Similar Alloys Research Articles

Effect of swaging on microstructure and mechanical properties of W-Ni-Co alloys

The effect of deformation during warm swaging on mechanical properties of W-Ni-Co alloys was investigated. The alloys, based on 92%W with Ni/Co ratio of 7/3 and 8/2, were processed through liquid phase sintering followed by heat treatment and swaging. Multistep swaging deformation at 400 °C leads to increase in strength at the expense of ductility. For a given deformation, the alloy with 7/3 NiCo shows higher strength and lower ductility as compared to the alloy with 8/2 NiCo ratio. This is attributed to the presence of fine W precipitates (0.2–0.3%) in the matrix phase, which is relatively more in 7/3. Higher ductility of the 8/2 alloy is characterized by shear lip failure of the matrix in contrast to shallow dimple failure of the matrix in 7/3 and this appears to be consistent with the presence of fine, undeformable W precipitates in the matrix phase. The analysis of work hardening shows a three slope behaviour in the heat treated condition where as the swaged specimens show a single slope behaviour. This has been explained in terms of deformation of softer matrix in the initial stage (Stage I and II) and that of the two phase aggregate later (Stage III). The results are discussed in relation to the studies carried out on similar alloys.

Vacuum melting of compressed powders and hot rolling of the as-cast Ti-48Al-2Nb-0.7Cr-0.3Si intermetallic alloy: Mechanical properties and microstructural analysis

The amalgamated effect of hot-rolling, rapid cooling and heat treatment on the grain refinement and the resultant mechanical properties of an intermetallic sheet of nominal composition Ti-48Al-2Nb-0.7Cr-0.3Si was investigated. The sheet of 4 mm thickness was fabricated by hot-pack rolling from the vacuum arc remelted (VAR) ingot using a conventional two-high rolling mill. After the final rolling pass, the canned specimen was rapidly cooled in the air to room temperature followed by heat treatment in the α + γ region. The scanning electron microscopy (SEM) micrographs of the as-rolled sheet revealed slightly elongated grains of a typical “duplex (DP)” microstructure with a mean grain size of about 3 μm which grew to about 4 μm and became more equiaxed and homogeneous after heat treatment. Moreover, the EBSD micro-texture indicated a weak cube texture in the rolled + heat-treated sheet. Furthermore, the results from the profilometry-based indentation plastometry of the rolled + heat treated specimen illustrated the balanced and improved mechanical properties compared to the as-cast and as-rolled samples, and also those of similar alloy systems found in the literature.

The Tensile, Hardness and Impact Behaviour of Friction Stir Welded Similar and Dissimilar Aluminium Alloys

The Tensile, Hardness and Impact Behaviour of Friction Stir Welded Similar and Dissimilar Aluminium Alloys

High strain rate deformation behavior of Al0.65CoCrFe2Ni dual-phase high entropy alloy

An industrially-cast high entropy alloy with a nominal composition of Al0.65CoCrFe2Ni, having FCC and BCC phases, was compressed at high strain rates using a split Hopkinson pressure bar under a range of test temperatures. The strain rate sensitivity and strain hardening behaviour of the alloy were analyzed. The alloy exhibited high strain hardening and excellent strain rate sensitivity owing to its large solid solution strengthening and low athermal strength contributors. The alloy also displayed outstanding dynamic strain rate sensitivity compared to similar dual-phase high entropy alloys of the AlCoCrFeNi alloy system. The alloy exhibited excellent resistance to thermal softening at high strain rate loading due to higher phonon drag associated with an increase in the operating temperature. The substructures formed in the alloy during high strain rate deformation at room temperature comprised of Lomer-Cottrell (L-C) locks, deformation twins, planar deformation bands, and high dislocation pile-ups at interphase boundaries and subgrain boundaries. The high strain rate deformation at high temperatures resulted in the formation of dislocation cells, kinks and jogs, enabling the alloy to retain strain hardening behavior. The Johnson-Cook (J-C) model accurately predicted the plasticity behavior of the alloy under high strain rate loading.

