Nanoscale physics

Effects of hydrogen on functional properties nanocrystal titanic alloys.
Mats O.V., Zhurba V.I., Mats V.O., Morozov O.
NSC-Kharkiv Institute of Physics and Technology of the NAS of Ukraine.
1, Akademichna St., , Kharkiv-61108, Ukraine.
E-mail: morozov@kipt.kharkov.ua

VT-6 and VT-16 alloys have a small mass, which exceeds the strength of many stainless and heat-resistant steels at operating temperatures of atomic reactors (up to 700 K). High performance characteristics are explained by the formation of an ultra-microgranular structure (UMS whis grain size 2-3 μm) of a two-phase (α + β) state with many components. Grains have a block structure with an average block size of 0.15 microns. Hardening is achieved by dispersing the structure and phase hardening — by precipitating titanium at the boundaries of the metals as a result of heat treatment. The tensile strength (ϬC) under tension is 103 MPa for VT-6 and 1.2x103 MPa for BT-16 with a plasticity margin of ԑ = 10%.
One of the requirements for reactor materials is the minimum tendency to hydrogen embrittlement during operation in corrosive environments. The objectives of this research are the formation of a structure that provides an increase in the short-term and long-term strength of these alloys and creation of the surface layer providing decrease of accumulation of hydrogen in titanic alloys.
Cold rolling for the VT-6 alloy by 60% leads to the formation of a nanograined state with an average grain size of 70 nm and a high concentration of high-angle boundaries; this is shown. As a result, the tensile strength (ϬC)  increased to 1.35×103 MPa, and to 15% due to the dislocation slip in the boundary phase. A surface stability of 120–150 nm in thickness from Me – H compounds by ion implantation of deuterium at T = 650 K (average reactor operating temperature) with an absorption dose of ~ 1018 D/cm2 was formed. Microhardness increased by 20% is shown. The temperature spectra of deuterium desorption during the destruction of the surface layer showed a significant shift of evaporation temperatures and evaporation maxima to higher temperatures for nanostructured alloys as compared to UMS. For BT-6, the temperature of the start of thermal desorption shifted from 700 K to 950 K, and the temperature peak from 1050 K to 1470 K. The data obtained show the dominant influence of a high concentration of boundaries and level of compressive stresses on the processes of deuterium retention in the titanium lattice.
The conducted researches testify, about expediency of carrying out of the researches directed on maintenance of prolongation of term of operation of high-strength titanic alloys in atomic engineering.