Evolution of carbon diffusion layer to oxidation film during cathodic plasma electrolysis on steel

Figures & data

Figure 1. Dependence of sample temperature on applied voltage during the CPE process.

Figure 2. (a) Cross-sectional image of the CPE treated steel at 340 V, (b) average grain sizes of three typical regions, I: steel matrix, II: transition region, III: surface region.

Figure 3. Cross-sectional morphologies of the CPE treated steel at 360 V for 1 min (a), 380 V for 1 min (b), and 380 V for 3 min (c).

Figure 4. XRD patterns of the steel substrate and the CPE treated steels at 360 V for 1 min, 380 V for 1 min, and 380 V for 3 min.

Table 1. Diffusion coefficient comparison of PEC and traditional pack carburizing at the same temperature.

Carburizing method	Carbon diffusion coefficient
PEC at 360 V	6.7 × 10^−8 cm^2 s^−1
Pack carburizing at the same temperature with 360 V	1.3 × 10^−9 cm^2 s^−1
PEC at 380 V	1.5 × 10^−7 cm^2 s^−1
Pack carburizing at the same temperature with 380 V	1.8 × 10^−8 cm^2 s^−1

Figure 5. Cross-sectional morphology (a) and XRD analysis (b) of the CPE treated steel at 400 V for 5 min.

Figure 6. (a) Typical emission spectrum of carburizing process at 380 V and (b) typical emission spectrum of oxidation process at 400 V.

Figure 7. Interfacial reactions and carbon evolution process during CPE on steel.

Table 2. Fe II lines with the wavelength λ, transition path, statistical weights of upper level g, excitation energy E and transition probability A.

Line	λ(nm)	Transition path	g	E (eV)	A (10^7 s^−1)
Fe II	516.65	3d^6(^5D2)4f→3d^6(^5D)4d	8	2.4	2.82
Fe II	697.57	3d^6(5D)5d→3d^6(^5D)5p	4	1.8	1.92