A cermet is a composite of hard ceramic particles, usually a carbide, held together by a tough metal binder, and it cuts steel at speeds and temperatures that ruin even high-speed steel. The ceramic supplies hardness and heat resistance and the metal supplies toughness, so more binder gives a tougher, softer tool and less binder a harder, more brittle one. Making them needs tungsten, fine powders and a controlled-atmosphere furnace, so the realistic route for a settlement is to salvage carbide tips and regrind them with silicon carbide.
Part of Composite Materials
Cermets are ceramic-metal composites in which hard carbide or nitride grains are bonded by a metal such as cobalt or nickel, used mainly for cutting-tool tips and wear parts.
Hardness And Toughness Come From Two Phases
Ceramics are hard but brittle and metals are tough but soft (see Advanced Ceramics). A cermet puts them side by side: hard grains do the cutting and a thin metal film between them stops cracks from running from grain to grain. The standard hard-metal tool is tungsten carbide grains in a cobalt binder, a material often called cemented carbide. It is sometimes kept separate from titanium-carbide cermets, but the principle is identical. The balance is set by the binder fraction, as in the Advanced Materials article’s reference to ceramic-metal composites for cutting tools.
Why It Beats High-Speed Steel
The Advanced Materials article describes high-speed steel as adding tungsten, chromium and vanadium and keeping its cutting ability at red heat, around 600 °C. Tool Steel covers the family. Hard-metal tips keep their hardness at far higher temperatures, which allows much faster cutting and the machining of hard steels. The cost is brittleness: a cermet tip chips under shock and interrupted cuts.
What A Settlement Can And Cannot Do
- Cannot (yet): make cemented carbide. It needs tungsten carbide powder, fine cobalt powder, and sintering above the binder’s melting point in a protective atmosphere or vacuum. This article gives no process figures because none are sourced.
- Can: recover carbide-tipped saw blades, drill bits, masonry bits and lathe inserts from salvage, and braze them onto holders.
- Can: regrind them. Ordinary aluminium oxide wheels wear away on carbide, so use silicon carbide, the hard abrasive described in Abrasives. Light, wet passes avoid cracking.
- Can: use the same idea in cruder form. A grinding wheel is hard grains in a vitrified bond, and clay-graphite crucibles are a ceramic composite, as in Crucibles.
Using A Salvaged Tip
- Mount it with a rigid, well-supported seat, because a carbide tip hates bending.
- Use positive support under the cutting edge and keep the tool short.
- Take steady cuts with no chatter or interrupted cutting.
- Avoid thermal shock: do not flood a red-hot tip with cold coolant. Start the coolant before the cut or not at all.
- Inspect the edge often for tiny chips.
Common Mistakes
- Dropping or hammering the tool — it is brittle.
- Grinding on an ordinary wheel — it wears the wheel and overheats the tip.
- Using it for low-speed hand cutting — a carbide tip’s advantage appears at speed.
Carbide dust and chips
Grinding and sawing carbide produces fine cobalt-bearing dust that is harmful to breathe. Grind wet and wear a mask. Hard chips fly from a chipped edge, so wear eye protection. Brazing tips needs fluxes whose fumes are harmful, so ventilate.
What’s Next
- Learn next: Polymer Engineering — a very different class of material
- Combine with: Tool Steel — the steel alternative