M.C. Naik

Diffusion of carbon in stainless steels

Abstract Using residual activity technique, diffusion of carbon-14 in 304, 347 and 316 steels has been studied in the temperature range of 450–1200°C. The temperature dependence of diffusivity could be expressed as Dc/304s. steel = 6.18 exp (−44 610/RT); Dc/347s. steel = 0.35 exp (−40 140/RT); Dc/316s. steel = 0.19 exp (−37 400/RT). The activation energy for the diffusion of carbon in steels has been explained on the basis of alloying effect of the constituents in steels. Furthermore, thermodynamic calculations for the free energy of formation of various carbides have been carried out to predict the carbon pick up by stainless steels as Cr23C6 from uranium carbide in a uranium carbidestainless steels system. In order to study the segregation of carbon along the grain boundaries of stainless steels, in the present investigation autoradiographie technique has been employed. The results indicate that the segregation of carbon is due to the preferential precipitation of Cr23C6 along the grain boundaries of stainless steels.

Lattice and grain boundary diffusion of chromium in superalloy Incoloy-800

The diffusion of chromium in Incoloy-800 has been studied by the serial sectioning technique using the radioactive tracer 51Cr in the temperature range 1060–1510 K for lattice diffusion and 775–1170 K for grain boundary diffusion. The lattice diffusion coefficient could be represented by the relation: DCr/Incoloy-800 = 3.24 × 10 −4 exp[(− 287.4 kJ/mol)/(RT)] m2/s. The grain boundary diffusion coefficients were evaluated for most of the experiments by Whipples method. For a few specimens, Suzuokas method was also applied. The two methods yielded values of grain boundary diffusion coefficients that were in good agreement with each other. The grain boundary diffusion coefficients could be represented by the equation: Dgb,Cr/Incoloy-800 = 5.80 × 10−5exp[(− 184.2 kJ/mol)/(RT)] m2/s. Segregation and mass transport along the grain boundaries have also been extensively studied by an autoradiographic technique. It has been observed that for small-grained specimens at low temperatures ( < 980 K) long-distance transport of the tracer atoms is mainly through the grain boundaries.

Mass transport of chromium and nickel in monel-400

Abstract Diffusion of51Cr and 63Ni in Monel-400 has been studied in the temperature ranges 1023–1573 K for volume diffusion and 713–1123 K for grain boundary diffusion, respectively. The volume diffusion coefficients can be represented by: D Cr/Monel-400 = (0.31 ± 0.08) × 10 −4 exp[ -(249.2 ± 2.5 kJ/mole)/RT]m 2 . D Ni/Monel-400 = (0.68 ± 0.16) × 10 −4 exp[ -(261.0 ± 4.1 kJ/mole)/RT]m 2 . Grain boundary diffusivities evaluated by Whipple and Suzuokas method were found to be in good agreement but Fishers analysis yielded values of diffusion coefficients that were 2 to 4 times lower. The grain boundary diffusion coefficients evaluated by Whipple and Suzuokas models can be represented by: Dg Cr/Monel-400 = 1.8 × 10 −5 expl[ -(1.47.8 kJ/mole)/RT]m 2 . Dg Ni/Monel-400 = 1.8 × 10 −5 exp[ -(156.7kJ/mole)/RT]m 2 . Segregation of 51Cr and63Ni has been studied by autoradiography. It was observed that at lower temperatures (≤900 K) material transport in specimens with 300 μm grain diameter is mainly through the grain boundaries.

Mass transport of cobalt and nickel in Incoloy-800

AbstractLattice diffusion of cobalt and nickel in Incoloy-800 has been studied in the temperature range 1070 to 1500K by serial sectioning and residual activity techniques using radioactive tracers60Co and63Ni. The lattice diffusion coefficient can be expressed by the relation:

The release of fission-recoiled xenon from Zircaloy-2

\begin{gathered} D_{Co/Incoloy - 800} = 2.54 x 10^{ - 5} exp \left( { - \frac{{249.5kJ mol^{ - 1} }}{{RT}}} \right)m^{^2 } sec^{ - 1} \hfill \\ D_{Ni/Incoloy - 800} = 8.62 x 10^{ - 5} exp \left( { - \frac{{255.9kJ mol^{ - 1} }}{{RT}}} \right)m^2 sec^{ - 1} \hfill \\ \end{gathered}

Mass transport of cobalt and copper in Monel-400

Segregation and mass transport studies of these tracers along the grain boundary in Incoloy-800 have also been carried out in the temperature range 750 to 1080 K. The grain boundary diffusion coefficients are evaluated by Whipple and Suzuoka methods and are found to be in good agreement. Grain boundary diffusivityDgb can be expressed by the equation

Effect of burnup on release of xenon from thoria

\begin{gathered} D_{gb Co/Incoloy - 800} = 1.06 x 10^{ - 5} exp \left( { - \frac{{152.72kJ mol^{ - 1} }}{{RT}}} \right)m^2 sec^{ - 1} \hfill \\ D_{gb Ni/Incoloy - 800} = 3.82 x 10^{ - 5} exp \left( { - \frac{{156.40kJ mol^{ - 1} }}{{RT}}} \right)m^2 sec^{ - 1} \hfill \\ \end{gathered}