Mushy Zone Depth Research Articles

Growth rate and composition of directionally solidified intermetallic TiAl–Nb alloys with different solidification conditions

Intermetallic Ti–xAl–8Nb (x = 41, 43, 45, 47, 49; at%) alloys were solidified unidirectionally upwards with a constant temperature gradient of G = 3.8 K·mm−1 at wide range of growth rates of v = 10–400 μm·s−1 using a Bridgman directional solidification (DS) furnace. Microstructural parameters including the primary dendrite arm spacing (λ 1), secondary dendrite arm spacing (λ 2), dendrite tip radius (R) and mushy zone depth (d) were measured statistically. The values of λ 1, λ 2, R and d decrease as the growth rate increases for a given composition (x). The values of λ 1, λ 2, R and v increase with the increase in x value, while the value of d firstly increases and then decreases with the increase in x value for a given v. The relationships between λ 1, λ 2 and R were analyzed by the linear regression. The average growth rate exponent of λ 1 is 0.29, which is in accordance with the previous experimental observations, and that of λ 2 is close to the previous experimental results, while those of R and d are lower than the results in other alloy systems. In addition, theoretical models for λ 1, λ 2 and R were compared with the experimental observations, and a comparison of the present experimental results with the theoretical models and previous experimental results was also made.

Measurements of Microstructural, Mechanical, Electrical, and Thermal Properties of an Al–Ni Alloy

The Al–7.5 wt% Ni alloy was directionally solidified upwards with different temperature gradients, $$G$$ ( $$0.86\,\text{ K}~{\cdot }~ \text{ mm}^{-1}$$ to $$4.24\,\text{ K}~{\cdot }~\text{ mm}^{-1})$$ at a constant growth rate, $$V$$ ( $$8.34\,\upmu \text{ m}~{\cdot }~\text{ s}^{-1})$$ . The dependence of dendritic microstructures such as the primary dendrite arm spacing ( $$\lambda _{1}$$ ), the secondary dendrite arm spacing ( $$\lambda _{2}$$ ), the dendrite tip radius ( $$R$$ ), and the mushy zone depth ( $$d$$ ) on the temperature gradient were analyzed. The dendritic microstructures in this study were also compared with current theoretical models, and similar previous experimental results. Measurements of the microhardness (HV) and electrical resistivity ( $$\rho $$ ) of the directionally solidified samples were carried out. Variations of the electrical resistivity ( $$\rho $$ ) with temperature ( $$T$$ ) were also measured by using a standard dc four-point probe technique. And also, the dependence of the microhardness and electrical resistivity on the temperature gradient was analyzed. According to these results, it has been found that the values of HV and $$\rho $$ increase with increasing values of $$G$$ . But, the values of HV and $$\rho $$ decrease with increasing values of dendritic microstructures ( $$\lambda _{1}, \lambda _{2}, R,$$ and $$d$$ ). It has been also found that, on increasing the values of temperature, the values of $$\rho $$ increase. The enthalpy of fusion ( $$\Delta {H}$$ ) for the Al–7.5 wt%Ni alloy was determined by a differential scanning calorimeter from a heating trace during the transformation from solid to liquid.

Investigation of directional solidified Al–Ti alloy

Al–1 wt% Ti alloy was directionally solidified upwards under argon atmosphere under the two conditions; with different temperature gradients (G = 2.20–5.82 K/mm) at a constant growth rate (V = 8.30 lm/s) and with different growth rates (V = 8.30–498.60 lm/s) at a constant temperature gradient (G = 5.82 K/mm) in a Bridgman furnace. The dependence of characteristic microstructure parameters such as primary dendrite arm spacing (k1), secondary dendrite arm spacing (k2), dendrite tip radius (R) and mushy zone depth (d) on the velocity of crystal growth and the temperature gradient were determined by using a linear regression analysis. A detailed analysis of microstructure development with models of dendritic solidification and with previous similar experimental works on dendritic growth for binary alloys were also made.

