Key Takeaways & Executive Findings
- •• • Graphene addition raised the Fenton system ORP from 337 mV to 347 mV at 30 min and increased the Ti4+ fraction in the surface oxide from 54.81 at.% to 60.13 at.%, directly accelerating chemical oxidation of TC4; this matters industrially because higher-valence oxide formation weakens the surface layer for subsequent mechanical removal, addressing the low material removal rate that plagues conventional polishing of titanium alloys. • • The average polishing force dropped 50%, from 0.26 N to 0.13 N, with reduced temporal fluctuation after graphene incorporation; this force reduction and stabilization is critical for uniform material removal and for suppressing subsurface damage in aerospace and biomedical implant components where surface integrity governs fatigue life and biocompatibility. • • Under optimized conditions of 1.0 mm machining gap and 400 rad/min spindle speed, surface roughness Sa decreased from 350 nm to 75 nm within 15 min; this removal rate and finish combination is industrially relevant because it demonstrates a viable throughput for finishing complex TC4 geometries without the multi-stage abrasive sequences typical of legacy processes. • • The dual chemical (catalytic Fenton oxidation) and mechanical (lubrication-stabilized polishing) pathways operate simultaneously, with gap and spindle speed governing the dynamic equilibrium between oxidation and removal; this process window definition provides engineers with actionable control parameters for scaling the method to production-level magnetorheological finishing platforms.
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Abstract
TC4 titanium alloy, a representative α+β dual-phase alloy, exhibits high specific strength, corrosion resistance, and biocompatibility but remains a classic difficult-to-machine material due to high chemical reactivity, low thermal conductivity, and complex phase-dependent mechanical behavior. Conventional polishing routes yield low material removal rates and poor surface consistency. This work formulates a graphene-assisted chemical magnetorheological polishing fluid comprising 0.40 wt.% monolayer graphene flakes, 15 wt.% carbonyl iron powder, 5 wt.% alumina abrasives, and 3.0 wt.% hydrogen peroxide as the primary oxidant. The catalytic role of graphene in the Fenton reaction is quantified via real-time oxidation-reduction potential (ORP) monitoring, immersion tests, and X-ray photoelectron spectroscopy (XPS). Graphene elevates the ORP from 337 mV to 347 mV at 30 min and increases the high-valence Ti4+ fraction in the surface oxide layer from 54.81 at.% to 60.13 at.%. Concurrently, graphene reduces the average polishing force by 50% (from 0.26 N to 0.13 N) and improves force stability, confirming a lubrication effect at the pad-workpiece interface. Single-factor experiments on machining gap and spindle speed identify an optimized condition of 1.0 mm gap and 400 rad/min, under which surface roughness Sa decreases from 350 nm to 75 nm within 15 min. The results establish that graphene delivers dual catalytic-oxidation and lubrication functions, enabling efficient, high-integrity finishing of TC4 titanium alloy and offering a viable route for ultra-precision surface treatment of complex hard-to-machine materials.
1. Introduction
TC4 titanium alloy dominates aerospace, marine, and biomedical applications because of its high specific strength, corrosion resistance, and biocompatibility, yet its high chemical reactivity, low thermal conductivity, and α+β dual-phase structure make it a persistent challenge for ultra-precision finishing. Commercial polishing routes—mechanical abrasion, electrochemical polishing, and conventional magnetorheological finishing—struggle to balance material removal rate against surface consistency. Mechanical methods induce subsurface damage and tool wear; electrochemical routes suffer from non-uniform current distribution on complex geometries; and standard magnetorheological fluids lack the chemical driving force to efficiently soften the hard titanium surface. The result is a well-documented bottleneck: low removal rates, inconsistent roughness across part surfaces, and high consumable costs that limit adoption in high-value component manufacturing.
This study addresses the bottleneck by integrating monolayer graphene into a Fenton-based magnetorheological polishing fluid containing hydrogen peroxide and carbonyl iron powder. Graphene serves two simultaneous functions: its high electrical conductivity and large specific surface area catalyze hydroxyl radical generation, accelerating chemical oxidation of the TC4 surface, while its lamellar structure lubricates the pad-workpiece interface, reducing and stabilizing polishing forces. The experimental protocol quantifies these effects through ORP monitoring, immersion tests, XPS analysis, and real-time polishing force measurement, then maps the process window via single-factor experiments on machining gap and spindle speed. The result is a dual-path mechanism—catalytic oxidation and lubrication—that delivers a 350 nm to 75 nm Sa reduction in 15 min, establishing a practical route for high-efficiency, high-integrity finishing of difficult-to-machine alloys.
