powder metallurgy

Powder metallurgy makes a metal part without ever melting it, by pressing fine metal powder into shape and then heating to bond the particles, a bit like pressing flour and butter into a cookie and baking it firm rather than pouring a liquid batter. You fill a die with powder, squeeze it hard into a fragile pressed shape (the green part), then heat it in a furnace below the melting point, where atoms diffuse across the touching particle surfaces and weld them together. That heating step is called sintering.

During sintering the tiny contact points between particles grow into solid necks, the pores between particles shrink, and the loose powder becomes a coherent solid, all through solid-state diffusion rather than melting. The result is a near-net-shape part that needs little or no machining, made with very little wasted material. It shines for making many identical small parts like gears and bushings, for porous parts (self-lubricating bearings that soak up oil in their pores), for hard cemented carbide cutting tools, and for refractory metals like tungsten whose melting points are too high to cast.

The honest limitation is leftover porosity. Pressed-and-sintered parts almost always keep some fraction of pores, and those voids lower strength, ductility, and especially fatigue resistance, because a pore is a built-in crack starter. Fuller density can be reached with extra steps (hot pressing, or hot isostatic pressing that squeezes from all sides at temperature), but at extra cost. So powder metallurgy trades some mechanical soundness for shape precision, low waste, and access to materials you simply cannot cast.