Low-cycle fatigue behavior of INCONEL 718 superalloy with different concentrations of boron at room temperature
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INTRODUCTION
IN the late 1950s, it was realized that small additions of boron (B) and zirconium (Zr) were extremely beneficial to the creep-rupture properties of nickel-base superalloys. Since then, the addition of B in superalloys is generally considered to be beneficial, especially for the grain boundary sensitive mechanical properties, such as creep resistance. Work by Pennington[1] showed that B (up to 0.01 pct) and Zr (up to 0.1 pct) improved high-temperature strength, ductility, and notch sensitivity of several alloys, and Darmara[2] observed that as little as 15 ppm B was sufficient to double the rupture life and ductility of WASPALOY* Much of the earlier *WASPALOY is a trademark of Special Metals Corporation, Huntington, WV.
work on the effect of minor elements in superalloys has been summarized in a review by Holt and Wallace.[3]
L. XIAO, Research Associate, and M.C. CHATURVEDI, Distinguished Professor and Canada Research Chair, are with the Department of Mechanical and Manufacturing Engineering, University of Manitoba, Winnipeg, MB, Canada, R3T 2N2. Contact e-mail: [email protected] D.L. CHEN, Associate Professor, is with the Department of Mechanical, Aerospace and Industrial Engineering, Ryerson University, Toronto, ON, Canada, M5B 2K3. Manuscript submitted December 20, 2004. METALLURGICAL AND MATERIALS TRANSACTIONS A
Cao and Kennedy[4] studied the effect of P and B on the creep deformation of INCONEL** 718 (IN 718).* They **INCONEL is a trademark of INCO Alloys International, Huntington, WV.
concluded that both P and B increased the resistance to creep deformation, but the effect of a combined addition of B and P on creep strength of IN 718 was much greater than the sum of the individual effects of P and B. Garosshen et al.[5] studied the effect of B, C, and Zr on the mechanical properties of nickel-base superalloy. They reported that both C and B had a strong influence on the formation of grain boundary precipitates, and B resulted in the formation of an intergranular M3B2 boride. Both B and Zr were observed to be critical for improvement in the mechanical properties of the alloys, although B levels above the solubility limit resulted in no further improvement or reduction in strength. Floreen and Davidson[6] studied the effect of B and Zr on the creep and fatigue crack growth behavior of Ni-base superalloy. They reported that additions of B and Zr markedly improved the smooth specimen creep properties and the threshold stress intensity values for creep crack growth. However, they had no effect on the crack growth rates during creep or fatigue deformation. No changes in microstructure, fracture appearance, or grain boundary sliding behavior due to B and Zr additions were observed. VOLUME 36A, OCTOBER 2005—2671
of nickel-base superalloys.[15] It was, therefore, considered necessary to further study the effect of B on the plastic deformation mechanism, especially at room temperature (RT), at which the grain boundaries may not play a significant role in plastic deformation of IN 718 and especial
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