Srdjan MilenkovicMadrid Institute for Advanced Studies | IMDEA · IMDEA-Materials
Srdjan Milenkovic
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71
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Publications
Publications (71)
New High Entropy Alloys based on the CoCrFe2Ni2 system have been developed by adding up to 10 at. % of Cu, Mo, and Cu + Mo in different amounts. These alloys showed a single face-centred cubic (FCC) structure after homogenization at 1200 °C. In order to evaluate their thermal stability, aging heat treatments at 500, 700, and 900 °C for 8 h were app...
Rapid alloy prototyping is quickly emerging as a manufacturing approach to design novel structural alloys since allows producing low volume of high quality castings quickly at low cost. Thus, a large number of alloys can be produced and tested for finding the optimal composition in an alloy system. In this work, a new high throughput method for rap...
Single crystalline Au nanoplates with square shape and unique {110} facets were synthesized by directional eutectoid decomposition. The average edge length and thickness are 70-100 nm and 20-25 nm, respectively. The surface of the nanoplates was cleaned by deposition/dissolution of PbO2 in an alkaline media. Furthermore, surface sensitive electroch...
NiAl-based eutectic alloys, consisting of an ordered bcc matrix (B2) and disordered bcc fibers (A2), have been a subject of intensive efforts aimed at tailoring the properties of many of the currently used nickel-based superalloys. A thermodynamic phase field model was developed on a thermodynamic foundation and fully integrated with a thermo-kinet...
A series of diffusion bonding tests are conducted on a high Nb containing TiAl alloy with full lamellar (FL) microstructure and the effect of interfacial recrystallization behavior on the shear strength is discussed. Microstructural observations reveal that bonding above 1100°C and 30MPa results in recrystallization at the bonding interface flanked...
Directional solidification of eutectic NiAl–W alloys offers an intuitive method to produce tungsten nanowires. Through the use of two different methods, the well-established Bridgman method and a newer type floating zone method, the direct influence of process parameters, like the withdrawal rate and the temperature gradient, onto the sample micros...
Development of investment casting process has been a challenge for manufacturers of complex shape parts. Numerous experimental casting trials are typically carried out to determine the optimum casting parameters for fabrication of high-quality products. In this work, it is demonstrated that physical simulation of investment casting can successfully...
Directional solidification of eutectic alloys has been recognized as promising technique for producing in situ composite materials exhibiting balance of properties. Therefore, an in situ NiAl-V eutectic composite has been successfully directionally solidified using Bridgman technique. The mechanical behavior of the composite including fracture resi...
A phenomenological crystal plasticity (CP) model is proposed to simulate the elasto-plastic behaviour of IN718 grains. The parameters of the CP model were fitted from micro-compression tests of a wrought IN718 alloy. A polycrystalline sample of IN718 was used for this investigation with an average grain size of 150 urn. Microstructural investigatio...
Investment casting is the only commercially used technique for fabrication of nozzle guide vanes (NGVs), which are one of the most important structural parts of gas turbines. Manufacturing of NGVs has always been a challenging task due to their complex shape. This work focuses on development of a simulation tool for investment casting of a new gene...
The control of grain structure, which develops during solidification processes in investment casting of nozzle guide vanes (NGVs), is a key issue for optimization of their mechanical properties. The main objective of this part of the work was to develop a simulation tool for predicting grain structure in the new generation NGVs made from MAR-M247 N...
Nanostructured eutectic NiAl–W, fabricated using a Bridgman-type directional solidification facility, combines the advantages of single individual nanowires with the benefit of a conductive macroscopic matrix. Through an electrochemical dissolution step, using conditions derived from the combined Pourbaix diagrams of all three elements involved, th...
The characterization of the wetting on superhydrophobic surfaces is rather
complex. Usual contact angle experiments are difficult to perform and the
lateral movement of droplets as well as the pinning at point defects on the
surface can disturb the measurements. Even if precise contact angle
measurements can be performed the information gain is lim...
