Insights on the Influence of Surface Chemistry and Rim Zone Microstructure of 42CrMo4 on the Efficiency of ECM

Abstract

The electrochemical machining (ECM) of 42CrMo4 steel in sodium nitrate solution is mechanistically characterized by transpassive material dissolution and the formation of a Fe3−xO4 mixed oxide at the surface. It is assumed that the efficiency of material removal during ECM depends on the structure and composition of this oxide layer as well as on the microstructure of the material. Therefore, 42CrMo4 in different microstructures (ferritic–pearlitic and martensitic) was subjected to two ECM processes with current densities of about 20 A/cm2 and 34 A/cm2, respectively. The composition of the process electrolyte was analyzed via mass spectrometry with inductively coupled plasma in order to obtain information on the efficiency of material removal and the reaction mechanisms. This was followed by an X-ray photoelectron spectroscopy analysis to detect the chemical composition and the binding states of chemical elements in the oxide formed during ECM. In summary, it has been demonstrated that the efficiency of material removal in both ECM processes is about 5–10% higher for martensitic 42CrMo4 than for ferritic–pearlitic 42CrMo4. This is on one hand attributed to the presence of the cementite phase at ferritic–pearlitic 42CrMo4, which promotes oxygen evolution and therefore has a negative effect on the material removal efficiency. On the other hand, it is assumed that an increasing proportion of Fe2O3 in the mixed oxide leads to an increase in the process efficiency.

Review: Modeling and Simulation of Membrane Electrode Material Structure for Proton Exchange Membrane Fuel Cells

“…(2) To obtain a low-cost and long-life PEMFC, it is necessary to find a suitable and cheaper preparation method for the MEA microstructure. In addition to traditional preparation methods, non-traditional machining methods, such as laser machining [122,123], electrical discharge machining [124,125] and electrochemical machining [126,127], also made good progress in the preparation of microstructures. This means that a future 3D digital simulation MEA model must also consider the influence of the preparation process on the microstructure, so as to establish a more accurate model.…”

Change of Oxidation Mechanisms by Laser Chemical Machined Rim Zone Modifications of 42CrMo4 Steel

“…All peaks were charge corrected by assigning the C-C component in the C1s peak to 284.8 eV. As already presented in previous publications by the authors [ 29 , 30 ], Shirley-type backgrounds and Gauss-Lorentz (30/70)-type line shapes were used for peak fitting for all components except metallic iron (asymmetric line shapes).…”

Low Temperature Interface Modification: Electrochemical Dissolution Mechanism of Typical Iron and Nickel Base Alloys

“…8G,H). When the current density reached 30 A/ cm 2 , the oxygen-rich region was broken and the oxy- gen content increased, attributed to the stronger electrolytic effect and anodic oxygen evolution [35][36][37]. Unlike surface of G1 at 1 A/cm 2 , there was no intergranular corrosion on the surface of G2 at low current density.…”