Key Engineering Materials Vols. 447-448

Abstract: We have developed advanced lapping and polishing methods for silicon carbide (SiC) substrates using an Fe abrasive particles and hydrogen peroxide (H2O2) solution. In this method, a SiC surface is oxidized by hydroxyl radicals (OH*), which was generated by Fe catalyst reactions, and the oxide layer on the SiC is mechanically and/or chemically removed by Fe abrasive particles and solution　[1-4]. In this study, we applied this planarization method for lapping and polishing SiC surface, in which catalytically generated hydroxyl radicals were utilized to oxidize the surface of a SiC wafer. The processed surfaces were observed by optical interferometric microscope, Nomarski differential interference contrast. These observations showed that surface roughness and flatness of a SiC substrate were markedly improved and scratch-free SiC surface was obtained. These results provide useful information for preparing a high-efficiency and high-accuracy SiC substrate.

Abstract: Magnesium alloys have been increasingly used in automotive and aerospace components and in portable microelectronic devices due to their “ultralightness” and high specific strength. Machining is an important method used to process magnesium alloys. The advantages of machining over other processing methods such as die casting include reduction in power consumption and excellent surface finish. However, the ignition of chips presents a dangerous problem during machining. This problem has attracted considerable research interests. Though coolants can be used effectively to prevent ignition, the pollution of environment and reclamation of chips can not be resolved easily. Therefore, one better approach is to control the machining parameters for minimizing ignition hazard of magnesium alloy chips during dry machining. A systematic study was conducted for a few different magnesium alloys (including AM50A and AZ91D) to understand effect of cutting parameters (cutting speed, feedrate and depth of cut) on ignition of chips during face milling. It is interesting to find that for any fixed cut depth ignition in the forms of sparks, flares or ring of fire occurs only in the moderate cutting speeds and feedrates and can thus be easily prevented by adopting either higher or lower cutting speeds or feedrates. Chips produced in different machining conditions were collected and their morphology was analyzed to understand mechanisms of ignition.

Abstract: To cope with increasing demands on ultraprecision profiling and finishing of aspheric lens molds, we have implemented an ultra/ nanoprecision aspheric grinding system to be mounted with an ELID- capability and on-line feedback capability of profile accuracy. A WC mold has successfully ground and finished to be with several nanometric surface smoothness and with ultraprecise profile accuracy by just grinding process with ELID mechanism. Some specific conditions have been investigated to achieve better accuracy and quality on molds. This paper presentation introduce those R&D activities and also discuss on the latest achievements on this topics, with showing injected aspheric lenses by the molds.

Abstract: Electrochemical polish technology could enhance the chemo-mechanical polishing efficiency of copper material. During the electrochemical polishing process, both the components and operation parameters of electrochemical polish solution are the key factors influencing planarization ability. This work measured the surface topography and roughness of copper material after mechanical polish by an atomic force microscope (AFM), and added glycerol in different ratios to the phosphoric acid (85 wt %), which was the main composition of experiment solution. Electrochemical polish was conducted within the potential action range in passivation area, and the surface topography and roughness of copper material after electrochemical polish was measured by AFM. The difference in surface topography of copper material after electrochemical polish was compared as well.The experiment indicated that after electrochemical polish in pure phosphoric acid for 50 sec, the surface roughness of copper material obviously decreased from 6.921nm (Ra) to 0.820nm (Ra), and the planarization was more obvious with the increase of electrochemical polish time. The above results could appear in different electrolyte formulas, indicating that electrochemical polish was a good processing method for copper material planarization. This work also proposed the effect of analyzing the electrochemical polish time on planarization through planarization efficiency. Based on the analysis, the planarization efficiency was decreased with the increase of electrochemical polish time, which indicated that longer electrochemical polish time did not yield better result. This work also found that the surface is not only flattened, but also glossed after electrochemical polish.

Abstract: A new ultrasonic vibration cutting device for ultraprecision elliptical vibration cutting has been developed. The elliptical vibration cutting device developed utilizes combination of bending and longitudinal modes of vibration of the stepped vibrator to generate circular or elliptical vibration locus at the cutting tool edge. The design principle as well as the structure and the performance of the elliptical vibration cutting device is introduced here. The experimental results of diamond cutting of Co-Cr-Mo Alloy proved that good surface quality with roughness of 20 nmPV can be obtained stably with the elliptical vibration cutting device developed.

Abstract: As demand for high-quality machined tools considerably grows, ELID, a new and efficient technology, has been successfully brought into the precise manufacturing industry of hard and brittle materials with mirror surface finish. Hence, besides conventional functions like lubrication, fluid solutions in this grinding process are required to serve more functions, especially as electrolyte. Writers of this paper mainly work on the methodology to optimize this kind of fluid by adding various related chemical additives. By varying the pH, the accretion of additives is controlled and consequential effects are studied which is the metallic oxide layer variation before and after each test. Corresponding experiments have been carried out with procedures and results analysis included in the paper.

Abstract: Nano-precision machining using focused ion beam (FIB) is widely applied in many fields. So far, FIB-based nanofabrication for specific nanoscale applications has become an interesting topic to realize more diversities for nano-construction. Through FIB machining, we can easily achieve the required nano- and micro-scale patterning, device fabrication, and preparation of experimental samples. Nowadays, there is an increasing trend to learn from nature to design novel multi-functional materials and devices. Thus, more interestingly, another advantage of FIB is that it can be conveniently used to analyze the natural photonic structures, e.g., those in the butterfly which exhibits amazing optical phenomena due to sub-wavelength structural color. Accordingly, in the present study, structural analyses for butterfly wings were carried out using FIB. It is found that the photonic structures for the backside and frontside of the butterfly wing studied differ considerably. The difference accounts for the different colors on the dorsal and ventral sides of butterfly wings.

Abstract: This research aims to develop a reverse simulation method to obtain the shape of tool electrode before machining from the shapes of workpiece before and after machining in sinking EDM. To apply the reverse simulation method to tool electrodes which have large curvatures, a special operation was added to the simulation program to consider the influence of the curvature. The validity of the principle of the modified reverse simulation was demonstrated in the machining of a V-shaped cavity.

Abstract: Surface characteristics of CZT wafers machined using wire sawing, free abrasives lapping and polishing and ultra-precision grinding were investigated. Wire sawing resulted in the removal of material in both ductile and brittle regimes, but both polishing and grinding led to a ductile removal. The grinding produced very smooth surfaces free of embeddings and scratches, which is thus considered to have better machinability than the free abrasive machining. The nanoindentation and nanoscratch on MCT wafers at nanometric scales resulted in considerable plastic deformation, but no fracture features. The hardness of the MCT wafer was 500 to 550 MPa, and the coefficient of friction was particularly high, ranging from 0.45 to 0.55.

Abstract: For applications of injection mould fabrication in the field of MEMS, proton beam writing (PBW) and UV lithography are combined to manufacture 2 mm thick Ni moulds with sub-10 µm fine features in 10 µm deep fluidic channels. PBW is capable of writing micro and nano features with straight and smooth sidewalls with sub-10 nm RMS roughness, while UV lithography has the advantage of large area structuring through a mask. A newly developed positive resist maP1275 hv is presented in combination with PBW and UV lithography for Ni injection mould fabrication. Fine micro pillars with straight and smooth sidewalls have been achieved by PBW and linked with UV lithography into a microfluidic channel. The new resist is successfully removed after electroplating without compromising the Ni mould.