Abstract
Pore annihilation was investigated in the single-crystal nickel-base superalloy CMSX-4. HIP tests at 1288 °C/103 MPa were interrupted at different times, then the specimens were investigated by TEM, metallography and density measurements. The kinetics of pore annihilation was determined. The pore closure mechanism was identified as plastic deformation on the octahedral slip systems. A model describing the kinetics of pore closure has been developed on the base of crystal plasticity and large strain theory. Mechanical tests with the superalloy CMSX-4 and the Ru-containing superalloy VGM4 showed, that HIP significantly increases the fatigue life at low temperatures but has no effect on creep strength.
Highlights
Single crystal turbine blades cast from nickel-based superalloys contain pores
A model describing the kinetics of pore closure has been developed on the base of crystal plasticity and large strain theory
A Corresponding author: alex epishin@yahoo.de. Such a hot isostatic pressing (HIP) optimization could be simplified, if the kinetics of pore annihilation would be known and the pore closure mechanism identified, because this would allow to develop a numerical model for pore closure and to study the effect of the different HIP parameters on the kinetics of pore annihilation
Summary
Single crystal turbine blades cast from nickel-based superalloys contain pores. These pores form at different steps of blade manufacturing (solidification, homogenization) and grow under long-term high temperature loading (creep conditions) [1]. Industrial manufacturing of single-crystal blades is performed by the Bridgeman method with a temperature gradient of 5–20 ◦C/mm and a withdrawal rate of 3–25 mm/min depending on the cooling method Under such solidification conditions the superalloy crystal grows by dendritic growth which has the side effect, that pores form between the developing dendritic arms. The parameters of industrial HIP (temperature T , pressure p, duration t) have to be carefully optimized under the conditions of complete pore annihilation, avoiding of material damage and minimization of processing costs Such a HIP optimization could be simplified, if the kinetics of pore annihilation would be known and the pore closure mechanism identified, because this would allow to develop a numerical model for pore closure and to study the effect of the different HIP parameters on the kinetics of pore annihilation. The results were compared with literature data about the HIP effect
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