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The present work describes the effect of tempering (T4 and T6) processes on the dry sliding wear properties of ilmenite reinforced aluminum alloy (LM30) composites, prepared through stir casting route. In this process the composites were heated to 540 °C for 0.5–2 h followed by water quenching. Then the samples were first given (a) T4 treatment (natural ageing at room temperature), and in second case (b) T6 treatment (aged at 180 and 250 °C for 4 h before air cooling). Optical microscopy revealed the homogeneous distribution of ilmenite particles and redistributed silicon around the ilmenite in the alloy matrix. Rockwell hardness values suggested the superiority of T6 treated composite samples as compared to T4 treated and untreated samples due to enhanced precipitation of intermetallic compounds viz. Al13Fe4, FeSn2, FeTiSi, and Al3Ti. Similarly, superior wear resistance (against steel disc) of T6 treated composite samples was also observed. A responsible mechanism has also been established with the help of scanning electron microscopy of worn surface and wear debris. Finally, a comparative study revealed the excellent (~ 4.0%) wear resistance (against EN31 steel disc) of T6 treated composite sample as compared to grey cast iron (traditional material) for brake drum applications. [ABSTRACT FROM AUTHOR]

The effect of Sr and cooling rate on the microstructure of Al-2.5%Mn alloy was studied by OM, SEM and XRD. The results showed that Sr not only refined the primary phase, but also refined eutectic microstructures. However, there was obvious delamination in the alloy. When the content of Sr was 0.2%–0.65%, the primary phase in the upper part of alloy changed from coarse needle and lath-shaped to fine block and needle-like. With the Sr content increased, the needle-like structure in the alloy tended to be more and longer, but the size of α -Al tended to be finer. At the bottom, there were many large massive phases, which were much more refined than the primary phase without Sr With the cooling rate increased, the primary phase was refined greatly and almost all of them transformed into eutectic microstructure. Besides, the delamination of microstructure disappeared.

Technology is developed for preparing semifinished sheet of hypereutectic alloys based on the aluminumcerium system intended for operation under conditions of x-radiation. The technology is based on creating a test alloy by casting and subsequent deformation treatment. Two versions of cast billet preparation are considered in the work. Sheet material prepared by rolling these billets exhibits good adaptability and may be used for producing engineering objects. [ABSTRACT FROM AUTHOR]

Diluted alloys of the binary system Ni–Si have been used as target of beam of ions, electrons, neutrons and so on because in this kind of alloy occurs transformations order–disorder, when the temperature is raised. This fact has permitted to evaluate the phenomena associated with the damage induced by irradiation (DII). The results of these works have been employed to understand the behavior under irradiation of complex alloys and to evaluate the reliability of the results of mathematical simulation of the evolution of the DII. The interest in the alloy system Ni-Si has been reborn due to the necessity of developing materials, which have better resistance against the corrosion on more aggressive environments such as those generated on the nuclear power plants or those that exist out of the Earth's atmosphere. Now, a growing interest to use concentrated alloys of this binary system on diverse fields of the materials science has been taking place because up to determined concentration of silicon, a regular eutectic is formed, and this fact opens the possibility to develop lamellar composite material by directional solidification. However, nowadays, there is a lack of fundamental knowledge about the behavior of this type of lamellar structure under aggressive environments, like those mentioned before. Hence, the task of this work is to evaluate the effect that has the irradiation over the microstructure of the concentrated alloy Ni22at%Si. The dendritic region of the hypereutectic alloy consists of an intermetallic phase Ni3Si, whereas the interdendritic region is formed by the alternation of lamellas of solid solution α-Ni and intermetallic phase Ni3Si. Such kind of microstructure has the advantage to get information of the DII over different phases individually, and at the same time, about of the microstructure influence over the global damage in the alloy. The hypereutectic Ni22at%Si alloy was irradiated perpendicularly to its surface, with 3.66 MeV – Ni ions up to 380 dpa at 650°C in a Tandetron linear accelerator. The level of irradiation dose was chosen similar to the irradiation conditions of the next-generation nuclear reactors. The theoretical maximum depth of the DII (maximum depth of damage (MDD)) was calculated as 1.35 µm using the SRIM-2013 program; the laminar microstructure of the eutectic was simulated using the lattice parameters of the eutectic before irradiation. The experimental MDD was 1.47 µm, as determined through transmission electron microscope (TEM) images and the DII was characterized using µX-ray diffraction and TEM. The elimination of cubic phase of the intermetallic Ni3Si, the suppression of lamellae of the α-Ni phase, the generation of dislocation loops and lines, all of these changes generated by the irradiation are clear evidences that the DII was severe. Based on theoretical and experimental evidence, we propose that the amount of phases, alternate of lamellae with different chemical concentrations of silicon and lamellae spatial distribution have a direct relation with the severe evolution of the DII. [ABSTRACT FROM AUTHOR]

The effect of microstructures on the room temperature fracture toughness of NiAl-32Cr-6Mo (at%) hypereutectic alloy was investigated. The solidification microstructure changed from planar eutectic to cellular eutectic and dendritic eutectic with increasing withdrawal rate. The fracture toughness of alloy with planar eutectic microstructure solidified at 10μms-1 was 23.74MPam1/2, and then it dropped to 15.35MPam1/2 when the alloy solidified at rate of 15μms-1. But higher fracture toughness of 22.92MPam1/2 was obtained when the alloy solidified at 25μms-1 and had a perfect cellular microstructure. In this case, the production efficiency can be markedly improved. The fracture surfaces of the NiAl-32Cr-6Mo hypereutectic alloy showed quasi-cleavage fracture mode, some cleavage steps and tearing ridges were observed. The alloys with cellular and dendritic eutectic microstructures exhibited transcellular fracture morphologies; the conically shaped ridges or valleys were observed in each eutectic cell. Owing to the perfect cellular microstructure, the bonding strength of the cell boundary was high; the eutectic cells could largely deform consistently and offer higher resistance of the crack propagation. [ABSTRACT FROM AUTHOR]