Dynamic recrystallization in friction stir welded AA2014 aluminium alloy joints to replace riveted joints

Abstract The demand for lightweight materials (aluminium and magnesium alloy) in structural applications is increasing due to strength ratio, corrosion resistance, formability, and recyclability. Fusion welding of aluminium and its alloy is difficult due to the formation of hot cracking, alloy segregation, porosity, etc. Henceforth, fusion welding is not an ideal process for joining aluminium and its alloy. Steel rivets are being used to join similar and dissimilar alloys in different joint configurations. Since the use of steel rivets, aircraft weight has increased drastically. Although, dissimilar metal corrosion has been encountered. These two are the main problems in structural fabrication industries. The solid-state welding friction stir welding process eliminates the issues mentioned earlier. This process can weld materials well below the melting point. Moreover, the formation of weld in the weld line could be achieved by severe plastic deformation and recrystallized grains. This metallurgical joint may replace the rivets.

Porous metal micro-pillars by thermomechanical molding of two-phase alloys

Creep-based thermomechanical molding of crystalline metals has emerged as a low-cost manufacturing technique for metal nanostructures. Here, we demonstrate the potential of such molding approach in fabrication of porous metal microstructures by using binary alloys such as Au-Si and Al-Cu. Two-phase alloys were isothermally molded against microscale templates followed by selective etching of one of the phases resulting in porous micro-pillars. The porosity of micro-pillars was varied by changing the phase fractions through alloy composition. Scanning electron microscopy is used to understand the different stages of molding and etching processes for two-phase metal alloys. While the nanoscale thermomechanical molding of similar alloys has been attributed to diffusional creep, the microscale forming presented here is dominated by the dislocation and grain boundary mediated deformation mechanisms. The molding and selective etching methodology can be potentially used to tailor the size and the distribution of pores by optimizing the microstructure of feedstock alloy.

VNbCrMo refractory high-entropy alloy for nuclear applications

Refractory high-entropy alloys (RHEAs) with high melting points and low neutron absorption cross-section are sought for generation-IV fission and fusion reactors. A high throughput computational screening tool, Alloy Search and Predict (ASAP), was used to identify promising RHEA candidates from over 1 million four-element equimolar combinations. The selected VNbCrMo RHEA was further studied by CALPHAD to predict phase formation, which was compared to an experimentally produced ingot aged at 1200 °C. The VNbCrMo RHEA was found to constitute a majority bcc phase, with a 6% area fraction of C15-Laves formed at interdendritic regions, in contrast to the predictions of single-phase. The prediction of the yield strength by a model based upon edge dislocation mechanisms indicated 2.1 GPa at room temperature and 850 MPa at 1000 °C for the equimolar single bcc phase. The hardness of the alloy with C15-Laves was 748 HV (yield strength ∼2.4 GPa). Finally, the macroscopic neutron absorption cross-section was modelled for a wide range of energies. Displacements per atom per year and activation calculations, up to 1000 years after 2 years of continuous operation, in typical fusion and fission reactor scenarios were also performed using the inventory code FISPACT-II. This work gives new insight into the phase stability and performance of the VNbCrMo RHEA, which is compared with a similar design concept alloy, to assess the potential of novel RHEAs for use in advanced nuclear applications.

Elastic–Plastic Properties of Mesoscale Electrodeposited LIGA Nickel Alloy Films: Analysis of Measurement Uncertainties

Abstract It is well documented that the microstructure and properties of electrodeposited films, such as lithographie, galvanoformung, abformung (LIGA) Ni and its alloys, are highly sensitive to processing conditions hence the literature shows large discrepancies in mechanical properties, even for similar alloys. Given this expected material variability as well as the experimental challenges with small-scale mechanical testing, measurement uncertainties are needed for property values to be applied appropriately, and yet are uncommon in micro- and mesoscale tensile testing studies. In a separate paper, we reported the elastic–plastic properties of 200 μm-thick freestanding films of LIGA-fabricated nanocrystalline Ni-10%Fe and microcrystalline Ni-10%Co, with specimen gauge widths ranging from 75 μm to 700 μm, and tensile tested at strain rates 0.001 s−1 and 1 s−1. The loads were applied by commercial miniature and benchtop load frames, and strain was measured by digital image correlation. In this paper, we examine the measurement uncertainties in the ultimate tensile strength, apparent Young's modulus, 0.2% offset yield strength, and strain hardening parameters, and compare them to the standard deviations. For several of these properties, the standard deviation cannot be interpreted as the statistical scatter because the measurement uncertainty was larger. Microplasticity affects the measurement of the Young's modulus, thus we recommended measuring the modulus after specimens have been cyclically loaded. These measurement uncertainty issues might be relevant to similar works on small-scale tensile testing and might help the reader to interpret the discrepancies in literature values of mechanical properties for LIGA and electrodeposited films.

