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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.

This work highlights new results on the synthesis of the TiAl 3 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 Ti 2 Al 5 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 TiAl 3 . This is a completely new finding; until now, many authors have believed in the preferential formation of the TiAl 3 phase. The second stage, the self-propagating strongly exothermic reaction, proceeds above the melting point of aluminum. It leads to the formation of the TiAl 3 phase accompanied by Ti 2 Al 5 and Ti 3 Al phases. The reaction mechanism was shown in the form of chemical equations, which were supported by calculating Gibbs energy. Reaction temperatures (T onset , T maximum , and T offset ) 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.

Composites consisting of iron aluminide and iron silicide phases were studied in this work. Powders of iron aluminide and iron silicide were prepared by mechanical alloying separately. Subsequently, they were blended in three different proportions and sintered by the SPS method under various conditions. After sintering, the composites are composed of FeAl and amounts of other silicides (Fe5Si3 and Fe3Si). Ternary Fe–Al–Si phases were not determined, even though their presence was predicted by DFT calculations. This disagreement was explained by steric factors, i.e., by differences in the space lattice of the present phases. Hardness and tribological properties were measured on composites with various weight ratios of iron aluminide and iron silicide. The results show that sintered silicides with the matrix composed of iron aluminide reach comparable hardness to tool steels. The composites with higher mass ratios of iron aluminide than silicide have higher hardness and better tribological properties. [ABSTRACT FROM AUTHOR]

Commercially supplied inoculation wires have a guaranteed chemical composition but not the size and distribution of individual phases, which are very important for nucleation. Therefore, two commercial alloys used for the inoculation of Al-Si alloys (AlTi3B1 and AlTi5B1) are investigated in this paper. The emphasis is placed on their structural analysis and the size and distribution of individual intermetallic phases. Furthermore, the grain refinement effect will be tested by adding these alloys to the AlSi7Mg0.3 alloy and testing the optimal amount of added inoculation wires. The results showed that the size and distribution of the individual phases in AlTi3B1 and AlTi5B1 meet the requirements for the successful inoculation of aluminum alloys, the intermetallic phases based on the TiAl3 phase are fine enough, and there is no agglomeration that would reduce the number of nuclei. This assumption was confirmed by adding these inoculants to the AlSi7Mg0.3 alloy, and it was found that the most ideal amount of inoculants added is 0.01 wt % when the structure was refined by approximately 32%. [ABSTRACT FROM AUTHOR]

Aluminothermic reduction without the separation of individual metals is currently considered as a possible method for processing ferromanganese sea nodules and creating new alloys. In this study, the product of their reduction—a manganese-based polymetallic mixture—was added to pure aluminum, as a mixture of alloying elements in their natural ratios. After extrusion, two new aluminum alloys with a total percentage of metallic additives ranging from 1 to 6 percent were prepared. The possibilities of the precipitation strengthening of these aluminum alloys, especially those containing Mn, Fe, Si, Ni, and Cu, were investigated under a wide range of heat treatment conditions. After each tested combination of annealing and artificial aging temperatures, the phase composition and the microstructure changes were recorded by X-ray diffraction, optical, and scanning electron microscopy with EDS analysis. Under none of the tested heat treatment conditions is a significant hardening effect observed, even though the precipitate phases are observed by TEM. However, the changes in the morphology of the present intermetallic phases caused by the heat treatment are revealed, which highlights the further possible development of these multicomponent alloys. [ABSTRACT FROM AUTHOR]

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]

Due to the lack of mineral resources, unconventional raw materials have to be considered. In this work, the use of reduced deep-sea nodules from Clarion-Clippertion Fracture Zone of Pacific Ocean was tested as the natural mixture of alloying elements for aluminum alloys. The nodules were reduced by aluminothermic process without the extraction of individual elements. As the technology for the manufacture of the alloys, the powder metallurgy comprising mechanical alloying and spark plasma sintering was applied. The produced Al-Mn based alloys are characterized by uncommon spherical morphology of Al-Mn intermetallics, which leads to a significant ductility even in the case of high total amount of additives (up to 20 wt%). The wear resistance of the alloys strongly increases with growing amount of the reduced deep-sea nodules. • New aluminum alloys with reduced deep-sea nodules prepared by powder metallurgy. • Unique rounded morphology of intermetallics was obtained. • Improved strength compared with common Al-Mn alloys. • Reduced deep sea nodules improve tribological properties of aluminum. [ABSTRACT FROM AUTHOR]

Quasicrystal-containing materials are usually prepared by rapid solidification of the melt (e.g. by melt spinning) or mechanical alloying. In this work, the method using exothermic reactions between compressed metallic powders called SHS (Self-propagating High-temperature Synthesis) was tested. The microstructure and phase composition of the product was described in dependence on cooling regime from the reaction temperature. Thermal stability of prepared Al-Cu-Fe quasicrystals was studied by annealing at the temperatures of 300 and 500 °C. [ABSTRACT FROM AUTHOR]

