Advanced Materials Research Vols. 83-86

Abstract: In the present study ,the shock wave consolidation technique was used to produce bulk samples from metal powders .To method of consolidation were used to produce bulk samples, single consolidation and Two-Coaxial consolidation .after explosion ,the container tubes were cut and density of bulk , ratio of RDX to mass of flying tube (R) ,ratio of RDX to mass of powder(K),detonation velocity ,detonation pressure ,kinetic energy of flyer tubes and plastic work were calculated for all tests and finally cross section of samples were observed by SEM. The results show modified situation for Two-Coaxial consolidation by comparison in single tube consolidation.

Abstract: The debris re-adhering on the machining surface will affect the workpiece precision in EDM; therefore, the main purpose of this research is to study the re-sticky phenomenon of the powder metallurgy (PMM) in EDM. PMM with different melting points from 1450oC to 3410oC were used as EDM materials, the copper and the tungsten were chosen as the electrodes. The polarity in EDM was depended on the pole of the electrode. For observing the re-sticky position of the debris, the electrode was set no rotation or with 200 rpm rotational speed in EDM. The results showed that the melting point of PMM did not exceed 3000oC (PMM did not contain tungsten); the debris of PMM would not re-stick on the working surface no matter what polarity was used in EDM. However, only negative polarity can cause the re-adhesive effect when the melting point of PMM exceeded 3000oC. The debris would re-stick on any machining position when the electrode was not rotated in EDM. However, the debris would adhere on the central of the working area with 200 rpm rotational speed of the electrode.

Abstract: Physical Vapour Deposition (PVD) technology, particularly magnetron sputtering process, enjoys the competitive advantages of depositing different new generation coatings (e.g., multicomponent, multilayer, graded, composite etc.) on three-dimensional objects (substrate) with excellent mechanical and tribological properties. In an industrial-scale sputtering chamber with a limited number of active magnetron sources (target) on the chamber wall, the density of coating species from different sources would not be uniform everywhere around the chamber. As a result, at a constant speed of rotating substrate table in a single revolution, the instantaneous deposition rate will be highest in front of the active targets and lowest when the substrate moves away from the active targets. In this work, a method of controlling the rotational speed (i.e., slower speed in front of active targets and faster speed in front of inactive targets in a revolution) of a substrate table installed in a magnetron sputtering chamber has been developed in order to improve the deposition rate of a multicomponent TiN+MoSx coating. The mechanical and tribological properties of TiN+MoSx coating have also been characterised to assess the beneficial effects of adding solid lubricant (MoS2) in hard TiN coating.

Abstract: The development and application of Titanium Aluminium Nitrate (TiAlN) coatings for cutting tools has led to dramatic tool life extension and the realisation of high speed machining for hardened materials. This results in longer tool life and makes it possible to employ higher cutting speeds and feed rates. In this study, a series of different TiAlN based coatings on micro grains solid carbides were tested on H13 Tool Steel. These advanced coatings are commercially available by coating manufacturer which are trade marks of Balzers UK. The aim of this experiment was to investigate the performance of micro tools coated with these coatings and compare with uncoated tools. The results will be used to determine whether coatings for micro tools will have any impact on the performance of the tools such as reducing cutting forces or improving machining quality. This will be achieved by means of analysing the cutting force data and 3-D surface roughness respectively. Result obtained shows that different coating had different performance, hence can be applied to specifically targeted machining operation. The results also highlight some of the differences in wear mechanism of micro tools.

Abstract: The study is about an experimental investigation of the different factors influencing the temperature occurring at the coating/substrate and chip interface when machining Assab steels 760 and DF2 with two different coated carbide tools. Results show that tool temperature was higher when turning Assab steel 760. Temperature along the major flank face was higher that that at the minor flank. However, the magnitude of temperature was lower than expected with maximum only around 260 oC near the tool tip. The performance of Al2O3 coated WC inserts appeared to be better compared to TiN coated WC inserts. The cutting temperature was lower with alumina coated tools. While turning Assab DF2 steel, cutting temperature was lower compared to Assab 760 steel for the same coated tool.

