M. Gündüz

Directional solidification of aluminium -copper alloys

Abstract Directional solidification experiments have been carried out on different Al–Cu alloys as a function of solidification parameters, temperature gradient G, growth rate V, and composition C0. The specimens were solidified under steady state conditions with a constant temperature gradient (7.4 K mm−1) at a wide range of growth rates (9–490 μm s−1) and with a constant growth rate of 9.5 μm s−1 at a wide range of temperature gradients (1.0–7.4 K mm−1). Microstructural parameters, the primary dendrite arm spacing λ1, secondary dendrite arm spacing λ2, dendrite tip radius R, mushy zone depth d were measured and expressed as functions of solidification parameters, G, V and C0 by using a linear regression analysis. The results were in good agreement with previous experimental work and current theoretical models suggested for dendritic growth.

Effect of growth rates and temperature gradients on the lamellar spacing and the undercooling in the directionally solidified Pb-Cd eutectic alloy

Lead-cadmium of high (99.99%) purity eutectic alloy was melted in a graphite crucible under vacuum atmosphere. These regular eutectic alloys were directionally solidified upward with a constant growth rate of 8.3 {mu}m/s, and different temperature gradients G ({approx}1.6-6.4 K/mm range), and also with a constant temperature gradient ({approx}6.4 K/mm) and different growth rates V (8.3-165.5 {mu}m/s range) in the Bridgman-type directional solidification furnace. The lamellar spacings {lambda} were measured from both transverse section and longitudinal section of the specimen. The variations of {lambda} with respect to G and V were determined by using linear regression analysis. The dependence of {lambda} on {delta}T{sub e} (the extremum undercooling) was also analysed. The variation of {delta}T{sub e} with V at constant G and with G at constant V were investigated. According to these results, it has been found that {lambda} decreases with the increasing values of G and V. Also {delta}T{sub e} increases with increasing V for a constant G and with the increasing G for a given V, respectively. The results obtained in this work have been compared with the Jackson-Hunt eutectic theory and the previous experimental results.

The dependence of lamellar spacing on growth rate and temperature gradient in the lead–tin eutectic alloy

Pb‐Sn eutectic samples were directionally solidified under an argon atmosphere in a Bridgman type furnace in order to determine the dependence of lamellar spacing,E, on the growth rate, V, the temperature gradient, G and the cooling rate, GV. Six samples were solidified with a constant V but different G and five samples were solidified with constant G but different V. The samples were solidified up to 10‐ 12 cm length to ensure that the steady-state condition was obtained, and then quenched. Grinding, polishing and etching techniques were applied to longitudinal and the transverse sections of the samples to observe E using an olympus BH-2 optical and a JEOL JSM 5400 scanning electron microscopy. Approximately 300‐500 transverse lamellar spacings and 60‐100 longitudinal lamellar spacings were measured and least-squares analysis was used to obtain the relationships between E and V, G and GV. It was found that the value of E decreases as the values of V, G and GV increase and that the results are in good agreement with the results of the previous work and with the Jackson‐Hunt eutectic theory. # 2000 Elsevier Science S.A. All rights reserved.

Solid-liquid interfacial energy of camphene

The Gibbs‐Thomson coefficient and the solid‐liquid interfacial energy for camphene have been measured to be (8.5890.96) 10 8 K m and (4.4390.49)10 3 Jm 2 , respectively, by a direct method. The grain boundary energy of camphene has also been calculated to be (8.3690.92)10 3 Jm 2 from the observed grain boundary groove shapes.

Effect of the Temperature Gradient, Growth Rate, and the Interflake Spacing on the Microhardness in the Directionally Solidified Al-Si Eutectic Alloy

An alloy of composition Al-12.6 wt.% Si was prepared using metals of 99.99% purity. Weighed amounts of aluminium and silicon were melted in the vacuum-melting furnace. This irregular eutectic alloys were directionally solidified upward with a constant growth rate V (8.3×10−3 mm/s) and different temperature gradients G (2.0–7.8 K/mm) and also with a constant temperature gradient G (7.8 K/mm) and different growth rates V (8.3–498.7×10 −3mm/s) in the directional solidification furnace. The interflake spacings λ and microhardness HV were measured from both transverse section and longitudinal section of the specimen. The variations of HV with respect to G, V, and λ have been determined by using the linear regression analysis method. It has been shown that HV increases with the increasing values of G and V. On the other hand HV values decreases with the increasing λ values. The Hall-Petch type relationships obtained in this work have been compared with the previous works.

