Optimizing wide temperature lubricity of Ni-Ti3AlC2 coatings by Bi2O3 modification: Microstructural tailoring and tribological mechanisms

This study develops a plasma sprayed nickel-based composite coating incorporating Ti 3 AlC 2 and Bi 2 O 3 (Ni-10/20 wt%Ti 3 AlC 2 -10/20 wt%Bi 2 O 3 ) as reinforcing and lubricating additives to synergistically enhance mechanical and tribological properties throughout a broad temperature range. The effects of increasing additive contents on microstructure evolution and mechanical behaviors of the composite coatings are investigated. Results show that the coatings are primarily composed of γ-Ni, Bi 2 O 3 , and Ti 3 AlC 2 , along with trace amounts of TiC and borides. The Ti 3 AlC 2 additions improves microhardness while an increase in Bi 2 O 3 content results in concurrent decline for both microhardness and interfacial bonding strength due to the heightened porosity. The tribological performance evaluated from room temperature (RT) to 800°C demonstrates a significant reduction in friction coefficients by 17.9–33.7 % at 800°C in comparison to Ni-(10/20 wt%)Ti 3 AlC 2 coatings. Among all compositions, Ni-20 wt%Ti 3 AlC 2 -20 wt%Bi 2 O 3 exhibits the optimal wear resistance across the entire temperature range, benefiting from the synergistic lubricating effect of Bi 2 O 3 and Ti 3 AlC 2 . Complementary wear mechanisms analysis indicates the formation of a tribo-oxidatively generated layer composed of NiO, Bi 2 O 3 , Al 2 O 3 , and TiO 2 . Molten Bi 2 O 3 enhances the density and viscoelasticity of this layer, thereby improving lubricity and contributing to reduced wear at elevated temperatures. • Ni-Ti 3 AlC 2 composite coatings modified with varying Bi 2 O 3 contents are achieved by APS technique. • Ti 3 AlC 2 addition improves the microhardness while higher Bi 2 O 3 content shows a negative correlation with it. • Temperature-dependent friction and wear are dominated by the composite oxide tribo-layer. • Rationally optimizing Bi 2 O 3 to 20 wt% dramatically enhances tribological performance under 800°C dry sliding.