Advanced Materials Research Vol. 1136

Abstract: The dynamic mechanical properties of oxygen free copper has been tested under the different strain rate (4700s-1~21000s-1) at the room temperature by split Hopkinson pressure bar (SHPB), the true stress-true strain curves has been obtained. Power-Law constitutive model and Johnson-Cook constitutive model have been built to fit the experimental result from SHPB test of oxygen free copper, meanwhile, the constitutive model can be applied to the simulation analysis of cutting process. The results show that the oxygen free copper is sensitive to the strain rate. In addition, the Johnson-Cook constitutive model predicts the plastic flow stress of the oxygen free copper more accurately than the Power-Law constitutive model at the high strain rate.

Abstract: In order to clarify the mechanical properties of single-crystal silicon carbide (SiC), nanoindentation was performed on a 4H-SiC wafer. The change of hardness with the angle between the wafer orientation flat and the indenter edge, the maximum load and the loading rate were investigated. The hardness reached maximum at an indentation load of 12 mN in the range of 3-50 mN. Hardness decreased under two conditions: when the edge of the indenter tip is parallel to the [11-20] direction, and when a very low loading rate was used. Transmission electron microscopy was used to observe dislocations and cracks under the indents. It was demonstrated that the deformation process of SiC involved three steps with respect to the increase of the indentation load. These results provide information for improving ductile machining process of single crystal SiC.

Abstract: PCBN-inserts have a high potential in the cutting of hardened steel, cast iron and super alloys due to their high hardness and heat resistance. Nevertheless they have a high purchase price, which lowers the economic benefits for the end user compared to other cutting materials. This is caused by the high production costs of the inserts. The grinding of PCBN-inserts causes a major proportion of these costs as a result of the high grinding wheel wear. The primary wear mechanism is grain breakout followed by clogging of the grinding layer. This study shows that the efficiency of the grinding process can be increased significantly by applying low cutting speeds and high feed rates. In this case, splintering of the grinding grain is the main wear mechanism.

Abstract: Nickel-based superalloys such as Inconel 718 are known as one of the most difficult-to-cut materials due to their mechanical and chemical properties and the tool life is extremely short. Recently, Cubic-Boron-Nitride (CBN) has received a considerable attention as a material for cutting tools and has been considered to be a major candidate for high performance cutting of Inconel 718. However, the detailed wear behavior of CBN tools in cutting of Inconel 718 is not sufficiently understood yet, and the performances of CBN tools are still insufficient in practical use. To overcome this problem, we first conducted orthogonal cutting experiments on Inconel 718 at low (20 m/min) and high (100 m/min) cutting speeds employing CBN cutting tools to clarify the detailed wear mechanisms. Moreover, relationship between surface microstructures of the cutting tool and wear resistance was investigated. As a result, it was found that a rake face with micro grooves significantly suppressed the crater wear at low cutting speed, although polished surface rake face reduced the initial crater wear by approximately 40 % compared to the non-polished tool in high speed cutting of Inconel 718.

Abstract: The effect of carbide orientation on the dry sliding wear behaviour of high chromium cast iron was studied by pin-on-disc type wear tests at room temperature. The carbide anisotropy was achieved by thermomechanical treatments at temperatures of 950 and 1150 °C. By cladding with low carbon steel, the brittle high chromium cast iron was hot compressed severely with crack free. The thermomechanical treatments not only change the carbide orientation, but also increase the volume fraction of carbides. Due to the long axis of carbide rods is parallel to the wear surface, the high chromium cast iron treated at 1150 °C has a superior wear resistance than the as-cast one, in which the long axis of carbides is perpendicular to the wear surface. For the high chromium cast iron treated at 950 °C, high volume fraction of carbide pits accelerates the wear rate significantly even though it has a similar carbide orientation as the sample treated at 1150 °C. The observations on wear tracks reveal that the ferrous matrix can be protected better from abrasion when the high chromium cast iron was treated at 1150 °C.

