Corrosion and wear products of metallic implants can lead to severe adverse tissue reactions. However, there is an absence of effective means to reduce the tribocorrosion of metal. The main purpose of this study is to reveal a mechanism of engineering a barrier layer on metal surfaces via adding functional particles into the polymer counterpart. B4C and BN particles were compounded into a polyetheretherketone (PEEK) matrix and their tribological performance of PEEK-based composites sliding against stainless steel was compared in simulated body fluid. Results demonstrate that the addition of B4C reduces significantly friction and wear. In particular, the addition of only 1 vol% B4C reduces wear of PEEK by up to 94.8%, and tribocorrosion of steel is also obviously mitigated. It is discovered that hydrolysis of B4C particles triggered by friction and deposition of Ca2+ and phosphate ions dominate formation of the barrier layer at the friction interface. The barrier layer endows the PEEK–metal sliding pair simultaneously enhanced anti-wear and anti-corrosion performance.