Dendritic microstructure

Provatas N., Goldenfeld N. and Dantzig J., Efficient Computation of Dendritic Microstructures Using Adaptive Mesh Refinement, Phys. Rev. Lett. 80, 3308 (1998). 

Figure 7.34 Grit-blasted titanium surface (a) and laser gas-nitrided Ti surface, etched to form a dendritic microstructure that promotes enhanced adhesion strength of a plasma-sprayed hydroxyapatite layer (b) (Yang et al., 2009). ( With permission by Elsevier.)...

Columnar or dendritic microstructure is found also in most metal and many compound films formed by chemical vapour deposition in certain ranges of condition. As a result of the same mechanism of uninterrupted crystal growth towards the direction of material supply it is further found in films obtained by some deposition techniques from solution, particularly in electroplated films. 

Growth front instability during transformation can lead to cellular or dendritic microstructures, depending on the severity of the instability. Minor instability leads to the formation of primary protuberances, called cells, which advance perpendicular to the interface. If the instability increases, these primary protuberances can themselves spawn secondary protuberances perpendicular to the primary protuberances, and a dendritic microstmcture develops. Cellular and dendritic microstructures are most commonly observed in vapor-solid or liquid-solid phase transformations, although they can also be formed in solid-solid phase transformations. 

Mesoporous multi-/ monolayer, high-level porosities > 40 % >1,000 °C - (100-750 Torr), H2 and vacuum Dendritic microstructure with higher initial porosity shows slower restracturing during heat treatment Ott et al. (2004) Zheng et al. (1997)... 

On the other hand, Xiao et al. [215] reported that smooth, dense, and erystalline PbTe films with nearly stoichiometric composition could be obtained by an optimized electrodeposition process from highly acidic (pH 0) tellurite solutions of uncomplexed Pb(II), on Au-coated silicon wafers. The results from electroanalyti-cal studies on Te, Pb, and PbTe deposition with a Pt rde at various temperatures and solution compositions supported the induced co-deposition scheme. The microstructure and preferred orientation of PbTe films was found to change significantly with the deposition potential and electrolyte concentration. At -0.12 V vs. Ag/AgCl(sat. KCl), the film was granular and oriented preferentially in the [100] direction. At potentials more negative than -0.15 V, the film was dendritic and oriented preferentially in the [211] direction (Pig. 3.13). 

Fukami, K., Nakanishi, S., Yamasaki, H., Tada, T., Sonoda, K., Kamikawa, N., Tsuji, N., Sakaguchi, H. and Nakato, Y. (2007) General mechanism for the synchronization of electrochemical oscillations and self organized dendrite electrodeposition of metals with ordered 2D and 3D microstructures./. Phys. Chem. C, 111, 1150-1160. 

In most Al-containing alloys, the shape of the particles was tear-drop like due to the tight surface oxide film. The typical shape was shown in Fig.l. The effect of rapid solidification on microstructures is shown in Fig. 5 for AI2CU (precursor for Raney Cu) with a small amount of Pd (11). In the case of slowly solidified (conventional) precursor, most of the added Pd was solidified as a secondary Pd rich phase shown by white dendritic structure in Fig.5 (a). On the other hand, no such secondary phase was observed in a rapidly solidified precursor as shown in Fig.5 (b). 

The phase-field simulations reproduce a wide range of microstructural phenomena such as dendrite formation in supercooled fixed-stoichiometry systems [10], dendrite formation and segregation patterns in constitutionally supercooled alloy systems [11], elastic interactions between precipitates [12], and polycrystalline solidification, impingement, and grain growth [6]. 

Connection between Transport Processes and Solid Microstructure. The formation of cellular and dendritic patterns in the microstructure of binary crystals grown by directional solidification results from interactions of the temperature and concentration fields with the shape of the melt-crystal interface. Tiller et al. (21) first described the mechanism for constitutional supercooling or the microscale instability of a planar melt-crystal interface toward the formation of cells and dendrites. They described a simple system with a constant-temperature gradient G (in Kelvins per centimeter) and a melt that moves only to account for the solidification rate Vg. If the bulk composition of solute is c0 and the solidification is at steady state, then the exponential diffusion layer forms in front of the interface. The elevated concentration (assuming k < 1) in this layer corresponds to the melt that solidifies at a lower temperature, which is given by the phase diagram (Figure 5) as... 

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