Microstructure of Nb substrates coated with Mo(Si,Al)2–Al2O3 composite and B-doped Mo5Si3 layers by spark plasma sintering

Abstract Niobium substrates were coated with Mo(Si,Al) 2 –Al 2 O 3 , B-doped Mo 5 Si 3 –SiO 2 , Nb 3 Si 5 Al 2 , Cr-doped Nb(Si,Al) 2 and NiAl layers by spark plasma sintering (SPS) and low-pressure plasma spraying (LPPS), and microstructure and oxidation behavior of the coated specimens were examined. Only B-doped Mo 5 Si 3 layer bonded to the Nb substrates, when Mo(Si,Al) 2 , B-doped Mo 5 Si 3 , Cr-doped Nb(Si,Al) 2 and NiAl powders were directly put on the substrates before the sintering. Nb substrates coated with B-doped Mo 5 Si 3 –5 wt% SiO 2 interlayer and MoSi 2 –2 wt% SiO 2 outerlayer by SPS showed extremely good oxidation resistance in the temperature range of 1473–1673 K. Al 2 O 3 interlayer, which is expected to work as a diffusion barrier, was formed between Mo(Si,Al) 2 layer and Nb substrates, when thin Al foil was inserted between the Mo(Si,Al) 2 powder and the substrates before the sintering. In addition, only B-doped Mo 5 Si 3 layer bonded to the Nb substrates, when they were coated with Nb 3 Si 5 Al 2 , B-doped Mo 5 Si 3 and Cr-doped Nb(Si,Al) 2 by LPPS.