Shuji Sakaguchi

Tribological properties of dimpled silicon nitride under oil lubrication

It is known that under lubricated conditions, dimpled surfaces can show improved tribological properties under planar/planar contact. This study investigates the effect of dimpling on the tribological properties of a silicon nitride ceramic against hardened bearing steel under oil lubricated, planar to curved surface contact conditions. Block-on-ring friction tests under oil lubrication were carried out over a range of sliding velocities, with a silicon nitride ceramic whose surface was dimpled by abrasive jet machining (AJM). The dimpled surface showed better tribological properties in terms of reduced friction coefficient compared with a lapped surface.

High-temperature properties of a silicon nitride/boron nitride nanocomposite

Hexagonal graphitic BN (h-BN) is interesting as a second phase for high-temperature structural ceramics because it has the same crystal structure as graphite, for which fracture strength and Youngs modulus increase with increased temperature. In this study, high-temperature mechanical properties of Si 3 N 4 /BN nanocomposite were evaluated to clarify the effect of fine h-BN particles at elevated temperatures. As a result, we found that high-temperature strength and hardness of the nanocomposite were maintained up to high temperatures; also, its Youngs modulus increased gradually, concomitant with elevated temperatures up to 1400 °C. Finally, these properties were compared with those of monolithic Si 3 N 4 and Si 3 N 4 /BN microcomposite.

Analysis of Internal Friction on Silicon Nitride with Visco-Elastic Model

Temperature dependence of internal friction on silicon nitride ceramics with yttria and alumina sintering aids was discussed using 4-elements visco-elastic model. It is known that the internal friction of this ceramic material shows a characteristic peak at around 1040 oC and an exponential increase over 1200 oC. This temperature dependence of internal friction was well approximated with using parallel Maxwell model. The parameters for this model and the relaxation time on this model were obtained. The relaxation time was very short, compared to the transient creep deformation of this ceramics. The analyzed results on internal friction could not be related with the creep deformation.

Instrumented Hardness Test on Alumina Ceramics and Single Crystal with Spherical Indenter

Ceramic materials are expected to be applied to the structural parts, especially to tribological application, as they have high hardness and high elastic constants. For this application, it is important to know the properties of mechanical behavior on the surface of ceramics. Instrumented indentation is one of the tests that can explain the mechanical properties on the surface, as it expresses the relation between the penetration depth of the indenter and the applied force. 1,2 For metallic materials, the standard test method in instrumented indentation is already published.3 We have tried the instrumented indentation tests on ceramic materials. Figure 1 is a typical example of the loading-unloading curve by this test on alumina ceramics.

Status and Standards in ISO/TC206 'Fine Ceramics'

ISO/TC206 Fine ceramics is one of a technical committee (TC) in the International Organization for Standardization (ISO), established in 1992. The first plenary meeting for this TC was held in 1994, and the latest meeting was held in August 2015, in Jeju, Republic of Korea. The scope of this TC covers very wide field concerning the ceramic materials for industrial applications, in forms of powders, monoliths, coatings and composites, and in functions of mechanical, thermal, chemical, electrical, magnetic, optical and their combinations. This TC consists of 18 participating member (P-member) countries and 13 observing member (O-member) countries. We already have 81 published standards from this TC. About 30 new work items are under discussion, about 15 items are waiting for starting the discussion, and about 10 items are in the process for revision of the published standards. In this TC, we have 12 working groups. More than twenty years have passed since starting this TC, generally speaking, the categories of the discussed items tends to shift, from some testing methods for fundamental properties (strength, density, thermal properties etc.), to some properties for specified applications, such as ceramic bearing materials, photocatalytic materials and electrical applications.

EVALUATION METHODS FOR PROPERTIES OF NANOSTRUCTURED BODY

Publisher Summary The functions inherent in nanoparticles can be maintained while lowering their reactivity by fabricating nanoparticles into nanostructures. Stable nanostructured materials, fully utilizing the functions of nanoparticles, can be created by fabricating composite and bulk materials from nanoparticles, depending on their intended use. This chapter deals with such nanostructured materials and their various functions and the characteristic evaluation by function. It summarizes the nature of nanostructures, relevant examples of the relations between nanostructures and their characteristics, and the functionality and the evaluation of the characteristics of nanostructures. The chapter describes an electrode of a solid oxide fuel cell (SOFC), the structure of which is controlled using surface-coating type composite particles and the inner-dispersion type composite particles, as an example to explain the relation between nanostructures and their functional performance. In fabricating nanostructures in the application of nanoparticles, new functionalities are expected to produce many applications ranging over almost all fields in the coming years, with the advancement of technology. The chapter discusses the functional characteristics that are expected to be implemented in nanostructures in the coming future, including mechanical characteristics, thermal characteristics, electrical characteristics, electrochemical characteristics, electromagnetic characteristics, optical characteristics, catalytic characteristics, and gas permeability and separation characteristics.