Mass transfer and adhesion in electrospark alloying of AL9 alloy with AlN - Ti(Zr)B2 - Ti(Zr)Si2 ceramic electrodes

Abstract

621.762A study has been made on the adhesion of the new composite ceramic AlN − Ti(Zr)B 2 − Ti(Zr)Si 2 with steel 45 and alloy AL9 in relation to the mass-transfer kinetics in spark working. There is a three-stage mass-transfer mechanism. The materials in the electrode and the substrate affect the electrical erosion of the electrode.A feature of coating by spark alloying (SA) is the mass transfer of the erosion products from the anode to the cathode, which determines the thickness and continuity of the alloyed layer, and also the process throughput. Various factors influence the mass-transfer coefficient K t which is equal to the ratio of the cathode mass increment ∆c to the anode erosion ∆a for a specific processing time t (K t = ∆c/∆a). In SA, there is the most active physicochemical interaction between the electroerosion products from the electrode with the substrate material in the liquid formed at the surface. Together with electrode erosion, the mass transfer kinetics are affected by the wetting and adhesion of the components in the coating-substrate system. In SA, a secondary structure with an altered composition is formed at the working surface of the alloying electrode [1] because of compaction of the surface layer and reverse transfer of cathode material to the anode. Therefore, the electroerosion of the secondary structure as the true object of erosion should be dependent under otherwise equal conditions on the substrate material. No research has been done on the effects of wetting and the substrate material on the mass-transfer coefficient.We examined the adhesion between components in the coating-substrate system as affecting the mass-transfer kinetics in SA for AL9 alloy (by comparison with steel 45 and alloy VT6) with the use of composite ceramic electrode materials from a new generation (without metal binding agent) in the AlN − Ti(Zr)B 2 − Ti(Zr)Si 2 system, which provide effective protection from wear and corrosion [2,3].The spark alloying was provided with an Elitron-21 apparatus under the following conditions: short-circuit current 0.9 A, pulse repetition frequency 1200 Hz, and pulse energy 0.08 J. The adhesion was examined under vacuum at 1200°C by the sessile drop method followed by analysis of the composition and structure of the phases formed in the contact zone [4].We examined the mass-transfer kinetics by a gravimetric method [5] by the use of a VLA-200-M balance with an error of down to 0.0002 g, and we determined the specific erosion of the anode ∆a and the specific mass gain in the cathode ∆c for each minute of treatment of 1 cm 2 of surface with allowance for the density of the material. These values

Spark-deposited coatings on magnesium alloys

“…The kinetics of mass transfer of ceramics onto ML6 alloy (Fig. 4a) shows that cathode increment Δ c is positive during the entire time t of deposition, which confirms the idea [18] that spark coatings can be deposited onto fusible alloys without weight loss of the part. The Δ c rate slows down at t > 4 min/cm 2 due to the brittle fracture of the cathode surface under residual thermal tensile stresses.…”

“…The alloying materials of the electrode should contain ≥50 wt.% [17,18] of the component that is responsible for the formation of a shielding cloud of nonconducting particles, which is the case for the composites in question.…”

“…The latter method primarily involves electrospark deposition (ESD), which consumes little energy and is simple and environmentally friendly though such coatings rapidly evaporate under spark discharge when deposited onto fusible aluminum and magnesium alloys [16]. It was established in [17,18] that ESD of aluminum alloys could proceed without weight decrement of the part (cathode) by using special alloying electrodes to shield the cathode from spark pulses. In this case, a cloud of dielectric particles forms in the interelectrode space due to spark erosion of dielectric components of the electrode and due to high-temperature oxidation of conductive components in the spark discharge plasma.…”

Structure and phase composition of composite detonation coatings based on TiCrB2 and ZrB2

“…This is evidence of partial hightemperature oxidation of the powders when sprayed and is confirmed by an electron microprobe analysis of the two coatings (Figs. [6][7][8]. The concentration maxima of oxygen and titanium (Figs.…”

“…Our previous research into the wetting and interaction in the TiCrB 2 -(Fe-Cr) [5] and (AlN-ZrB 2 -ZrSi 2 )-(Fe-Cr) systems [7] revealed complete wetting in them: the wetting angles are close to zero. Bounding solid solutions form in the contact area, thus ensuring strong adhesion between the coating and steel substrate.…”