Kinetics analysis and enhancement mechanism of aluminum-enhanced plasma nitriding for 42CrMo steel

Abstract

Aluminum-enhanced plasma nitriding (Al-PN) was developed by a complex treatment of electrolyzing aluminum nitrate and plasma nitriding (PN) for 42CrMo steel; the kinetics and enhancement mechanism was analyzed. Optical microscope and X-ray diffractometer were used to determine the microstructure and phases constituents of the samples. The results show that much thicker case depth is obtained, with hard phases of AlN and FexAl formed in the surface layer by Al-PN treatment, which brings about much harder surface layer and excellent wear resistance. The kinetics analysis shows that the diffusion coefficient is enhanced by Al-PN, and the diffusion activation energy is reduced from 100.531 kJ/mol by PN to 45.177 kJ/mol by Al-PN. The relationship between case depth, temperature T (K) and holding time t (s) is obtained as: dAl-PN = 1.17 × 10−5 exp(−5434T)t. (753 K ≤ T ≤ 793 K). Finally, the verification tests confirmed that the developed kinetics agrees quite well with the measured values; therefore, it can be used to predict the case depth for a designed process parameters in practical applications.

Keywords

• Aluminum nitrate
• Plasma nitriding
• Kinetics
• Case depth
• 42CrMo steel