Papers by Keyword: Eutectic

Abstract: High entropy alloys possess excellent properties and a great deal of research is being carried out on them. AlCrCo_(1-x)Fe_(1+x)Ni₂ (x= 0, 0.5, 1) alloys were arc melted and suction cast in strip form in a controlled atmosphere. The alloys were characterized for crystal structure, phases and Vickers hardness. A two phase vermicular structure was observed for alloys with x = 0 – 0.5 consisting of Ni rich BCC and Cr rich FCC phases while a widmanstatten structure formed in alloy with x = 1 (without Co). An increase in the amount of BCC phase and hardness was noted with the replacement of Co with Fe caused mainly due to increase in Al and decrease of Cr in composition obtained through EDS. Vickers hardness of 251 H_V was measured in alloy without Co.

Abstract: MoSi₂/Mo₅Si₃ eutectic composites have been considered as one of the promising candidates for ultra-high temperature structural applications owing to their high melting point, good oxidation resistance, and low mass density. Their mechanical properties can be improved by controlling the eutectic structure (i.e. script lamellar structure) in directional solidification. It is important to elucidate the dominant factors underlining the unique pattern formation. We conducted a comprehensive phase field study to examine the influence of various factors on the MoSi₂/Mo₅Si₃ eutectic microstructure with complicated morphology. First, the inclined lamellae have been attributed to the minimization of elastic strain energy due to the lattice mismatch between MoSi₂ and Mo₅Si₃, which are partially relaxed by forming semi-coherent phase boundaries. Second, the maze-like pattern on the horizontal cross-section appeared when a two-fold anisotropy of interfacial energy is superimposed on the MoSi₂/Mo₅Si₃ boundary. Third, the random and intersected lamellae have been obtained by assuming the instability of the solid-liquid interface and introducing successive nucleation of Mo₅Si₃ phase. These findings provide guidance for manipulating the eutectic structure and act as footsteps for further theoretical investigation.

Abstract: Grain refinement is one of the most important and popular melt treatment process for Al-Si alloy casting. Microstructure and mechanical properties of commercially available Aluminium Silicon alloy LM6 can be improved with the addition of grain refiners and modifiers as these provide technical and economic advantages. This paper is an effort to study the effects of addition of grain refiners and modifiers to the eutectic Al – Si alloy LM6. Commercially available Al - Si alloy LM6 (eutectic = 12% Si) is grain refined with Al-5Ti-1B and Al-3B; and modified with Al-10Sr master alloys. These were added individually and then tested for its unique mechanical properties such as ultimate tensile strength, hardness and wear; which are co-related with the machining tests such as turning, surface roughness and drilling. The test results are compared with microstructure of the samples observed through SEM.The mechanical properties of this alloy can be altered after addition of master alloys, which in turn alter the grain size. Thus the results conclude that the mechanical properties of Al-Si alloys in general are controlled by a number of principal microstructural features. A fine grain size is desirable, leading to improvement of mechanical properties.

Abstract: This research work reports on the investigation on the suitability of prepared Al-Mg binary alloys of hypo-eutectic and eutectic compositions, for making metal matrix composites for light weight applications. Commercial pure aluminium, and magnesium blocks were used for the purpose of making binary alloys of Al-Mg, with the Mg in weight percentages 15%, 20%, 25%, 30%, and 37%. composition prepared by stir-casting under Argon cover gas. The cast Al-Mg alloys were cut to standard specimens to investigate its microstructure and mechanical properties. Test results revealed that the Vicker’s Hardness Number (VHN) of the alloys increases with the increased weight percentage of Mg and Ultimate Tensile Strength (UTS) were also increasing with increasing Mg content. The SEM images revealed the presence of micro-voids in alloys of higher Mg contents. The test values indicates the suitability of hypo-eutectic alloys as candidates for metal matrix composites for light weight applications.

