

Engineering of Adhesion at Metal-Poly(lactic acid) Interfaces by Poly(dopamine): The Effect of the Annealing Temperature.

Control over adhesion at interfaces from strong bonding to release between thermoplastic polymers (TPs) and metal oxides is highly significant for polymer composites. In this work, we showcase a simple and inexpensive method to tune adhesion between a TP of growing interest, poly(lactic acid) (PLA), and two commercial metal alloys, based on titanium and stainless steel. This is realized by coating titanium and stainless steel wires with polydopamine (PDA), thermally treating them under vacuum at temperatures ranging from 25 to 250 °C, and then comolding them with PLA to form pullout specimens for adhesion tests. Pullout results indicate that PDA coatings treated at low temperatures up to a given threshold significantly improve adhesion between PLA and the metals. Conversely, at higher PDA annealing temperatures beyond the threshold, interfacial bonding gradually declines. The excellent control over interfacial adhesion is attributed to the thermally induced transformation of PDA. In this work, we show using thermogravimetric analysis, X-ray photoelectron spectroscopy, Fourier transform infrared, and 13C solid-state NMR that the extent of the thermal transformation is dependent on the annealing temperature. By selecting the annealing temperature, we vary the concentration of primary amine and hydroxyl groups in PDA, which influences adhesion at the metal/PLA interface. We believe that these findings contribute to optimizing and broadening the applications of PDA in composite materials.

Basic Research on Multi-Directional Forging of AZ80Mg Alloy for Fabrication of Bulky Mechanical Components

In this study, a commercial hot-extruded AZ80Mg alloy was multi-directionally forged (MDFed) at room temperature by employing pass strains of Δε = 0.1. The effects of the combined processes of MDFing and ageing on the microstructural evolution and strengthening were precisely examined in advance. The coarse initial grains were gradually subdivided into ultrafine grains by multiple mechanical twinning and kinking. As observed, the multiple twinning effectively suppressed the evolution of the sharp basal texture and enabled MDFing at room temperature to high cumulative strains. Although the combined processes of MDFing and ageing tended to increase the hardness and yield stress compared to those fabricated using simple MDFing at lower cumulative strain regions, the mechanical properties were almost comparable and independent of the processes at regions of higher cumulative strain beyond ΣΔε = 2.0. Yield strength over 505 MPa, ultimate tensile strength of 612 MPa and ductility of 7% were constantly achieved in all the processes. Although certain selected processes were applied to bulk samples for fabricating the mechanical components, frequent cracking hindered the MDFing to high cumulative strain regions. This finding signified that adequate MDFing process is dependent on sample size. However, MDFing with smaller pass strains than Δε = 0.1 enabled MDFing to regions of high cumulative strain. Thus, bulk AZ80Mg alloy with well-balanced mechanical properties—yield strength of 420 MPa, ultimate tensile strength of 540 MPa, and ductility of 10%—could be successfully fabricated.

Effect of Initial Microstructure Prior to Extrusion on the Microstructure and Mechanical Properties of Extruded AZ80 Alloy with a Low Temperature and a Low Ratio

Magnesium (Mg) alloys are the lightest metal structural material for engineering applications and therefore have a wide market of applications. However, compared to steel and aluminum alloys, Mg alloys have lower mechanical properties, which greatly limits their application. Extrusion is one of the most important processing methods for Mg and its alloys. However, the effect of such a heterogeneous microstructure achieved at low temperatures on the mechanical properties is lacking investigation. In this work, commercial AZ80 alloys with different initial microstructures (as-cast and as-homogenized) were selected and extruded at a low extrusion temperature of 220 °C and a low extrusion ratio of 4. The microstructure and mechanical properties of the two extruded AZ80 alloys were investigated. The results show that homogenized-extruded (HE) sample exhibits higher strength than the cast-extruded (CE) sample, which is mainly attributed to the high number density of fine dynamic precipitates and the high fraction of recrystallized ultrafine grains. Compared to the coarse compounds existing in CE sample, the fine dynamical precipitates of Mg17(Al, Zn)12 form in the HE sample can effectively promote the dynamical recrystallization during extrusion, while they exhibit a similar effect on the size and orientation of the recrystallized grains. These results can facilitate the designing of high-strength wrought magnesium alloys by rational microstructure construction.

