Influence of powder size on the crystallization behavior during laser solid forming Zr55Cu30Al10Ni5 bulk amorphous alloy

The Zr55Cu30Al10Ni5 bulk metallic glasses (BMGs) were prepared using laser solid forming (LSF) process from the plasma rotating electrode process (PREP) powder. The effect of the powder size on the crystallization behavior of the remelted zone (RZ) and heat affected zone (HAZ) was investigated. It was found that the as-prepared powders were composed of the amorphous phase and Al5Ni3Zr2-type phase. The RZ mainly kept the amorphous state after LSF. The residual Al5Ni3Zr2-type phase could be observed in RZ only if the powder size was larger than 106 mu m. Meanwhile, the NiZr2-type nanocrystals at the boundary of RZ primarily formed from the solidification of remelted liquid. With the increase of the powder size, the lower overheating temperature and shorter existing time of the molten pool enhanced the heredity of Al5Ni3Zr2 clusters and other intermetallic clusters in remelted alloy melt, which decreased the thermal stability of the already-deposited layer. The volume fraction of crystallization in the deposit increased with the increase in powder size. There was no crystallization occurred in the HAZ between the adjacent tracks and layers for the deposit prepared by the powder with the size range of 53-75 mu m. However, the wide crystalline band with Al5Ni3Zr2-type faceted phase, CuZr-type dendrite, CuZr2-type spherulite and NiZr2-type nanocrystal were observed in the entire HAZ for the deposit prepared by the powder with the size range of 106-150 mu m. The finer powder was benefit to prepare the BMGs by LSF. (C) 2016 Elsevier Ltd. All rights reserved.