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Showing papers on "Alloy published in 2015"


Journal ArticleDOI
TL;DR: In this article, an equiatomic CoCrFeMnNi high-entropy alloy (HEA), produced by arc melting and drop casting, was subjected to severe plastic deformation (SPD) using high pressure torsion.

887 citations


Journal ArticleDOI
TL;DR: A new approach is developed to rapidly assess structural metals by combining calculated phase diagrams with simple rules based on the phases present, their transformation temperatures and useful microstructures, finding the surprising result that solid solution alloys become less likely as the number of alloy elements increases.
Abstract: Recent multi-principal element, high entropy alloy (HEA) development strategies vastly expand the number of candidate alloy systems, but also pose a new challenge--how to rapidly screen thousands of candidate alloy systems for targeted properties. Here we develop a new approach to rapidly assess structural metals by combining calculated phase diagrams with simple rules based on the phases present, their transformation temperatures and useful microstructures. We evaluate over 130,000 alloy systems, identifying promising compositions for more time-intensive experimental studies. We find the surprising result that solid solution alloys become less likely as the number of alloy elements increases. This contradicts the major premise of HEAs--that increased configurational entropy increases the stability of disordered solid solution phases. As the number of elements increases, the configurational entropy rises slowly while the probability of at least one pair of elements favouring formation of intermetallic compounds increases more rapidly, explaining this apparent contradiction.

587 citations


Journal ArticleDOI
TL;DR: In this article, a liquid metallurgy synthesized, non-equiatomic Fe 40 Mn 40 Co 10 Cr 10 high entropy alloy is designed to undergo mechanically-induced twinning upon deformation at room temperature.

577 citations


Journal ArticleDOI
TL;DR: The microstructural and mechanical properties of Inconel 718 were determined on the specimens manufactured by selective laser melting (SLM) of prealloyed powder as mentioned in this paper, showing that columnar grains of supersaturated solid solution with internal microsegregation of Nb and Mo, demonstrated by fractions of Laves eutectic or its divorced form in interdendritic regions.
Abstract: The microstructural and mechanical properties of Inconel 718 were determined on the specimens manufactured by selective laser melting (SLM) of prealloyed powder. High- density (99.8%) cylindrical specimens were built with four orientations (0°, 45°, 45°×45° and 90°) in relation to the building and scanning directions. Because of directional, dendritic-cellular grain growth, microstructure of the as-built specimens was characterized by columnar grains of supersaturated solid solution with internal microsegregation of Nb and Mo, demonstrated by fractions of Laves eutectic or its divorced form in interdendritic regions. Such a heterogeneous microstructure is unsuitable for direct post-process aging and makes the alloy sensitive to subsolidus liquation during rapid heating to the homogenizing temperature. In homogenized and aged condition, the alloy received a very good set of mechanical properties in comparison with the wrought material. In heat-treated condition, like in as-built condition, weak anisotropy of properties was found, manifested by lower Young's modulus, yield strength and tensile strength of the specimens extended along the build direction in comparison to the values for the other variants of the specimens. This is attributed to the fact that the grains maintained their geometric and crystallographic texture obtained during solidification.

512 citations


Journal ArticleDOI
TL;DR: An ultralow density (1.4 g cm(-3)) Mg-Li-based alloy is designed that is strong, ductile, and more corrosion resistant than M g-based alloys reported so far.
Abstract: Ultra-lightweight alloys with high strength, ductility and corrosion resistance are desirable for applications in the automotive, aerospace, defence, biomedical, sporting and electronic goods sectors. Ductility and corrosion resistance are generally inversely correlated with strength, making it difficult to optimize all three simultaneously. Here we design an ultralow density (1.4 g cm−3) Mg–Li-based alloy that is strong, ductile, and more corrosion resistant than Mg-based alloys reported so far. The alloy is Li-rich and a solute nanostructure within a body-centred cubic matrix is achieved by a series of extrusion, heat-treatment and rolling processes. Corrosion resistance from the environment is believed to occur by a uniform lithium carbonate film in which surface coverage is much greater than in traditional hexagonal close-packed Mg-based alloys, explaining the superior corrosion resistance of the alloy. A magnesium-based alloy with large lithium content demonstrates high specific strength in combination with corrosion resistance, associated with the formation of a lithium carbonate surface film that protects the alloy from its environment.

