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In this work, the structure and mechanical properties of innovative Al-Cu-Fe based alloys were studied. We focused on preparation and characterization of rapidly solidified and hot extruded Al-Cu-Fe, Al-Cu-Fe-Ni and Al-Cu-Fe-Cr alloys. The content of transition metals affects mechanical properties and structure. For this reason, microstructure, phase composition, hardness and thermal stability have been investigated in this study. The results showed exceptional thermal stability of these alloys and very good values of mechanical properties. Alloying by chromium ensured the highest thermal stability, while nickel addition refined the structure of the consolidated alloy. High thermal stability of all tested alloys was described in context with the transformation of the quasicrystalline phases to other types of intermetallics. [ABSTRACT FROM AUTHOR]

Our previous works on the synthesis of intermetallics by Self-propagating High-temperature Synthesis revealed strong dependence of microstructure of the products on heating rate. In this paper, the application of various heating regimes and sources was tested in preparation of Ni Ti shape memory alloy. It was found that high heating rate (approx. over 100 °C min −1 ) was required to obtain the material with maximized amount of NiTi shape memory phase and no unreacted metals. Heating in electric resistance furnace preheated to the process temperature or induction heating furnace seemed to be promising for this purpose. On the other hand, Spark Plasma Sintering was found to be inapplicable, because the strongest increase of the temperature occurred on the surface of the particles, producing layers of intermetallics that further acted as diffusion barriers. [ABSTRACT FROM AUTHOR]

In this work, the formation of intermetallics in Ni–Ti system by reactive sintering at 500 and 650 °C was studied. Mechanism and kinetics of the reactions leading to Ni–Ti phases were determined by DTA and the application of an experimental model consisted of nickel-plated titanium. It was found that Ti 2 Ni phase forms already at 500 °C. At 650 °C this phase undergoes a reaction with nickel to NiTi and Ni 3 Ti. The reactions were determined to be diffusion-controlled. The formation of Ni 3 Ti contributes to the porosity evolution during reactive sintering production of NiTi alloy. [ABSTRACT FROM AUTHOR]

Abstract: This work is devoted to the preparation of ultrafine material based on Al–Cu–Fe quasicrystalline phase by powder metallurgy using mechanical alloying and Spark Plasma Sintering. The dependence of microstructure and phase composition of powders on the conditions of mechanical alloying was described. It was found that the Al60Cu30Fe10 quasicrystalline phase forms directly already after 2 h of milling under optimized conditions. The stability of this quasicrystalline phase was studied at various temperatures of Spark Plasma Sintering compaction process. [Copyright &y& Elsevier]

Abstract: Alloys formed by Ti–Al intermediary phases have low density and very good high-temperature oxidation resistance. Further improvement of high-temperature behaviour can be achieved by a suitable addition of silicon. In this work, Ti–Al–Si alloys containing 20wt.% of aluminium and 10–20wt.% of silicon produced by a reactive sintering technology were tested. Isothermal oxidation tests were carried out at 1000°C in air. The oxidation rate was determined from weight gains caused by oxide formation. Microstructure and phase composition of the oxide layers were studied. Microstructure and hardness changes after various annealing durations were described. [ABSTRACT FROM AUTHOR]

Abstract: In this work, the dependence of microstructure of Fe–Al–Si alloy on conditions of reactive sintering was studied. It was shown that heating rate strongly affects the structure of this alloy. The microstructure consisting of uniformly distributed Al2Fe3Si3 particles in Al2FeSi matrix can only be obtained in this material by rapid heating (over 300Kmin−1). Sufficient reactive sintering temperature to obtain Al2Fe3Si3–Al2FeSi two-phase structure is 750°C. Further increase of the reaction temperature reduces porosity but causes a growth of Al2Fe3Si3 particles. Reactive sintering process is completed during less than 10min in the investigated material. Temperatures over 1050°C produce material composed of FeSi, FeAl and Al2Fe3Si3 phases. However, strongly exothermal reaction of FeSi formation causes melting of the sample. [Copyright &y& Elsevier]

