HPSN ceramic

Flexural strength tests were performed in accordance with MIL-STD-1942 (MR) [10,11] on all bars that are ground in this research. For HPSN ceramic. 

Flexural strength as a function of grit depth of cut, /imax (test condition number 1 through number 9), for HPSN ceramic. 

The objectives of this chapter are to determine the parameters of a new technology for high productivity, low cost of hot-pressed silicon nitride (HPSN) ceramic materials and to determine if an available grinding wheel system can be used for these applications. 

Ceramic materials are commonly brittle materials with varying degrees of brittleness. The aim of this research is to increase the ductility of HPSN ceramic materials by the aid of laser preheating process and in process. With this method, it will be possible to increase the depth of cut (productivity of the process) more than 20 times and at the same time, keep the process in the ductile mode (free of surface and subsurface damages). 

This research is unique in that the grinding system will be considered as a thermal-tribo system and the laser energy and friction energy together will provide indications for the necessary energy for increasing the ductility of HPSN ceramic materials. 

Fig. 33. Parabolic rate constant Kp of different Si3N4 ceramics [455], (SSN Mg/Al [465] SSN-Y/Al [466] HPSN Y/0.2 Al [466] HPSN Mg/Y [467] HPSN Y and HIPSN (no additives)...

Table 15.1 Values of the thermal shock resistance parameters R, R, R"" for a range of ceramic materials where HPSN is hot pressed silicon nitride and RBSN is reaction bonded silicon nitride (reprinted from Table 11.1 on p 213 of Ceramics Mechanical Properties, Failure Behaviour, Materials Selection by Munz and Fett, 1999, published with permission from Springer-Verlag GmbFI)...

The tensile fracture strengths of three different structural ceramics are listed below hot-pressed silicon nitride (HPSN), reaction-bonded silicon nitride (RBSN), and chemical vapor-deposited silicon carbide (CVDSC), measured at room temperature. 

The ceramic materials investigated in this paper are hot-pressed silicon nitride (HPSN), reaction-bonded silicon nitride (RBSN), zirconia-toughened alumina (AI2O3), and porous SiC. The available material properties for these ceramics are given in Table 4.3. The HPSN and zirconia-toughened alumina ceramics were in the shape of flexural strength test bars cut from billets. The RBSN ceramic was molded into bars of the shape of flexural test specimens. The porous SiC ceramic was provided in the shape of flexural test specimens. 

For investigating ground strength of HPSN and RBSN ceramics, the grit sizes of the wheels employed are shown in Table 4.4. The wheels have a concentration of 150 and an uncoated diamond. The width and thickness of... 

Since the 1970s, the search for improved materials has led to a better understanding of the role of additives in the densification and microstructural development of silicon nitride-based ceramics and the consequences for final properties [1, 6]. Improvements in powder manufacture and forming techniques and the development of alternative firing processes has led to a complete family of materials including RBSN, HPSN, sintered silicon nitride (SSN), sintered reaction-bonded silicon nitride (SRBSN), gas-pressure sintered silicon nitride (GPSSN), hot isostatically pressed silicon nitride (HIPSN) and silicon nitride alloys or solid solutions termed SiAlONs, based on their elemental components. 

The SiC/HPSN combination is probably acceptable in respect of flash temperature as the higher temperatures are not likely to daitiage ceramics. 

Although coatings have been successfully used on the shaft, improvements may be possible in light of the work discussed in Section f>, by replacing the HPSN with silicon carbide and employing a silicon carbide sleeve on the shaft. However the technical difficulties of fitting ceramic sleeves to shafts are well known and such problems have not been definitively resolved. 

Bodur, C. T. and Kromp, K., Investigation of the strength behaviour of HPSN with yttria at high temperatures, (in German).In Fortschritts-berichte der Deutschen Keramischen Gesellschaft (Cfi ceramic forum international), to be published. 

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