Variation of microindentation hardness with solidification and microstructure parameters in the Al based alloys

The Al based alloys (Al–3 wt%Si, Al–3 wt%Cu and Al–1 wt%Ti) were prepared using metals of 99.99% high purity in the vacuum atmosphere. These alloys were directionally solidified upward with a constant growth rate ( V = 0.008 mm/s) at the different temperature gradients ( G = 1.1–6.8 K/mm) and also with a constant temperature gradient ( G) in a wide range of growth rates (0.008–0.499 mm/s) with a Bridgman type directional solidification furnace. The microstructure parameters (primary dendrite arm spacing, λ 1, secondary dendrite arm spacing, λ 2, dendrite tip radius, R, and mushy zone depth, d, were measured from both transverse and longitudinal section of the specimens as a function of G and V. The dependence of microhardness ( H V) on the solidification process parameters ( V and G) and the microstructure parameters were determined by using linear regression analysis in the Al based alloys. The results obtained in this work have been compared with the previous similar experimental results obtained for binary or ternary alloys.

DENDRITIC GROWTH OF THE BINARY SUCCINONITRILE-CAMPHOR SYSTEM

Succinonitrile (SCN)–2 wt% Camphor (CAMP) alloy was unidirectionally solidified with a constant temperature gradient (G = 3.01 K/mm ) at different growth rates (V = 6.5–113 μ m/s ) and with a constant growth rate (V = 6.5 μ m/s ) at different temperature gradients (G = 1.93 - 3.01 K/mm ). Microstructural parameters (primary dendrite arm spacings, λ1, secondary dendrite arm spacings, λ2, dendrite tip radius, R, and mushy zone depth, d) were measured as a function of growth rate and temperature gradient. The experimental results have been compared with theoretical models and previous experimental works. The stability constant (σ) for this alloy system was calculated and compared with similar experimental results.

Effects of electric current pulse on stability of solid/liquid interface of Al–4.5 wt.% Cu alloy during directional solidification

This paper investigates the effects of the electric current pulse (ECP) on the interface stability of Al–4.5% Cu alloy during the directional solidification. Experimental results show both the cellular spacing and the mushy zone depth decrease with increasing current density, moreover, the solid–liquid interface morphology transforms from dendritic to cellular or even planar interface. The secondary dendrites are suppressed due to the homogeneous distribution of the solute and the increase of temperature gradient originated from ECP. The decrease of the cellular spacing results from branching of the cellular tip caused by Joule heat of the current exerting on cellular tip.

Dendritic Growth in an Aluminum-Silicon Alloy

Unidirectional solidification experiments have been carried out on an Al-3 wt.% Si alloy as a function of temperature gradient, G and growth rate, V. The samples were solidified under steady-state conditions with a constant growth rate of 8.20 μm/s at different temperature gradients (1.97-6.84 K/mm) and with a constant temperature gradient (6.84 K/mm) at different growth rates (8.20-492.76 μm/s). Microstructure parameters (primary dendrite arm spacing, λ1, secondary dendrite arm spacing, λ2, dendrite tip radius, R and mushy zone depth, d) were measured as a function of temperature gradient and growth rate. The experimental results have been compared with the current theoretical models and similar experimental works.

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, λ 1, 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.

Directional solidification of aluminium–copper alloys

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 C 0. 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 λ 1, secondary dendrite arm spacing λ 2, dendrite tip radius R, mushy zone depth d were measured and expressed as functions of solidification parameters, G, V and C 0 by using a linear regression analysis. The results were in good agreement with previous experimental work and current theoretical models suggested for dendritic growth.

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 λ 1, secondary dendrite arm spacing λ 2, 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.

Investigation of the structure parameters according to the solidification parameters for pivalic acid

Pivalic acid was unidirectionally solidified in a temperature gradient stage. The microstructure parameters; 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 depending of the microstructure parameters to the solidification parameters (V, G and GV) for pivalic acid were determined by linear regression analyze. The stability constant, σ* was calculated by using the experimental values of R and V. The results were compared with the previous works.