Ordered B2-NiAl intermetallic compound powder was successfully synthesised by mechanical alloying after 20 h in an attritor mill, starting from elemental Ni and Al powders and without subsequent heat treatment. NiAl powder obtained was homogenous and had a nanocrystalline microstructure. It was consolidated by field assisted hot pressing (FAHP), in...
Due to the high cost and variability of investment casting process, simulation tools are needed to reduce the number of trials and ensure the required metallurgic quality. For this reason, the adaptation of modelling capabilities to investment casting foundry conditions is required.
This work aims to present an investment casting modelling tool (Pr...
The effect of thermal variations on the secondary dendrite arm spacing (SDAS) in a MAR-M247 Ni-based superalloy has been studied by a novel method based on a physical simulation of melting/solidification experiments with a constant cooling rate and variable temperature gradient. The method proved to be effective as it yielded a spread of microstruc...
The effect of solidification parameters on the secondary dendrite arm spacing in a MAR-M247 Ni-based superalloy has been studied by a novel approach, based on physical simulation of melting/solidification experiment with a constant cooling rate and variable temperature gradient. The applied experimental method proved to be efficient as it yielded a...
Oxidation behavior and thermal stability of a NiAl–V alloy with eutectic composition processed by directional solidification technique has been investigated. The surface analysis at the elevated temperature indicated that the investigated microstructures are stable at the isothermal conditions and an inert atmosphere. The oxidation testing in the s...
This study introduces a novel high-throughput method for establishing the solidificationmicrostructure
relationship. It involves performing melting/solidification experiments in a stateof-
the-art Gleeble 3800 facility, with a constant cooling rate and variable temperature gradient.
In a single sample cooled at 10 �C/s, a range of temperature gradi...
This work studies the microstructure and hardness evolution in MAR-M247 Ni-based superalloy processed by controlled cooling and double heat treatment. The solidification experiments with controlled cooling rates in the range of 0.25-10 K/s were carried out using GLEEBLE thermo-mechanical simulator. In the as-solidified material, with increasing coo...
The nickel-based superalloys Inconel alloy 600, Udimet alloy 720, and Inconel alloy 718 were produced by electron beam melting (EBM), casting, and directional solidification (DS). The distance between dendrites and the size of the precipitates indicated the difference in solidification rates between the three processes. In this study, the solidific...
A precise knowledge and understanding of the thermal stability of nanowires is a prerequisite for the reliable implementation of nanowire-based devices. Single crystalline Au nanobelts with {1 1 0} surface either in free standing arrays with identical crystallographic orientation or lying on the substrate were prepared by a combination of direction...
Three different AlFeNb alloys of various compositions were prepared by arc melting. X-ray diffraction (XRD) investigation of the melted samples proved the presence of two phases identified as a bcc α(Fe,Al) solid solution and a hexagonal C14 (Fe,Al)2Nb Laves phase. Subsequent electrochemical treatment allowed for a selective dealloying of the α(Fe,...
The effect of cooling rate on the microstructure of MAR-M247 Ni-based superalloy was investigated via physical simulation of the casting process. Solidification experiments with cooling rates in the range of 0.25–10 K/s showed smooth temperature profiles with measured cooling rates matching the set values. The MAR-M247 showed cellular (0.25 K/s) an...
A novel concept for the preparation of alloy nanowires has been developed. By combining two pseudobinary eutectic systems NiAl–W and NiAl–Cr with a completely miscible system Cr–W, a pseudoternary system was created in which there is large two-phase field between NiAl and W(Cr) solid solutions, separated by a eutectic trough. This enables the fabri...
Pseudobinary NiAl–W section in the range 0.7–1.8 at% was characterised regarding solidification microstructure and constitution. The existence of eutectic reaction was confirmed and occurs at temperature of 1664 ± 2 °C and the composition of 1.5 at% W. As-cast microstructures indicated that the NiAl–W system is an anomalous eutectic with skewed cou...
