Electropolishing and electrolytic etching of Ni-based HIP consolidated aerospace forms: a comparison between deep eutectic solvents and aqueous electrolytes

A J Goddard,R C Harris,S Saleem,M Azam,C Hood,D Clark,J Satchwell,K S Ryder

doi:10.1080/00202967.2016.1270616

A J Goddard, R C Harris + Show 6 more

Open Access

https://doi.org/10.1080/00202967.2016.1270616

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Abstract

It is reported in this study that the deep eutectic solvent (DES), (Ethylene glycol)2(Choline chloride), (2Eg:ChCl) is an effective medium in the electrolytic removal of the Fe-rich layer from Ni-based hot isostatic press (HIP) consolidation and that it is capable of sustaining etching at higher rates and at higher current efficiencies than a comparable aqueous electrolyte formulated from methane sulphonic acid/glycolic acid (MSA/GA). At high etch rates, the surface finish is not as good using 2Eg:ChCl, but high etch rates, current efficiency and excellent surface finish can be obtained from a 90%/10% hybrid mixture of 2Eg:ChCl MSA/GA electrolytes. This study has set out to compare the electropolishing and bulk electrolytic etching of HIP-formed bodies fabricated from RR1000 Ni-based superalloys in aqueous methane sulphonic acid/glycolic acid (MSA/GA) electrolyte and in DES-type ionic liquids. It is shown that the HIP alloy can be effectively removed under mild conditions using DES electrolytes that are of low toxicity, environmentally sustainable, relatively low cost and without the use of strong acids or chemical etchants.

Highlights

Nickel based superalloys are ubiquitous in use by the modern aerospace industry for applications in many parts of civilian and military aircraft engines
We have described a new methodology for the removal of the iron rich diffusion layer in Hot Isostatic Press (HIP) consolidated forms fabricated using powder metallurgy methods with Ni-based superalloy RR1000 using 2Eg:ChCl, a novel choline chloride based deep eutectic solvent
We have set out to compare the electropolishing and bulk electrolytic etching of HIP consolidated test pieces fabricated from RR1000 Ni-based superalloys in aqueous methane sulphonic acid / glycolic acid (MSA/glycolic acids (GA)) electrolyte and in Deep Eutectic Solvent (DES) type ionic liquids

Summary

Introduction

Nickel based superalloys are ubiquitous in use by the modern aerospace industry for applications in many parts of civilian and military aircraft engines. To determine if 2Eg:ChCl is effective in the polishing of RR1000 HIP consolidated samples relative to established MSA/GA electrolytes, and to quantify relative etch rates and current efficiencies of the two processes.

Results

Conclusion