TC4 titanium alloy is a representative α+β type titanium alloy widely utilized in aerospace, marine engineering, and biomedical implants due to its high specific strength, excellent corrosion resistance, and superior biocompatibility. However, its inherent characteristics such as high chemical reactivity, low thermal conductivity, and the complex mechanical properties of its dual-phase structure make it a typical "difficult-to-machine" material. Traditional polishing methods often suffer from low material removal rates and poor surface consistency. To address these challenges, the work aims to propose a novel graphene-assisted chemical magnetorheological polishing method. By integrating the catalytic properties and lubricating effects of graphene into a magnetorheological Fenton-based system, it is expected to achieve a synergistic equilibrium between enhanced chemical oxidation and stable mechanical abrasion, thereby realizing high-efficiency and high-integrity surface finishing of TC4 alloy.
A customized magnetorheological polishing fluid was formulated, consisting of 0.40wt.% monolayer graphene flakes, 15wt.% carbonyl iron powder, 5wt.% alumina abrasives, and a 3.0wt.% hydrogen peroxide solution as the primary oxidant. The catalytic mechanism of graphene on the Fenton reaction was firstly investigated. The oxidation-reduction potential was monitored in real time to evaluate the generation of hydroxyl radicals. To verify the chemical modification of the TC4 surface, immersion tests and X-ray photoelectron spectroscopy were performed to analyze the evolution of titanium oxides. Furthermore, the mechanical behavior of the polishing process was scrutinized by measuring the tangential polishing force with a Kistler dynamometer. A series of single-factor experiments were conducted to evaluate the effect of critical process parameters, specifically the machining gap (ranging from 0.4 mm to 1.6 mm) and the spindle speed (varying from 200 rad/min to 600 rad/min), on the material removal rate and surface roughness.
The experimental results demonstrated that the addition of graphene significantly accelerated the electron transfer during the Fe2+/Fe3+ cycle, thereby enhancing the Fenton reaction's efficiency. The ORP values in the graphene-assisted system increased from 337 mV to 347 mV within 30 minutes, indicating a higher oxidative capacity. XPS analysis revealed that graphene promoted the transition of titanium from lower valence states to higher valence states. Specifically, the concentration of Ti4+ on the workpiece surface increased to 60.13%, while the metallic Ti content significantly decreased. This chemical transformation resulted in a thicker, relatively loose sacrificial oxide layer that was more susceptible to mechanical removal. Regarding mechanical stability, the introduction of graphene as a solid lubricant led to a 50% reduction in the average polishing force (from 0.26 N to 0.13 N). More importantly, graphene suppressed the force attenuation typically caused by the degradation of the MR fluid's structure, ensuring a consistent removal rate throughout the process. Under the optimized conditions of a 1.0 mm machining gap and a 400 rad/min spindle speed, the surface roughness Sa of the TC4 workpiece was successfully reduced from an initial 350 nm to a final 75 nm within 15 minutes. The surface morphology analysis showed a significant reduction in typical defects such as micro-pits, scratches, and phase-boundary relief, yielding a mirror-like finish.
It is concluded that graphene plays a dual-functional role in the CMRP process. It acts as a heterogeneous catalyst that intensifies the Fenton-based chemical softening of the TC4 surface, and simultaneously functions as a high-performance lubricant that stabilizes the mechanical shear force of the MR flexible "brush". The synergy between graphene-enhanced chemical oxidation and stabilized mechanical removal effectively overcomes the polishing resistance of TC4 titanium alloy. This G-CMRP technique provides a theoretically grounded and practically effective strategy for the ultra-precision manufacturing of complex titanium components, offering significant potential for applications requiring extreme surface integrity.
Key words
graphene /
chemical magnetorheological polishing /
TC4 titanium alloy /
Fenton reaction /
surface roughness /
material removal rate
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Funding
Applied Basic Research (Basic Research) Project of Wenzhou City (GK20250148); National Natural Science Foundation of China (General Program) (52475446); Anhui Provincial Natural Science Foundation Project (General Program) (2308085ME170); Major Key Project of Anhui Province Science and Technology Innovation Tackle Plan (202423i08050035); Zhejiang Provincial Department of Education General Research Project (Y202454613); Major Science and Technology Innovation Project of Wenzhou City (ZG2022029); Zhejiang Provincial College Students' Science and Technology Innovation Activity Program (Xinmiao Talent Program) (2025R444C066)
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