Study of the effects of Ge addition on the microstructure of Nb-18Si in situ composites

作者：Li Zifu; Tsakiropoulos Panos^*

来源：Intermetallics, 2010, 18(5): 1072-1078.

DOI：10.1016/j.intermet.2010.02.012

• Silicides
• various
• Phase transformations
• Phase identification
• Casting
• Microstructure

The effects of Ge addition on the microstructure and hardness of the as cast and heat treated (1200 degrees C/100 h and 1500 degrees C/100 h) Nb-18Si-5Ge (ZF1) and Nb-18Si-10Ge (ZF2) (at%) alloys were studied. The as cast microstructures of both alloys consisted of Nb(ss) and beta Nb(5)Si(3). The latter silicide was the primary phase and the two phases formed high volume fractions of Nb(ss) + beta Nb(5)Si(3) eutectic. The Ge addition destabilized the Nb(3)Si and the Nb(ss) + Nb(3)Si eutectic. After heat treatment at 1200 degrees C for 100 h, the beta Nb(5)Si(3) was partially transformed to the alpha Nb(5)Si(3) in both alloys, and the two phase lamellar mixture was stable. After heat treatment at 1500 degrees C for 100 h, the microstructure of both alloys had become coarser and consisted of the Nb(ss) and the Nb(5)Ge(3) based 5-3 silicide (isomorphous with alpha Nb(5)Si(3)). The Ge partitioned to the Nb(5)Si(3) rather than the Nb(ss), and substituted for Si atoms in the lattice of the Nb(5)Si(3). The addition of Ge increased the microhardness of the Nb(5)Si(3); the two phase lamellar mixture played a dominant role in determining the macrohardness of the as cast and heat treated alloys.

• 出版日期2010-5