The effect of ultrasonic treatment during casting of a hypereutectic Al-Si alloy (Etial 195) containing 18%Si on the microstructure and some mechanical properties has been investigated. For this purpose, a steel mould was placed inside an ultrasonic bath, and molten aluminium alloy at 740°C was poured into the mould. Ultrasound was applied to the casts from the external side of the mould during solidification. Cooling curves were obtained by measuring and recording the temperature of the cast. The samples were subjected to X-ray diffraction analysis and hardness, wear and impact tests. The microstructure of the samples was examined by optical and scanning electron microscopies and investigated statistically with image analysis software. Hardness values increased from 49·8-52·3 to 57·7-61·6 HRB upon ultrasonic treatment during solidification. The application of ultrasonic vibration to the cast from the external side of the mould resulted in modification of the microstructure and improvement in mechanical properties. [ABSTRACT FROM AUTHOR]

Abstract: The article deals with the solidification microstructures of the rapidly solidified powder of 3% C–3% Cr–12% V (wt.%) hypereutectic iron alloy Ch3F12 (C3Cr3V12). Five different solidification microstructures were classified in powder particles: microstructure with eutectic spherulites, microstructure with eutectic colonies without primary carbides, microstructure with the primary carbides in the centers of eutectic colonies, microstructure with star-like carbides and microstructure with dispersed globular carbides. Light microscopy, scanning electron microscopy and transmission electron microscopy were used for experimental observations. X-ray diffraction analysis proved the presence of M4C3 carbide, austenite and indicated the presence of M7C3 carbides. The chemical composition of primary carbide phase was determined by energy-dispersive X-ray analysis. [Copyright &y& Elsevier]

• The eutectic Mg 2 Si in Al-11Mg 2 Si alloy was modified to spherical particles with 0.2 wt% Ca-Sb addition. • Adding 1.0 wt% Ca-Sb resulted in a microstructure transition from hypoeutectic to hypereutectic characteristics in Al-11Mg 2 Si alloy. • The 0.2 wt% Ca-Sb modified alloy exhibits an improvement in elongation to failure and ultimate tensile strength. • The modification mechanisms and the reasons for the enhanced mechanical properties were discussed in detail. The combined addition of 0.2 wt% Ca-Sb in Al-11Mg 2 Si alloy led to significant refinement of the eutectic Mg 2 Si from a coarse, needle-like morphology to spherical particles. Specifically, a further increase of Ca-Sb addition to 1.0 wt% resulted in the microstructure transition from hypoeutectic to hypereutectic characteristics. The refinement of eutectic Mg 2 Si could be attributed to the selective adsorption of Ca and Sb atoms on Mg 2 Si surfaces, which inhibited the growth of the eutectic phase in the preferential growth direction. Importantly, Ca and Sb elements were involved in the formation of heterogeneous nuclei for primary Mg 2 Si when Ca-Sb content increased to 1.0 wt%, which introduced the transition of composition from hypoeutectic to hypereutectic structures. Comparing to the unmodified alloy, the Al-11Mg 2 Si alloy modified with 0.2 wt% Ca-Sb exhibited significantly enhanced elongation to failure of ~7.9% (from ~1.3% of the unmodified alloy) and ultimate tensile strength of ~222 MPa (from ~180 MPa of unmodified alloy). The spheroidization of eutectic Mg 2 Si after complex modification is believed to be the underlying reason for the greatly enhanced tensile properties. [ABSTRACT FROM AUTHOR]

Hypereutectic Al–Fe and Al–Ni alloys offer a potentially attractive combination of properties, e.g. high-temperature strength and stability, high elastic modulus and low coefficient of thermal expansion. This potential, however, cannot be reached unless the structure of these alloys is refined so that their processing becomes possible. In this study, we for the first time apply ultrasonic melt processing for refining the structure of hypereutectic Al-4% Fe and Al-8% Ni alloys with 0.3 wt% Zr addition. Both primary Al 3 Fe and Al 3 Ni particles as well as aluminum/eutectic grains are significantly refined. It is suggested that cavitation-induced fragmentation of primary Al 3 Zr crystals plays a significant role in the nucleation of intermetallics as well as aluminum. Furthermore, the hardness and tensile properties of the alloys substantially increase after ultrasonic treatment due to the refined structure, which also contributes to the considerably enhanced ductility of the alloys. As a result, the fracture mode changes from brittle fracture to ductile fracture. The increase in ductility makes the alloys suitable for hot deformation, which is demonstrated by lab-scale hot rolling. In addition, precipitation hardening of the alloys can be achieved by high-temperature annealing at 450 °C due to retained Zr in the Al solid solution upon solidification. The results are supported by the analysis of the composition of a supersaturated solid solution of Zr in Al and scanning and transmission electron microscopy that confirms the precipitation of coherent Al 3 Zr nanoparticles. It is demonstrated that a combination of ultrasonic melt processing and alloying with Zr makes it feasible to develop new class of hypereutectic casting and wrought alloys based on the Al–Fe and Al–Ni systems. • A new class of cast and wrought hypereutectic Al alloys was studied upon ultrasonic melt processing (USP) and Zr addition. • Structure refinement in hypereutectic Al–Fe and Al–Ni alloys is enabled by a combination of USP and addition of Zr. • The strength and ductility of the hypereutectic alloys can be achieved by structure refinement upon USP and precipitation. • After USP, refined hypereutectic Al–Fe and Al–Ni alloys can be successfully hot rolled. [ABSTRACT FROM AUTHOR]