A novel high-entropy alloy with exceptional strength and elongation via bimodal grains and lamellar nano-precipitates

This study presents a new effective approach for enhanced mechanical properties of the high-entropy alloy (HEA) Al7.3Co21.3Cr10.7Ti4.9Fe21.3Ni32.0Cu2.5 obtained by cold-rolling of columnar grains and subsequent annealing. This processing strategy aims to construct a microstructure of bimodal grains and coherent lamellar nano-precipitates. An ultrahigh strength of ∼1.68 GPa and a high elongation of ∼13.5% after annealing at 700 °C for 4 h were obtained, which are superior to those of previously reported similar HEAs. The ultrahigh strength originates mainly from the lamellar nano-precipitates strengthening and the bimodal grain size; however, the large elongation correlates to a progressive work-hardening mechanism regulated by the collaborative deformation of the ultrafine grains and the coarse grains and the unique nano-lamellar precipitates. This study provides a new strategy to utilize bimodal grains and coherent nano-precipitates in the development of HEAs or other similar alloys.

Creep Analysis and Microstructural Evaluation of a Novel Additively Manufactured Nickel-Base Superalloy (ABD®-900AM)

Abstract Nickel-base superalloys containing 30 to 50% gamma prime (γ') volume fraction are typically used in hot section components (e.g., guide vanes or blades) for power generating gas turbines, and suitable time-dependent properties are required for long-term elevated temperature operation. Additive manufacturing (AM) has recently been used to develop complex hot-section parts utilizing innovative designs with enhanced cooling features which improve efficiencies by reducing cooling air consumption. To further explore the opportunity to improve time-dependent AM superalloys, this paper focuses on a fundamental creep study and characterization of a novel nickel-base superalloy (ABD-900AM) that was manufactured using a laser-based powder bed fusion (LBPBF) AM process. The material was subjected to a subsolvus solution anneal and multistep aging heat treatment (HT) to produce a bi-modal distribution with ∼35% volume fraction of gamma prime without postprocessing hot isostatic pressing (HIP). Microstructural characterization was carried out for the as-built and fully heat-treated structures, and a creep-rupture test program was conducted to study the resultant creep properties. Activation energies and stress exponents in addition to rupture strength and deformation resistance were compared to traditionally cast IN939 and IN738 materials. After testing, specimens were evaluated using a variety of microscopy tools to determine location and features associated with creep damage. The optimized chemistry for ABD-900AM was printed crack free and fully dense in contrast to studies on similar alloys where significant process development and postbuild heat treatments were required. High-temperature mechanical properties in the heat-treated material showed some decrease in creep strength when compared to traditional casting. This strength and rupture life debit was dependent on build orientation, but a considerable increase in creep ductility was observed due to differences in the microstructure when compared with similar AM alloys. Analysis of creep data showed differences in creep mechanisms compared to traditional cast alloys. The relationship between microstructure and creep mechanisms is discussed, and ongoing work to further improve rupture strength through heat-treatment optimization will be highlighted.

Influence of oxygen on performance of multi-principal element alloy as braze filler for Ni-base alloys

