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Fretting wear of nickel-aluminum bronze (NAB) alloys and 15 wt% Ti 3 SiC 2 /NAB composites against the 42CrMo4 steel was studied through flat-on-flat testing at oil-lubrication conditions with varying free-water contents (0, 26.8, 52.3 and 76.7 wt%). Tribological test results revealed that the addition of Ti 3 SiC 2 substantially reduced the fretting wear and the friction coefficient of NAB alloys at all testing conditions, which could be attributed to high absorption of the fracture energy on the wear track by the deflection of fatigue cracks along Ti 3 SiC 2 /NAB interfaces. In addition, microstructural analyses and dissipative particle dynamics simulations revealed that high free-water contents facilitated the propagation of cracks and break of the oil film, which resulted in the transformation of wear mechanisms from abrasion and mild oxidation at the low free-water contents to abrasion, deformation and oxidation at the high contents. Accordingly, the steady-state friction coefficient of Ti 3 SiC 2 /NAB composites increased from 0.09 to 0.17 as the free-water content increased from 0 to 76.7 wt%. [ABSTRACT FROM AUTHOR]

This work investigated the effect of sintering temperatures (600–750 °C) on mechanical and tribological behaviors of nickel-aluminium bronze (NAB) alloys developed by gas atomization and spark plasma sintering. Results indicated an increase of the volume fraction of B2-type NiAl precipitates with increasing sintering temperature, leading to an improvement of the yield strength and the wear resistance. Specifically, detailed microstructural analyses of sintered NAB alloys at 750 °C showed the presence of ultrafine grains with an average size of 367 nm, nanoscale twins with a volume fraction of 11.7% and dislocations with a density of 1.3 ± 0.1 × 10 14 m −2 . A much higher yield strength of 620 MPa was obtained in NAB, if compared to that of conventional cast counterparts (280–440 MPa). Estimations of strengthening mechanisms suggested the predominant mechanism of grain boundary strengthening (335 MPa) for NAB alloys with contributions from precipitate strengthening (54 MPa), dislocation strengthening (75 MPa), twin boundary strengthening (89 MPa) and solid solution strengthening (50 MPa). Moreover, dislocations was blocked at twin boundaries to form complex dislocation barriers and networks, further contributing to the high strength. The high wear resistance of NAB could be ascribed to the reduction of the local stress around crack tips due to the high elastic modulus mismatch ( E NiAl / E Cu ), and to the crack extension toughening near the interface of the matrix and the precipitate caused by the high plastic mismatch ( σ NiAl / σ Cu ). [ABSTRACT FROM AUTHOR]