Particles of a layer-forming agent containing at least one element for forming a surface layer of e.g. a carbide on the material to be treated are disposed in a furnace below and/or at the side of the material to be treated. A fluidizing gas is introduced into the furnace below the layer-forming agent for fluidizing a powder of alumina or other refractory material to form a fluidized bed above the layer-forming agent, while the agent is not fluidized. The furnace is heated and a solid halide is supplied into the furnace below the layer-forming agent. The halide is sublimable to produce a gas which activates the element, so that it may combine with a particular element which the material to be treated contains, whereby the surface layer is formed thereon. An apparatus for forming such a surface layer is also provided.