Directional solidification of eutectics is a route to produce iso-oriented metallic single crystalline nanowires (NWs). Etching or electrochemical oxidation allows selective dissolution of either of the phases to produce NW arrays, isolated NWs, nanopore arrays and also derived structures by combining various process steps.
A good understanding of...
In the Feature Article by Achim Walter Hassel et al. (pp. 2380–2392), a novel approach of producing metallic nanostructures is reviewed. Directional solidification of eutectics is a route to produce iso-oriented metallic single crystalline nanowires. Etching or electrochemical oxidation allows selective dissolution of either of the phases to produc...
Gold nanobelts were synthesized by directional solidification of the Fe-Au eutectoid followed by selective phase dissolution. Cleaning from organic molecules was performed in alkaline solution by PbO(2) deposition/dissolution to avoid surface reconstruction. The electrochemical behaviour of the Au nanobelts was determined by structure-sensitive ele...
One gram of tungsten nanowires equivalent to 5 billion single wires was produced by electrochemically processing a directionally solidified eutectic NiAl-W alloy. Their release is realised by selective dissolution of the matrix with a yield beyond 98%. The nanowires are single crystals, homogeneous in diameter, and have extremely high aspect-ratios...
A technique for the electrochemical structuring of directionally solidified NiAl–Mo eutectic by selective phase dissolution is presented. Local matrix dissolution at 200 mV SHE in 1 M HCl of pH 1 yielded the grid of Mo nanowires spanning along the central part of the sample. On the other hand, the dissolution of the fibrous minor phase while passiv...
The irregular structure of an Al–Si eutectic has been chemically modified by adding small amount of Sr (300ppm). The initially coarse flake structure was converted into technologically preferable fine fibrous morphology. The selective phase dissolution has been investigated using two different electrochemical approaches, derived from superimposed P...
This work describes a novel fabrication method of single crystalline Mo nanowires and nanowire arrays. The method utilizes directional solidification (ds) of a NiAl-Mo eutectic alloy and its subsequent electrochemical processing. In the first step, a self-organized array of Mo nanowires embedded in a NiAl matrix is obtained. By combining the Pourba...
Self-organised tungsten nanowire arrays were produced by a recently established templateless method. Control of spatial features such as diameter and spacing of nanowires was successfully achieved by changing the growth rate during directional solidification. An increase in the growth rate from 1.4 μm s–1 to 55.5 μm s–1 led to a decrease in the nan...
Well dispersed, single crystalline gold nanobelts, with unique {110} crystallographic facets, were synthesized by a combined method consisting of directional solid-state transformation of an Fe–Au eutectoid and a selective phase dissolution without the presence of any surfactant. They have an average thickness of 25–30 nm, a width of 200–250 nm, an...
This study is devoted to a thorough crystallographic and microstructural characterisation of gold nanowire arrays. The nanostructures were produced by directional solid-state decomposition of the Fe–Au eutectoid. The system structure and microstructure were investigated using differential thermal analysis (DTA), field emission scanning electron mic...
An Fe–26Al–9.5Nb (in at.%) eutectic alloy produced by directional solidification (DS) has been characterised regarding its microstructure and basic mechanical properties and the latter are compared with an as-cast (AC) alloy of about the same composition. The DS alloy exhibits a regular fibrous eutectic Fe3Al+(Fe,Al)2Nb (Laves phase) microstructure...
The electrochemical potentials of tungsten nanowire samples, covered with their own oxide, were measured in dependence of the pH value. The samples were prepared by selective etching of a directionally solidified eutectic NiAl–W alloy. Directional solidification in a Bridgman-type crystal growth furnace yields nanostructured two-phase materials. El...
For the first time single crystalline gold nanobelt arrays with identical crystallographic orientation were obtained. A combined method consisting of directional solid-state transformation of a Fe-Au eutectoid and a well controlled electrochemical treatment enables production of arrays of nanobelts with a desired length. They have an average thickn...
