Stasiuk O. The general laws of high-modulus refractory compounds influence on structure and properties of sintered titanium alloys.

The dissertation is dedicated to solution of important scientific and technical task for perfection of manufacturing technology of titanium metal matrix composites possessing high mechanical and exploitation characteristics. Development and optimization of technology is preformed on the base of establishing of general laws for structure and properties formation upon sintering of powder blends of titanium hydride and high-modulus armoring compounds. On the base of comparative analysis it was shown great efficiency for using of titanium hydride powder instead of titanium powder for synthesis of titanium metal matrix composites with TiC and TiB2 additions. It was shown the influence of armoring additions (TiC, TiB2, В and В4С) on peculiarities of structure formation of sintered metal matrix composites. Considerable dependence of sintered microstructure of metal matrix composites on type of armoring additions was demonstrated. The most useful is using of ТіС and ТіВ2 powders as armoring phase in titanium matrix. Dilatometric investigation results established that shrinkage upon sintering of compacted ТіН2 + ТіВ2 powder blends is considerably lower than for titanium hydride powder alone. Such result is due to high temperature reaction of TiB formation as well as formation of Kirkendall`s porosity. It was shown, the increase of titanium diboride content in starting blends leads to reduced shrinkage. Addition of 5 % ТіВ2 reduces linear shrinkage down to 4 % (while shrinkage is 10 % for titanium hydride powder without diboride additions); increase in ТіВ2 content to 10 % resulted in 2% linear shrinkage. Contrary, this phenomenon was not observed for synthesis of Ті-ТіС metal matrix composites, since titanium carbide is thermodynamically stable compound and did not react with titanium matrix. Hot stamping resulted in noticeable growth of velocity of elastic waves propagation in various composites. When influence of porosity factor on elastic modulus is excluded, increase in armoring phase content and matrix alloying leads to increase in Young modulus for all composites. Elastic modulus of sintered Ti-TiВ and (Ті-6Al-4V)-ТіС composites goes up with increase of armoring powders in the blends from 5 to 10 %. Contrary, elastic modulus for sintered (Ті-6Al-4V)+TiВ composites drops while TiВ2 powder content in starting blends increased from 5 to 10 % due to high porosity of sintered materials. All sintered materials and hot stamped composites with TiC are characterized with Еxx/Еyy ratio close to 1, where Еxx is elastic modulus determined for pressing direction and Еyy - modulus for orthogonal direction. This value proves isotropy of material characteristics. This ratio is some lower for hot stamped composites with TiB due to reorientation of needle-like TiB particles and their arrangement in direction perpendicular to direction of stamping force. Complex investigation of sintering kinetics for compacts of different composition proved possibility to obtain titanium-based composites with layered (gradient) structures. Layers of different chemical compositions demonstrated uniform shrinkage within each layer and integrity of adjacent layers owing to optimization of powder size and compaction pressure. The possibility obtaining sintered layered composites without shape distortion was established owing to proper selection of powder sizes for each individual layer. It was established that deformation energy for 2-layered articles is an order of magnitude higher than for single layer materials. The influence of thickness of individual layers on mechanical characteristics of 2-3 layered structures was investigated. Optimization of thickness of ductile Ті-6AL-4V alloy layer and thickness of adjacent composite layer with high content of armoring phases resulted in regulation of strength/ductile characteristics for 2-layered structures. It was shown that location of ductile layer (without armoring particles) and hard layer (with high-modulus armoring particles) provides production of sintered composites with optimized combination of high strength (to 2000÷2200 МPа) and ductility (10÷20 %) at flexure tests. Tribological tests carried out for sintered composites demonstrated that increase in armoring phase content from 5 to 10 % leads to increase in wear resistance up to 20 %. Hot stamping of sintered samples of determined chemical composition resulted in considerable increase (up to 5 times) of wear resistance. Evaluation of antiballistic characteristics for sintered and sintered and hot stamped composites was performed. Hot stamping at proper selection of chemical composition and thickness of layers resulted in armor materials which met requirements for 6 class protection. Employment of layered titanium-based composites as armor materials for antiballistic protection provides 40-50 % weight saving in comparison to steel armor materials.