Papers by Keyword: Primary Dendrite Arm Spacing

Abstract: Al-5 wt.% Zn samples were prepared using high purity (99.99%) metals in graphite crucibles. The samples were directionally solidified upward with a constant temperature gradient (G = 5.5 Kmm^-1) and different growth rates, V, (8.25-165 μm/s) in a Bridgman type directional solidification apparatus. The dendritic spacings (λ₁: Primary dendrite arm spacing, and λ₂: Secondary dendrite arm spacing) were measured from the longitudinal sections of the samples and λ₁ was also measured from the transverse sections. The measured spacings were expressed as functions of the growth rates by using a linear regression analysis. The effect of V on λ₁ and λ₂ were investigated. The experimental results were compared with the results of the current theoretical and numerical models and similar previous experimental results.

Abstract: Under the condition that the solid-liquid interface bends periodically in continuous casting, the expression of solid-phase growth rate adapting to continuous casting was set up, and then the growth rates were calculated. On this basis, the morphologic of crystal growth and the variation of primary dendrite spacing during continuous casting slabs were studied. The results show that the growth rate is the fastest when solid-phase moves to wave crest within a deformation periodicity, whereas the growth rate is the slowest when the crystal moves to wave hollow. The bigger the bulge size is, the greater the variation amplitude of the growth rate will become. The variation of the growth rate results in the S/L interface to develop towards a planar surface. Because the value is much smaller than the critical value of the transformation from cells to dendrites, and the crystals only grow in the fashion of dendrites. The primary dendrite spacing at wave crest is bigger than the primary dendrite spacing at wave hollow in early stage of columnar crystal growth, and the dendrite spacing at wave crest is basically equal with the dendrite spacing at wave hollow in the late stage of solidification, and they quickly simultaneous increase. Good correlation is obtained between the experimental results and the calculation results of the dendrite arm spacing.

Abstract: This paper presents the results of an investigation on the interrelationship between thermophysical properties, processing conditions and primary dendrite arm spacing for a nickel-base superalloy. The research was realized for CMSX-4, directionally solidified in a Bridgman furnace. For a systematic, fast and cost-efficient investigation numerical finite element models were applied. The numerical model, composed of thermophysical material data, geometric data and boundary conditions, was calibrated and experimentally validated. Microstructural parameters of the castings were determined for a broad range of processing conditions and varying thermophysical properties in order to study general influences. Withdrawal speed, furnace temperature, enthalpy of fusion, solidification range, heat conductivity and specific heat were varied accordingly. The primary dendrite arm spacing is predominantly influenced by withdrawal speed and furnace temperature, but shows only a weak dependency on thermophysical properties.

Abstract: Al-rich Al-Cu-Mg alloys have wide range of applications for automotive and aerospace where the control of the original solidification microstructure is important to achieve desired properties. Under constant temperature gradient G (4.84±0.13 K.mm-1), a series of directional solidification experiments were performed at 6 different growth rates V (16.7 – 166.7 µm/s) and 6 different Mg contents C0-Mg (0 – 5 wt.% Mg) of Al – 5wt.% Cu – (0-5)wt.% Mg alloys. The solid-liquid interface was investigated in as-quenched specimens. Primary dendrite arm spacing λ1 was measured on longitudinal and transverse sections of the specimens. The variations of λ1 with respect to V and C0-Mg were determined and the results were compared to the related theoretical models and the published data.