Application of plasma surfacing for additive formation of titanium alloy billets

Abstract

This paper presents the findings of an investigation on the main formation regularities of structure and properties of VT20 (ВТ20) superalloy of Ti -Al -V -Mo -Zr system in hybrid technology of additive manufacturing with the use of plasma surfacing with layer-by-layer strain hardening. When studying the effect of forging on the structure and properties of surfacing material, three processing schemes were implemented: surfacing with forging of a next to last layer; surfacing with forging of the last layer; surfacing with forging of each layer. Investigated is the morphology of the built-up layers' structure, which is associated with various cooling rates at the stages of crystallization and transformations in the solid state: at high cooling rate, a basket weave structure is forming, and a martensite-like lamellar structure arises on slow cooling. Different dispersities of the plates of D-colonies were fixed -from 200 to 500 μm, the size of individual needles varies from fractions of a micron to 100 μm. It is established that the layer-by-layer deformation impact, which contributes to the titanium alloy structure grinding and a rise in dispersion of the D-phase plates, is accompanied by an increase in microhardness to the level of 6000 HV. The formation of a finer structure during surfacing with a layer-by-layer deformation effect is obviously bound up with the martensate phase lightened growth on a pre-crushed metal substrate with an increased dislocation density. It is established that the strength properties of the obtained VT20 alloy surfacings exceed the strength level of materials made by traditional forming technologies, and there is no decrease in the plasticity characteristics.