Machining High-Temperature Alloys by Means of Solid Ceramic End Mills

Russian Engineering Research - The cutting of high-temperature alloys is considered. The performance of solid ceramic end mills is assessed by experimental comparison of five different designs with...     

Tribological behaviour of a 3Y-TZP/Ta ceramic-metal biocomposite against ultrahigh molecular weight polyethylene (UHMWPE)

This study aims to evaluate the tribological behaviour of 3Y-TZP/Ta (20 vol%) ceramic-metal composites and 3Y-TZP monolithic ceramic prepared by spark plasma sintering (SPS) against ultrahigh molecular weight polyethylene (UHMWPE). According to the results of pin (UHMWPE)-on-flat wear test under dry conditions, the UHMWPE – 3Y-TZP/Ta system exhibited lower volume loss and friction coefficient than the UHMWPE – monolithic ceramic combination due to the presence of an autolubricating layer that provides sufficient lubrication for reducing the friction. Owing to the lubrication of the liquid media, under wet conditions obtained using simulated body fluid (SBF), similar behaviour is observed in both cases. Additionally, the ceramic and biocomposite materials were subjected to a low temperature degradation (LTD) process (often referred to as “ageing”) to evaluate the changes in the tribological behaviour after this treatment. In this particular case, the wear properties of the UHMWPE-biocomposite system were found to be less influenced by ageing in contrast to the case of the UHMWPE-zirconia monolithic material. In addition to their exceptional mechanical performance, 3Y-TZP/Ta composites also showed high resistance to low temperature degradation and good tribological properties, making them promising candidates for biomedical applications, especially for orthopaedic implants.     

Electrically conductor black zirconia ceramic by SPS using graphene oxide

The use of graphene as a component for developing electroconductive ceramic composites is being profusely studied. It is a very promising additive as it has excellent mechanical properties, high electrical and thermal conductivities, it is lightweight and its aspect ratio allows reaching percolation with low contents.In the particular case of zirconia, preparation of black coloured materials remains a challenge while many high added value applications are waiting for a solution. Graphene appears as a candidate for fulfilling all these requirements. In this work, 3Y–TZP/rGO composites were prepared by Spark Plasma Sintering Zirconia-rGO mixtures. Simultaneous sintering and in-situ reduction of graphene oxide opens a very interesting technological route for preparing this type of materials. The influence of graphene content on the electrical, mechanical and optical properties was studied. An rGO content as low as 0,29 vol% allows nanostructured black zirconia to be obtained but it has to be increased up to 1 vol% in order to reach electrical resistivity values <100Ωcm, required for electrodischarge machining.     

A method for correcting the satellite camera position by referencing space photographs to a ground map

A method for highly accurate estimation of the geometry of photographing from space (the coordinates of the principal point and the camera orientation), with the use of ground reference points is proposed and experimentally tested. The method is based on the matching of projective and geographic coordinates of given landmarks on space photos and ground digital maps. A precise estimate of the camera geometry uses the singular value decomposition technique and the nonlinear root mean square method. The dependence of error in determining the absolute orientation angles on the number of points used for the calculation is obtained. This work was partially supported by the Ministry of Science and Industry of the Russian Federation, state contract no. 37.011.11.0014.     

Hydrogen permeability of a nickel alloy after high-temperature holding in technical helium

Translated from Fiziko-Khimicheskaya Meckhanika Materialov, No. 6, pp. 61–63, November– December, 1989.     

Solid Ceramic Toroidal End Mill

Russian Engineering Research - The possibility of designing solid ceramic end mills with different geometry is considered. A mathematical model is developed for the cutting section of the mill on...     

Refining the outer camera orientation in synchronized shooting from two spacecrafts

Methods for simultaneous refining the outer orientation parameters of satellite cameras in synchronized shooting from two spacecrafts moving in the same orbit are proposed and investigated. The methods are based on taking into account perspective relations between corresponding coordinates of projections of region elements in a synchronized series of stereograms under assumption that the common aiming point of the cameras does not change during shooting. A method for space shooting simulation is described and used for investigating the dependences of the errors of estimating the orientation angles of the cameras on the number of stereograms and the noise level in projective coordinates of region element images.     

Longer‐lasting Al2O3‐SiCw‐TiC cutting tools obtained by spark plasma sintering

In this work, an electrically conductive powder mixture of alumina, silicon carbide whiskers, and titanium carbide has been used to obtain cutting tools with a standard SNGN geometry after machining spark plasma sintered disks with 150 mm in diameter and 10 mm height. The obtained cutting inserts from the sintered blanks were used in real conditions in order to make a wear study of this composition compared to the alumina‐silicon carbide whiskers inserts available in the market. In parallel, pin on disk wear studies were performed. Results are discussed in terms of the different properties and microstructural features of the different ceramic composites.     

Manufacture of graphite electrodes for the electrospark machining of complex high-precision components

The manufacture of complex graphite electrodes for electrospark broaching is considered. Recommendations are made regarding the milling of graphite, and the design features of the electrodes are shown for a specific example.