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SHEN Jiangnan, TAO Xiyue, FENG Ming, ZHANG Xianglei, LI Min, CHEN Tonghao, FENG Qingxiang (2026). Graphene-Assisted Chemical Magnetorheological Polishing of TC4 Titanium Alloys. Surface Technology (表面技术). https://doi.org/10.16490/j.cnki.issn.1001-3660.2026.09.007
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Frequently Asked Questions
What is the dominant failure mechanism of the graphene-assisted Fenton magnetorheological polishing fluid under prolonged operation, and how does it affect removal rate stability?
The primary degradation pathway is consumption of hydrogen peroxide and depletion of hydroxyl radical generation as the Fenton reaction proceeds, combined with graphene flake sedimentation and carbonyl iron particle oxidation. The ORP data show a rise to 347 mV at 30 min, but extended operation beyond this window risks ORP decline as H2O2 is consumed. Industrial impact: batch life must be managed to maintain Ti4+ oxide fraction near 60.13 at.% for consistent removal; replenishment or fluid recirculation strategies are required for production-scale runs exceeding 30 min.
How does the 50% polishing force reduction (0.26 N to 0.13 N) translate to subsurface damage control in biomedical implant finishing?
Lower and more stable polishing forces reduce the depth of mechanically induced microcracks and residual stress in the near-surface layer. For TC4 biomedical implants, where fatigue life and osseointegration depend on surface integrity, the 0.13 N average force combined with chemical softening via Ti4+ enrichment (60.13 at.%) enables material removal predominantly through oxide layer shearing rather than bulk abrasive ploughing. This reduces the risk of subsurface damage that would otherwise require post-polishing annealing or etching steps.
What are the scalability bottlenecks for implementing this graphene-assisted chemical magnetorheological polishing process on industrial magnetorheological finishing platforms?
Three bottlenecks dominate: (1) graphene dispersion stability in the 15 wt.% carbonyl iron and 5 wt.% alumina suspension, which affects catalytic uniformity across large workpiece areas; (2) H2O2 concentration control at 3.0 wt.% within the recirculating fluid, since peroxide decomposition rates vary with temperature and iron particle contact; and (3) the 1.0 mm gap and 400 rad/min optimized condition must be maintained across complex geometries, requiring adaptive gap control. The 15 min polishing time to reach 75 nm Sa provides a throughput baseline, but fluid management hardware and real-time ORP feedback are prerequisites for production scaling.
Does the graphene-assisted Fenton chemistry introduce corrosion risk or chemical incompatibility with TC4 substrates during extended polishing?
The Fenton reaction generates hydroxyl radicals that oxidize the TC4 surface to a Ti4+-enriched oxide layer (60.13 at.% versus 54.81 at.% without graphene). This oxide is intentionally formed to facilitate mechanical removal. Corrosion risk arises if the oxide is not fully removed or if residual H2O2 remains on the surface post-polishing. Industrial practice requires a post-polish rinse and verification that surface Ti4+ levels return to baseline. The 3.0 wt.% H2O2 concentration is moderate, but immersion tests confirm progressive oxidation, so process time control at the 15 min optimized window is essential to avoid excessive oxide growth.
How does the cost of graphene-assisted chemical magnetorheological polishing compare with legacy multi-stage mechanical polishing for TC4 components?
Direct cost parity depends on graphene flake cost, H2O2 consumption, and carbonyl iron powder replacement rates. The 0.40 wt.% monolayer graphene loading is low, which limits per-batch material cost. The 15 min cycle to achieve 75 nm Sa from 350 nm replaces multiple mechanical polishing stages that typically require 30–60 min and generate abrasive waste. The 50% force reduction also lowers pad wear and machine power draw. However, the need for ORP monitoring and fluid recirculation adds capital and control system cost. For high-value aerospace and biomedical TC4 components, the reduced cycle time and improved surface consistency provide a favorable cost-benefit ratio, but high-volume low-margin applications require further fluid life optimization.
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