Cermet (cutting material)

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Cermets ( ceramics and metals ) are hard metals that contain little or no tungsten carbide (WC). Instead, titanium carbide or titanium nitride and mixtures thereof, titanium carbonitride, are used as hard materials in cermets . Above all, nickel is used as the binding phase . Cermets are used as cutting materials for turning and milling. Because of their high brittleness and diffusion resistance and low toughness, they form the transition from hard metals to cutting ceramics. The raw materials titanium and nickel required for cermets are readily available worldwide, which is an important advantage over other hard metals.

The short name as a cutting material according to ISO 513 is HT ( H style metal, T itancarbid (nitride) -based). Cermets are also available with coatings.

Composition and structure

Cermets essentially consist of titanium carbide TiC, titanium nitride TiN and mixtures of these, titanium carbonitride. These materials give the cermets a sufficiently high hardness for machining, even at high temperatures. There is a binding phase between the hard material grains, which is responsible for the toughness. Above all, nickel is used as a binder. However, mixtures of nickel, molybdenum and cobalt are also used.

The structure consists of rounded, shell-like grains between which the binding phase lies, i.e. nickel or cobalt mixed crystals. The order of the shells is different: there are grains with titanium nitride in the core, followed by a shell made of (Ti, Ta, W) (C, N) with predominantly titanium and nitrogen and an outer shell made of (Ti, Ta, W, Mo ) (C, N) with predominantly titanium and carbon. Other grains contain the latter phase in the core followed by a single shell of (Ti, Ta, W, Mo) (C, N) with predominantly nitrogen compounds.

Physical and technological properties

Since the density of titanium is very low compared to tungsten carbide, cermets are very light. They have a lower thermal conductivity and greater thermal expansion than hard metals based on tungsten carbide. The fracture toughness is lower, but the chemical resistance, especially to iron, is higher. Tools made from cermets have high edge strength and wear out more slowly.

The following table shows the properties of the cermets HT-P05, HT-P10 (both fine machining), HT-P20 (medium machining), the tungsten carbide hard metal HW-P20 (medium machining) and the aluminum oxide cutting ceramics.

variety HT-P05 HT-P10 HT-P20 HW-P10 Alumina -
cutting ceramics
Composition [% by mass]
(TiC + TiN / Co + Ni)		 89.6 / 10.4 86.5 / 13.5 83.3 / 16.7 55% WC / 36% (TiC / TaC / NbC) / 9% Co 85-95% Al 2 O 3 + 5-15% ZrO 2
Density [g / cm −3 ] 6.1 7.0 7.0 10.6 4.0-4.2
Hardness [ HV 30 ] 1650 1600 1450 1560 ----------
Compressive strength [N / mm 2 ] 5000 4700 4600 4500 4500-5000
Flexural strength [N / mm 2 ] 2000 2300 2500 1700 600-800
Modulus of elasticity [10 3 N / mm 2 ] 460 450 440 520 380-410
Fracture toughness [Nm 1/2 / mm 2 ] 7.2 7.9 10.0 8.1 3.5-5.8
Thermal conductivity [W (mK) −1 ] 9.8 11.0 15.7 25th 15-25
Thermal expansion coefficient [10 −6 K −1 ] 9.5 9.4 9.1 7.2 7-8

Areas of application

Cermets were initially used for precision turning. Ever since the tougher grades have existed, it has also been used for turning with medium loads, for threading and for milling. Steel and cast materials are processed. They are particularly widespread in series production with small allowances. The cutting speeds when turning steel are 80 to 500 m / min with feeds of 0.03 mm and cutting depths of 0.05 to 3 mm.

Aluminum and copper cannot be machined with cermets, as built- up edges develop . Nickel alloys react with the binding metal and weld on the rake face.

See also

Individual evidence

  1. ^ Fritz Klocke, Wilfried König: Manufacturing process 1 - turning, drilling, milling , 8th edition, 2008, Springer, p. 125f.
  2. ↑ Denkena: Spanen , 3rd edition, pp. 177, 183
  3. ↑ Pauksch: Zerspantechnik , 12th edition, pp 60-62.