Investigation on Tribological Characteristics of AISI 4140 Steel by Nitriding and AlCrN Coating
Dola Mullage, Pasan Rangana (2025)
2025
Master's Programme in Materials Science and Engineering
Tekniikan ja luonnontieteiden tiedekunta - Faculty of Engineering and Natural Sciences
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Hyväksymispäivämäärä
2025-12-04
Julkaisun pysyvä osoite on
https://urn.fi/URN:NBN:fi:tuni-2025120411244
https://urn.fi/URN:NBN:fi:tuni-2025120411244
Tiivistelmä
This study investigates how plasma nitriding pre-treatment influences the adhesion, residual stress, wear behaviour and hardness of AISI 4140 steel coated with AlCrN. Although both plasma nitriding and AlCrN PVD coatings individually enhance the surface performances, the synergetic effect regarding adhesion behaviour and microstructural evolution and especially the stress development has not been fully explored. The primary objective of this study was to compare the mechanical and tribological properties of four conditions: untreated, plasma nitrided, AlCrN-coated, and duplex-treated (Plasma nitrided + AlCrN-coated) AISI 4140 steel. This study specifically investigates how plasma nitriding pre-treatment affects the adhesion, residual stress and wear behaviour of AlCrN coating.
A comprehensive set of experimental, analytical and characterization techniques was used including XRD, SEM-EDS and EBSD, microhardness testing, Surface profilometry, Scratch adhesion testing and reciprocating wear testing. The results show that both plasma nitriding and AlCrN coating individually produce a compressive residual stress and improve surface hardness. The duplex-treated specimen showed the best wear performance, exhibiting the lowest wear constant of 0.0032 mm³/Nm due to the synergetic effect of duplex treatment. However, a reduction in coating adhesion and residual stress was observed likely resulting from stress relaxation during the AlCrN coating deposition and interfacial mismatch or micro cracking on nitrided surface.
In conclusion, the duplex treatment offers significantly enhanced wear resistance while maintaining acceptable adhesion making it a promising surface engineering strategy for demanding industrial components such as gears, shafts and forming dies.
A comprehensive set of experimental, analytical and characterization techniques was used including XRD, SEM-EDS and EBSD, microhardness testing, Surface profilometry, Scratch adhesion testing and reciprocating wear testing. The results show that both plasma nitriding and AlCrN coating individually produce a compressive residual stress and improve surface hardness. The duplex-treated specimen showed the best wear performance, exhibiting the lowest wear constant of 0.0032 mm³/Nm due to the synergetic effect of duplex treatment. However, a reduction in coating adhesion and residual stress was observed likely resulting from stress relaxation during the AlCrN coating deposition and interfacial mismatch or micro cracking on nitrided surface.
In conclusion, the duplex treatment offers significantly enhanced wear resistance while maintaining acceptable adhesion making it a promising surface engineering strategy for demanding industrial components such as gears, shafts and forming dies.