504 citations


Journal ArticleDOI
05 Feb 2015-Nature
TL;DR: It is shown that an FeAl-type brittle but hard intermetallic compound (B2) can be effectively used as a strengthening second phase in high-aluminium low-density steel, while alleviating its harmful effect on ductility by controlling its morphology and dispersion.
Abstract: Although steel has been the workhorse of the automotive industry since the 1920s, the share by weight of steel and iron in an average light vehicle is now gradually decreasing, from 68.1 per cent in 1995 to 60.1 per cent in 2011 (refs 1, 2). This has been driven by the low strength-to-weight ratio (specific strength) of iron and steel, and the desire to improve such mechanical properties with other materials. Recently, high-aluminium low-density steels have been actively studied as a means of increasing the specific strength of an alloy by reducing its density. But with increasing aluminium content a problem is encountered: brittle intermetallic compounds can form in the resulting alloys, leading to poor ductility. Here we show that an FeAl-type brittle but hard intermetallic compound (B2) can be effectively used as a strengthening second phase in high-aluminium low-density steel, while alleviating its harmful effect on ductility by controlling its morphology and dispersion. The specific tensile strength and ductility of the developed steel improve on those of the lightest and strongest metallic materials known, titanium alloys. We found that alloying of nickel catalyses the precipitation of nanometre-sized B2 particles in the face-centred cubic matrix of high-aluminium low-density steel during heat treatment of cold-rolled sheet steel. Our results demonstrate how intermetallic compounds can be harnessed in the alloy design of lightweight steels for structural applications and others.

486 citations


Journal ArticleDOI
TL;DR: In this article, an as-fabricated Al-12Si alloy with controllable ultrafine microstructure and excellent mechanical properties can be achieved by using selective laser melting and subsequent solution heat treatment.

479 citations


Journal ArticleDOI
TL;DR: Inconel 718 superalloy has been fabricated by selective laser melting technology (SLM), and its microstructure and mechanical properties were studied under solution+aging (SA) standard heat treatment, homogenization+solution+solutionsolution + aging (HSA), and as-fabricated conditions as discussed by the authors.
Abstract: Inconel 718 superalloy has been fabricated by selective laser melting technology (SLM). Its microstructure and mechanical properties were studied under solution+aging (SA) standard heat treatment, homogenization+solution+aging (HSA) standard heat treatment and as-fabricated conditions. Precipitated phases and microstructures were examined using OM, SEM, TEM and X-ray analysis methods. The fine dendrite structures with an average dendrite arm spacing of approximately 698 nm accompanying some interdendritic Laves phases and carbide particles can be observed in the as-fabricated materials. After standard heat treatments, dendrite microstructures are substituted by recrystallization grains, and Laves phases also dissolve into the matrix to precipitate strengthening phases and δ particles. The test values of all specimens meet Aerospace Material Specification for cast Inconel 718 alloy, and the transgranular ductile fracture mode exists for the three conditions. The strength and hardness of heat-treated SLM materials increase and are comparable with wrought Inconel 718 alloy, whereas their ductility decreases significantly compared with the as-fabricated material. This is because of the precipitation of fine γˊ and γ〞strengthening phases and needle-like δ phases. For the as-fabricated alloy, the formation of finer dislocated cellular structures that develop into a ductile dimple fracture shows excellent ductility. Due to dislocation pinning from γˊ and γ〞strengthening phases and the impediment of dislocation motion caused by the needle-like δ phases, the ductility of the SA materials decreases and causes a transgranular fracture, compared with the as-fabricated samples.

467 citations


Journal ArticleDOI
TL;DR: In this paper, the authors investigated the effect of the fundamental solid solution strengthening (SSS) effect on the tensile strength of Hastelloy X, a common nickel-base superalloy of known high crack susceptibility when processing SLM.

462 citations


Journal ArticleDOI
TL;DR: A low-density, nanocrystalline high-entropy alloy, Al20Li20Mg10Sc20Ti30 was produced by mechanical alloying as discussed by the authors, which formed a single phase fcc structure during ball milling and transformed to single phase hcp upon annealing.
Abstract: A low-density, nanocrystalline high-entropy alloy, Al20Li20Mg10Sc20Ti30 was produced by mechanical alloying. It formed a single-phase fcc structure during ball milling and transformed to single-phase hcp upon annealing. The alloy has an estimated strength-to-weight ratio that is significantly higher than other nanocrystalline alloys and is comparable to ceramics. High hardness is retained after annealing.

448 citations


Journal ArticleDOI
TL;DR: In this article, the composition of HfNbTaTiZr was modified with an aim to improve its strength at high temperature, while retaining reasonable toughness at room temperature.

Journal ArticleDOI
TL;DR: In this paper, a set of model FeCrAl alloys containing 10−20Cr, 3−5Al, and 0−0.12Y in weight percent, were prepared by conventional arc-melting and hot-working processes to explore the effect of composition on the properties of FecrAlY alloys.

Journal ArticleDOI
TL;DR: In this paper, the microstructure evolution in high-entropy alloy CoCrFeNiMn during plane-strain multipass rolling to a thickness strain of 80% at 293 and 77 K was studied.

Journal ArticleDOI
TL;DR: A series of five-component CoCrFeNiNbx high entropy alloys were synthesized to investigate alloying effects of the large atom Nb on the structure and tensile properties as discussed by the authors.

