Abstract
	Alloys based on inter-metallic phase ?-TiAl are much sought-after and perspective material for applications in internal combustion engines, turbines, etc.  Apart from very favourable properties, such as low density and good resistance to corrosion, some other important properties, such as strength, ductility, fracture toughness, can gain various values in dependence on purity and microstructure. It is possible to influence microstructure of products (castings) by suitable chemical composition or by processes at production. Microstructure is being formed in products (castings) during their crystallisation and it remains in this form during the full service life of the product. It is therefore important to know processes of crystallisation in order to be able to set the parameters at production in a manner that best contributes to enhancement of the product properties. This article is focused on inter-metallic alloy Ti-46Al-5Nb-1W (at. %), which was subjected to directional crystallisation by five constant rate within the range from 20 to 425 mm/h. The samples of this alloy were inserted into ceramic corundum tubes Al2O3. The obtained microstructure of the samples was investigated metallographically. It was ascertained that lamellar microstructure is formed by alternating lamellas of the phases ?2 and ?. The obtained lamellar microstructure was documented. Cell and dendritic microstructure was investigated on cross sections. Rate of crystallisation has a significant impact on microstructure – both lamellar and dendritic. With the growing rate there occurs shortening of inter-lamellar distance and distances of primary dendritic arms. Influence of parameters of directional crystallisation on microstructure of this alloy was evaluated as well.