Effect of boron and carbon on the fracture toughness of IN 718 superalloy at room temperature and 650 °C |
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Authors: | Lin Xiao Mahesh C Chaturvedi Daolun Chen |
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Affiliation: | (1) Department of Mechanical and Manufacturing Engineering, University of Manitoba, R3T 2N2 Winnipeg, Manitoba, Canada;(2) Department of Mechanical and Industrial Engineering, Ryerson University, 350 Victoria Street, M5B 2K3 Toronto, Ontario, Canada |
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Abstract: | The effect of B and C microadditions on the fracture toughness of IN 718 superalloy was investigated at room temperature (RT)
and at 650 °C. At RT, the fracture toughness was observed to increase with increasing B and C concentrations. C had a relatively
weak effect on the fracture toughness at 650 °C, but the influence of B was significant. At RT the highest fracture toughness
value was obtained for the alloy with 29 ppm B and 225 ppm C at RT, and at 650 °C the alloy with 60 ppm B and 40 ppm C had
the highest fracture toughness. An increase in the concentration of B to 100 ppm, however, resulted in a reduction in the
fracture toughness at 650 °C. Fractographic observations showed that the formation and coalescence of microvoids was the predominant
fracture mechanism at RT. In contrast, at 650 °C, the fracture surface exhibited intergranular cracking in the alloy with
lower B concentrations and transgranular cracking coupled with fine dimples in the alloy with higher B concentrations. It
is suggested that B impedes intergranular cracking by increasing the cohesion of grain boundaries and improving the grain
boundary stabilization. The RT increase in the fracture toughness of the material caused by the addition of C is attributed
to the formation of intergranular and intragranular carbides that increased the resistance to the plastic deformation. |
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Keywords: | fracture toughness J integral J IC K IC K Q microstructure |
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