High Temperature Self-Lubricating Ti-Mo-Ag Composites with Exceptional High Mechanical Strength and Wear Resistance

Titanium alloys are of keen interest as lightweight structural materials for aerospace and automotive in-dustries. However, a longstanding problem for these materials is their poor tribological performances. Herein, we designed and fabricated a multiphase Ti-Mo-Ag composite (TMA) with heterogeneous triple-phase precipitation (TPP) structure by spark plasma sintering. A lamellar alpha-phase (alpha L) precipitates from the $-phase under furnace cooling conditions and maintains a Burgers orientation relationship (BOR) with $-matrix. An active eutectic transition also occurs in the titanium matrix, resulting in TiAg phase. The intersecting acicular TiAg and lamellar alpha L cut $ grains into fine blocks and the primary equiaxed alpha phase also provides many interfaces with $ phase, which together effectively impede dislocation move-ment and increase strength. Compared with other titanium composites, TMA with TPP microstructure gets an excellent combination of strength (yield strength 1205 MPa) and toughness (fracture strain 27%). Furthermore, the TPP structure endows TMA with strong cracking resistance, which aids in reducing abra-sive debris at high temperatures during sliding and obtaining a low wear rate. Simultaneously, Ag parti-cles distributed at grain boundaries will easily diffuse to the wear surface, in situ forming the necessary lubricating phase Ag2MoO4 with Mo-rich matrix debris via oxidation. TMA possesses excellent tribologi-cal properties with especially low wear rate of 8.0 x 10 -6 mm3N -1m -1 and friction coefficient (CoF) of merely 0.20 at 600 degrees C. Unlike other self-lubricating composites with high volume fraction of soft ceramic lubricants, which inevitably sacrifice their mechanical strength and ductility, the composite TMA pos-sesses well-balanced strength, toughness and self-lubricating properties. It holds important implications to design other metal matrix self-lubricating composites (MMSCs) used for load-bearing moving parts. (c) 2023 Published by Elsevier Ltd on behalf of The editorial office of Journal of Materials Science & Technology.