Descaling of heat-resistant nickel alloy VZh176

Issue 24(3) 2019
Pages 22-31

S. S. Vinogradov, FSUE «All-Russia scientific research institute of aviation material» State Research Center of the Russian Federation («VIAM» FSUE RF SRC), Moscow, Russian Federation
Yu.Yu. Nikitin, FSUE «All-Russia scientific research institute of aviation material» State Research Center of the Russian Federation («VIAM» FSUE RF SRC), Moscow, Russian Federation
M, V. Akhmedzyanov, FSUE «All-Russia scientific research institute of aviation material» State Research Center of the Russian Federation («VIAM» FSUE RF SRC), Moscow, Russian Federation


Keywords: nickel alloy, scale removal, etching, electrochemical polishing, sandblasting, surface roughness

http://www.doi. org/10.31615/j.corros.prot.2019.93.3-3

 

By production of such details as the combustion tube body, the leaf of heat resisting VZh176 nickel alloy is used which after hot and cold rolling and thermal processing becomes covered by tight coat of difficult deleted scale. Such scale consisting mainly of oxides of basic components of alloy, not only disturbs the subsequent welding, but also significantly worsens properties of details. For removal of scale, both widely known solutions of etching of nickel alloys and new, on the basis of mix of nitric and phosphoric acids have been tested. Besides, electrochemical polishing and sandblasting have been used. The use of solutions based on a mixture of different acids (sulfur and chromium; sulfuric, hydrochloric and nitric; sulfuric, hydrofluoric and nitric; sulfuric and hydrochloric; nitric and hydrofluoric acids) did not give a positive results. The removal of scale in the solution of phosphoric acid and a mixture of phosphoric acid with hydrochloric and hydrofluoric acids was somewhat better. However, the surface quality after treatment of Nickel alloy in these solutions is also unsatisfactory. Chemical etching of Nickel alloy VZh176 with scale in a mixture of dilute HNO3 and H3PO4 at a temperature of 25 °C for 7 minutes or anodic treatment in the electrolyte of electrochemical polishing of stainless steel at a current density of 10 A/dm2 at a temperature of 25 °C for 10 minutes provide complete removal of scale and obtaining a bright surface of the alloy, however, lead to the formation of grain boundary surface etching. In a hot solution of a mix of nitric and phosphoric acids there is a complete removal of scale without visible damage to the surface of the Nickel alloy VZh176. The alloy surface becomes bright and shiny without damage (etching) surface Nickel-alloy VZh176. Sandblasting also cleans the surface of the heat-resistant Nickel alloy VZh176 from scale but significantly increases its roughness.