Tribological Performance of Boronized, Nitrided, and Normalized AISI 4140 Steel against Hydrogenated Diamond-Like Carbon-Coated AISI D2 Steel

Abstract

In the current work, AISI 4140 steel was pack-boronized at 950°C for 3 h and gas-nitrided at 550°C for 72 h. All specimens used in this work were prepared from the same steel bar. A 3-µm-thick diamond-like carbon (DLC) coating (a-C:H) was deposited on the AISI D2 high-carbon, high-chromium, cold-worked tool steel by a plasma-assisted chemical vapor deposition technique. Normalized, boronized, and nitrided steel pins were tested against DLC-coated AISI D2 steel at various normal loads (15, 30, 60, and 80 N) for 1,000 and 3,000 m sliding distance in ambient air. Specific wear rate of all pins decreased with increasing load, and a similar trend was observed for the coefficient of friction (COF). Microscopic and energy-dispersive spectroscopic (EDS) analysis confirmed the role of the transfer layer for a low COF with increasing load. At all loads, the specific wear rate of boronized pins was lower than that of the nitrided and normalized pin specimens. Boronized pins showed a specific wear rate in the range of 0.27 × 10⁻⁸ to 0.44 × 10⁻⁸ mm³/Nm and the COF was about 0.1.

KEY WORDS:

• Boronizing
• DLC Coating
• Nitriding
• Tribology
• Pin on Disc Test
• AISI 4140 Steel

ACKNOWLEDGEMENT

The authors are thankful to Onkar Chinmalli, Chetan Mahajan, Hemant Patil, and Vicky Kharat for their timely help during this study.

FUNDING

The authors are thankful to Crompton Greaves Ltd., Mumbai, India, for sponsoring this work.