Abstract: This study aims to develop an ultrasonically assisted grinding technology for precision internal grinding of a small hole measuring several millimeters in diameter, such as those formed in a fuel injector for an automotive engine. In a previous work, an experimental apparatus mainly composed of an ultrasonic vibration spindle was designed and constructed, and grinding experiments were carried out. The previous investigation found that applying ultrasonic vibration to the wheel decreased the normal and tangential grinding forces, respectively, and improved the surface roughness in surface grinding. The purpose of this paper is to examine the effect of ultrasonic vibration on grinding force and surface roughness in internal grinding when the grain sizes of small cBN grinding wheel are changed. The experimental results indicate that applying ultrasonic vibration to the wheel decreases the normal and tangential grinding forces by more than 83 % and 80 %, respectively, and improves the surface roughness by as much as 62 % while the wheel grain size is changed. In addition, over the range of grinding conditions employed in this paper, the grain size as small as 3 µm can be used in ultrasonically assisted internal grinding.

Abstract: In this study, statistical models were developed using the capabilities of Response Surface Methodology (RSM) to predict the surface roughness in high-speed flat end milling of Ti-6Al-4V under dry cutting conditions. Machining was performed on a five-axis NC milling machine with a high speed attachment, using spindle speed, feed rate, and depth of cut as machining variables. The adequacy of the model was tested at 95% confidence interval. Meanwhile, a time trend was observed in residual values between model predictions and experimental data, reflecting little deviations in surface roughness prediction. A very good performance of the RSM model, in terms of agreement with experimental data, was achieved. It is observed that cutting speed has the most significant influence on surface roughness followed by feed and depth of cut. The model can be used for the analysis and prediction of the complex relationship between cutting conditions and the surface roughness in flat end milling of Ti-6Al-4V materials. The developed quadratic prediction model on surface roughness was coupled with the genetic algorithm to optimize the cutting parameters for the minimum surface roughness.

Abstract: In this research, Air mist-abrasion machining method for corrective figuring of a rough isotropic quartz surface before polishing process has been proposed. By this method, not only the next polishing time decreases, but also figuring efficiency increases through the possibility of using bigger abrasive grain size. Since the restrictions of laser interferometer measuring devices, capacitor probe has been used for measuring “out of flatness” of a rough isotropic quartz surface and creating error map for corrective figuring. By the proposed Air mist-abrasion figuring method, flatness of a rough isotropic quartz surface improved from PV= 0.4μm to PV=0.1μm without any change in surface roughness value.

Abstract: The present work is devoted to research the influence of micro-structural evolution of the compound zone (iron (carbo)nitrides zone) upon development of hardness profiles in diffusion zone. A different phase structure of iron (carbo)nitrides zone on steel as compared to iron, further changing with the process, may result in upsetting the quasi-equilibrium of nitrogen concentration in the iron (carbo)nitrides zone/diffusion zone interface and may as a result have impact on the kinetics of this layer’s growth. Aimed at solving this problem there was a research carried out to evaluate influence of (carbo)nitrides zone, with intentionally created diametrically different phase composition, on hardness profiles in the diffusion zone. Based on the research conducted, it was shown that the evolution of phase structure of the compound zone contributes significantly, regardless of nitrogen potential and temperature, to the formation of the diffusion zone and in particular to its effective thickness. It makes this complex picture of nitrided case development on steel even more intricated.

Abstract: In the present study, the surface of St52 steel was alloyed with preplaced powders Fe-Cr-C and Fe-Cr-Si-C by using a tungsten-inert gas (TIG) heat source. Then microstructure of the alloyed surfaces was investigated. Following the surface alloying, conventional characterization techniques, such as optical microscopy, scanning electron microscopy (SEM) and X-ray diffraction were employed to study the microstructure of the alloyed surface. Microhardness measurements were performed across the alloyed zone. The tribological behavior of the coatings was compared in room temperature dry sliding wear tests. It was found that the as-deposited coatings consisted of higher volume fraction of carbides (Cr7C3). No crack formation was found on the coatings. As a result, TIG arc heat source can be used effectively for performing surface alloying on St52 steel with a preplaced powder in order to improve its surface wear resistance.