| CMT,as a new welding process technology without slag spatter,can greatly limit the welding heat input,weaken the effect on the interface structure,and has a wide application prospect in repair.GH4169 alloy is widely used in aircraft engines.The repair of GH4169 alloy parts has always been an important issue for aircraft engine maintenance.Compared with the traditional arc welding repair and laser cladding repair,the CMT arc additive repair method has greater repair efficiency,and the strict control of heat input is more conducive to the maintenance of the metal matrix structure and performance.The repaired parts have better organization and uniformity of mechanical properties.In order to solve the problem of high efficiency and high performance repair of damaged parts,the CMT arc additive repair method with low heat input was used to achieve rapid repair of GH4169 alloy samples.Different heat treatment modes are used for the repaired samples to improve the mechanical properties of the repaired area and the interface area.The optical microscope(OM)and scanning electron microscope(SEM)are used to observe the structure of the samples before and after the heat treatment.The hardness tester and tensile tester are used to test the samples microhardness and tensile properties.Finally,the fatigue performance and failure mode of each area of the repaired specimen were analyzed through the fatigue crack growth rate test.The paper mainly draws the following conclusions.The repair samples can be roughly divided into four areas: repair zone,semi-melted zone,HAZ and substrate.The width of the HAZ is about 200 μm,and the repair zone is a typical epitaxial growth of columnar crystals.Morphology,the growth direction of dendrites gradually tends to repair the surface vertically with the increase of the layer.Heat treatment has been done of the repaired samples separately,the strip-shaped Laves phase in the repair area of the S-HSA sample was dissolved,and more small-sized Laves phases remained;the semi-melted area near the fusion line precipitated more δ phases,and the grain boundary at the HAZ precipitated a amount of short needleshaped δ phase.The dendrite structure and Laves phase morphology of the HSA-DA sample repair area did not change significantly,and no δ phase precipitated in the HAZ.After heat treatment,there was no significant difference in the morphology of the two groups of sample base materials.After heat treatment,the hardness of the repair area has been greatly improved.The average hardness of the repair area of the S-HSA sample is slightly lower than that of the substrate,reaching445HV;the average hardness of the repair area of the HSA-DA sample is 457 HV,which is equivalent to the hardness value of the substrate.The hardness of the HAZ of the group of samples is lower than that of the repair zone.The tensile strength of the HSA-DA sample is 1271 MPa,the elongation is 13%,the tensile strength of the S-HSA sample is 1218 MPa,and the elongation is 25%.The fracture locations of the two groups of samples are repair areas,and a large number of tough dens are found at the fracture,and the fracture modes of the two groups samples are all tough fracture.The S-HSA sample occupies Nb element due to the large size Laves phase dissolution and the precipitation of δ phase in the repair area,which reduces the precipitation amount of the γ″ phase,so the strength and hardness are slightly lower than the HSA-DA sample,but the extension The length ratio has greatly increased,greatly improving the deformation coordination ability of the parts.Fatigue crack growth rate tests show that when the prefabricated cracks are located near the repair area and the fusion line,the cross-region propagation of cracks occurs only in HSA-DA samples.The small size Laves phase in the repaired area of the S-HSA specimen is not conducive to the rapid propagation of the crack and the δ relative cracks precipitated near the fusion line to cause pinning,so it shows good fatigue performance.The HSA-DA specimen has a large Laves phase in the repair area,and the cracks are easily propagated through the Laves phase.The large grain size and the missing of particle phase in the interface area,so the sample shows poor fatigue performance.When the prefabricated crack perpendiculars to the fusion line,the crack growth rate of the HSA-DA sample was significantly higher than that of the S-HSA sample.The phenomenon of Laves phase "guided" the crack growth found in the fatigue fracture,and the fatigue cracks mainly propagated along the grain boundary in the HAZ.HSA heat treatment eliminated the elongated Laves phase in the repair zone,weakened the rapid propagation of the crack,and the δ phase at the fusion line hindered the propagation of cracks.Thus,the S-HSA samples exhibit much better fatigue performance. |
