OBRABOTKAMETALLOV MATERIAL SCIENCE Vol. 25 No. 4 2023 1 to 2.0 mm in the beam scanning plane, as shown in fig. 7, b. The nature of the change in microhardness values in the presented planes also indicates structural inhomogeneities in the forming grains (fig. 7, c). The average microhardness values calculated for XZ and XY planes differ from each other, viz. 334±14 HV0.1 and 304±16 HV0.1, respectively. Unlike the EDX analysis of the microhardness distribution, the EDX analysis of the elemental distribution in weight percentage (fig. 7, d) at different points shows no significant change, which indicates the leading role of inhomogeneity of the structure, rather than the phase. Ultrasonic gauging of elastic modulus and Poisson’s ratio The elastic modulus and Poisson’s ratio for specimens prepared from different alloys are presented in table 2. Ta b l e 2 Elastic properties determined by the 38DL PLUS Alloys → Properties↓ VT1-0* VT6* Ti-6Al-4V* 3D printed VT6sv Elastic modulus E, GPa 109±1 120±1 130±1 131±1 Poisson’s ratio, ν 0.33±0.03 0.32±0.03 0.31±0.03 0.27±0.03 * As-rolled alloys As reported in early research [40] on the values of elastic moduli of commercially pure Ti alloy and Al- and V-doped Ti alloys, this parameter for cast alloys was 92 and 108 GPa at 160 and 294 HV, respectively. At the same time, the sensitivity of the elastic modulus to the phase composition and crystal structure was observed. The structure formation and properties of such alloys were investigated in [34, 41]. The structure consisted of lamellas and a + b phase colonies of different length and width. β-phase lamellas were smaller and located between a-phase lamellas, as presented in fig. 7а, b. It is very important that the presence of the β-phase provided its hardness growth even in the presence of the martensitic α’-phase. That indicated the predominant role of the solid solution hardening. The elastic modulus decreased with increasing content of the β-phase [42]. It was important to compare the data of titanium master alloys and commercially pure titanium, since the latter possessed a homogeneous structure unlike binary master alloys [43]. According to reference data in recent research, the elastic modulus is 100 to 110 GPa for pure titanium and Ti-6Al-4V system alloys, either cast or rolled [43] and 120 to 125 GPa at 400 to 420 HV hardness of the master alloy, respectively [27]. At the same time, the elastic modulus measured by ultrasonic gauging is 120 GPa for pure titanium in the initial state [43]. As can be seen from table 2, the elastic modulus for VT1-0 and VT6 alloys is in good agreement with that obtained in [27, 43], whereas the elastic modulus for the Ti-6Al-4V alloy significantly differs due to, probably, significant difference in its structure and phase composition. Instrumental indentation [19, 22, 33, 36, 43] and nanoindentation [27] measurements of the elastic modulus for Ti alloys obtained by both conventional methods and additive manufacturing, are more common than ultrasonic gauging [19, 43]. Macro-indentation of elastic modulus and microhardness The macro-indentation depth is ~150 mm, indentation point diameter is 0.5 mm (fig. 3d), which does not violate the integrity of the sample material and does not change its physical properties. At the same time, the dimensions of the material involved in the measurements exceed those analyzed during nanoindentation by more than an order of magnitude and are commensurate with the grain sizes. The elastic modulus is detected using the load-unload curves obtained by the above-described procedure and presented in fig. 8. The indenter penetration in the material induces its stress-strain state.
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