Thermochemical Nitriding and Oxynitriding of Ti Alloys

Oleh Yaskiv; Iryna Pohrelyuk; Waheed Ali Abro; Muhammad Ali Abro; Kun Sang Lee; Dong Bok Lee

doi:10.1166/jnn.2019.16267

Thermochemical Nitriding and Oxynitriding of Ti Alloys

J Nanosci Nanotechnol. 2019 Jul 1;19(7):4090-4096. doi: 10.1166/jnn.2019.16267.

Authors

Oleh Yaskiv¹, Iryna Pohrelyuk¹, Waheed Ali Abro², Muhammad Ali Abro³, Kun Sang Lee², Dong Bok Lee⁴

Affiliations

¹ Physico-Mechanical Institute of National Academy of Sciences, Lviv 79601, Ukraine.
² Department of Earth Resources and Environmental Engineering, Hanyang University, Seoul 04763, Republic of Korea.
³ Department of Mechanical Engineering, Mehran University of Engineering and Technology, SZAB Campus, Khairpur Mir's 66020, Pakistan.
⁴ School of Advanced Materials Science and Engineering, Sungkyunkwan University, Suwon 16419, Republic of Korea.

PMID: 30764975
DOI: 10.1166/jnn.2019.16267

Abstract

Nitrided and oxynitrided coatings that formed on α alloy (c.p.-Ti), near-α alloy (Ti-2.1Al-2.5Zr), (α + β) alloy (Ti-6Al-4V), and β alloy (Ti-6Al-2Zr-1Mo-1V) were microstructurally characterized. The nitriding at 950 °C and P_N₂ ═ 10⁵ Pa for 5 h formed TiN, Ti₂N, and α-Ti(N) layers from the surface. The nitriding tendency increased in the order of β alloy, (α + β) alloy, near-α alloy, and α alloy. The Ti-N coatings transformed to Ti-N-O coatings when the nitrided alloys were exposed to P_O₂ ═ 10^-2 Pa during cooling at the final stage of the nitriding. This oxynitriding process led to the formation of TiN_xO_1-x, Ti₂N, and α-Ti(N,O) layers from the surface where a small amount of rutile-TiO₂ coexisted. Oxynitriding was more effective than nitriding in increasing the surface microhardness, with the former accumulating more compressive residual stress than the latter.