Journal ArticleDOI
TL;DR: In this article, an equiatomic FeCoCrNi high-entropy alloy is used as an input material for selective laser melting, and the material is characterized using X-ray diffraction, scanning electron microscopy, thermal analysis and mechanical testing.

Journal ArticleDOI
TL;DR: In this article, the mechanisms of corrosion and hydrogen pickup and the role of alloy selection in minimizing both phenomena are considered on the basis of two principal characteristics: the pretransition kinetics and the loss of oxide protectiveness at transition.
Abstract: During operation, nuclear fuel rods are immersed in the primary water, causing waterside corrosion and consequent hydrogen ingress. In this review, the mechanisms of corrosion and hydrogen pickup and the role of alloy selection in minimizing both phenomena are considered on the basis of two principal characteristics: the pretransition kinetics and the loss of oxide protectiveness at transition. In zirconium alloys, very small changes in composition or microstructure can cause significant corrosion differences so that corrosion performance is strongly alloy dependent. The alloys show different, but reproducible, subparabolic pretransition kinetics and transition thicknesses. A mechanism for oxide growth and breakup based on a detailed study of the oxide structure can explain these results. Through the use of the recently developed coupled current charge compensation model of corrosion kinetics and hydrogen pickup, the subparabolic kinetics and the hydrogen fraction can be rationalized: Hydrogen pickup incr...

Journal ArticleDOI
TL;DR: In this article, phase composition and microstructure of the alloys were analyzed employing criteria for solid solution/intermetallic phase formation, and the effect of alloys' chemical composition on the volume fraction of constitutive phases was discussed.

Journal ArticleDOI
TL;DR: In this article, the crystal structure, microstructure, density, microhardness and mechanical properties of new AlNbTiV high entropy alloy were examined and the specific yield strength of the alloy was found to be comparable with strength of multiphase refractory high entropy alloys.

Journal ArticleDOI
TL;DR: An equiatomic CoCrFeNiMn high-entropy alloy was synthesized by mechanical alloying (MA) and spark plasma sintering (SPS) as mentioned in this paper.

Journal ArticleDOI
TL;DR: In this article, a hydrophobic surface was fabricated through the micro-arc oxidation (MAO) and subsequent stearic acid surface modification of AZ31 Mg alloy, achieving a maximum water contact angle of 151.5° after 10h of modification.

Journal ArticleDOI
TL;DR: In this article, the effects of carbon on microstructures, mechanical properties and twinning activities were investigated in two different temperatures (77 and 293 K) and they found that these materials can be cold rolled and recrystallized to produce a microstructure with equiaxed grains.

Reference EntryDOI
20 Feb 2015
TL;DR: The Unified Numbering System (UNS) is the accepted alloy designation system in North America for wrought and cast coppers and copper alloys as mentioned in this paper, which is used to identify marine alloys.
Abstract: Copper was among the first metals to be put into utilitarian service. The Unified Numbering System (UNS) is the accepted alloy designation system in North America for wrought and cast coppers and copper alloys. Identification is by five-digit numbers preceded by the letter C. Preferred marine alloys include copper nickels, which exhibit the highest corrosion and erosion resistance among copper metals, and also offer relatively high strengths, and aluminum bronzes, which are stronger still, as well as ultrahigh-strength beryllium copper, inhibited aluminum brass, phosphor bronzes, arsenical admiralty brass, and nickel silvers. Copper alloys that perform well in seawater are also often acceptable for use with industrial and process. Copper casting alloys are widely used in the manufacture of plumbing, electrical, and mechanical products and for bearings and industrial valves and fittings. Copper nickels, aluminum bronzes, silicon bronzes, manganese bronzes, and tin and phosphor bronzes should be considered for such environments. Keywords: copper alloys; marine alloys; Unified Numbering System (UNS)

Journal ArticleDOI
TL;DR: In this paper, the evolution of the structure and microstructure of the equimolar CrMnFeCoNi high entropy alloy was investigated during processing under varying conditions (cooling rate and annealing duration).