In manufacturing of multi-principal element alloys (MPEAs), the casting process is often a primary point of oxygen introduction to the material system, which was demonstrated by the laboratory scale button arc-melting process. Oxygen introduction raises concerns for the mechanical performance of these alloys if employed as structural materials alone or in engineering applications, such as serving as filler materials to enable joining of similar or dissimilar alloy pairs that are conventionally considered difficult to join. In this work, oxide inclusions in an as-cast off-equiatomic MnFeCoNiCu MPEA and Ni-base alloy braze joints made with this MPEA were evaluated by synchrotron x-ray diffraction mapping and electron microscopy. MnO was found to be prevalent throughout the cast MPEA and was chemically reduced during brazing by trace Al from the base material, Ni-base Alloy 600. Incomplete reaction of the MnO with Al, and some alternative reaction with Cr, left a mixture of MnO, Al2O3, and Cr2O3 in the as-brazed joint, with the oxides concentrated near the braze centerline due to directional solidification. In the braze joints, the non-oxide constituent phases detected were an FCC matrix and particles of Cr23C6, Cr7C3, and TiN which are all native to Alloy 600. The evolution of oxides within the brazed joints at elevated service temperatures of 600–800 °C was also evaluated. While MnO and Al2O3 were stable during high-temperature service, Cr2O3 particles grew to several hundred microns, with dissolved oxygen in the MPEA providing a significant source for oxide growth. Comparing tensile performance of the as-brazed condition with post-service conditions showed that the evolution of oxide particles contributed to an increase in strength and decrease in ductility of the brazed joints. Evaluating particle morphologies among fracture surfaces of individual specimens demonstrated that large Cr2O3 particles and continuous cluster networks of Al2O3 were the features most detrimental to total elongation. Hence, unmitigated evolution of oxygen-containing species during brazing and service conditions is detrimental to the ductility of the brazed joints, which highlights the importance of oxygen control in initial manufacturing of MPEAs for engineering applications.

Microstructure and Mechanical Properties of Hypereutectic Al-High Si Alloys up to 70 wt.% Si-Content Produced from Pre-Alloyed and Blended Powder via Laser Powder Bed Fusion.

Hypereutectic Al-high Si alloys are of immense interest for applications in the automotive, space or electronic industries, due their low weight, low thermal expansion, and excellent mechanical and tribological properties. Additionally, their production by laser powder bed fusion (LPBF) technology provides high flexibility in geometrical design and alloy composition. Since, most of the alloy properties could be improved by increasing the Si content, there is much interest in discovering the maximum that could be realized in LBPF Al-high Si alloys, without the appearance of any material failure. For this reason, in this work the production of Al-high Si alloys with extremely high silicon content of up to 70 wt.% was fundamentally investigated with respect to microstructure and mechanical properties. Highly dense (99.3%) and crack-free AlSi50 samples (5 × 5 × 5 mm3), with excellent hardness (225 HV5) and compressive strength (742 MPa), were successfully produced. Further, for the first time, AlSi70 LBPF samples of high density (98.8%) without cracks were demonstrated, using moderate scanning velocities. Simultaneously, the hardness and the compressive strength in the AlSi70 alloys were significantly improved to 350 HV5 and 935 MPa, as a result of the formation of a continuous Si network in the microstructure of the alloy. With respect to the powder source, it was found that the application of powder blends resulted in similar alloy properties as if pre-alloyed powders were used, enabling higher flexibility in prospective application-oriented alloy development.

Performance analysis of similar and dissimilar self-piercing riveted joints in aluminum alloys

In this work, similar (2A12) and dissimilar (6061) aluminum alloy sheets are validly joined using self-piercing rivet process. A quasi-static experiment is proposed to investigate the mechanical behaviors, failures mode, and mechanism of the different joints. Moreover, a method based on deep learning algorithm is anticipated to detect the appearance defects of the SPR welded joints. The results indicated that 2A12 joints of similar sheets contained the advantageous static strength and 6061 similar sheet joints had superior anti-vibration performance conducts. The joints with 6061-2A12 sheets introduced the most decent and comprehensive mechanical properties. The main failure mode of 2A12 similar sheet joints was substrate fracture. The performance of the substrate affects the failure mode of the joint and the plasticity of the substrate is better. When the time comes, the failure mode is mostly pull-off failure. Poor plasticity of the substrate can easily lead to substrate breakage. The reason for joint pull-off and button fall-off failure is that there is large plastic deformation in the lower plate of the joint and the mechanical internal locking structure is damaged. 2A12 substrate breakage belongs to a composite fracture that combines intergranular fracture and microvoid aggregation type fracture. The area of the 6061 substrate near the edge of the sample is shear fracture and the area near the center of the sample thickness is dominated by microvoid aggregation type normal fracture. The effectiveness of the method was verified by conducting a series of experiments and the detection accuracy of the method can reach about 90%. The detection speed was as high as 50 frames per second (FPS), which can effectively solve the problem that the rivet quality was difficult to monitor.

