Metallurgical and Materials Transactions A: Physical Metallurgy and Materials Science
Transient-liquid-phase (TLP) bonding was used to fabricate a Haynes 230 Ni-base superalloy/sapphire fiber composite for high-temperature applications. Boron was used as a melting-point depressant for the Ni, to aid superalloy infiltration of the fibers. Preliminary study of the composite indicated an incomplete TLP bonding cycle. Therefore, microstructural and microchemical analyses were carried out to determine the TLP bonding mechanism. It was found that the TLP process did not occur under local thermodynamic equilibrium conditions at the solid/liquid interfaces, contrary to the primary assumption of conventional models, so a modified model for TLP bonding is proposed. The main differences between the proposed and the conventional models are: (a) the concentration of the melting-point depressant increases with time during isothermal solidification, (b) extensive boride segregation at grain boundaries and boride precipitation occurs within grains adjacent to the interlayer in the initial composite assembly, (c) because of the relatively high boron concentration in the interlayer, the TLP bonding cycle was incomplete, resulting in residual-liquid borides. To achieve ideal TLP bonding, four modifications are recommended: (i) use less boron, (ii) use finer sapphire fibers, (iii) create smaller initial grain sizes in the matrix and (iv) increase the homogenization time.
Asthana, R.; Tewari, Surendra N.; and Draper, S. L., "Strength Degradation of Sapphire Fibers During Pressure Casting of a Sapphire-Reinforced Ni-Base Superalloy" (1998). Chemical & Biomedical Engineering Faculty Publications. 15.
Asthana, R., Tewari, S.N., & Draper, S.L. (1998). Strength Degradation of Sapphire Fibers During Pressure Casting of a Sapphire-Reinforced Ni-Base Superalloy. Metallurgical and Materials Transactions A: Physical Metallurgy and Materials Science 29, 1527-1530.
Copyright 1998 ASM International. This paper was published in Metallurgical and Materials Transactions A: Physical Metallurgy and Materials Science, Vol. 29.5, 1527-1530 and is made available as an electronic reprint with the permission of ASM International. One print or electronic copy may be made for personal use only. Systematic or multiple reproduction, distribution to multiple locations via electronic or other means, duplications of any material in this paper for a fee or for commercial purposes, or modification of the content of this paper are prohibited.
Available on publisher's site at: http://www.asminternational.org/portal/site/www/AsmStore/ProductDetails/?vgnextoid=743cc777b3426210VgnVCM100000621e010aRCRD.