AZ31/GNP magnesium composites with excellent comprehensive mechanical properties prepared by friction stir processing and rolling

In order to further improve the comprehensive mechanical properties of commercial AZ31 Mg alloy, AZ31/graphene nano particulates (GNP) composites were prepared by AZ31 Mg alloy and graphene through friction stir processing (FSP) and following rolling. The microstructure and mechanical properties of as-FSPed and as-rolled alloys were investigated in this study. Compared with base metal, the ductility of FSPed alloys is greatly increased, while the strength is somewhat decreased. After further rolling on the FSPed plate, the strength of the alloy is improved. AZ31/GNP composites processed by FSP and rolling (50% reduction ratio) exhibits excellent mechanical properties with ultimate tensile strength of 296 MPa and elongation of 15.7%. The improved performance is attributed to the refinement of the grain and the homogenization of the second phase, which are the result of the severe plastic deformation characteristics of FSP. The multiplication of dislocations originated from rolling deformation and the reinforcement of GNP also contribute to the strength. The results verify that FSP as an intermediate step before rolling can be used as an effective mean to add reinforcement particles. On the other hand, the improved microstructure induced by severe plastic deformation of FSP is beneficial for further rolling.

Plasticity in irradiated FeCrAl nanopillars investigated using discrete dislocation dynamics

In this paper, we investigate plasticity in irradiated FeCrAl nanopillars using discrete dislocation dynamics simulations (DDD), with comparisons to transmission electron microscopic (TEM) in situ tensile tests of ion- and neutron-irradiated commercial C35M FeCrAl alloy. The effects of irradiation-induced defects, such as a/2<111> and a<100> type loops and composition fluctuations representative of phase separation in irradiated FeCrAl alloys, are investigated separately as well as superposed together in simulations. We explore the effects of defects on the stress-strain behavior, specifically yield strength and hardening response, of FeCrAl nanopillars. Our simulations confirm the widely accepted fact that irradiated alloys exhibit a stress-strain response with higher yield strength as compared to unirradiated alloys. However, our DDD calculations reveal an atypical superposition of the hardening contributions due to composition inhomogeneity and irradiation loops wherein composition inhomogeneity annihilates the hardening due to irradiation loops at small scales. As a result, we observe that the yield strength in irradiated alloys, after taking into consideration the effects of both composition inhomogeneity and irradiation loops, is smaller than the yield strength of the alloys with only irradiation loops and is approximately same for the alloy with composition inhomogeneity alone. This is referred to as “destructive interference” between the hardening contributions due to composition fluctuations and irradiation loops in the paper. We also identify this destructive interference in the superposition in our parallel TEM in situ tensile tests on unirradiated, ion-irradiated, and neutron-irradiated C35M FeCrAl alloy. This destructive interference in the hardening contributions contrasts with the dispersed barrier hardening (DBH) models widely utilized by the experimental community to model the hardening contributions due to different irradiation induced defects. The effects of the loading orientations on the yield strength and hardening are investigated and the mechanisms for the hardening in irradiated FeCrAl alloys are also reported.

Ultrafine-grained Ti6Al7Nb-xCu alloy with ultrahigh strength and exceptional biomedical properties