Deep-sea manganese nodules are polymetallic oxidic ores that can be found on a seabed. Aluminothermic reduction is one of the possibilities of manganese nodules processing. This process obtains the polymetallic alloy with a high content of Mn and a varying content of Al, depending on the ratio between aluminum and nodules. The corrosion behaviors of three experimental Mn-based alloys produced by aluminothermic reduction with a content of Mn > 50 wt % were studied. The electrochemical testing in potable water and model seawater was used to explain the corrosion mechanism of Mn-based alloys. The results showed that the corrosion rate of experimental Mn-based alloy decreases with the increase in aluminum content in both potable water and model seawater. It was observed that the uniform corrosion of experimental Mn-based alloys is changed with an increase in aluminum content in alloy to localized corrosion, which was caused by microcells in an environment of model seawater. In contrast, the formation of a semi-protective layer of corrosion products was observed on the surface of Mn-based alloys with a higher content of aluminum in potable water. Moreover, the pitting corrosion of tested Mn-based alloys was observed neither in potable water nor in model seawater. [ABSTRACT FROM AUTHOR]

Abstract: The aim of this work was to evaluate the corrosion and abrasive-wear resistance of plasma-nitrided PM tool steel with increased content of niobium (2.6 wt.%). It was found that the wear behaviour was significantly influenced not only by surface hardness, but also by other factors, mainly by surface roughness and by the presence and properties of a compound layer. The maximum wear resistance was achieved by plasma nitriding at 500 °C for 180 min. It was also shown that nitriding led to an increase of the free corrosion potential and that the compound layer on the surface acted as a barrier against corrosion attack. The nitriding conditions that resulted in the maximum wear resistance also provided significantly increased corrosion resistance. In addition, it was observed that the conventional gas nitriding conducted at the same conditions did not produce such significant improvement of the wear resistance. [Copyright &y& Elsevier]

Novel high-entropy (multi-principal elements) alloy based on Fe-Al-Si-Ni-Ti in equimolar proportions has been developed. The alloy powder obtained by mechanical alloying is composed of orthorhombic FeTiSi phase with the admixture of B2 FeAl. During spark plasma sintering of this powder, the FeSi phase is formed and the amount of FeAl phase increases at the expense of the FeTiSi phase. The material is characterized by a high compressive strength (approx. 1500 MPa) at room temperature, being brittle. At 800 °C, the alloy is plastically deformable, having a yield strength of 459 MPa. The wear resistance of the material is very good, comparable to the tool steel. During the wear test, the spallation of the FeSi particles from the wear track was observed locally. [ABSTRACT FROM AUTHOR]

A new powder production method has been developed to speed up the search for novel alloys for additive manufacturing. The technique involves an ultrasonically agitated cold crucible installed at the top of a 20 kHz ultrasonic sonotrode. The material is melted with an electric arc and undergoes pulverization with standing wave vibrations. Several different alloys in various forms, including noble and metallic glass alloys, were chosen to test the process. The atomized particles showed exceptional sphericity, while powder output suitable for additive manufacturing reached up to 60%. The AMZ4 metallic glass powder remained amorphous below the 50 μm fraction, while tungsten addition led to crystallization in each fraction. Minor contamination and high Mn and Zn evaporation, especially in the finest particles, was observed in atomized powders. The innovative ultrasonic atomization method appears as a promising tool for material scientists to develop powders with tailored chemical composition, size and structure. [ABSTRACT FROM AUTHOR]

This article describes issues related to the machining of parts made of sintered nickel-cobalt alloy. Longitudinal turning with a CBN (cubic boron nitride) tool was analyzed. The results of experiments showed the influence of cutting parameters in the field of finishing machining on the values of cutting forces and specific cutting force, taking into account the wear of the cutting edge. Measurements and analysis of the topography and roughness parameters of the machined surface, as well as the cutting tool wear, were presented. The microscopic examination showed that the average grain size of the sintered nickel-cobalt alloy was 3.22 ± 0.1 (μm). The presence of the hardening state variability of the material during machining, as well as the value of the cutting force fluctuation as a function of the tool wear VB, were stated. The specific cutting force values increased to a small degree for the tool wear in the range of VB = 0–0.2 mm, and reached similar values in the range kc = 5500–7500 N/mm2. The specific cutting force values increased significantly for wear VB > 0.2 mm and were characterized by a large variability. The occurring phenomena were analyzed and several explanations were proposed. A recommendation was developed for the machining of parts made of sintered nickel-cobalt alloy. The Taguchi method was used in the experiment methodology. [ABSTRACT FROM AUTHOR]