Abstract: In this work, Ti–Al–Si alloys were prepared by reactive sintering. The contents of silicon and aluminium ranged between 0–30wt.% and 0–36wt.%, respectively. Powders of titanium, aluminum, silicon and AlSi30 master alloy prepared by mechanical machining and/or milling were used for sintering. Powders were blended and pressed at room temperature. Sintering was carried out at 900°C for 30min. It was found that it is possible to produce compact materials with the structure corresponding to the as-cast materials when silicon is in the range of 15–20wt.% and aluminium content between 8 and 30wt.%. It was shown that these materials contain two phases—Ti5Si3 and TiAl. The central porosity can be reduced by induction heating. [Copyright &y& Elsevier]

This work is devoted to the preparation of alloys based on intermetallic compounds in the Ti-Al-Si system by powder metallurgy using mechanical alloying and the spark plasma sintering (SPS) method. The aim was to describe the formation of intermetallic phases during mechanical alloying of TiAl15Si15 (wt-%) alloy and to consolidate the powder prepared by optimised conditions. Phase composition, microstructure and hardness of compacted alloy were determined. Four hours of mechanical alloying is sufficient time for preparation of pure elements free material composed only of intermetallic phases. After consolidation, the TiAl15Si15 alloy has a homogeneous structure composed of silicide (Ti5Si3) in aluminide (TiAl) matrix. The hardness of the material reaches 865 ± 42 HV 5. [ABSTRACT FROM AUTHOR]

Abstract: Rapidly solidified aluminum alloys are promising materials with very fine microstructure. The microscopy observation of these materials is complicated due to overlay of fcc-Al matrix and different intermetallic phases. A possible way to solve this problem is to dissolve the Al matrix. By this process powder formed by single intermetallic phase particles is obtained. In this paper a new aqueous based dissolving agent for Al-based alloy is presented. The influence of oxidation agent (FeCl3) concentration on quality of extraction process was studied. [Copyright &y& Elsevier]

This work describes carbides present in the tool steel containing 2.5% C, 3.3% Si, 6.2% Cr, 2.2% Mo, 2.6% V, 2.6% Nb, 1.0% W, prepared by the powder metallurgy (PM) process. The influence of thermal treatment conditions on carbide behavior is investigated. During austenitization, some dissolution of M7C3 occurs, while MC carbides are thermally stable. So, the quenched steel is composed of two types of carbides: chromium rich M7C3 and niobium rich MC, besides martensite and retained austenite. During tempering of the hardened steel at the temperatures above 480°C, the precipitation of very fine carbides and martensite recovery occur, which results in secondary hardening. Precipitated particles are predominantly vanadium and molybdenum rich MC, M2C, and M6C carbides. [ABSTRACT FROM AUTHOR]

• Ti-Al-Si-X (X˭Co, Cr, Fe, Mo, Nb, Ni) alloys prepared using mechanical alloying and Spark Plasma Sintering. • Alloys have fine-grained and homogeneous microstructure with low porosity. • Alloyed elements increased hardness and compressive strength values. Intermetallic alloys based on Ti-Al-Si system are significant for their excellent high-temperature properties, especially for resistance against oxidation and for achieving good mechanical properties at elevated temperatures. The main problem of these materials is high brittleness at room temperature. In the previous work, selected alloying elements were added into the Ti-Al-Si alloys prepared by reactive sintering, but the properties did not meet the requirements for subsequent use in the automotive or aerospace industry, since the materials had a very porous microstructure. Here, the addition of cobalt, chromium, iron, molybdenum, niobium and nickel into the TiAl15Si15 alloy prepared by mechanical alloying and Spark Plasma Sintering is tested and it is expected to improve the mechanical and high-temperature properties. In this paper, the Ti-Al-Si alloys have been assessed on basis of microstructure, phase composition, mechanical and tribological properties, such as hardness, fracture toughness and compressive strength. Cyclic oxidation tests were performed for 400 h at the temperatures of 800 and 1000 °C. The cyclic oxidation tests simulate industrial processes, where the material is alternately exposed to elevated temperature and subsequent cooling (eg, engine components). From the viewpoint of most of the tested properties, alloying by niobium seems to be the most promising. [ABSTRACT FROM AUTHOR]

