Research on the Tribological Properties and Wear Mechanism of Nitrided 38CrMoAl Steel/YL10.2 Cemented Carbide Tribo-Pair Under Impact-Sliding Drilling Conditions

Abstract

Abstract. The all-metal positive displacement motor (AMPDM) is a key downhole power tool for deep well drilling, but its service life is severely limited by wear from the synergy of stator–rotor impact-sliding, abrasive particles, and drilling fluid. Conventional studies fail to address this issue as they cannot replicate AMPDM's complex impact-sliding motion and multifactor coupled wear mechanisms. This study developed a multifunctional test system to simultaneously simulate impact-sliding motion and dynamic abrasive interactions in drilling fluid, and investigated the tribological performance of a novel nitrided 38CrMoAl steel/YL10.2 cemented carbide tribo-pair. The results show that the nitrided 38CrMoAl steel/YL10.2 cemented carbide pairing reduces the friction coefficient by 75% compared with the untreated 38CrMoAl steel/YL10.2 carbide pair under identical working conditions, demonstrating that the novel tribo-pair achieves substantially enhanced tribological performance. A critical load of 600 N was identified, at which contact pressure exceeds SiO2 abrasives' compressive strength, triggering wear mechanism evolution from mild rolling abrasive wear to severe abrasive wear that increases wear volume by 175% due to deep particle embedding, and finally to oxidative wear as abrasives fragment and a protective friction oxidation film forms. Additionally, aligning rotor surface texture with abrasive sliding direction significantly reduces wear volume compared to perpendicular orientation, providing a rotor design optimization criterion. This study clarifies the coupled effect of impact load and abrasives on AMPDM wear, offering engineering guidance to extend its lifespan in deep resource exploration.