Electroposition Of Crack-free NiCr Alloys Against High Temperature Oxidation

At present,China’s aerospace,nuclear energy and military industries are developing rapidly.Advanced aeroengine and marine engine blades may need to be used under severe conditions such as high temperature,high humidity,high salinity and strong load.It is well known that Ni Cr alloys with the Cr contents more than 20 mass%are oxidation resistant at high temperatures below 1000 ^oC,because they can thermally grow a protective scale of Cr₂O₃.Unfortunately,up to now,there has been almost no progress on the development of the oxidation-resistant Ni Cr alloys through a simple electrodeposition method.There is an insurmountable technical problem that the high Cr containing Ni Cr alloy during electrodeposition intrinsically generates cracks,which severely decreases the alloy resistance to high temperature oxidation.In this thesis,a method to breakthrough the existing bottleneck of the technology to electroplate the cracking-free Ni Cr alloys has been successfully explored,through modification of the chemical composition of an environment-friendly bath using Cr³⁺instead of Cr⁶⁺in combination with optimization of the processing parameters,based on the knowledge of how to adjust and control the co-electrodeposition potentials of alloying elements.Using direct current electroplating method and orthogonal test to study the process parameters in the citrate,potassium salt and urea coordination system,the current density,temperature,p H and other suitable parameters are obtained.As a result,the crack-free Ni Cr alloys containing 15 mass%and 20 mass%Cr have been prepared using the new bath for the alloy codeposition.Oxidation at 900 ^oC shows that the Ni-15Cr alloy can form a protective scale of Cr₂O₃ scale,while a better oxidation-resistant and adherent Al₂O₃ scale was formed on the Ni-20Cr alloy.The relative results have been interpreted and discussed.