Grain refinement has been found to be able to improve the strength of metals without reducing their plasticity or ductility. In this work, ultrafine-grained Ti6Al7Nb-xCu (x = 0, 3 wt%, 6 wt%, 9 wt%) alloys were fabricated based on the clinically used Ti6Al7Nb alloy via Cu alloying fabrication strategy combined with dynamic recrystallization (DRX) from martensite during hot work. Our results indicate that Cu alloying is not only effective in reducing the width of martensite laths after quenching in the β phase region but also increases the nucleation rate of DRX during the high-temperature deformation. Additionally, the Ti2Cu phase that precipitates from the matrix can pin the grain boundaries and inhibit their growth during the high-temperature deformation. The optimal Cu concentration of Ti6Al7Nb-xCu alloy is determined to be 6 wt%, and the optimal deformation temperature is determined to be 750 °C. At this Cu content and deformation temperature, the grain size is only 270 nm, the tensile strength is up to 1266±10 MPa, and the elongation is 17%. Compared with the commercial Ti6Al7Nb alloy, the ultrafine-grained Ti6Al7Nb-6Cu alloy has better overall mechanical properties, good biocompatibility, and unique antibacterial properties. This work provides a theoretical basis for fabricating the new antibacterial titanium-based alloys with high strength.

Solidification cracking nature and sequence of different stainless steels

For magnesium, nickel, and stainless steel, solidification cracking is a critical failure mode that has been extensively studied for decades. The nature of solidification cracking can be investigated through experiments or theoretical calculations. Different models have been proposed for these calculations, including the cracking susceptibility index (CSI), which was developed in the last decade. Building a CSI map for a group of metals facilitates referencing or comparison when the metal is applied in casting, welding, or developing new alloys. In this study, the CSI of various types of stainless steel was examined, and CSI maps were constructed. For each type of alloy, the calculations include more than ten experimentally determined compositions from commercial alloys. The CSI maps of stainless steel were constructed and compared with those of the Cr and Ni equivalents, as well as their respective phase diagrams. The CSI sequence matched the cracking results of previous studies on austenitic steels. The ferritic type had a lower CSI but a higher cracking rate, which could be attributed to the ductility gap during the austenite-ferrite transformation, as reported in previous studies.

Electrochemical Oxide Growth on Nickel and Commercial Nickel Alloys: Influence of Chromium and Molybdenum

Nickel-chromium-molybdenum (NiCrMo) alloys are well-known for having exceptional corrosion resistance, but their electrocatalytic properties have not been extensively studied. In this paper, the development of electro-active nickel-oxyhydroxide (NiOOH) phases and kinetics of the oxygen evolution reaction (OER) have been examined on alloys G35, B3, and C276 in alkaline electrolyte at 25 °C. Reproducible oxide layers were grown by potential cycling between 0.85 and 1.52 V vs RHE up to 600 cycles, and the transition between Ni(OH)2 and NiOOH was monitored by cyclic voltammetry throughout. Onset potentials, Tafel slopes, and turnover frequencies (TOF) were measured at OER overpotentials between 270 and 390 mV. Alloys with dissimilar Cr:Mo ratios had significantly higher electrochemical surface area and increased γ-NiOOH formation, suggesting higher metal dissolution rates. The equal Cr:Mo concentration alloy and pure Ni developed a primarily β-NiOOH surface, and had 1.8–2.0 times larger TOF values than those containing significant γ-NiOOH. The NiCrMo alloys required smaller overpotentials (54–80 mV) to produce 10 mA cm−2 of OER current, and had comparable Tafel slopes to pure Ni. The findings here indicate a β-NiOOH-developed surface to be more OER-active than a γ-NiOOH-developed surface, and suggest certain NiCrMo alloys have promise as OER electrocatalysts.

On selection of advanced compositions of flame resistant magnesium alloys

Magnesium alloys are among the most advanced structural materials in aviation and mechanical engineering industry due to their low density and high strength-weight ratio, but their ability to ignite at temperatures from 500°C, while actively sustaining combustion, can cause disastrous consequences even in the event of minor emergencies. This paper is intended to investigate the compositions that can enhance flame resistance of magnesium alloys. Comparison was made between ignition temperatures of commercial cast alloy ML10, LPSO-structure alloy, advanced cast alloy with rare earth metals, and variations of these alloys with different additives — agents that improve flame resistance. It has been established that the maximum flame resistance is provided by those alloys that contain both the LPSO phase and the Yb or Ca additive as agents capable of raising the ignition temperature to 1000°C or even higher.