Formation of a unidirectional gradient structure in titanium alloy using reversible hydrogen alloying

Abstract

The paper discusses the use of titanium alloys, for example, the VT6 alloy, for local armoring, which, with their minimum specific surface area, should provide high absorption of impact energy and a slow rate of crack propagation. It is shown that the achievement of such contradictory requirements is possible due to the creation of a directional gradient structure in the semi-finished product, which varies linearly from one side of the surface to the opposite. It is shown that the creation of such structures is possible due to the combined use of thermal and chemical-thermal treatments. The regularities of the formation of a unidirectional gradient structure in plates made of titanium alloy VT6 by means of thermal hydrogen treatment are investigated. It has been established that oxide and nitride coatings formed at isother-mal holdings for 4 hours and 30 minutes, respectively, work effectively as a barrier to hydrogen penetration. It has been found that the barrier oxide and nitride coatings most effectively perform the “protective” function when hydrogen is introduced up to 0.4%. It is shown that by varying the concentration of the introduced hydrogen, it is possible to change the depth of its diffusion penetration and, accordingly, the structure in the near-surface layers. It is shown that the finely dispersed structure formed on the surface of semi-finished products gives it increased strength characteristics, and the coarse-lamellar structure in the center of the samples provides good toughness and slows down the rate of crack propagation. It has been found that the barrier properties of the oxide coating during the thermal hydrogen treatment of large-sized items are slightly inferior to the same properties of the nitride coating. It is shown that the creation of a unidirectional gradient structure in plates made of VT6 alloy with a thickness of 12 mm provides them with good dynamic resistance when fired with 5.45 mm high penetration ammunition and 7.62 mm with a steel core bullet.