A quantitative metallographic assessment of the evolution of porosity during processing and creep in single crystal Ni-base super alloys

作者：Buck H^*; Wollgramm P; Parsa A B; Eggeler G

来源：Materialwissenschaft und Werkstofftechnik, 2015, 46(6): 577-590.

DOI：10.1002/mawe.201500379

• Single crystal Ni-base superalloy
• casting
• heat treatment
• creep fracture
• porosity

The present work reviews previous research on the evolution of porosity. It presents new results from a detailed study on the evolution of porosity during casting, heat treatment and creep of a single crystal Ni-base superalloy subjected to uniaxial tensile creep at 1050 degrees C and 160 MPa in [001] and [110] directions. A quantitative metallographic study was performed on carefully polished metallographic cross sections, monitoring sampling fields of 4500 x 1000 mu m(2) using the back scatter contrast of an analytical scanning electron microscope; evolutions of pore sizes and pore form factors were analyzed and all important details which were previously revealed in a synchrotron study could be reproduced. In addition, it was observed that micro cracks form at larger cast pores. They interlink and thus initiate final rupture. The [110] tensile creep tests showed lower rupture strains than the [001] experiments. In agreement with earlier work, this can be rationalized on the basis of aligned porosity along primary dendrites.

• 出版日期2015-6