Diffusion annealed

Diffusion Annealing. Mixed preformed carbides can be diffusion-annealed at temperatures giving solid solutions. Additives, such as Co, Ni, Fe, or Cr (0.5—1%) promote diffusion. 

An interesting application of sprayed aluminium is for resistance to high-temperature oxidation up to 900°C. The article is grit-blasted and aluminium sprayed, usually to a thickness of 0-008 in (0-2 mm). It is then treated with a sealing composition which may be bitumen or water-glass, and is diffusion annealed in a furnace at 850 C for approximately 30 min. The final coating... 

Ion implanter-both medium high current Furnaces-diffusion annealing oxidation... 

In one dimensional diffusion experiments (e.g., starting with a thin film source of A on a B crystal surface) one often finds an exponential decrease in the A concentration at the far tail of the concentration profile. This behavior has been attributed to pipe diffusion along dislocation lines running perpendicular to the surface. Models have been introduced which assume a (constant) pipe radius, rp, inside which Dl = p-D, b and p denoting here bulk and dislocation respectively. P values of 103 have been obtained in this way. It is difficult to assess the validity of these observations. The model considerably simplifies the real situation. During diffusion annealing, the structure of the dislocation networks is likely to change because of self-stress (see Chapter 14) and chemical interactions. 

On the other hand, the value of r achieved at the end of an isothermal diffusion anneal of duration to + At is... 

Equation 5.18 offers a convenient technique for measuring self-diffusion coefficients. A thin layer of radioactive isotope deposited on the surface of a flat specimen serves as an instantaneous planar source. After the specimen is diffusion annealed, the isotope concentration profile is determined. With these data, Eq. 5.18 can be written... 

Suppose that a very thin planar layer of radioactive Au tracer atoms is placed between two bars of Au to produce a thin source of diffusant as illustrated in Fig. 5.8. A diffusion anneal will cause the tracer atoms to spread by self-diffusion as illustrated in Fig. 5.3. (A mathematical treatment of this spreading out is presented in Section 4.2.3.) Suppose that the diffusion ex-... 

Diffusion annealings were performed in a quartz tube under an oxygen atmosphere enriched to 70% with the lsO isotope at a pressure of 0.21 X 105 Pa. The isotope composition of the gaseous phase was maintained constant throughout... 

Sections of the pressure tube were hydrided to produce required hydrogen concentration using an electrolytic method and diffusion annealing treatment. 

If a surface is sputtered at sufficiently low temperature to avoid bulk diffusion, atoms of the species preferentially sputtered can reach the surface by displacement mixing and radiation-induced segregation. This leads to a so-called altered layer, which has a composition different from that of the bulk and a thickness close to the penetration depth of the projectiles. Since surface diffusion has a much lower activation barrier than bulk diffusion, annealing a sputtered alloy surface first leads to a local equilibrium between the surface and the immediate subsurface layers, which still belong to the altered layer. Only after the onset of bulk diffusion is reached, usually around 60 - 70% of the melting temperature, the altered layer equilibrates with the bulk and true equilibrium segregation is observed [45]. For alloys of atoms with different size the existence and dissolution of an altered layer can be studied by STM because of the development of a misfit dislocation network between the altered layer and the bulk [46] (Fig. 7). 

Fig. 1. (a) Schematic view of graded multilayer. The two basic components otthe multilayer are Ti and TiC layers. The basic unit of the multilayer is a juxtaposed double layer of Ti and TiC. This basic unit has a constant L width. The relative width of the two components of this basic unit varies, however, as one proceeds from one end of the multilayer to its other. In the vicinity of the Ti substrate, the Ti component makes up most of the basic unit on side, this basic unit consists mostly of the TiC component, (b) Schematic drawing of the possible outcome of the diffusion anneal on the microstructure of the functionally gradient region. 

There are many techniques by which diffusion coefficients can be measured. The most common is to anneal a solid in an environment that well defines the activity or concentration of the diffusing species at a given location for a given time and then to measure the resulting concentration profile, that is, c(.Y, t), of the diffusing species. The profile will clearly depend on the diffusivity (the larger D, the faster the diffusing species will penetrate into the material), time, and temperature of the diffusion anneal and the boundary-and initial conditions. To determine the diffusivity. Pick s second law... 

An alternative approach to deposition of alloys could be to put down layers of pure metals and use a diffusion anneal. Unfortunately, this complicates the process and reduces the overall deposition rate. 

These reactions may be stimulated to provide 80% decomposition by using a plasma process to excite the methane molecule. In this case, the molecular breakdown may occur in the plasma to produce charged species. Hydrocarbons other than methane may be used as the feedstock. The usual operating sequence involves flushing and evacuation, heating to temperature under the inert atmosphere, carburizing for a predetermined time followed by a diffusion anneal in a carbon-free atmosphere. This cycle is designed to provide the optimum surface carbon content and carburized depth. - ... 

FIGURE 20.21 Pitting potential of diffusion annealed X3CrNiMoN 17 13 S in sodium chloride (NaCl) solution as a function of chloride ion activity and temperature. 

FIGURE 20.22 Pitting potential Up of diffusion annealed X3CrNiMoN 17 13 S (material no. 1.4439) in NaCl solutions as a function of temperature. 

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