Sliding wear resistance of nickel boride layers on an Inconel 718 superalloy

New results about the wear resistance of nickel boride layers under dry sliding conditions were obtained in this work. For this purpose, an Inconel 718 superalloy was borided under different conditions: 1173 K with 2 h of exposure and 1223 K with 6 h of exposure, using the powder-pack process. Before the wear tests, the nickel boride layer was characterized by the depth-sensing Vickers microindentation technique to determine indentation properties such as hardness, Young's modulus, residual stresses and fracture toughness. The dry sliding wear tests were performed on the borided Inconel 718 superalloy obtained for the two boriding conditions, and on the surface of the reference material (Inconel 718 superalloy), using the ball-on-flat technique, under a constant load of 20 N and considering relative wear distances between 50 and 200 m. In addition, the development of the failure mechanisms over the surface of the wear tracks was analyzed by scanning electron microscopy (SEM) and energy dispersive X-ray spectrometry (EDS) techniques. For the overall set of experimental conditions, the results showed that the presence of nickel boride layers on the surface of the Inconel 718 superalloy increased the wear resistance compared with the reference material. However, the presence of a deeper zone of compressive residual stresses at the inner-zone of the nickel boride layer formed at 1223 K with 6 h of exposure, enhanced the wear resistance by approximately two- and three-fold compared with the values estimated for the nickel boride layer obtained at 1173 K with 2 h of exposure.