Takao Nishioka

High temperature deformation of silicon nitride ceramics with different microstructures

Abstract The deformation of some silicon nitride ceramics which consist of elongated β-Si 3 N 4 grains in a fine-grained matrix containing an amorphous grain boundary phase was studied by tensile testing at elevated temperature. Superplastic elongations larger than 250% could be observed, and characteristic microstructural development during deformation was studied.

Indentation cracks in superplastically deformed silicon nitride consisting of strongly aligned rod-shaped grains

Vickers indentation in silicon nitride, which was produced by superplastic tensile deformation of 150%, was conducted. The specimen had a highly anisotropic microstructure, where rod-like grains aligned along the tensile direction, and showed unusual crack systems. In the case of the indentation whose diagonals point to 0°/90° (0° direction is the tensile direction), two V-shaped surface cracks were propagated from each 90° edge and one crack from each 0° edge. In the case of the 45°/45° indentation, surface cracks emanated from the edges of the indent and deflected towards the tensile direction. Subsurface crack systems also showed unique shapes, differing from a cross-shaped crack system in isotropic brittle materials. Three-dimensional crack systems were estimated on the basis of the observation, and the crack evolution process was considered. Furthermore, the mechanical properties of the anisotropic silicon nitride were measured, and showed superior bending strength and fracture toughness in specific directions, compared to the undeformed material.

Study on Electrolytic Re-Insulation Grinding of Soft Magnetic Powder Cores

Soft magnetic powder cores are used for electromagnetic conversion coils, which are essential parts in automotive, home appliance, and other electronics industries. These cores are manufactured through the process of compacting pure iron powder covered with an insulation layer, and are distinguished by high electromagnetic conversion efficiencies. However, soft magnetic powder cores suffer from one problem: their electromagnetic conversion efficiencies drastically decrease when they are subjected to conventional finishing processes. This is directly attributable to the formation of conductive layers on finished surfaces, which significantly reduce the electrical resistance of material surfaces. As a solution to this problem, we developed an electrolytic re-insulation grinding method that finishes materials while applying a current between the material and the grinding wheel. This method regenerates the insulation properties of soft magnetic powder cores through the electrolytic removal of conductive layers formed during finishing, thereby improving electrical resistance. This development enables the finishing of soft magnetic powder cores without compromising their electromagnetic conversion efficiencies.

Estimation of Grinding Wheel Performance by Dressing Force Measurement

Dressing force measuring equipment was developed and the performance of a single-point diamond dresser was examined focusing on the relationship between dressing force and grinding performance. It was found that a distinct relationship exists between dressing force and grinding performance, and that the sharp-edged single-point diamond dresser can control grinding performance with low dressing force. The single-point diamond dresser and multipoint diamond rotary dresser induce the same dressing force if their wear widths are equal.

Development of a high-strength Si3N4 sintered body☆

Due to its heat-, wear- and corrosion-resistant properties, Si3N4 ceramic is a promising material for cutting tools and other wear-resistant products, and for automotive engines, gas turbines, and other structural items. Sumitomo Electric has successfully developed sintered bodies (σ1 = 130 to 150 kg/mm2 at room temperature) with high strength by controlling grain shapes grain diameter and aspect ratio. The high strength Si3N4 materials have fracture toughnesses of KIC = 5–7 MPa/m, thermal shock resistance of ΔT = 9000°C, good acid-resistant properties, and other properties all superior to those of conventional Si3N4 materials. Highly reliable Si3N4 materials with high Weibull modulus (m > 20) have also been developed by reducing metal inclusions that would cause defect factors leading to breakup. The high strength Si3N4 is already in practical use for plastic machining tools for non-ferrous metals (Al, Cu alloys), forging tools, and other wear-resistant products and structures of steel facilities. It is also being used for automotive parts and other items requiring high reliability. The high strength Si3N4 sintered bodies fully satisfy the requirements of these products.