Single crystalline tungsten nanowires were prepared from directionally solidified NiAl-W alloys by a chemical release from the resulting binary phase material.
Electron back scatter diffraction (EBSD) proves that they are single crystals having identical crystallographic orientation.
Mechanical investigations such as bending tests, lateral force...
The method of fabricating metallic nanowires from directionally solidified eutectics was applied to the silver–copper system. The silver–copper alloy, 39.9at.% copper, was directionally solidified in a Bridgman-type oven held at 850°C. SEM imaging revealed a mixed fibrous and lamellar microstructure. The fastest solidification rates produced fibres...
The yield stress of monocrystalline Rhenium nanowires grown by directional solidification was measured by nanobending testing. The average yield stress calculated from the deflection was between 10 and 60 GPa , which represents roughly 10% of the rhenium Young modulus along the nanowire’s direction. Analytical results are compared to the ones obtai...
Superhydrophobicity and superhydrophilicity of surfaces are key properties for fabrication of self-cleaning surfaces (Lotus effect). It is well known that the mechanism behind this is based on the surface roughness and surface functionalization. To obtain an understanding of the details of the underlying mechanism, a metal system based on a eutecti...
A directionally solidified eutectic NiAl–W alloy was employed as a source for NiAl nanopore arrays, W-nanowire arrays and W-nanowires. The NiAl–W eutectic alloy containing 1.5 at.% W. A growth rate of 30 mm h−1 was used at a temperature gradient of 40 K cm−1 in a Bridgman-type directional solidification furnace. A combined stability diagram was der...
This study addresses a novel approach of obtaining gold nanostructures, via directional eutectoid decomposition and selective
etching of Fe-Au alloys. The eutectoid transformation occurs at 2.3%Au, which agrees perfectly with existing DTA and calculated
data. The results are thus experimentally supporting the calculated part of the binary Fe-Au pha...
The effects of the solidification parameters, such as growth rate and temperature gradient, on the distance and diameter of Re nanowires have been examined. Both the spacing and diameter increase with decreasing growth rate and temperature gradient, respectively. The ratio of fiber spacing to diameter is 9.1. In addition, it was demonstrated that t...
Rhenium nanowires have been fabricated via directional solidification and selective etching of a eutectic alloy. A NiAl–1.5 at.%Re eutectic alloy was directionally solidified using a constant growth rate and temperature gradient, in the Bridgman-type directional solidification furnace. The selective dissolution of the NiAl matrix was achieved with...
Directional solidification of a eutectic is a novel route for the production of nanostructures. This method was applied to the quasibinary NiAl–Re system. Re as the minor phase forms fibers, which are parallel aligned in the NiAl matrix. At a temperature of 1690±10°C using a thermal gradient of 40°Ccm−1 and a growth rate of 30mmh−1, the fibers form...
In situ composite materials obtained by directional growth of eutectic alloys usually show improved properties, that make them potential candidates for high temperature applications. The eutectic alloy found in the Al–Nb system is composed of the two intermetallic phases Al3Nb (D022) and Nb2Al (D8b). This paper describes the directional solidificat...
The exciting microstructures found in several eutectic alloys are a result of a cooperative growth, which is connected to the atomic transfer in the melt ahead the solid/liquid interface. In a eutectic system, the growth of solid phases depends on the simultaneous rejection of constituents to the liquid phase, which causes adjustments of the melt c...
The Al–Nb system exhibits a eutectic transformation at , which results in Al3Nb (D022) and Nb2Al (D8b) phases. This paper is concerned with the processing of this eutectic by directional solidification. Alloys were prepared by arc melting and directionally solidified in Bridgman-type equipment. The resulting samples were utilized to evaluate the so...
In the Ni–Si system, the eutectic structure composed of Ni–Ni3Si presents inherent thermal stability, allowing composite materials to be obtained with well-aligned and finely dispersed microstructures. The work reported here consisted of an investigation into the microstructure and morphology of such a eutectic alloy from the standpoint of its grow...