Abstract: The effect of overheating of the melt and cooling rate of alloys of the Al-Cu system with a copper content of 25.0 – 36.0% ( mass.), the rest of the aluminum is investigated. It is shown that an overheating of the liquid at 50 – 100 K above the liquid-liquid line leads to the formation of a fine-dispersed eutectic structure and the inhibition of the formation of primary aluminum crystals in the pre-evacuation of alloys and the Al₂Cu phase in hypereuvtectic alloys, in accordance. An increase in the melt overheating temperature by 150 K above the liquid-liquid line and the subsequent cooling at 10³ – 10⁴ K/s leads to the complete inhibition of the formation of primary crystals. An overheating of the melt on 100 – 150 K alloys above the liquid line and subsequent cooling with a velocity of 10³ – 10⁴ K /s reduces the rate of corrosion by 30 – 45% and increases the numerical value in 1.3 – 1.45 times the relative wear resistance, and the brittleness of alloys decreases in 1.2 – 1.35 times in comparison with the samples after casting.

Abstract: The process of a eutectic alloy crystallization is considered when the eutectic alloy is instantly cooled from the liquid state to below the eutectic transformation temperature. The features of such crystallization are considered. The mathematical model of the process is constructed that takes into account the nucleation of new phases particles, their growth and the associated change the concentrations of the melt components. The nuclei of new phases are supposed be spherical. As they grow, they come into contact and become lamellar. The developed approach was applied to the amorphization process of the eutectic alloys. An amorphous state has been reached if the clusters of solid phases can’t grow above nanosize. The model allows researching the necessary amorphization conditions.

Abstract: Sn-0.7Cu-0.05Ni is a widely used Pb-free solder that solidifies into a near-eutectic microstructure and a small fraction of primary Cu₆Sn₅. This paper overviews in-situ time-resolved imaging experiments on the solidification of Sn-0.7Cu-0.05Ni solder under three conditions: (i) directional solidification, (ii) continuous cooling in a near-uniform thermal field, and (iii) solder joint solidification on a Cu substrate. Primary Cu₆Sn₅ grow as rods along [0001] in each case but can also grow as X-shaped crystals in (iii). There are significant differences in eutectic growth due to nucleation difficulties for tin in conditions (ii) and (iii).

Abstract: The microstructure and microhardness distribution in surface of low carbon Hardox 450 steel coated with alloyed powder wires of different chemical compositions are studied. It is shown that the microhardness of 6-8 mm thickness surfaced layer exceeds that of base metal by more than 2 times. The increased mechanical properties of surfaced layer are caused by the submicro and nanoscale dispersed martensite, containing the niobium carbides Nb₂C, NbC and iron borides Fe₂B. In the bulk plates a dislocation substructure of the net-like type with scalar dislocation density of 10¹¹ cm^-2 is observed. The layer surfaced with the wire containing B possesses the highest hardness. The possible mechanisms of niobium and boron carbides formation in surfacing are discussed.

Abstract: The paper investigates the influence of alloying of high manganese steel with various materials on its wear resistance. It describes the results of differential scanning calorimetry and thermo-gravimetric analysis obtained in the process of thermal investigation of high manganese steel alloyed with different materials. The processes taking place in alloyed high manganese steel during heat treatment were considered. Besides, the paper shows the results of investigation of kinetics of oxidation of high manganese steels, temperatures of the start and completion of carbide decomposition and carbon burning; the comparative analysis of these processes was carried out. The research group determined the qualitative characteristics of the steel decarburization process depending on the implemented alloying scheme of high manganese steel. Scientific justification was given to the results obtained in the research work. The technological recommendations, which make it possible to calculate the optimum hardening temperature of high manganese steels, were given. General conclusions were made in the final part of the paper.

Abstract: The Al-Si alloy is a structural material which generally consists of two or more particulates. However, Al-Si alloys are the most common alloys and commercially available ones due to their economical production. The utilization of Al-Si alloys has given the scope of study to improve in its properties using some grain refiner like Al-5Ti-1B, Al-3B and modifiers like Al-10Sr. The Al alloys were selected based on the economical uses and also, on the basis such that hypoeutectic (i.e., LM-25), eutectic (i.e., LM-6) and hypereutectic (i.e., LM-30). This project aimed to synthesize Al alloys (LM-6, LM-25 and LM-30) by melt stirring method with varying amount of grain refiners and / or modifier. The Prepared composites were characterized for machining properties. Alloys were evaluated for their machining properties which include surface roughness, lathe and drill tool dynamometer and comparing the machining properties with the minor addition of grain refienrs and/or modifier. The study concluded that, the addition of Al-3B to eutectic (i.e., LM-6) alloys has better surface finish.