Study On Formation Mechanism And Evolution Law Of FGH96 Alloy Original Powder Particle Boundary

The second-generation powder metallurgy(P/M)superalloy FGH96 has been applied to produce turbine disc and other hot parts for thrust-weight ratio aero engine,this alloy has shown the advantages of crack propagation resistance,superior creep strength and damage tolerance.The original particle boundary(PPB)is generally present in the tissue after hot isostatic pressing,when the FGH96 alloy powder is prepared by argon atomization(AA)or rotary electrode(PREP)method.PPB is one of the three major defects in P/M superalloys,which is very unfavorable to the organization and performance of alloys.Based on the PPB of FGH96 alloy,the main contents are as following:(1)The formation mechanism and influencing factors of PPB were studied by using the powder size and powder oxygen content as the hot isostatic pressing(HIP)variates.Research shows,PPB is a kind of boundary aggregates that is formed by the surface adsorption of C,O and surface enrichment of Ti,C r,Al oxide at HIP with the internal migration of Ti,Nb and other elements,it is mainly composed by large size ?? phase and a small amount of oxide,carbide or carbon oxide.PPB is precipitating along the powder particle boundary during the hot isostatic pressing and the precipitating degree has nothing with powder size but is proportional to powder oxygen content.(2)The FGH96 alloy in HIP state was used to study the evolution of PPB by thermal deformation(HIF)and heat treatment(HT).Research shows,The large size ?? phase at the PPB and the second and third ?? phases in the tissue are gradually assimilating into the matrix during the thermal deformation and heat treatment,turning to precipitate a large amount of small size ?? phase and some carbides,oxides or carbon oxides.(3)The damage mechanics behavior of FGH96 alloy was studied by in-situ tensile and in-situ fatigue tests.Research shows,in situ tensile test,the material is in an overload state and the fracture is characterized by a brittle fracture along the PPB.In situ fatigue test,the initiation and propagation of fatigue cracks are dominated by slip,twinning and grain boundary and the instantaneous fracture zone of fatigue fracture has the feature of cracking along PPB,the fatigue life of the material is inversely proportional to the relative rank of PPB.