Oxide ceramics
Oxide ceramics are of great importance as cutting materials in machining production . In addition to oxide, there are also non-oxide cutting ceramics. Ionic bonds predominate in oxide ceramics. With a usage share of approx. 85%, aluminum oxide (Al 2 O 3 ) is the most important representative of oxide ceramics.
Technically important oxide ceramics are:
- Aluminum oxide (Al 2 O 3 )
- Zirconium dioxide (ZrO 2 )
- Titanium (IV) oxide (TiO 2 )
- Magnesium oxide (MgO)
- Zinc oxide (ZnO)
- Aluminum titanate (Al 2 O 3 + TiO 2 )
- Barium titanate (BaO + TiO 2 )
properties
Oxide ceramics are harder , more wear-resistant and more heat-resistant, but also more brittle than hard metals and therefore only suitable to a limited extent in machining mechanics for production with interrupted cuts, as inevitably occurs during milling . The advantages of cutting ceramics are their high hardness and high temperature resistance as well as their high chemical and thermal resistance. They are highly corrosion-resistant even at high temperatures in the application range up to> 1000 ° C. Their low toughness and the low tolerance to rapid temperature changes have a disadvantage . Oxide ceramic "jumps" when suddenly cooled, e.g. B. by cooling lubricants .
Depending on the oxide used and the manufacturing process, oxide ceramics have thermal properties ranging from good insulators to good heat conductors :
- Aluminum titanate : approx. 1.5 to 3 W / (m K)
- Zirconium dioxide : ~ 3 W / (m K)
- Titanium (IV) oxide : approx. 3 to 4 W / (m K)
- Aluminum oxide : 24 to 28 W / (m K)
Oxide ceramic tools
Tools made from cutting ceramics are available as indexable inserts . They are thicker than carbide inserts and are usually heavily chamfered to reduce the risk of breakage and to enable (desired) chip breaking even at higher machining speeds.
That is why the main field of application for these cutting materials is the machining of hardened steel and cast iron without cooling. All ceramics can be coated with a hard material layer (e.g. titanium carbide , tantalum carbide or tungsten carbide ), which further increases wear resistance. The area of application in machining production is fine and finishing machining. Vibration, impact and temperature change sensitivity must be taken into account.
Due to their white color, oxide ceramics are colloquially called pure ceramics in production.