Applied Surface Science, Vol.409, 367-374, 2017
Microstructure of rapidly solidified Nb-based pre-alloyed powders for additive manufacturing
For powder-based additive manufacturing, sphere-shaped Nb-37Ti-13Cr-2A1-1Sipre-alloyed powders were prepared by plasma rotating electrode processing (PREP). The microstructure, surface oxidation and microhardness of the pre-alloyed powders were systematically investigated. Results showed that the main phases were Nb solid solution (Nbss) and Cr2Nb. The Cr2Nb phases were further determined using transmission electron microscopy (TEM). Fine dendrite structures were observed in the as-fabricated pre alloyed powders, which transformed to large grains after heat treatment (HT) at 1450 degrees C for 3 h. With the increase of powder size, the secondary dendrite arm spacing (SDAS) increased and the microhardness (HV) decreased. A clean powder surface free of oxide particles was obtained by PREP and an oxide layer with 9.39 nm in thickness was generated on the powder surface. Compared with Cr- and Nb-oxides, more Ti-oxides were formed on outmost powder surface with a higher content of Ti (up to 47.86 at.%). The differences upon the microstructure and microhardness of the pre-alloyed powders with different sizes were discussed. (C) 2017 Elsevier B.V. All rights reserved.