Ceramics, advanced cutting tools

As discussed previously, ceramic matrix composites were originally developed to overcome the brittleness of monolithic ceramics. Thermal shock, impact and creep resistance can also be improved, making CMCs premium replacement choices for some technical ceramics. Industrial applications such as in automotive gas turbines or advanced cutting tools are already taking advantage of such characteristics. 

Advanced ceramics have a wide range of application (Figure 5.3). In many cases, they do not constitute a final product in themselves, but are assembled into components critical to the successful performance of some other complex system. Commercial applications of advanced ceramics can be seen in cutting tools, engine nozzles, components of turbines and turbochargers, tiles for space vehicles, cylinders to store atomic and chemical waste, gas and oil drilling valves, motor plates and shields, and electrodes for corrosive hquids. 

Miao H, Qi, L, Cui G (1995) Silicon Nitride Ceramic Cutting-Tools and their Applications. In Low IM, Li XS (eds) Advanced Ceramic Tools for Machining Application - II Key Engineering Materials 114, Trans Tech Publications Ltd, Switzerland, p 135... 

ZS-7. [Advanced Refractory Tech.] Zirconium diboride for oxidation-resistant ctxnposites, burble absorber of neutrons, elec, contacts, mdten metal crucibles, refractory roughener, cutting tool composites, structural ceramics, wear conqxxients, metal matrix omi-posites. 

Both the demands for advanced grinding tools and for the precise machining of hard cast iron and hardened steel with cutting ceramics are expected to promote the further development of powder technologies for the manufacture of highly perfect submicrometer microstructures for applications in fields where diamond or cBN tools are too expensive. 

H. Tanaka, A Recent Tendency of Si3N4 Cutting Tools , Advanced Materials Ceramics, Powders, corrosion and Advanced Processing, 14A, 1994, 541-545. 

Recent advances further enhance their commercial potential in metal matrix composites such as aluminum, nickel, and copper ceramic matrix composites, such as alumina, zirconia and silicon nitride and glass ceramic matrix composites such as lithium aluminosilicate. Silicon carbide whiskers increase strength, reduce crack propagation, and add structural reliability in ceramic matrix composites. Structural applications include cutting tool inserts, wear parts, and heat engine parts. They increase strength and stiffness of a metal, and support the design of metal matrix composites with thinner cross sections than those of the metal parts they replace, but with equal properties in applications such as turbine blades, boilers and reactors. 

In contrast to the above proposals, it is likely that other advanced ceramics-notably alumina, beryllia, sihcon carbide and sUicon nitride (see Chapter 11)-will demonstrate below-average growth rates owing to environmental concerns, competition from other ceramics (see Table 6.4), and an increasing reUance on slower-growing market segments such as cutting tools that are based on ceramic alloys (e.g., modified alumina and SiAlONs). In this situation, whilst alumina will surely remain the prominent material, its market share wiU be eroded by ferrites, and by beryllia- and zirconia-based ceramics. 

New trends in the development and application of hard ceramic grinding and cutting materials will be discussed in this Chapter. For both groups of tools, modern technical demands drive the development of submicrometer microstruc-tures that exhibit significantly increased hardness and reliability. Manufacturing approaches and resulting properties will be described for both advanced single phase sintered alumina materials and for composite ceramics. 

Figure 19. Cutting edge displacement on turning hardened steel with advanced ceramic tools (a) at V = 220 mmin (above), (b) at 300mmin (below) see Table 4 for materials characterization.

---