Study On Crack Growth Life Of Powder Metallurgy Superalloy Turbine Disk Containing Inclusions

Turbine disks will endure higher temperature and higher stress due to increasing demanding on the performance, reliability and life of aeroengines, and traditional superalloys couldn't meet the demand. Powder metallurgy (PM) superalloys has the advantage of homogeneous organization, superfine grain, high yield strength and high elevated temperature fatigue strength, so it becomes the first choice material for the new turbine disks. But being limited in the level of manufacturing technique, inclusions (mainly nonmetallic inclusion) is unavoidable. So it is essential to study the effect of inclusion on the strength and life of PM superalloy turbine disks. The main contents are as following:(1) Finite element method (FEM) is used to study the effects of broken inclusion and debonded interface on the stress intensity factors (SIF). In the material of FGH95 containing Al2O3 inclusions, broken inclusion and debonded interface decrease the value of SIF comparing with that of the same size crack without inclusions.(2) The interaction between a round inclusion and a crack under thermal and remote mechanical loading is analyzed based on the body force method (BFM). The traction-free condition on the crack line is mended to get more accurate results. It can be expressed by a series of integral equations which can be discretized to a set of linear equations and then it can be solved easily. Stress intensity factors (SIF) are gotten through the root of the linear equations. The calculation results in this paper is compared to that in other references to validate the method and program. The method is used to the material of FGH95 PM superalloy containing Al2O3 inclusions, and the key factors that affect the SIF are the size of the inclusion, the distance between the inclusion and the crack and the crack length. The thermal stress has little effect on SIF.(3) The finite element model, in which the contact between the crack lines is considered, is more accurate than traditional FE model to simulate the crack growth and crack closure. This model is used to calculate the opening stress of FGH95 PM superalloys. The calculating results in the case of debonded interface show that the opening stress is increased and the amplitude of SIF is decreased.(4) The crack growth life of a PM superalloy turbine disk containing inclusions is studied. Total life of PM superalloy turbine disks can be divided into three parts: the crack (nearthe inclusion) initiation life, the life from the initial crack expanding to the visible crack (0.78mm), and the life from the visible crack expanding to the critical crack. The life of the initial crack expanding to the visible crack is the majority of the life of FGH95 PM superalloy turbine disks containing AlO3 inclusions.(5) The ANSYS user subroutines for the simulation of elastic visco-plastic behavior for PM superalloys is developed by using the Bodner-Partom constitutive equations. The calculation result is compared with that of some experiments and other references, and it is satisfactory. The subroutines can be applied to the stress analysis of turbine disks in aeroengines.