Growth Kinetics and Some Mechanical Properties of Plasma Paste Borided Layers Produced on Nimonic 80A-Alloy

Abstract

Plasma paste boriding was employed in order to produce the boride layers on Nimonic 80A-alloy. The process was carried out at temperatures of 1023 K, 1073 K and 1123 K for 3, 4 and 6 h in a gas mixture of 50% H2-50% Ar. Borax paste was used as a boron source. The microstructure of the produced surface layers consisted of the mixture of nickel borides and chromium borides. The effect of processing temperature and duration on the thickness of the borided layers was observed. The theoretical thicknesses of the borided layers were estimated using an integral diffusion model. A good correlation was obtained between the theoretical (modeled) and experimental depths of the plasma paste borided layers. The boride layers were characterized by a high hardness ranging from 1160 HV to 2132 HV. The multiphase character of the produced layers resulted in differences in hardness. A significant improvement of the wear resistance of the plasma paste borided Nimonic 80A-alloy was observed in comparison with the non-borided alloy.

Growth kinetics of diiron boride (Fe2B) layer on a carbon steel by four approaches

“…The analytic solution for the integral method with Equation (8) also yields the same results. Figure 3 describes the time evolution of simulated Fe 2 B layers'thicknesses at 1123, 1173 and 1223 K by using the integral diffusion model [14] along with the experimental thicknesses [9]. The predicted thicknesses are in line with the experimental values highlighting a parabolic trend for the growth of Fe 2 B layers with incubation times which are dependent on the process temperature.…”

“…The integral diffusion model [14] is relying on the numerical resolution of the following system of differential algebraic equations (DAE):…”

“…After using a particular solution of DAE system [14], The boron diffusion coefficient in Fe 2 B was found and expressed by Equation ( 7): (7) with The thickness of Fe 2 B layer can be assessed theoretically with the help of Equation ( 8): ( 8)…”

“…These values of energies were taken from the slopes of ln D Fe 2 B = = f (1/T) as per the Arrhenius relationship [6]. For the alternative diffusion model [10], a mean arithmetic value for the Φ parameter was set to 0.905 to estimate the diffusion coefficients of boron in Fe 2 B at 1123, 1173 and 1223 K. For the integral diffusion model [14], the ε parameter was determined as 0.1370 by taking the maximum and lower values of boron contents in Fe 2 B. It is noted that the boron activation energies are quite similar regardless of the applied diffusion models with pre-exponential factor value that may differ by a factor of 1 to 2.79.…”

“…An additional boronizing condition (at 1198 K during 6 hours) was utilized to experimentally verifiy the validitiy of the four models. The boride incubation period for generating the Fe 2 B layer on SAE 1020 steel was taken as equal to 3426.5 s according to the fitting of experimental data reflected by the temperature-dependent parameter Φ. Equations ( 3), ( 8), (10) and (13) besides the numerical solution of DAE system for the integral diffusion model were employed to get the estimated values of Fe 2 B layer thickness at 1198 K during 6 h. For the integral method [14], the Interactive Thermodynamics Software, running under (Version 3.2), was used by setting: (a 0 = 0.90, b 0 = 0.0453 and u 0 = = 0.18 µm) as the initial conditions for assuring the convergence of iterative computation. The analytic solution for the integral method with Equation (8) also yields the same results.…”