The structure and properties of titanium casting alloys VT5L, VT2OL, and VT21L with various impurity contents are studied. A classification is developed for the cast structure of these alloys, lhe change in the cast structure under constant cooling is shown to depend on the impurities as well as on the concentration of alloying elements. An interrelation is established among the structure of alloys, the fracture topography, and the mechanical properties.The structure of shaped castings of o~ and pseudo-titanium alloys are characterized by large /3 phase grains with a lamellar structure (/3 transformations of the structure). Second-phase inclusions between the c~ lamellae have different structures and compositions, depending on the content of alloying elements and impurities in the alloys as well as on the cooling conditions [1, 2].We studied specimens of the c~ alloy VT5L (4.1-6.2% A1) and the pseudo-a alloys VT20L (5.5-6.8% AI, 0.5-2.0% Mo, 0.8-1.8% V, 1,5-2.5% Zr) and VT21L (5.8-7.2% AI, 0.4-1.0% Mo, 0.8-1.5% V, 4-6% Zr, 0.2-0.5% Cr) in the cast state.Melts of these alloys were ~hosen so as to ensure that the effect of various constants impurities could be estimated when dley varied between fairly wide limits (0.032-0.15% O, 0.02-0.13% C, 0.002-0.007% H, 0.011-0.05% N, 0.03-0.28% Fe, 0.01-0.15% Si).The alloys were melted in arc skull furnaces and poured into graphite molds made from consumable patterns, The specimen blanks measuring 15 x 15 x 80 mm were placed on feeders. The cooling conditions of all of the specimens were identical: the cooling rate (-7°C/sec) was in the range characteristic of medium-sized titanium castings, thus ensuring the formation of typical structures of cast titanium alloys.The microstructure of the alloys was studied on MMR-2R and NEOFOT-2 microscopes and a VS-300 scanning electron microscope. The latter was also used for microfractographic analysis. The distribution of the components and the impurities in the structural constituents of the alloys was determined by x-ray spectral microanalysis on a CAMEBAX MICROBEAM instrument.The present scales of structures of titanium alloys have been developed primarily for deformed semifinished products [3] and do not reflect the salient features of the morphology of the cast structure. On the basis of an analysis of the microstructure of cast structures of the alloys VT5L, and VT20L, and VT21L with different contents of components and impurities (within the technical specifications) we have distinguished the parameters underlying the classification of cast structures:-the shape of the boundaries of the c~ colonies (presence or absence of serrated boundaries); -the width of the e~ lamellae; K. t~. Tsiolkovskii Aviation Technology Institute, Moscow. Rybinski Aviation Technical Institute.
