A Critical Load Threshold for the Lubricant‐to‐Abrasive Transition of h‐ BN in PTW / PEEK Composites

ABSTRACT The functional role of solid lubricants in polymer composites can critically reverse under extreme pressure, yet the specific load conditions triggering this detrimental transition in complex hybrid systems are often unknown. This work addresses this gap by investigating polyetheretherketone (PEEK) composites reinforced with potassium titanate whiskers (PTW) and hexagonal boron nitride (h‐BN). A critical load threshold of approximately 2 MPa was identified, which dictates a fundamental transition in h‐BN's function. Below this threshold, h‐BN acts as an effective solid lubricant, enabling the optimal composite to achieve a low coefficient of friction (~0.40) and a specific wear rate of 7.16 × 10 −6 mm 3 /(N m). However, above this threshold, h‐BN debonds and transforms into third‐body abrasives, causing a dramatic increase in wear rate (up to 5.3 times) and a shift to severe abrasive wear. Microstructural and tribochemical analyses (SEM, XPS) attribute this reversal to the interfacial failure and oxidation of h‐BN. These findings establish a quantitative design rule for PTW/h‐BN hybrid PEEK composites, defining a safe operating load window (below 2 MPa) essential for leveraging their synergistic potential and ensuring long‐term tribological reliability in engineering applications.