Avaliação do efeito de modificações superficiais a plasma no desempenho frente ao desgaste de um aço baixa liga: estudo da correlação entre profundidade de endurecimento e melhoria de desempenho

Abstract

Attempting to improve the wear resistance of an AISI 4140 low alloy steel, two surface treatments were applied: plasma nitriding and PAPVD coating. Wear resistance against cavitation erosion and microabrasion of: AISI 4140 steel, 2 and 4 hours nitrided AISI 4140 steel, Cr-Al-N coated AISI 4140 steel and nitrided/Cr-Al-N coated AISI 4140 steel was investigated. Cavitation erosion tests were performed according to the ASTM G32-03 standard. Microabrasion tests were carried out using SiC abrasive slurry and load of 0,2 N. The systems were characterized by SEM, EDS, GDOES, XRD -2 and glancing angle configuration, 2D and 3D perfilometry, Rockwell C adhesion test, scratch test, Knoop microhardness and instrumented indentation hardness. Concerning to cavitation, Cr-Al-N coating deposition was effective to increase the incubation time, whereas the plasma nitriding was more effective to decrease the wear rate. The thicker was the coating, the longer was the incubation time, and the bigger was the nitriding time the lower was thecavitation erosion rate. From a technological point of view, the plasma nitriding process seemed to be more worth to promote an increase in the AISI 4140 cavitation erosion resistance, since it has reduced the mass loss in at least 6 times in comparison with the untreated steel. Concerning to microabrasion, plasma nitriding and Cr-Al-N coatingdeposition, alone, have not leaded to a significant increase in the wear resistance. However, when combined in the duplex systems, a decrease of 76% to 90% in the wear coefficient k was observed. The hardening depth was more important for the cavitation erosion process,whereas, for microabrasion the load carrying capacity of the nitrided layer was more significant.