Intermetallic matrix composites (IMCs) are considered candidate materials for high-temperature applications provided that the proper combination of properties can be developed. Among a large number of intermetallics, a particular interest has been shown in the NiAl-based composites. Attractive properties of this compound include higher melting temp...
A novel ternary eutectic reaction L → Nb2Al + Al3Nb + AlNbNi occurs at the composition of Al–40.4Nb–2.42Ni and the temperature of 1553.6 °C. The third phase is an Al-rich AlNbNi phase with the composition Al–33.3Nb–12.3Ni. Ternary Nb–Al–Ni eutectic exhibits regular microstructure with the predominantly fibrous morphology.
Directional solidification (DS) of the eutectic alloys is an interesting concept of reinforcing intermetallics with in situ refractory metals. Considering that the morphology of eutectic microstructure governs the mechanical behavior of the material, the addition of a quaternary element to the NiAl–V system could, principally, modify the solidifica...
Solidification of a eutectic alloy from the melt produces composite materials, composed of two or more solid phases. Processing by directional solidification presents interesting and different properties when compared to the properties of its constituent phases. One of the ternary systems that has been little studied and exhibits eutectic reaction...
Microstructure of the Ni–Ni3Si eutectic system from the nickel rich portion of the nickel–silicon phase diagram was studied as a function of the growth conditions and parameters. In the as-solidified condition the microstructure presents a high degree of regularity and uniformity, with an orientation clearly dependent on the heat flux direction. Di...
Intermetallic matrix composites (IMCs) offer attractive properties, such as high toughness of the metal coupled with low density, high modulus and high strength of the intermetallics. Among a large number of the intermetallics, a particular interest has been shown in the NiAl intermetallic compound, since it exhibits several advantages over the cur...
Composite materials show attractive properties resulting from the combination of properties of their constituent phases. Special interest has been devoted to the intermetallic matrix composites, since they have been recognized as potential substitutes for the superalloys. An interesting and efficient means of preparation of the composite materials...
The directional solidification technique (D.S.) permits processing of the various materials for diverse applications. Among a wide variety of materials, the composite materials obtained by directional solidification of the eutectic alloys have gained significant attention. A special interest have gained the intermetallic-based in situ composites, s...
The solidification microstructure of a Ni-Ni3Si eutectic alloy from the Nickel-rich portion of the Ni-Si phase diagram has been investigated regarding the processing conditions and composition. In the as-solidified condition the microstructure presented a high degree of regularity and uniformity, exhibiting an orientation clearly dependent on the h...
The microstructures and solidification behaviour of Ni–Ni3Si eutectic composite have been studied systematically. Samples were processed in a Bridgman type solidification furnace using induction heating with growth rates ranging from 6.5 to 20.0 mm/h. During directional solidification, Ni–Ni3Si eutectic is characterised by cell and dendrite–free an...
This paper presents the most important aspects of a process/device optimization technique based on neural network models. A reverse model neural network, trained to learn the inverse dynamic of semiconductor manufacturing processes effectively determines the optimum process conditions for realizing the desired device performances. Moreover, this op...
Projects
Project (1)
The objective of the proposed project was to develop the next generation of Ni-based superalloy nozzle guide vane (NGV) design and manufacturing capability for low pressure turbines of advanced aircraft engines. This result was achieved by building an improved modelling tool to simulate mold filling, solidification and microstructure evolution during investment casting processes. These NGV designs and casting technologies were evaluated using a combination of optimization studies using the enhanced software code and the casting trials and analyses that were performed.
NGV’s play a critical role in the thermodynamic efficiency, aerodynamic performance, and cost of ownership of turbine engines. The industrial benefits for the aviation industry of new NGV designs include reduced emissions, and improved fuel efficiency, reduced weight, and lower operating costs.
