Effect of boron addition on the microstructure and wear resistance of laser beam directed energy deposited high chromium white irons

Abstract

There is a demand for alloys produced by laser beam directed laser deposition (DED-LB) with better wear resistance than the traditionally manufactured alloys. In DED-LB of high chromium white iron (HCWI), the refined carbides at the micron scale can lead to inferior wear performance than the cast alloy of the same composition. In this study, various concentrations of FeB powder were mixed with HCWI powder and produced by DED-LB. The microstructural evolution and its relationship with the wear resistance in high stress abrasion wear test were studied. The B addition is a C equivalent element in HCWI, which can change the composition from hypoeutectic to hypereutectic. In the hypereutectic alloys, B promotes hard phases in the form of M7(C,B)3 and M3(C,B) (M mainly represents Cr and Fe). With the B additions, the volume loss in high stress wear testing is reduced due to the increase in the fraction of the hard phases and their coarsening. With the predominantly austenitic matrix, the alloy with 1.09 wt % B consisting of near 60 vol% hard phases showed a superior wear performance than the heat-treated cast alloy. This was attributed to the microstructure in the contact. The high fraction of refined hard phases and the relatively ductile austenitic matrix (compared with the martensitic matrix) work synergistically, showing a worn surface of plastic deformation without brittle spalling and pitting.