The phase composition and portion of individual phases in advanced high-strength steels (AHSS) CP1000 and DP1000 was studied by complementary microscopic and diffraction techniques. CP1000 and DP1000 steel grades have a high strength-to-density ratio and they are used in many applications in the automotive industry. The microstructure of the CP1000 "complex phase" steel consists of ferrite, bainite, martensite and a small amount of retained austenite. DP1000 is a dual phase steel, which has a structure of a ferritic matrix with islands of martensite and a minor amount of retained austenite. The influence of selected etchants (Nital, LePera, Beraha I, Nital followed by metabisulfite, Nital followed by LePera, and Nital followed by Beraha I) on the microstructure image is described. X-ray diffraction, neutron diffraction and light optical, scanning and transmission electron microscopy were used in this work for advanced characterization of the microstructure and phase composition. The information provided by each technique is critically compared. [ABSTRACT FROM AUTHOR]

Hydrogen diffusivity and trapping have been studied in two advanced high strength steel grades and model samples using electrochemical permeation test. Microstructures of CP1000 and DP1000 steels consist of ferrite, martensite and a small fraction of retained austenite. In addition, bainite is present in CP1000. Model phases with predominance of a particular phase have been prepared by specific heat treatment. DP1000 has shown the lowest diffusivity among all materials, while ferritic model sample has shown the highest. Differences in hydrogen diffusion coefficient values are linked to trapping microstructural characteristics and grain size. [ABSTRACT FROM AUTHOR]

The microstructure, phase composition, and microhardness of both gas-atomized and mechanically milled powders of the Al7075 + 1 wt % Zr alloy were investigated. The gas-atomized powder exhibited a cellular microstructure (grain size of a few µm) with layers of intermetallic phases along the cell boundaries. Mechanical milling (400 revolutions per minute (RPM)/8 h) resulted in a grain size reduction to the nanocrystalline range (20 to 100 nm) along with the dissolution of the intermetallic phases. Milling led to an increase in the powder's microhardness from 97 to 343 HV. Compacts prepared by spark plasma sintering (SPS) exhibited negligible porosity. The grain size of the originally gas-atomized material was retained, but the continuous layers of intermetallic phases were replaced by individual particles. Recrystallization led to a grain size increase to 365 nm in the SPS compact prepared from the originally milled powder. Small precipitates of the Al3Zr phase were observed in the SPS compacts, and they are believed to be responsible for the retainment of the sub-microcrystalline microstructure during SPS. A more intensive precipitation in this SPS compact can be attributed to a faster diffusion due to a high density of dislocations and grain boundaries in the milled powder. [ABSTRACT FROM AUTHOR]

Super duplex stainless steel SAF2507 is characterized by good mechanical properties and corrosion resistance. However, the combination of high strength and corrosion resistance requires the balanced ratio of austenite and ferrite in microstructure. At the same time, the presence of other secondary phases such as intermetallic phases (σ, χ), carbides (M 7 C 3 , M 23 C 6) and nitrides (π, CrN, Cr 2 N) is strongly undesirable. Additive manufacturing of duplex stainless steel has not been described in detail yet and the existing studies deal with the duplex stainless steels deposited by powder bed methods primarily. This study investigates the properties of steel SAF2507 prepared by the directed energy deposition (DED) method in the as-built state and after post-manufacturing solution annealing at 1100 °C for 60 min followed by water quenching and compares them with the duplex stainless steel additively manufactured by powder methods and conventional ways of preparation. Microstructure, phase composition and mechanical properties of both materials were studied in detail. The material after DED contains of about 28 wt% austenite, which is much more compared to additively manufactured duplex stainless steels by powder bed. The as-built state contained allotriomorphic grain boundary austenite (GBA), Widmanstätten austenite (WA) and intragranular austenite (IGA). Coarsening of austenite occurred during solution annealing, while ferrite's grains size decreased. The solution annealed material achieves approximately the desired ratio of austenite-ferrite 50:50. Yield strength decreased slightly during solution annealing from 680 MPa to 540 MPa, whereas elongation and notch toughness increase. The ductile to brittle transition temperature (about −100 °C) did not change significantly during solution annealing. • The as-built state of the DED contains significantly higher amount of austenite compared to powder bed methods. • Near balanced ferrite/austenite microstructure was achieved after post-manufacturing solution annealing. • Austenite grain size increases while ferrite grain size decreases during solution annealing. • Similar mechanical properties regardless of the orientation to the building direction. • Notch toughness increases during solution annealing. [ABSTRACT FROM AUTHOR]

