| 1Cr15Ni36W3Ti is a Fe-Ni base superalloy,which is based on ? matrix and strengthened by ?' phase.Due to it's good anti-relaxation properties,creep limit and long creep rupture life,this alloy has been used in air-seal springs,turbine blades and high temperature bolts.In this dissertation,the effect of carbon content and heat treatment on the microstructure,properties and ?' phase precipitation behavior of the alloy,along with the study of the microstructure stability in long-trem aging was studied systematically.It provides experimental basis for optimizing carbon content and heat treatment system of this alloy.The main result in this dissertation are as follows.(1)The primary carbide precipitation in as-cast structure increases with the increase of carbon content,and microscopic morphology changed from block to skeleton.After solid solution,grain size of alloy decreases with the increase of carbon content,owing to the increased pinning effect of carbide.After aging treatment,?' phase precipitates from the alloy,and secondary TiC can be observed at the grain boundary.Because of the nucleation rate of ?'phase decreases with the increase of carbon content,size of ?' phase increase from 10nm to more than 55nm,phase spacing increase from 25nm to more than 250nm,and precipitation amount decrease from 13.5%to less than 4.5%.However it has no effect on grain boundary carbides.Tensile tset at room temperature show that the interaction mechanism between dislocation and gamma phase changes from cutting to bypassing when the carbon content increase form 0.02wt.%to 0.1 0wt.%.Yield stress and tensils stress also decrease with the decrease of the effect of precipitation strengthening.(2)The results of heat treatment research show that the grain size increase from 45.2?m to 207.3?m along with the solution temperature increase from 1000? to 1180?.And the peak value of room temperature tension occurs at 1080?.After 870?x10h.AC+700?×25h.AC aging treatment,fine dispersed ?' phase precipitated from matrix,blocky secondary TiC appear at grain boundary.?' phase coarsening when aging system is 700?×50h.AC,and morphology of grain boundary carbides changes into a film-like structure,a 0.2?m wide precipitation free zone is observed near the grain boundary.After 780?×10h.AC+730?×25h.AC aging treatment,Precipitated phases with two sizes of 20nm and 55nm separately precipitated from the matrix,the width of PFZ is wider than other systems,reaching 0.8 ?m.It can be found in the testing of mechanical properties that the best mechanical properties of the alloy after 870?×10h.AC+700?×25h.AC aging treatment.(3)After 3000h long-trem aging at 580?,no detrimental phase precipitated.?' phase coarsening with the prolongation of aging time,Oswald coefficient k is 0.312nm3/h.Room temperature strength is increase with the prolongation of aging time,and elongation,area reducation and impact ductility are decrease with the prolongation of aging time.The mechanical properties tend to be stable after aging 1000 hours.fracture morphology after rupture testing at 550? is composed of intergranular fracture and dimple fracture,and the area of intergranular fracture is decrease with the increase of loading stress.The relationship between applied loading stress and stress rupture life at 550? is log ?=0.08338 logtR+2.89474.The relationship between loading stress with Larson-Miller parameter(P)is log ?=4.6235-1.01295 × 10-4P(?).In the process of stress rupture experimentation,dislocation cutting ?' phase. |
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