Exfoliated nano-hBN additives for enhancing tribological performance of ATSP coatings deposited on AISI 316L steel: Role of SMAT pre-treatment

The current study investigates the role of hexagonal boron nitride (hBN) content (1, 5, and 10 wt%), the extent of exfoliation (magnetic stirring for 1, 5 and 12 h duration) and substrate conditions (with/without surface mechanical attrition treatment (SMAT)) on tribological performance (under dry sliding condition) of aromatic thermoset polymer (ATSP) coatings deposited on AISI 316L stainless steel using Mayers bar technique. The thickness of hBN particles is decreased from ~115 to ~14 nm after 12 h of stirring. The coating thickness is slightly higher for the SMATed (S) substrate than for the non-SMATed (NS) substrate. The coefficient of friction (COF) reduction of ~57 and ~86 % is observed for ATSP@hBN composite coating (containing 10 wt.% hBN) deposited on NS and S specimens (after 1 h stirring), respectively. The ATSP coating’s volume loss is reduced by ~70 % when deposited on SMATed substrate. Further, COF and volume loss are decreased with increased hBN content and stirring time. Composite coatings deposited on non-SMATed specimens show a considerable reduction in COF to ~0.036 after 12 h of stirring and 10 wt.% of hBN content. The minimum COF of ~0.018 and volume loss of ~0.0095 mm 3 are achieved when this composite coating is deposited on the SMATed substrate. The ATSP-coated NS specimen suffers more severe damage during wear by adhesion, scratching, and oxide formation, which is considerably reduced after adding hBN. The wear track width and surface damage are negligible in the case of composite coated SMATed substrate. The factors like better load-bearing capacity, traces of coating on the wear track and thick transfer film on the counter ball are responsible for lowering the COF of ATSP and ATSP@hBN composite coatings deposited on SMATed substrate. The reduced COF generates less frictional heat, causing lower oxidation and enhanced coating durability. • Content and exfoliation of hBN alter ATSP coating's tribological behaviour. • Thickness of the hBN sheets reduces from ~115 to ~14 nm after 12 h of stirring. • SMAT pre-treatment decreases COF by 86 % for ATSP@10 wt% hBN coating (1 h stirring). • COF of ~0.018 is achieved with 10 wt% hBN, 12 h of stirring and SMATed substrate. • Thin hBN sheets curtail COF, prevent oxidation, and enhance coating durability.