Schupp Alexander, Beyss Oliver, Rommes Bob, Klink Andreas, Zander Daniela
Chair of Corrosion and Corrosion Protection, Foundry Institute, RWTH Aachen University, Intzestr. 5, 52072 Aachen, Germany.
Laboratory for Machine Tools and Production Engineering (WZL), RWTH Aachen University, Campus-Boulevard 30, 52074 Aachen, Germany.
Materials (Basel). 2021 Apr 22;14(9):2132. doi: 10.3390/ma14092132.
The electrochemical machining (ECM) of 42CrMo4 steel in sodium nitrate solution is mechanistically characterized by transpassive material dissolution and the formation of a FeO 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/cm and 34 A/cm, 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 FeO in the mixed oxide leads to an increase in the process efficiency.
42CrMo4钢在硝酸钠溶液中的电化学加工（ECM）在机理上的特征是过钝化材料溶解以及在表面形成FeO混合氧化物。据推测，ECM过程中的材料去除效率取决于该氧化层的结构和组成以及材料的微观结构。因此，对不同微观结构（铁素体-珠光体和马氏体）的42CrMo4分别进行了两个ECM过程，电流密度分别约为20 A/cm²和34 A/cm²。通过电感耦合等离子体质谱法分析工艺电解液的成分，以获取有关材料去除效率和反应机理的信息。随后进行X射线光电子能谱分析，以检测ECM过程中形成的氧化物中化学元素的化学成分和结合状态。总之，已证明在两个ECM过程中，马氏体42CrMo4的材料去除效率比铁素体-珠光体42CrMo4高约5-10%。一方面，这归因于铁素体-珠光体42CrMo4中渗碳体相的存在，它促进析氧，因此对材料去除效率有负面影响。另一方面，据推测混合氧化物中FeO比例的增加会导致工艺效率提高。
