Effect of constitutional supercooling on the numerical solution of species concentration distribution in laser surface a
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Effect of Constitutional Supercooling on the Numerical Solution of Species Concentration Distribution in Laser Surface Alloying Fig. 4—CaO solubility as a function of P2O5, SiO2, and Al2O3 concentration in CaF2-CaO-P2O5, CaF2-CaO-SiO2, and Al2O3-CaF2-CaO melts.
dependence of CaO solubility on the concentrations of P2O5, SiO2, and Al2O3 in CaF2 ⭈ CaO-P2O5, CaF2 ⭈ CaO ⭈ SiO2, and Al2O3 ⭈ CaF2-CaO melts is shown in Figure 4. Addition of these oxides increases the solubility of CaO. Maximum solubility is 65, 56, and 41 at compositions saturated with CaO ⭈ 3CaO ⭈ P2O5, CaO ⭈ 3CaO ⭈ SiO2, and CaO-11CaO ⭈ 7Al2O3 ⭈ CaF2, respectively. The CaO solubility increases linearly with the increase in the SiO2 or Al2O3 added. In the CaF2-CaO-P2O5 system, the substitution of P2O5 for CaF2 increases the solubility of CaO markedly above 15 mass pct P2O5. That means some part of CaF2 can be substituted by P2O5. The standard free energy change of formation 4CaO ⭈ P2O5 is reported.[7] At liquidus saturated with CaO and 4CaO ⭈ P2O5, the activities of CaO and 4CaO ⭈ P2O5 are unity. Therefore, the activity of P2O5 in the composition referred to pure solid P2O5 is calculated as 4.3 ⫻ 10⫺43. The phase relations show high solubility of P2O5 and low activity of P2O5 at the liquidus saturated with CaO and 4CaO ⭈ P2O5. Effective dephosphorization would be conducted with the slag in the region of three phases equilibria: liquidus, CaO, and 4CaO ⭈ P2O5. Isothermal phase relations for the CaF2-CaO-P2O5 system were investigated by a chemical equilibration technique at 1623 K and the following conclusions were drawn: 1. In the low CaF2 region of the system at 1623 K, the liquid contains 20 to 30 mass pct P2O5 and is surrounded by the primary phase fields of CaO, 4CaO ⭈ P2O5, and CaF2 ⭈ 9CaO ⭈ 3P2O5. 2. The liquid of this system at the composition of CaO and 4CaO ⭈ P2O5 doubly saturated is the most effective for dephosphorization. REFERENCES 1. A. Tagaya, H. Chiba, F. Tsukihashi, and N. Sano: Metall. Trans. B, 1991, vol. 22B, pp. 499-502. METALLURGICAL AND MATERIALS TRANSACTIONS B
SUMAN CHAKRABORTY, SUPRIYA SARKAR, and PRADIP DUTTA Laser surface alloying (LSA) is the process of localized heating of an elemental layer of a substrate by means of laser and a simultaneous feeding of the alloying element over the molten surface in order to achieve desirable surface properties, without affecting the bulk properties of the base material. It has been generally perceived that convection is a dominant mechanism of transport of the added species inside the molten pool,[1] and, hence, has a much bigger role to play in the overall alloying process than species diffusion. This may lead to a situation in which the role of the species diffusion coefficient may be overlooked or underestimated. In addition, accurate numerical values of the same are hardly available for a wide range of material combinations. In such situations, it is possible that an inaccurate value of the species diffusion coefficient may lead to unrealistic solutions for the final species concentrat
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