Design of new Al-Si-Mg alloys by multi-modal mixed input simulation experiment

On the basis of a large number of experimental data, it is a challenge to establish a data-driven non-linear law between mixing characteristics and mechanical properties for the proportioning and process design of new alloy compositions. This paper proposes a performance-oriented “composition-process-property” design strategy for Al-Si-Mg alloys based on a machine learning approach, aiming to adopt multimodal experimental data on the composition, melting and heat treatment processes of divergent grades of the same system as features, and a random forest algorithm is used to find the non-linear pattern between the features and the tensile strength. Afterward, this paper sets the composition and process parameters of some of the alloys in the dataset as the target null values and uses the chain equation multiple interpolation algorithms to predict the interpolation of the target missing data. The errors of both experimental and predicted values of tensile strength of the alloys predicted or guided by this strategy are kept within ±5%; The composition ratio of Al-6.8Si-0.6Mg-0.05Sr and the heat treatment scheme of 540 ℃×10 h+170 ℃×10 h are experimentally confirmed to have a quality index <i>Q</i><sub>DJR</sub> of 517.3 for comprehensive tensile properties, which is higher than that of similar alloys below a <i>Q</i><sub>DJR</sub> value of 500. The result indicates that this strategy helps to enhance the long cycle time, high cost, and low efficiency of the traditional design method for Al-Si-Mg system alloys.

Nitriding of chromium-nickel alloys synthesized by laser melting

The effect of nitriding on the structure and hardness of chromium-nickel alloy obtained by selective laser melting has been studied. It has been shown that after nitriding a weakly developed ε-phase nitride zone with a thickness of about 10 μm and an internal nitriding zone with a thickness of more than 300 μm are formed on the surface of the alloy, which is twice as much as that of nitrided similar alloys obtained by the conventional method. The microhardness of the nitrided layer is 3500 MPa, this is 1.5 times higher than the hardness of the core, so nitriding of powder materials produced by additive technologies can be recommended for surface hardening of parts operating under conditions of wear and cyclic loads.

A Review on the Friction Stir Brazing for Joining Dissimilar Materials

Friction stir brazing (FSB) is a new technology developed for its ability to join similar and dissimilar metals and alloys resulting in a joint with considerable characteristics through the use of interlayer (braze) material under the action of a pinless rotating tool and other FSB parameters. The frictional heat during FSB is responsible for the melting of the braze material between the two workpieces, while the shoulder action must be satisfactory for the extrusion of the excess braze liquid phase depending on the FSB parameters used. The parameters of FSB also have a considerable impact on the microstructure and mechanical characteristics of friction stir brazed (FSBed) joints. Sound interfacial bonding can be observed in the central zone of FSBed joints, where intermetallic compounds (IMCs) can be formed by direct diffusion among the dissimilar workpieces after extrusion of liquid phase rather than by mechanical mixing or solidification of braze material. Increasing the transverse speed at a constant rotational speed has an influence on the peak temperature, but it remarkably reduces the holding time owing to the increased cooling rate. The use of vibration in the FSB increments the fluidity of the molten braze material among the joining workpieces resulting in a more homogeneous distribution of IMCs particles. In this review article, FSB parameters, bonding mechanisms, as well as the microstructure, and mechanical properties of FSBed joints are reviewed.

Experimental investigations on cryogenic friction-stir welding of similar ZE42 magnesium alloys

In this research, the cryogenic friction stir welding (CFSW) process has been performed using a liquid nitrogen medium to join two similar ZE42 magnesium alloy plates. The new experimental setup has been designed and fabricated to supply low-temperature (−196 °C) liquid nitrogen into the welding zone. The effects of welding parameters (tool pin profile, tool rotational speed, welding speed, and axial load) on the welding characteristics (tensile strength, hardness, and wear rate) have been investigated by the Taguchi technique. The impacts of welding parameters have been analysed to predict the optimum welding characteristics. The predicted best welding settings have been utilized to compare the CFSW and normal friction stir welding (NFSW) performances. The fractography of tensile-tested specimens, hardness distributions, and microstructure of worn-out CFSW welding surfaces have been examined by scanning electron microscopy (SEM) analysis. When compared to the NFSW process, the tensile strength and hardness of CFSW are improved by 41.36 % and 35.13 %, respectively, and the wear rate has decreased by 23.53 %.

