Influence of Substructure on Tribological Properties of Titanium Alloy

The influence of the microstructure features of the Ti–6Al–4V alloy obtained by selective electron-beam melting and subsequent hot isostatic pressing on the tribological properties (hardness, friction coefficient, abrasive wear resistance) is experimentally studied. It is shown that the Ti–6Al–4V alloy obtained by electron-beam additive manufacturing is in a quenched state with the phase composition: ~97% α′-phase and ~3% β-phase. The grains have a columnar morphology. The microstructure consists of colonies of α-plates with a thickness of ~2 μm and interlayers of β-phase with a thickness of ~0.2 μm. During hot isostatic pressing, complete recrystallization of the alloy occurs and instead of columnar grains a structure close to equiaxed is formed with a grain size in the central part of the template of ~0.9 mm. The alloy microstructure becomes coarser, and the size of the α- and β-phase plates increases approximately twofold. At the same time, the alloy retains the viscous nature of the fracture. The density of the samples is the same. The values of microhardness HV and macrohardness HIT of the alloy obtained directly by selective electron-beam melting and with subsequent hot isostatic pressing under the same load are practically the same. Hot isostatic pressing does not affect the friction coefficient or the adhesive properties of the sample surface. The wear characteristics of the Ti–6Al–4V alloys obtained using both technologies are different. On average, hot isostatic pressing increases abrasive wear resistance by 15–17%. All the studied samples have a developed substructure in the form of cells with an average size of ~0.4 µm. Playing the role of grains the substructure ensures similar properties of the alloy after various types of processing.