Abstract: The microstructure and crystallization behavior of a conventionally cast Fe-38 at.% Al-1 at.% C alloy and a set of crystals obtained from this alloy by the Bridgman and the floating-zone methods were investigated. A significant redistribution of elements during crystallization was observed. A two-phase microstructure of the κ-phase in the B2 matrix was found in regions with composition below 37 at.% Al and 0.5 at.% C. A microstructure consisting of the κ-phase and B2 matrix with a limited amount of graphite globules was obtained in the fast-solidified Bridgman sample. An enhanced growth of graphite lathes in the Bridgman crystal was observed at a growth rate of 28 mm h−1. These graphite lathes were oriented parallel to the {100} and {110} planes. The κ-phase precipitates have no orientation relationship with the matrix. [Copyright &y& Elsevier]

The effect of phase composition and morphology on high-temperature strength in the compression of Fe-Al-Si-based iron aluminides manufactured by casting was investigated. The structure and high-temperature strength in the compression of three alloys—Fe28Al5Si, Fe28Al5Si2Mo, and Fe28Al5Si2Ti—were studied. Long-term (at 800 °C for 100 h) annealing was performed for the achievement of structural stability. The phase composition and grain size of alloys were primarily described by means of scanning electron microscopy equipped with energy dispersive analysis and Electron Backscatter Diffraction (EBSD). The phase composition was verified by X-ray diffraction (XRD) analysis. The effect of Mo and Ti addition as well as the effect of long-term annealing on high-temperature yield stress in compression were investigated. Both additives—Mo and Ti—affected the yield stress values positively. Long-term annealing of Fe28Al5Si-X iron aluminide alloyed with Mo and Ti deteriorates yield stress values slightly due to grain coarsening. [ABSTRACT FROM AUTHOR]

This work highlights new results on the synthesis of the TiAl3 intermetallic phase using self-propagating high-temperature synthesis. This method is considered a promising sintering route for intermetallic compounds. It was found that the reactions proceed in two stages. Below the melting point of aluminum, the Ti2Al5 phase forms at 450 °C after long annealing times by a direct solid-state reaction between the aluminum and titanium, and is converted consequently to TiAl3. This is a completely new finding; until now, many authors have believed in the preferential formation of the TiAl3 phase. The second stage, the self-propagating strongly exothermic reaction, proceeds above the melting point of aluminum. It leads to the formation of the TiAl3 phase accompanied by Ti2Al5 and Ti3Al phases. The reaction mechanism was shown in the form of chemical equations, which were supported by calculating Gibbs energy. Reaction temperatures (Tonset, Tmaximum, and Toffset) were determined after induction heating thanks to recording by an optical pyrometer. This finding provides completely new opportunities for the determination of activation energy at heating rates, in which common calorimeters are not able to detect a response or even measure. Now, the whole procedure will become accessible. [ABSTRACT FROM AUTHOR]