A process optimization framework for laser direct energy deposition: Densification, microstructure, and mechanical properties of an Fe[sbnd]Cr alloy

Laser Direct Energy Deposition (DED) is a metal additive manufacturing technique with the ability to fabricate large and complex parts through deposition of metal powders. However, achieving high-density parts and targeted build heights using DED can be challenging due to the large number of highly sensitive process variables. This work proposes a robust fabrication parameter optimization framework to generate process maps for primary parameters in DED, including laser power, scan speed, mass flow rate, hatch spacing, and layer height. Simple single-track experiments were utilized to map out the parameter space, and a combination of geometric criteria for hatch spacing and layer height were proposed to determine parameter sets that achieve both targeted build heights and mitigate porosity formation. Using this framework, specimens with >99 % density and consistent mechanical properties were successfully fabricated over a wide range of process parameters for an Fe-9wt.%Cr (Fe9Cr) alloy, a surrogate for radiation damage-resistant reduced activation ferritic/martensitic (RAFM) steels. Processing these materials using DED is of particular interest in the development of plasma facing components for nuclear fusion applications. The microstructure and mechanical properties of as-printed Fe9Cr were characterized using optical and electron microscopy, X-ray diffraction, and uniaxial tensile tests. As-printed Fe9Cr displayed ~25 % elongation and ultimate tensile strengths of up to 475 MPa which is comparable to similar wrought alloys. The proposed framework will allow for accelerated DED parameter optimization for novel alloy systems, as well as open the possibility for local microstructure control while simultaneously mitigating defect formation.

The Estimation of Taylor-Quinney Coefficients Using Small Ring Specimens

BackgroundThe use of the Taylor-Quinney coefficient for introducing a thermal dissipation term into material models relies on understanding its dependencies. These are usually determined through extensive experimentation, wherein temperature variations are monitored in a test piece during mechanical loading.ObjectiveThis study aims to reduce the cost and time necessary to determining the dependencies of the Taylor-Quinney coefficient by proposing a novel small specimen inverse testing method and demonstrating its use on aluminium alloy 7175.MethodsThe method proposed is based on mechanical testing of a novel small ring specimen in parallel with FEA simulations. In the experiments, small rings of 7175-T7351 aluminium alloy, 20 mm in outer diameter, were loaded between two pins for different pin displacement rates (namely 1, 1.5 and 2 mm/s) at room temperature and the local specimen temperature field was monitored using an infra-red thermal camera. Fully coupled thermal-mechanical simulations of the tests were performed using a range of Taylor-Quinney coefficients, and the resulting temperature evolutions compared to the experimental results in order to determine appropriate coefficient values for the material.ResultsThe method presented shows good repeatability and allows for clear observation of thermal dissipation. Taylor-Quinney values ranging 0.51-0.59 are reported for the 7175 alloy, in line with values reported in the literature for similar alloys. Density, specific heat capacity and thermal conductivity, fundamental thermal material properties necessary for the simulations, are also reported for the alloy.ConclusionsThe method detailed shows promise for determining Taylor-Quinney coefficients in a wide range of experimental conditions and is proposed as a cheap and fast alternative to full-scale specimen testing of Taylor-Quinney coefficients. Taylor-Quinney values obtained for 7175 aluminium are shown to be much lower than the value of 0.9 often proposed for materials.

High Symmetry Metal‐Dielectric Photonic Crystal Organic Light Emitting Diodes With Single‐Cavity Unit Cells

AbstractVertically‐stacked organic light emitting diode (OLED) microcavities form 1D metal‐dielectric photonic crystals (MDPC) with many degrees of freedom for engineering complex emission profiles. The photonic band structure of the MDPC OLED is determined by the underlying unit cell and is particularly sensitive to the properties of the metallic electrodes. The electronic requirements of microcavity OLED fabrication often necessitate dissimilar metallic electrodes to achieve good performance. This can profoundly impact the photonic properties of a MDPC by doubling the unit cell length. This work presents a MDPC OLED formed with single‐cavity unit cells by employing optically similar Ag alloys as the semi‐transparent electrode materials. The crystal is found to display a single photonic band without a band gap up to eight stacked cavities. The states within the band are evenly‐spaced and clearly resolved, which is critical for applications seeking to utilize specific photonic states. Design considerations are presented for optimizing the photonic behavior of MDPC OLEDs through selective control of the optical properties of metallic alloys.