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Investigation of the heat-affected zone fracture in Ni3Al welds

Published online by Cambridge University Press:  31 January 2011

G.H. Chen  and
C. Chen
G.H. Chen
Affiliation:
Institute of Materials Science and Engineering, National Taiwan University, Taipei, Taiwan 10764, Republic of China
C. Chen
Affiliation:
Institute of Materials Science and Engineering, National Taiwan University, Taipei, Taiwan 10764, Republic of China
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Abstract

Ternary Ni77Al23−yXy (X = Zr or Hf, y = 0.5 or 1) + 500 ppm boron compounds with various grain sizes were welded by a CO2 laser. Fractographic examinations of the heat-affected zone (HAZ) in the welds with or without postweld heat treatment (PWHT) were performed on the impact-fractured specimens. In laser welds, the fracture appearance of the HAZ was mixed transgranular/intergranular modes for fine-grained alloys and intergranular mode for coarse-grained materials. However, an entirely transgranular mode was observed in the base metal regardless of the grain size of the compounds. Boron desegregation at high temperatures during the thermal cycle of welding could be used to explain the fractographic change from originally ductile mode into less-ductile or even brittle fracture in the HAZ. Short-term PWHTs along with slow cooling provided sufficient time for boron segregation back to the grain boundary, resulting in a completely transgranular fracture mode in the fine-grained HAZ. Nevertheless, such a phenomenon was not observed in the HAZ of coarse-grained welds. Cracks in the HAZ of coarse-grained welds after long-term PWHT, if not so severe, could be healed by a sintering process.

Type
Articles
Information
Journal of Materials Research , Volume 7 , Issue 5 , May 1992 , pp. 1076 - 1082
Copyright
Copyright © Materials Research Society 1992

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