Advanced Materials Research Vols. 53-54

Abstract: A simulation system was developed to forecast machining quality and optimize grinding parameters for the machining of ceramic die material. The system can forecast the surface quality of machined ceramic die material with high precision, optimize machining parameters and analyze the dominant factors. Based on the process database, the simulation system is applicable to various machining methods. It can help to raise the automaticity for the machining of ceramic die material and develop the farther intelligent system.

Abstract: Surface integrity has a great effect on the fatigue property of titanium alloy. The surface integrity and fatigue property of a high speed milled Ti-6.5Al-2Zr-1Mo-1V (TA15) titanium alloy were investigated in this research. The main objective of this paper is to study the influence of milling speed on the surface integraty and fatigue property of the machined part. The surface roughness, work hardening, metallurgical structure and residual stress of the machined surface were studied in a cutting speed range of from 50m/min to 300m/min. To verify the relationship between cutting speed and the surface integrity of machined surface, the fatigue property of titanium alloy specimens milled at four different cutting speeds ranging from 50 to 200m/min were compared at two stress levels. This research shows that the cutting speed has little effect on the work hardening, metallurgical structure and residual stress, but the surface roughness decreases with the increasing cutting speed. Therefore, increasing milling speed has a positive effect on the surface integrity and fatigue property of the machined surface.

Abstract: Surface integrity of Sapphire wafer is the frontier technology to grow high quality AlN/GaN films for high brightness light-emitting diode. Surface damage measurement methods for single crystal sapphire were introduced firstly. Classical types of surface deformation induced by abrasive machining, such as lattice deformation, strain, scratch, crack versus abrasive grits and chemical reaction were compared. With the development of modern grinding technology, depth of the damaged surface layer decreases from 10μm to 2μm or much less. Both crack, lattice deformation, twinning and strain were detected along the ground surface, only dislocation and strain were appeared for polished sapphire surface. Usually, depth of the damaged layer was less than 300nm using mechanical polishing process. Chemical mechanical polishing achieved the lowest depth of the damaged surface and best surface roughness, scratch depth was used to descript the damaged depth, which is about 1 nm, and so called no damage to the layer remains during chemical mechanical polishing process.

Abstract: In modern surface modification manufacturing technology, laser cladding is a high-tech which has good prospects for development. However, for the large area laser cladding surface modification, there has the contradiction between cladding efficiency and cladding accuracy of the cladding. If using the smaller spot, it will be inefficient, if the spot increasing, the accuracy of marginal part of the cladding will be poor, the "stage effect" will be obvious. The variable spot powder feeder is designed, and the variable spot cladding process with small facula outlining border and big facula filling in central section is introduced, which resolves the contradiction between the two effectively. Experimental proves that surface quality with variable spot cladding is better. In the overlap area, due to the second lixiviation caused by repeated heating, the microhardness value of multi-track overlap cladding is higher than the structure in the non-overlap area.

Abstract: A simple method capable of producing uniform, large-area cone arrays of carbon films was found in a planar inductively coupled RF plasma source. The technique employs a DC or RF bias to substrate holder. Si substrates were mechanically pretreated using diamond paste. Cone-shaped carbon crystals preferentially nucleate and grow on the scratches using relatively low bias. Variation of the depositing conditions enables control of the cone density, geometry, and height. The cone arrays are believed to can significantly improve the field emission properties and have a tempting perspective in the microelectromechanical system (MEMS).

Abstract: The influence of surface morphology of diamond films on their friction behaviors was investigated under both ambient air and water environments. The diamond films with three different surface morphologies were deposited on the Co-cemented tungsten carbide (WC-6wt%Co) substrate using hot filament chemical vapor deposition (HFCVD) method and their frictional behavior were studied on a ball-on-plate type reciprocating friction tester, where the ball-bearing steel was used as the counterface materials. The coefficient of friction (COF) of diamond films showed strong surface morphology dependence, those samples with smaller diamond grain size and smoother surface finish represented lower COF in both dry and water lubricating conditions. Water lubricating was significantly favor to decrease the COF of diamond films, which might mainly due to the lubricating effect of physisorbed water layer formed on the sliding interface. In addition, the transferred materials layer adhered on the worn surface of diamond films were supposed to be another factor that was beneficial for reducing the COF.

Abstract: With high diffractive efficiency, Continuous Relief Diffractive Optical Elements (CR-DOE) can be used to eliminate chromatic aberration, partial aberration and simplify optical system. The technology for CR-DOE with Laser Direct Writing method has advantages of simple process, short period and low cost. The paper studied on the characterization method of laser power for the technology. The principle of mask fabrication of CR-DOE by Laser Direct Writing is described in the paper. The relations between microstructure depth and laser power, exposing position radius and laser power were studied. The results showed that microstructure depth changes in direct ratio to laser power and laser power should change in direct to exposing position radius while several same depth microstructures were fabricated at different radius. At the end, the paper gave the charactering method and also fabricated the mask of a kind of centrosymmetric continuous relief diffractive focus lens with the method.

Abstract: A series of diamond-like carbon (DLC) films with different Si concentration were prepared by changing the ratio of the number of Si-doped graphite target and pure graphite target. As the Si concentration in the thin film keep on increasing, the concentration of C-Si bond will increase leading to decrease of hardness and stress and increase of friction coefficient. In order to synthesize DLC films on metal substrates 3 types of interlayer have been made. The first and second interlayer is made up Ti/TiCx, and the second is thicker, the third interlayer is made up Ti/TiNx/TiNxCy, with the same thickness of the second. We also prepared DLC films with 6.7 at.% Si concentration on TC4 and Cr12 substrates with the third interlayer, and the thickness, hardness and fiction coefficients is about 0.652m, 4200Hv and 0.15, respectively. The adhesion of films had been greatly strengthened with a proper interlayer, and the value is more than 39N/mm2

Abstract: Thin films composed of mixtures of metals and dielectric are being considered for use as solar selective coatings for a various applications. By controlling the metal distribution, the solar selective coatings can be designed to have the combined properties of high absorptance, and low infrared emittance. We have studied the preparation of the Al-Al2O3 cermet composite films deposited on the flexible Kapton substrate by pulsed direct current (DC) magnetron sputtering technique. The complex films include infrared reflective layers, interference absorptive layers, and anti-reflective layers. The measurements of the samples show that the spectral absorptance in the region of 0.2~2.5μm and thermal emittance in the region of 2.5~25μm were 92% and 7%, respectively.

Abstract: Current jet cutting systems experience severe nozzle erosion and associated maintenance and downtime costs. An experimental investigation was conducted to qualitatively and quantitatively analyse the generation of cavitation in a high pressure water jet cutting system, and to characterise cavitation induced accelerated surface erosion by slurries. The analysis of surface morphology indicates that the shearing induced by cavitation played a major role in the erosion process. The results promise a feasible solution to reduce nozzle wear, and to enhance material removal in the jet cutting process.