Evaluation of diamond dressers and estimation of grinding performance by dressing force measurement

Equipment to measure the dressing force exerted by diamond dressers was developed and the performances of two types of diamond dresser, a single-point dresser and a multipoint rotary dresser, were examined focusing on the relationship between dressing force and grinding performance. It was found that both types of diamond dresser induce the same dressing force if their wear widths are equal and that a strong relationship exists between dressing force and grinding performance; a sharp-edged single-point diamond dresser can be used to control grinding performance with a low dressing force. The truing accuracy depends on the dresser type and a lower dressing force results in better truing accuracy.

Iron-Based P/M Soft Magnetic Material for Electric Devices Operating at High Frequencies

Recently, there has been a growing demand for soft magnetic materials with high conversion characteristics in the high-frequency range due to the trend where electric devices are being operated at higher frequencies. P/M soft magnetic materials, which were developed for such devices, utilizing iron-based powder and alloy powder. Through this work, we were able to reduce core loss and achieve remarkable magnetic characteristics in the high frequency range. Core loss, which includes hysteresis loss and eddy-current loss, is predominant in the high-frequency range. Two methods can be used to reduce eddy-current loss: using fine-grained powder, and using high-resistivity powder. However, both these present compressibility problems, with high-resistivity iron-based alloy powders such as Fe-Si being particularly poor in deformability. By studying composition of the material, we successfully developed a material that offers both high resistivity and high compressibility, reduction of core loss by more than 20% over the conventional material was achieved.

Study on the High-Efficiency Smoothness Grinding of Soft Magnetic Powder Cores

Soft magnetic powder cores are materials manufactured by pressing pure iron powder covered with insulating film into shape. These are widely known soft magnetic materials which are used as essential electromagnetic conversion parts in automobiles and household appliances. In recent years, demand for higher magnetic properties and dimensional precision has been growing with respect to soft magnetic powder cores. It has therefore become necessary to develop a high-efficiency, high-precision finishing method. The issues to be addressed with regard to this kind of method are: (1) the pure iron used in these materials displays ductility resulting in burring and cohesion to machining tools, (2) these materials are green compacts with low binding forces between powder particles and high tendencies towards cracking and gouging, and (3) these materials possess residual pores at levels of several percent thus resulting in microscopically intermittent processing which causes heavy machining tool wear. We have solved these issues through the development of a super-smooth finishing method designed for soft magnetic powder cores.

Observations on Orthogonal Cutting Processes - Effect of Friction between Tool and Work Material -

In this paper, orthogonal cutting tests of alloy steel, aluminum alloy and Ti6Al4V have been carried out to consider the cutting mechanism from the viewpoint of friction between the tool and workpiece. The cutting processes were observed in detail using a high-speed video camera. The cutting process of alloy steel was greatly affected by its tribological properties compared with those of the other two work materials. In the cutting process of alloy steel, there were three stages in relation to the state of the tool rake face and temperature. The difference between non coated and coated tools was marked in the later stages. From the discussion on the experimental results, it is considered that the thrust force is suitable for representing the tribological properties between the tool and workpiece. It is concluded that the orthogonal cutting test is a good method for evaluating tribological properties between the tool and workpiece.

Development of P/M Aluminum Alloy with Fine Microstructure

We successfully developed Al -Si -Transition Metal (TM) -Rare Earth (RE) Powder Metallurgy (P/M) alloy with fine microstructure, which has high strength at high temperature. For example, at 473K, the ultimate tensile strength was 290MPa and fatigue strength on 107 cycles was 130MPa, which is an 80% improvement compared with conventional Aluminum cast alloys. This material was compacted rapidly solidified powder and directly consolidated by hot extruding or forging. The microstructure consists of fine Al crystal grains (grain size; around 200-500nm), and inter-metallic compounds. Before consolidating, rapid heating was performed on powder compaction in order to keep the fine microstructure in powder state. The effect of plastic deformation on consolidating was examined to stabilize properties of this material. The mechanical properties of the present alloy are expected] to contribute to improve performance of various automobile engine parts.