The surface work of the critical dimension nucleus formation.

In the formation of the crystallization nucleus, the part of the energy is released when the bulk phase occurs, and part of the work is spent on creating the surface partition, the system resists, prevents the formation of the interface. We substitute rкр values into the energy balance formula:

If the amount of energy released by the passage of the certain volume of a liquid phase with a large level of free energy into the solid phase with a lower level of free energy would be equal to the amount of energy spent on the formation of the interface, then ΔG would be equal to zero. If the energy was released (allocated) more than was expended, then ΔG would be less than zero. In our case, ΔG is positive and equal to 1/3A of the nucleus formation. This means that the system Continue reading →

The isolation of the excess phase from the supersaturated solid solution (Part 2).

With the appearance of β-phase crystals, the α-solution surrounding them is depleted by component B. Near the β phase, the solid α-solution has the Сг composition, and in the distance the composition remains the same. This heterogeneity of the solution is weakened with diffusion in the α-phase and the β-phase release. If the exposure at Тв is prolonged, the separation of the β phase will cease and the stable equilibrium between the α crystals of the Сг and β composition will be established by crystals of the composition Сд. The quantitative ratio of the phases in this case is β/α = гв/вд. To further isolate the phase β, it is necessary to cool the alloy. When it is super cooled, for example, to the Те temperature, the α phase of the composition Сг is supersaturated by the component B (the degree of Continue reading →

The amount of metal evaporating from the cathode spot (Part 2).

At present, it is considered that the value of the ion fraction of the current in the welding arcs is approximately β ≈ 0.5. Assuming that the value of β does not depend on the value of the welding current (I), we determine the number of ions transferring the ion current in the cathode region (Ni) at different currents by the formula

Ni = Ii/е = βI/е,

where e — the electron charge, Кл, and the corresponding number of atoms evaporated from the cathode spot (Nп), according to the formula Nп = Gп/ mFe, Continue reading →

The crystals shape (Part 2).

With the increase in the growth rate of crystals, the dimensions of the cells decrease. With intensive heat removal through the solidified metal, when the growth rate of the crystals is high, the cellular structure does not arise. Thus, at the low cooling rates, the surface of the crystallization front is almost smooth. At medium – the cellular structure appears, the elements of which are crushed with the acceleration of cooling. At the high cooling rate, the branches appear in place of the cells, indicating the initiation of dendritic crystallization.

In the presence of a super cooled melt zone in front of the crystallization front, in Continue reading →

Tests to determine the chemical properties.

Earlier we considered those types of tests that allow us to know the mechanical properties of metals. The metals also have important chemical properties. In fact, it is the chemical composition of the metal and its heat treatment that largely determines its mechanical properties. The part is necessary to determine the chemical composition of the metal. To do this, there are three common methods: spectral analysis, combustion analysis and analysis of the effects of liquid reagents.

The welding inspector rarely has to practice chemical analysis. However, the inspector may need assistance in the sampling and sampling process for analysis or Continue reading →

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