Ni-Ti alloys are considered to be very important shape memory alloys with a wide application area including, e.g., biomaterials, actuators, couplings, and components in automotive, aerospace, and robotics industries. In this study, the NiTi46 (wt.%) alloy was prepared by a combination of self-propagating high-temperature synthesis, milling, and spark plasma sintering consolidation at three various temperatures. The compacted samples were subsequently heat-treated at temperatures between 400 °C and 900 °C with the following quenching in water or slow cooling in a closed furnace. The influence of the consolidation temperature and regime of heat treatment on the microstructure, mechanical properties, and temperatures of phase transformation was evaluated. The results demonstrate the brittle behaviour of the samples directly after spark plasma sintering at all temperatures by the compressive test and no transformation temperatures at differential scanning calorimetry curves. The biggest improvement of mechanical properties, which was mainly a ductility enhancement, was achieved by heat treatment at 700 °C. Slow cooling has to be recommended in order to obtain the shape memory properties. [ABSTRACT FROM AUTHOR]

Composite material prepared by spark plasma sintering (SPS) from a powder mixture of AlCrFeSi rapidly solidified alloy and 5 wt. % of Ni particles was studied in this work. It was proven that during SPS compaction at 500 °C, no intermetallic phases formed on the surface of Ni particles. The material exhibited sufficient mechanical properties obtained by tensile testing (ultimate tensile stress of 203 ± 4 MPa, ductility of 0.8% and 0.2% offset yield strength of 156 ± 2 MPa). Tensile samples were pre-stressed to 180 MPa and annealed at 450 and 550 °C for 1 h. Annealing at 450 °C did not lead to any recovery of the material. Annealing at 550 °C caused the full recovery of 0.2% offset yield strength, while the ductility was decreased. The self-healing behaviour originates from the growth of intermetallic phases between the Ni particle and the Al matrix. The sequence of NiAl, Ni2Al3 and NiAl3 intermetallic phases formation was observed. In particular, the morphology of the NiAl3 phase, growing in thin dendrites into the Al matrix, is suitable for the closing of cracks, which pass through the material. [ABSTRACT FROM AUTHOR]

FeAlSi intermetallics are materials with promising high-temperature mechanical properties and oxidation resistance. Nevertheless, their production by standard metallurgical processes is complicated. In this study, preparation of powders by mechanical alloying and properties of the samples compacted by spark plasma sintering was studied. Various initial feedstock materials were mixed to prepare the material with the same chemical composition. Time of mechanical alloying leading to complete homogenization of powders was estimated based on the microstructure observations, results of XRD and indentation tests. Microstructure, phase composition, hardness and fracture toughness of sintered samples was studied and compared with the properties of powders before the sintering process. It was found that independently of initial feedstock powder, the resulting phase composition was the same (Fe3Si + FeSi). The combination of hard initial powders required the longest milling time, but it led to the highest values of fracture toughness. [ABSTRACT FROM AUTHOR]

The compact samples of an Al7075 alloy were prepared by a combination of gas atomization, high energy milling, and spark plasma sintering. The predominantly cellular morphology observed in gas atomized powder particles was completely changed by mechanical milling. The continuous-like intermetallic phases present along intercellular boundaries were destroyed; nevertheless, a small amount of Mg(Zn,Cu,Al)2 phase was observed also in the milled powder. Milling resulted in a severe plastic deformation of the material and led to a reduction of grain size from several µm into the nanocrystalline region. The combination of these microstructural characteristics resulted in abnormally high microhardness values exceeding 300 HV. Consolidation through spark plasma sintering (SPS) resulted in bulk samples with negligible porosity. The heat exposition during SPS led to precipitation of intermetallic phases from the non-equilibrium microstructure of both gas atomized and milled powders. SPS of the milled powder resulted in a recrystallization of the severely deformed structure. An ultra-fine grained structure (grain size close to 500 nm) with grains divided primarily by high-angle boundaries was formed. A simultaneous release of stored deformation energy and an increase in the grain size caused a drop of microhardness to values close to 150 HV. This value was retained even after annealing at 425 °C. [ABSTRACT FROM AUTHOR]