Development of magnetic nanoparticle based nanoabrasives for magnetorheological finishing process and all their variants

Efficacy and the outcome of the magnetorheological finishing (MRF) related processes depends on two crucial factors, (i) a finishing abrasive and (ii) a magnetic particle. However, the magnetic particles although necessary, become a hindrance for non-magnetic abrasive particles in directly reaching the surface to be finished. This study relates to the development of SPION-based smart material for MRF and all their variant processes. The SPION particles possess dual nature such as nanoabrasives and magnetic nanoparticle. The superparamagnetic property of the developed SPION particle has been confirmed by alternating gradient magnetometer with the saturation magnetization value of 82.23 emu/g. The polishing performance of the developed SPION-based particle as abrasive has been investigated on a BK-7 optical glass and the polishing is done via a 5-axes automated ball end magnetorheological finishing (BEMRF). The developed SPION abrasive enhanced the finishing process of the BEMRF technique and provided surface finishing on the BK-7 substrate up to the surface roughness (Ra) values of 22.3 nm with the Ra improvement of 88.14%.     

Investigation on ultrasonic vibration-assisted femtosecond laser polishing of C/SiC composites

This paper proposed a novel ultrasonic vibration-assisted femtosecond laser polishing method for C/SiC composites. The effect of near-field convection enhancement of ultrasonic vibration can improve the cooling of ablated particles and reduce their tendency of bonding to the material surface, reducing surface oxidation and improving the machined surface quality, removal depth and material removal rate. Through optimizing defocusing distance and scanning speed, a specific relationship between ultrasonic amplitude, pulse energy density, and spot overlap rate was established, obtaining a smooth and flat surface without defects. The residual stress of carbon fibers was investigated, and found that the coupling effect of ultrasonic energy and laser energy fields can enhance the residual compressive stress of carbon fibers. The formation of typical features of fiber fracture and pulling-out, banded pits, voids and deposition, was explained. This paper proposes new research ideas for better understanding of the removal mechanism of C/SiC composites using ultrasonic vibration-assisted femtosecond laser.     

Ultra-smooth surface with 0.4 Å roughness on fused silica

Ultra-smooth surface with sub-nanometer roughness is of great significance in various fields, including Ring Laser Gyro (RLG), high-power laser apparatus, ultraviolet optical systems, and the semiconductor industry. However, the mechanism of the ultra-smooth polishing process remains to be studied, which is of great value for understanding and optimizing optical-fabrication methods. This paper establishes a relationship between surface densification characteristics and surface roughness in conventional polishing. Moreover, we conclude that the densification process created by the longitudinal pressure, which avoids non-uniformity, is beneficial to forming super-smooth surfaces in the conventional polishing methods. Under this guidance, we can stably fabricate ultra-smooth surfaces on fused silica with 0.4 Å roughness. This result overturns the mainstream view that the longitudinal pressure in polishing should be minimized. This conclusion is meaningful for the understanding of the ultra-smooth surface formation not only in conventional polishing but also in other optical-fabrication technologies.