Evaluation of the corrosion performance of selective laser melted 17-4 precipitation hardening stainless steel in Ringer’s solution

Abstract

This study aims to evaluate the microstructure and corrosion resistance of selective laser-melted 17-4 precipitation hardening (PH) martensitic stainless steel and the corresponding wrought specimen in Ringer’s solution. The results showed that the selective laser melting (SLM) process improved the corrosion behavior of the alloy in the solution. Microscopic studies revealed that the wrought sample has fine lath martensite with elongated δ-ferrite stringers, while selective laser-melted (SLMed) alloy did not show any obvious phase. However, at higher magnifications, the SLMed specimen exhibited a fine cellular/columnar microstructure owing to the high cooling rate in the SLM technique and uniform distribution of elements. In addition, corrosion studies emphasized that the SLMed alloy possessed a higher charge transfer resistance than the wrought sample. Charge transfer resistances of the SLMed and the wrought sample were about 14.1 and 1.5 KΩ cm2, respectively. Moreover, corrosion current density of the SLMed alloy after 100 h of immersion was about ten times lower than the wrought one. The improved electrochemical behavior of SLMed 17-4 PH stainless steel can be attributed to the reduction of nonuniform distribution of alloying elements such as Nb during the solidification process as a consequence of high cooling rate of the SLMed alloy. Moreover, the development of galvanic cells and a low anode/cathode area ratio are other factors related to the decreased corrosion performance of the wrought alloy.