E. Çadırlı

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.

Solid—liquid surface energy of pivalic acid

Abstract The Gibbs–Thomson coefficient and the solid–liquid surface energy for pivalic acid have been measured by a direct method. The grain boundary energy of the pivalic acid also has been calculated from the observed grain boundary groove shapes.

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.

The directional solidification of Pb-Sn alloys

Directional solidification experiments have been carried out on different Pb-Sn alloys as a function of temperature gradient G, growth rate V and cooling rate GV. The specimens were solidified under steady state condition with a constant temperature gradient (50 °C/cm) at a wide range of growth rates ((10–400) × 10−4 cm/s) and with a constant growth rate (17 × 10−4 cm/s) at a wide range of temperature gradient (10–55 °C/cm). The primary dendrite arm spacing, λ1, and secondary dendrite arm spacing, λ2, were evaluated. This structure parameters were expressed as functions of G, V and GV by using the linear regression analysis. The results were in good agreement 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 solidification parameters on mechanical properties of directionally solidified Al-Rich Al-Cu alloys

Al(100−x)-Cux alloys (x=3 wt%, 6 wt%, 15 wt%, 24 wt% and 33 wt%) were prepared using metals of 99.99% high purity in vacuum atmosphere. These alloys were directionally solidified under steady-state conditions by using a Bridgman-type directional solidification furnace. Solidification parameters (G, V and ), microstructure parameters (λ1, λ2 and λE) and mechanical properties (HV, σ) of the Al-Cu alloys were measured. Microstructure parameters were expressed as functions of solidification parameters by using a linear regression analysis. The dependency of HV, σ on the cooling rate, microstructure parameters and composition were determined. According to experimental results, the microhardness and ultimate tensile strength of the solidified samples was increased by increasing the cooling rate and Cu content, but decreased with increasing microstructure parameters. The microscopic fracture surfaces of the different samples were observed using scanning electron microscopy. Fractographic analysis of the tensile fracture surfaces showed that the type of fracture significantly changed from ductile to brittle depending on the composition.

Effect of growth rate and composition on the primary spacing, the dendrite tip radius and mushy zone depth in the directionally solidified succinonitrile–Salol alloys

The succinonitrile (SCN)–Salol alloys for four different concentrations Salol were unidirectionally solidified for five different growth rates in a constant temperature gradient. The microstructure parameters, viz., the primary dendrite arm spacing, λ1, dendrite tip radius, R and mushy zone depth, d, were measured. The dependence of the microstructure parameters on the solidification parameters for SCN–Salol alloys were determined by linear regression analysis. The results are compared with theoretical models and published data.

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.