Journal ArticleDOI
TL;DR: In this article, the effects of Al on microstructure and mechanical properties of AlxCoCrFeNi (x=0.1, 0.75 and 1.5) high-entropy alloys were systematically studied by using various characterization methods.
Abstract: The effects of Al on microstructure and mechanical properties of AlxCoCrFeNi (x=0.1, 0.75 and 1.5) high-entropy alloys were systematically studied by using various characterization methods. It was found that the crystalline structure of AlxCoCrFeNi high-entropy alloy varies markedly with Al content, which changes from the initial single face-centered cubic (fcc) to fcc plus ordered body-centered cubic (bcc) structure (B2) and then to a duplex bcc structure (A2+B2) as the Al content is increased. The chemical composition analysis reveals that Al primarily partitions to B2 phase, suggesting Al is a stabilizer of B2 structure. With increasing Al content, more Ni and Al partition to the B2 phase due to the very negative mixing enthalpy of Ni and Al, and another phase enriched in Cr and Fe transforms from fcc to disordered bcc. Nano indentation measurements show that the hardness of AlxCoCrFeNi high-entropy alloy increases with Al content, accompanied by the decrease of ductility. The stability of single-phase solid solution in AlxCoCrFeNi HEAs is deduced from various criteria. Combined with the experiment results of other similar HEA systems, such as AlxCoCrFeNiCu, the effects of Al addition on the microstructure of AlxCoCrFeNi HEAs are discussed based on the Gibbs free energy of all competing phases and the fundamental properties of constituent elements. The aim of current study is to provide experimental evidence to establish a correlation between the microstructure and mechanical properties to search for high-entropy alloys with higher performances.

Journal ArticleDOI
TL;DR: In this paper, the microstructure, phase stability and mechanical properties of a new refractory MoNbHfZrTi high-entropy alloy were reported, which consists of disordered body-centered cubic (BCC) solid solution phase in as-cast and homogenized states.

12 Oct 2015
TL;DR: In this article, an equimolar CrMnFeCoNi HEA was processed by electromagnetic melting, casting, and annealing under varying conditions (cooling rate and cooling duration) and the evolution of the structure and microstructure.
Abstract: High entropy alloys are single phase metallic materials, composed of more than 4 elements in equi-atomic proportion which is the maximum in the configurational entropy. In order to study the thermodynamics of those alloys, an equimolar CrMnFeCoNi HEA was processed by electromagnetic melting, casting and annealing under varying conditions (cooling rate and annealing duration) and the evolution of the structure and microstructure was studied. After casting, a dendritic microstructure was formed whose characteristic length depends on the cooling rate. Annealing leads to a chemical homogenization of the microstructure. Indeed a true solid-solution down to the atomic scale was evidenced in an HEA by atom probe tomography. It was shown that this face-centered cubic single-phase solid solution is the high temperature stable state of the equimolar CrMnFeCoNi alloy. By analogy with completely miscible binary alloy, the CrMnFeCoNi HEA can be described by a schematic phase diagram of the CrFeCo - MnNi system consisting of a liquidus and a solidus.

Journal ArticleDOI
TL;DR: In this article, direct laser fabrication was employed to fabricate bulk samples of three alloys based on the Al x CoCrFeNi HEA system, where x was 0.3, 0.6 and 0.85 m fraction of Al.
Abstract: High entropy alloys (HEA) are a relatively new metal alloy system that have promising potential in high temperature applications. These multi-component alloys are typically produced by arc-melting, requiring several remelts to achieve chemical homogeneity. Direct laser fabrication (DLF) is a rapid prototyping technique, which produces complex components from alloy powder by selectively melting micron-sized powder in successive layers. However, studies of the fabrication of complex alloys from simple elemental powder blends are sparse. In this study, DLF was employed to fabricate bulk samples of three alloys based on the Al x CoCrFeNi HEA system, where x was 0.3, 0.6 and 0.85 M fraction of Al. This produced FCC, FCC/BCC and BCC crystal structures, respectively. Corresponding alloys were also produced by arc-melting, and all microstructures were characterised and compared longitudinal and transverse to the build/solidification direction by x-ray diffraction, glow discharge optical emission spectroscopy and scanning electron microscopy (EDX and EBSD). Strong similarities were observed between the single phase FCC and BCC alloys produced by both techniques, however the FCC/BCC structures differed significantly. This has been attributed to a difference in the solidification rate and thermal gradient in the melt pool between the two different techniques. Room temperature compression testing showed very similar mechanical behaviour and properties for the two different processing routes. DLF was concluded to be a successful technique to manufacture bulk HEA׳s.

Journal ArticleDOI
TL;DR: It is observed that the incorporation of the alloy nanoparticles enhances the thermal conductivity of the base fluid (water) showing nanofluid application and the nitric oxide and hydroxyl radical scavenging activity shown by the nanoparticles promise the potential application in biomedical field.

Journal ArticleDOI
TL;DR: In this paper, the discovery of a hexagonal high-entropy alloy (HEA) with hexagonal crystal structure was reported, and the results of electron diffraction investigations and high resolution scanning transmission electron microscopy are consistent with an Mg-type hexagonal structure.
Abstract: We report on the discovery of a high-entropy alloy (HEA) with a hexagonal crystal structure. Equiatomic samples in the alloy system Ho–Dy–Y–Gd–Tb were found to solidify as homogeneous single-phase HEAs. The results of our electron diffraction investigations and high-resolution scanning transmission electron microscopy are consistent with an Mg-type hexagonal structure. The possibility of hexagonal high-entropy alloys in other alloy systems is discussed.