This paper describes the effect of silicon on the manufacturing process, structure, phase composition, and selected properties of titanium aluminide alloys. The experimental generation of TiAl–Si alloys is composed of titanium aluminide (TiAl, Ti3Al or TiAl3) matrix reinforced by hard and heat-resistant titanium silicides (especially Ti5Si3). The alloys are characterized by wear resistance comparable with tool steels, high hardness, and very good resistance to oxidation at high temperatures (up to 1000 °C), but also low room-temperature ductility, as is typical also for other intermetallic materials. These alloys had been successfully prepared by the means of powder metallurgical routes and melting metallurgy methods. [ABSTRACT FROM AUTHOR]

The Critical Raw Materials (CRMs) list has been defined based on economic importance and supply risk by the European Commission. This review paper describes two issues regarding critical raw materials: the possibilities of their substitution in iron-based alloys and the use of iron-based alloys instead of other materials in order to save CRMs. This review covers strategies for saving chromium in stainless steel, substitution or lowering the amounts of carbide-forming elements (especially tungsten and vanadium) in tool steel and alternative iron-based CRM-free and low-CRM materials: austempered ductile cast iron, high-temperature alloys based on intermetallics of iron and sintered diamond tools with an iron-containing low-cobalt binder. [ABSTRACT FROM AUTHOR]

Intermetallic compounds based on Ti-Al- (Si) are attractive materials with good thermal stability and low density. However, the production of these materials is quite complicated. Partially modified conventional methods of melting metallurgy are most often used due to availability, possible high productivity, and relatively low production costs. Therefore, some technologies for the production of intermetallics based on Ti-Al are currently available, but with certain disadvantages, which are caused by poor casting properties or extreme reactivity of the melt with crucibles. Some shortcomings can be eliminated by modifying the melting technology, which contributes to increasing the cost of the process. The work deals with the preparation of Ti-Al-Si intermetallic compounds with different contents of aluminum and silicon, which were produced by centrifugal casting in an induction vacuum furnace Linn Supercast-Titan. This process could contribute to the commercial use of these alloys in the future. For this research, the TiAl15Si15(in wt.%) alloy was selected, which represents a balanced ratio of aluminides and silicides in its structure, and the TiAl35Si5 alloy, which due to the lower silicon content allows better melting conditions, especially with regard to the melting temperature. This alloy was also investigated after HIP ("Hot Isostatic Pressing") treatment. [ABSTRACT FROM AUTHOR]

A low-cost titanium alloy (Ti–5Al–2Fe–3Mo wt.%) was designed and fabricated by blended elemental powder metallurgy (BEPM) process. The high-temperature deformation behavior of the powder metallurgical Ti–5Al–2Fe–3Mo wt.% (PM-TiAlFeMo) alloy was investigated by hot compression tests at temperatures ranging from 700 to 1000 °C and strain rates ranging from 0.001 to 10 s−1. The flow curves were employed to develop the Arrhenius-type constitutive model in consideration of effects of deformation temperature, strain rate, and flow stress. The value of activation energy (Q) was determined as 413.25 kJ/mol. In order to describe the workability and predict the optimum hot processing parameters of the PM-TiAlFeMo alloy, the processing map has been established based on the true stress–true strain curves and power dissipation efficiency map. Moreover, microstructure observations match well with the analyses about deformation mechanisms, revealing that dynamic recovery and dynamic recrystallization are dominant softening mechanisms at relatively high temperatures. However, the kinking and breaking of microstructure prefer to occur at relatively low temperatures. [ABSTRACT FROM AUTHOR]

This paper brings an innovative processing route of manganese deep-sea nodules, which results in completely new grades of alloys. Deep-sea nodules were processed by aluminothermic method without the extraction of individual elements, producing complexly alloyed manganese-based "natural alloys". Three levels of the amount of aluminum were used for the aluminothermic reduction, and hence the alloys differ strongly in the amount of aluminum, which has a significant effect on their phase composition. The alloys have very high wear resistance, comparable with tool steel. The disadvantage of low-aluminum alloy is the susceptibility to local thermal cracking during friction, which occurs especially in the case of a dry sliding wear against the static partner with low thermal conductivity. [ABSTRACT FROM AUTHOR]

Titanium and its alloys belong to the group of materials used in implantology due to their biocompatibility, outstanding corrosion resistance and good mechanical properties. However, the value of Young's modulus is too high in comparison with the human bone, which could result in the failure of implants. This problem can be overcome by creating pores in the materials, which, moreover, improves the osseointegration. Therefore, TiSi2 and TiSi2 with 20 wt.% of the pore-forming agent (PA) were prepared by reactive sintering and compared with pure titanium and titanium with the addition of various PA content in this study. For manufacturing implants (especially augmentation or spinal replacements), titanium with PA seemed to be more suitable than TiSi2 + 20 wt.% PA. In addition, titanium with 30 or 40 wt.% PA contained pores with a size allowing bone tissue ingrowth. Furthermore, Ti + 30 wt.% PA was more suitable material in terms of corrosion resistance; however, its Young's modulus was higher than that of the human bone while Ti + 40 wt.% PA had a Young's modulus close to the human bone. [ABSTRACT FROM AUTHOR]

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]

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]