Journal of Materials Science and Engineering with Advanced TechnologyAuthor's: Swati Biswas, M. D. Ganeshachar, B. R. Sridhar, V. N. Satish Kumar and S. Ramachandra
Pages: [109] - [131]
Received Date: April 30, 2014
Submitted by:
Corrosion and heat resistant, precipitation hardenable superalloy components are widely used for high temperature applications. They exhibit excellent mechanical properties at elevated temperatures up to which the precipitates are stable. However, difficulties are encountered when used in cast form due to larger elements segregation leading to deleterious phase formation and reduced mechanical properties. Investment cast components manufactured from a corrosion and heat resistant nickel based superalloy Su 718 were subjected to solution treatment and aging and were planned to be used in gas turbine engines. However, hardness on the samples was found to be less than the minimum requirement. Homogenization treatment was introduced for the components before subjecting it to solution treatment and aging. Higher homogenization treatment was found to be more effective in obtaining hardness almost comparable to the wrought product after the final heat treatment. In order to understand the effect of homogenization treatment on the microstructural changes in the material, scanning electron microscopic (SEM) studies were carried out on the samples in as-cast condition and after homogenization treatments. Back scattered electron (BSE) imaging indicated presence of large compositional heterogeneity in the inter-dendritic region in as-cast condition. X-ray dot mapping and X-ray line scanning revealed niobium (Nb) and molybdenum (Mo) segregation in those regions. Homogenization treatment was carried out to have uniform distribution of Nb and Mo. Heterogeneity was found to reduce with increasing homogenization temperature.
superalloy, casting, segregation, homogenization, solution treatment, aging, hardness.