Abstract: The present study reports the influence of graphene layers on the tribological performance of CVD diamond films when they are used as the solid lubricants. Friction tests are conducted on a ball-on-plate friction tester, where the stainless steel is used as the counterpart material. The CVD diamond film sample is a typical microcrystalline diamond (MCD) coating which is deposited on a flat tungsten carbide substrate using the hot filament chemical vapor deposition method (HFCVD). Besides the MCD sample, a polished MCD film (pMCD) and a polished tungsten carbide (pWC) are also adopted in frictional tests, aiming at illustrating the influence of the surface morphology, as well as the physical property, of the sample on the lubricative effect of graphene layers. The experimental results show that graphene layers can effectively reduce the coefficient of friction (COF), regardless of the samples. The MCD sample presents the lowest stable COF, which is 0.13, in dry sliding period when the graphene flakes are sparyed on the sliding interface; while the pMCD and pWC samples exhibit slightly higher COFs, which are 0.16 and 0.18, respectively. Comparatively, the COFs of these three samples obtained in dry sliding process without graphene are 0.20, 0.25 and 0.64. In additon, the MCD sample exhibits a much longer stable dry slidng process which is more than 5000 cycles. Comparatively, the other two tribo-pairs only exhibit a stable low-COF dry sliding period for around 2000 cycles. The reduction of COF could be attributed to the graphene flakes adhered on the sliding interface. It forms a layer of solid lubricative film with extremely low shear strength and significantly decreases the interactions between two contacted surfaces. The rugged surface of the MCD film provides sufficient clogging locations for graphene flakes, which allows the generated lubricative film enduring a long sliding duration. It can be arrived from this study that the tribological properties of the MCD film could be enhanced by simply adoping graphene layers as a solid lubricant. Furthermore, an improved performance of a variety of MCD coated cutting tools or mechanical components could be expected when they are utilized with graphene layers.

Abstract: Applicability of a generic optical spectrum analyzer that is familiar with laser experiments is investigated for on-site wafer thickness measurements in the thinning process, to resolve the issues regarding mismatch in the thickness range of previous thickness measurement system. The optimizations in terms of the spectral range, the spectral resolution and the dynamic range are successfully conducted by use of the optical spectrum analyzer. Owing to both high spectral resolution and wide dynamic range in near infrared spectral measurements, full range thickness measurements for the initial thickness 775μm and the terminal thickness 1μm and nanometer order accuracy are implemented.

Abstract: Knowing temperatures at the tool-chip interface is extremely important to optimize the machining condition and to improve the machining performance, furthermore to design high performance materials. In order to grasp the temperature distribution at the tool-chip interface, this study has devised an indexable insert with seven pairs of built-in micro Cu/Ni thermocouples on the rake face near the cutting edge. This paper shows the performance of the indexable insert with built-in micro thermocouples developed. The thickness of each element of the micro thermocouple is approximately 15 μm. The result of unsteady heat conduction analysis employing FEM shows that the temperature difference by installing the micro thermocouples is less than 10 K or 1.2 %. The temperature measurement experiments by cutting of aluminum alloy were carried out by changing the cutting speed. The results provided the evidence that the temperature distribution at the tool-chip interface can be grasped with the indexable insert with built-in micro thermocouples developed.

Abstract: Superfinishing is widely used as a final finishing method for sliding surfaces of bearings. In superfinishing, a fine finished surface can be obtained by transiting the machining states from the cutting action to the finishing one as the tool loading is encouraged. To obtain good machining conditions, it is necessary to judge the transition of the machining state reliably. However, it is difficult to judge the transition of the machining states. In this study, we focused on the change of the dynamic component of the machining force, which was applied to the oscillation direction of the superfinishing stone, during machining process. With machining experiments, the relationship between the declination of the dynamic machining force and the transition of the machining state was confirmed.

Abstract: In surface grinding of a large workpiece used for a sliding surface of the machine tool, high shape accuracy is required for the ground surface. Therefore, it is important to investigate the causes of the shape error observed in a large workpiece machined by surface grinding. In this study, we focused on the thermal deformation and residual stress as the causes of shape error. The in-process measurement of the workpiece temperature distribution was carried out to estimate the effect of the thermal deformation to the shape error. The estimated value of the shape error calculated from the measured temperature distribution was much less than the actual measured shape error. Therefore, the residual stress on the ground surface was measured with a portable X-ray stress measurement device. The residual stress was changed from compressed state to tensile state as the grinding pass increased. The ground shape was also deformed to concave shape as the grinding pass increased. The value of the shape error was finally reached to the constant value in several grinding conditions. From these experimental results, it is suggested that the shape error of the large workpiece is caused by the residual stress applied to the ground surface.