Study of the mechanical properties and fracture of Ti-6Al-4V metal matrix composites fabricated under low temperature superplasticity conditions
Experimental results are reported for a three-layer metal matrix composite produced by pressure welding at different temperatures. It is shown that the composite can be well reinforced by a structural layer of a nanocrystalline Ti-6Al-4V titanium alloy. According to metallographic analysis, in the composite fabricated at a temperature of 900°C the reinforcing layer becomes microcrystalline. With decreasing temperature to 700°C, the grain size of the reinforcing layer does not change, although the α-phase grain size slightly increases compared to the initial one. The geometric changes of micropores, the growth dynamics and spatial arrangement of grains in the zone of the solid state weld are described. Mechanical tensile tests confirmed that the strength of the composite produced at 700°C can exceed the strength of the composite fabricated at 900°C. The fracture behavior of the composite in the weld zone was studied in tensile testing at room temperature. Three stages of fracture were distinguished. The test results showed that the mechanical behavior of the composite depends on the welding temperature. Fracture begins under the action of the principal stresses and propagates in the direction normal to them. The formation of a less strong but more ductile reinforcing layer leads to a sharp increase in plastic strains in the composite, due to which the crack growth is impeded and the crack propagation path changes.