Laser beam induced surface alloying of aluminum with niobium

Abstract

A summary is presented of the investigations on the mechanism of alloyed layer formation during laser beam surface alloying of aluminum with Nb. Surface alloys were produced by a two-step process: at first, commercially pure Al substrates were alloyed with Nb by injecting an Al-Nb powder mixture into the melt pool generated using a CO2 laser; the microstructure was then refined by laser melting. In the first step, Nb concentrates near the surface of the melt pool during solidification, resulting in the production of surface layers of Al-Nb alloys. These alloys are heterogeneous and contain pores and undissolved Nb particles for all the processing parameters used. Their microstructure is formed from large dendrites of Al3Nb and interdendritic α-Al solid solution. Laser remelting of the alloyed layers results in a complete elimination of the defects and homogenization of the material. The Vickers microhardness of the surface alloys varies from 450 to 650 HV, depending on the volume fraction and dendrite spacing of Al3Nb. © 2008 IOP Publishing Ltd.