Application-Oriented Comparative Screening of SiO2, DLC, and Raydent-Labeled Commercial Coating for High-Precision LM Guide Rails

This study comparatively evaluated Raydent (here interpreted as a standard black chrome-type industrial condition in the present specimen context), DLC, and SiO2 coatings for high-precision LM-guide applications as an application-oriented initial screening study. The emphasis was placed on dimensional preservation, surface integrity, and mechanical surface response rather than on complete coating-mechanism validation. Cross-sectional FE-SEM, EDS, Vickers hardness testing, surface profilometry, AFM, and SEM analyses were conducted to compare coating thickness, composite surface hardness, roughness, and morphology, and the influence of plasma pretreatment on the SiO2 system was additionally investigated. Among the investigated coatings, SiO2 exhibited the smallest thickness (1.03 μm), highest composite surface hardness (719.8 HV), and lowest average roughness (213.5 nm), suggesting favorable dimensional compatibility and surface integrity under the tested conditions. Plasma pretreatment increased the EDS-detected Si signal from 0.77 to 2.81 wt% and improved the composite surface hardness from 580 to 720 HV, suggesting an altered near-surface response and improvement in coating formation during pretreatment-assisted processing. AFM and SEM observations further indicated that the SiO2 coating provided a more uniform and flatter surface morphology on the coupon specimens, whereas the DLC specimen prepared under the present commercial condition showed localized protrusions that may be associated with initial local contact disturbance. The comparative results suggest that SiO2 coatings provide a favorable balance of thickness control, surface uniformity, composite surface hardness, and roughness for precision LM-guide applications. Although additional rolling-contact durability, adhesion, wear, friction-coefficient, and rolling-contact-fatigue studies are still required, the present findings should be interpreted as an initial screening result indicating that SiO2 is a candidate coating condition for further engineering consideration in precision motion-guide systems, rather than as a direct validation of full tribological or long-term durability performance.