The dissertation work is devoted to the solution of an actual problem, namely the development and research of technological parameters for the manufacturing of layered Ti(Ti-TiB)/Al composite materials with increased physical and mechanical characteristics by the liquid-phase method.
The technological bases of layered Ti/Al composite materials liquid-phase manufacturing are presented. Using the KF-AlF3 eutectic alloy flux ensures uniform impregnation of the aluminum melt between the titanium based plates. It was established that transition layer at the interface between solid titanium grade VT1-0 and liquid aluminum is formed. Thickness of transition layer remains stable at melt temperatures from 700 to 800 °C, the width of the gap between the titanium plates from 0,5 to 1,5 mm, and holding time 900 s. The phase composition of the transition layer corresponds to solid solutions of titanium in aluminum and aluminum in titanium. It was determined that the minimum holding time is sufficient for the interaction of titanium and aluminum. 300 seconds holding in the melt after infiltration ensures formation of a uniform transition layer. An increase of the width of the gap between the titanium plates from 0,5 to 1,5 mm leads to rising of melt lifting speed between them from 1,6±0,12 to 2,9±0,20 mm/s.
The thickness of the formed transition layer remains stable for all investigated values of the width of the gap between the titanium-based plates in VT1-0/Al, VT6/Al, and Ti-TiB/Al systems, and on average, is 2,8, 3,8-4,2 and 6,3-6,5 μm, respectively. The layer thickening as a result of changing the original plates is due to their chemical composition and structure. Mechanisms of interphase interaction between solid titanium or its alloy and liquid aluminum are presented for the studied systems. According to the presented in the dissertation technological parameters, not only three-layer but also five- and seven-layer materials of the VT1-0/Al and VT6/Al systems were manufactured. An increasing in the number of layers in the material does not lead to a change in the microstructure of the interaction zone.
As a result of the three-point bending test, it was found that the three-layer composite materials of the VT1-0/Al system don’t destroy. When the bending angle of the samples in the range of 130-120 ° is reached, cracks with a maximum size of up to 20 μm are formed at the interface. It doesn’t lead to delamination and separation of the titanium plates from the aluminum layer.
During tensile tests, the three- and five-layer materials of the VT1-0/Al system demonstrate plastic behavior. Maximum strength values were achieved with a minimum width of the gap of 0,5 mm and reached 305±16 MPa at a total strain of 32,1±3,0 %. Three-layer composites of the VT6/Al system demonstrate similar behavior during tests. The maximum tensile strength is 602±15 MPa with a total strain of 15,3±2,4%. Unlike the previous ones, materials of the Ti-TiB/Al system demonstrate brittle behavior during destruction. The tensile strength of the three-layer material with the width of the gap between plates of 1,5 mm, is 479±18 MPa on average, and the deformation is 14,96±1,7 %.
It was experimentally established that the value of the tensile strength of layered composite materials satisfactorily agrees with the values calculated by the rule of mixtures, taking into account the volume fraction, number, physical and mechanical properties of titanium and aluminum layers. It makes it possible to predict the mechanical properties of layered Ti/Al composites.
As a result of rolling in an air atmosphere without preheating, the liquid-phase formed three-layer materials of the VT1-0/Al system retain the integrity of the interface. Materials with a reduction ratio of 0,27-0,45 were obtained by plastic deformation. The transition layer, formed as a result of the interaction of the original metals, fragments and passes into the aluminum layer. The strength of the rolled composites increases to 401-491 MPa compared to the original ones. Anisotropy of tensile strength in the studied materials is practically not occur and doesn't depend on the direction of tension of the studied samples relative to the direction of rolling.
As a result of three-layer composite materials of the Ti-TiB/Al system vacuum rolling with preheating, a maximum reduction ratio of 0.36 was achieved. Increasing of the composite rolling temperature leads to a thickening of the transition layer, which formed at the interface. The strength of the material with a reduction ratio of 0,2 is on average 725±20 MPa, and the plastic deformation is 0,98±0,12%. It indicates an increase in strength and a decrease in plasticity compared to the original material.
Ashby graphs showed that in terms of specific mechanical characteristics, the layered Ti/Al composites manufactured by liquid-phase method exceed the known titanium and aluminum alloys.