Dependency of the microstructure parameters on the solidification parameters for camphene

Camphene (>95% purity) was unidirectionally solidified in a temperature gradient stage. The microstructure parameters, viz., the primary dendrite arm spacing λ1, secondary dendrite arm spacing λ2, dendrite tip radius R, and mushy zone depth d, were measured for five different growth rates in a constant temperature gradient G and for five different temperature gradients in a constant growth rate V. The dependency of the microstructure parameters on the solidification parameters (V, G, and GV) for camphene were determined by linear regression analysis. Our results are in good agreement with previous works.

Effect of growth rates and temperature gradients on the spacing and undercooling in the broken-lamellar eutectic growth (Sn-Zn eutectic system)

The Sn-Zn system has a eutectic structure of a broken lamellar type. Dependence of the broken-lamellar spacing λ and the undercooling ΔT on V and G were investigated, and the relationship between them was examined. A Sn-Zn (99.99%) high-purity eutectic alloy was melted in a graphite crucible under vacuum atmosphere. This eutectic alloy was directionally solidified upward with a constant growth rate V (8.30 µm/s) and different temperature gradients G (1.86–6.52 K/mm), and also with a constant temperature gradient (6.52 K/mm) and different growth rates (8.30–165.13 µm/s) in a Bridgman-type directional solidification furnace. The lamellar spacings λ were measured from both transverse and longitudinal sections of the specimen. The λ values from the transverse section were used for calculations and comparisons with the previous works. The undercooling values ΔT were obtained using growth rate and system parameters K1 and K2. It was found that the values of λ decreased while V and G increased. The relationships between lamellar spacing λ and solidification parameters V and G were obtained by linear regression analysis method. The λ2V, ΔTλ, ΔTV−5, and λ3G values were determined using λ, ΔT, V, and G values. The experimentally obtained values for the broken-lamellar growth (Sn-Zn eutectic system) were in good agreement with the theoretical and other experimental values.

Thermal and electrical conductivities of Cd-Zn alloys

The composition and temperature dependences of the thermal and electrical conductivities of three different Cd-Zn alloys have been investigated in the temperature range of 300-650 K. Thermal conductivities of the Cd-Zn alloys have been determined by using the radial heat flow method. It has been found that the thermal conductivity decreases slightly with increasing temperature and the data of thermal conductivity are shifting together to the higher values with increasing Cd composition. In addition, the electrical measurements were determined by using a standard DC four-point probe technique. The resistivity increases linearly and the electrical conductivity decreases exponentially with increasing temperature. The resistivity and electrical conductivity are independent of composition of Cd and Zn. Also, the temperature coefficient of Cd-Zn alloys has been determined, which is independent of composition of Cd and Zn. Finally, Lorenz number has been calculated using the thermal and electrical conductivity values at 373 and 533 K. The results satisfy the Wiedemann-Franz (WF) relation at T 373 K), the WF relation could not hold and the phonon component contribution of thermal conductivity dominates the thermal conduction.

The interfacial free energy of solid Sn on the boundary interface with liquid Cd–Sn eutectic solution

Equilibrated grain boundary groove shapes for solid Sn in equilibrium with Cd?Sn liquid were directly observed after annealing a sample at the eutectic temperature for about 8 days. The thermal conductivities of the solid phase, KS, and the liquid phase, KL, for the groove shapes were measured. From the observed groove shapes, the Gibbs?Thomson coefficients were obtained with a numerical method, using the measured G, KS and KL values. The solid?liquid interfacial energy of solid Sn in equilibrium with Cd?Sn liquid was determined from the Gibbs?Thomson equation. The grain boundary energy for solid Sn was also calculated from the observed groove shapes.

Determination of thermal conductivities of solid and liquid phases for rich-Sn compositions of Sn-Mg alloy

The variations of thermal conductivities of solid phases versus temperature for pure Sn and Sn-1 wt% Mg, Sn-2 wt% Mg, and Sn-6 wt% Mg binary alloys were measured with a radial heat flow apparatus. Thermal conductivity variations versus temperature for pure Sn and Sn-1 wt% Mg, Sn-2 wt% Mg, and Sn-6 wt% Mg binary alloys were found to be 60.60 ± 3.63, 61.99 ± 3.71, 68.29 ± 4.09, and 82.04 ± 4.92 W/Km, respectively. The thermal conductivity ratios of liquid phase to solid phase for pure Sn and eutectic Sn-2 wt% Mg alloy at their melting temperature were found to be 1.11 and 1.08, respectively, with a Bridgman type directional solidification apparatus. Thus the thermal conductivities of liquid phases for pure Sn and eutectic Sn-2 wt% Mg binary alloy at their melting temperature were evaluated to be 67.26 ± 4.03 and 73.75 ± 4.42 W/Km, respectively, by using the values of solid phase thermal conductivities and the thermal conductivity ratios of the liquid phase to the solid phase.