OBRABOTKAMETALLOV TECHNOLOGY Vol. 26 No. 4 2024 confi rmed by optical microscopy (Fig. 10, b, c) and XRD analysis (Fig. 11, c, d). The melt zone contains relatively large cracks throughout its length (marked as 1 in Fig. 10, e). Near the surface within the fusion zone, the presence of protrusions (marked as 2 in Fig. 10, f) and discontinuities (marked as 3 in Fig. 10, g) can be identifi ed. Due to oxidation in the subsurface layers, there is a noticeable increase in microhardness (Fig. 11, a). The most signifi cant increase in microhardness, reaching up to 8 GPa, occurs in the lower part of the cut zone, with the depth of this zone exceeding 1 mm in this case. In contrast, in the upper part of the cut, both the thermal impact on the material and the degree of edge oxidation are signifi cantly lower, with the depth of these aff ected zones not exceeding 0.3 mm. The oxidation of the titanium alloy in the surface layers is more pronounced compared to that of aluminum alloys, which is attributed to the higher reactivity of titanium and its melting temperature. In the lower part of the cut zone, at the set power of the plasma-generating arc, the complete penetration of the plasma jet through the plate was hindered, resulting in prolonged thermal exposure to the material. It can be determined that in this case, the cut was formed at the limit of the process capability, on the verge of full penetration of the plate and the occurrence of a defect in the form of incomplete cutting. This resulted in more signifi cant oxidation of the edge in the lower part and a deterioration in the overall cut quality. For machining titanium alloy workpieces, this is generally unacceptable, and post-cutting shot blasting is required to remove the scale after plasma cutting. The use of nitrogen as a shielding and plasmagenerating gas is also possible, but for plates of this thickness, slow cooling of the edge is characteristic, HAZ FZ BM BM BM FZ HAZ BM FZ FZ FZ a b c d e f g Fig. 10. Macrostructure (a), images of the microstructure obtained by optical (b–г) and scanning electron (e–g) microscopy of a specimen of titanium alloy Ti-5 Al-5 Mo-5 V
RkJQdWJsaXNoZXIy MTk0ODM1