Influence of Growth Rate on Eutectic Spacing, Microhardness, and Ultimate Tensile Strength in the Directionally Solidifi
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DUCTION
SOLIDIFICATION from the melt is an essential step in nearly all established sequences of metal processing. The solidification and melting are phase transformations between solid and liquid phases of the materials. Understanding the mechanism of solidification is crucial in controlling the electrical, thermal, and mechanical properties of metals.[1] Directionally solidified binary or ternary eutectics can produce well-aligned regular structures consisting of fibrous (rodlike) or lamellar constituents. Such structures may offer substantial increases in high-temperature strength, fracture properties, or creep resistance over those of conventionally cast alloys.[2] The directional solidification method was first used in the 1960s to produce a turbine blade.[3] This method provides understanding of the relationship between alloys and their microstructure, process conditions, and geometry. Additionally, rapid solidification has been applied to aluminum alloys to improve both individual and combinations of properties in conventional alloys and
U¨MIT BAYRAM is with the Department of Physics, Faculty of _ Science, Erciyes University, 38039 Kayseri, Turkey. NECMETTIN MARASLı is with the Department of Metallurgical and Materials Engineering, Faculty of Chemistry and Metallurgical Engineering, Yildiz Technical University, 34210 Istanbul, Turkey. Contact email: [email protected] Manuscript submitted April 3, 2018.
METALLURGICAL AND MATERIALS TRANSACTIONS B
thermal stability and elastic stiffness by means of nonconventional alloy additions that are detrimental at normal rates of solidification.[4] Commercial aluminum and its alloys can be divided into three grades: work-hardenable wrought compositions, including the metal itself in various grades of purity (1xxx series); with or without solid solution alloying additions of Mg (5xxx series); or with dispersion hardening additions of Mn (3xxx series) age-hardenable wrought compositions, embracing those based on Al-Cu, Al-Mg-Si, and Al-Zn-Mg (2xxx, 6xxx, and 7xxx series, respectively).[4] The 2xxx series (Al-Cu alloys) have been used extensively in the cast and wrought form where strength and toughness are required. These alloys exhibit high strength and hardness at room and elevated temperatures. Also, copper is typically the alloy basis for improved mechanical properties at elevated temperature, often with nickel additions.[5] Considering the studies performed,[6–10] some workers examined the Al-Cu-Ni system due to the interesting feature of thermoelastic martensitic transformation revealed by specific compositions of these alloys. This feature is answerable for the original mechanical treatment of these alloys, such as superplasticity, stress-induced martensitic transformation, and the shape memory effect.[11] As can be seen from the literature,[12–36] the experiments on directional solidification were usually performed within a growth range of 2.0 to 500 lm s1 at a constant low-temperature gradient by using a Bridgman-type growth apparatus, and the influence of the growth rat
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