Surface modification of titanium VT6 alloy obtained by additive technologies using reactive electrospark treatment

Abstract

Using additive technologies, in particular selective electro-beam melting (EBM), it is possible to obtain products of a high degree of complexity, reducing production costs while minimizing the required amount of material. However, products obtained by the EBM method are characterized by surface defects and high surface roughness, which limits their use. Electric spark treatment (EST) makes it possible to eliminate defects and strengthen the surface layers of EBM products during the reactive phase formation, the conditions of which are studied in the work. The structure and phase composition of electric spark layers formed on VT6 samples under different treatment modes with a low-melting near-eutectic Al-9Si electrode are studied. Due to the reactive phase formation during electric spark treatment, a modified layer with a thickness of more than 10 µm containing nanoscale grains of TixAly intermetallics was formed. The surface roughness after EST is several times lower, and the wear resistance is higher by an order of magnitude compared to the original EBM sample made of VT6 alloy. It is shown that EST for 310 seconds using a hypoeutectic Al-9Si electrode, applied energy 47,6 kJ and a pulse frequency of 3200 Hz, reduces the surface roughness by ~ 9 times due to plasma smoothing of protrusions and filling in cavities during the spreading melt drops on surface.

Study of the Influence of Coating Roughness on the Properties and Wear Resistance of Electrospark Deposited Ti6Al4V Titanium Alloy

“…The results of our present and previous studies [12,15,16,[22][23][24]26] and the literature data [10,13,25,27,30,32] show that the following approaches are possible to obtain on titanium surfaces uniform ESD coatings with reduced roughness higher thickness:…”

“…-The amount of solid phases carried by the electrode, the newly formed compounds and the degree of dispersity and amorphousness also increase [16,[22][23][24][25][26]. The coatings of KW and NW electrodes, whose thickness is the highest, and the lowest values -of the coatings of TN, KNT16 and AlSi12 electrodes, show the highest values of the roughness parameters.…”

“…-Rmax and Rt -most researchers affirm that these are the most significant parameters affecting friction [17,24,25]. Rt is the maximum roughness height (Rt=Rp + Rv, defined by the maximum height Rp of the protrusions and depth Rv of the troughs), and Rmax, is the maximum roughness depth;…”

“…-To reduce the energy of single pulses (current, capacitance and pulse duration) [10,12,13,16,25,27,[33][34][35]. This will result in coatings with fewer defects and lower roughness, but also lower thickness and the formation of a smaller amount of wear resistant phases and compounds in the coating composition.…”

“…This will result in coatings with fewer defects and lower roughness, but also lower thickness and the formation of a smaller amount of wear resistant phases and compounds in the coating composition. At the same time, however, the use of lower energy creates conditions for the Е= 0.04 J Е=0.07 J E=0.04 J formation of a higher amount of amorphous and nanostructured phases in the composition of coatings, which, according to many authors [12,13,25,[33][34][35], favourably affects their wear and corrosion resistance;…”