Research On Process And Growth Behavior In Laser Repairing Of Nickel-base Single Crystal Superalloy

Repairing of aeroengine single-crystal blade can prolong its service life, which is of great economic value. The controlling of dendrites growth is the key point of repairing of single crystal(SX) blades in aero engine. The aim of this paper is to investigate dendrites growth behavior in the laser cladding process, and to explore the conditions of dendrite epitaxial growth of single crystal.The influence of experimental parameters on the dendrites growth was studied,and a suitable parameter window was obtained by two kinds of laser process, laser remelting and laser cladding, in which the SX DD5 and DD6 were taken as research object. On this basis, laser claddings were performed on the substrates with various orientation and shape, and samples were studied through metallographic analysis and EBSD(Electron Back scattered Diffraction).Important conclusions were as follows:The dendrites growth and orientation of SX cladding layers relate to substrate orientation. The gradient direction in different zone in molten pool has an angle for each optimal growth direction, and the dendrites in SX cladding layer tend to grow along with the very optimal growth direction, which corresponds to the minimum angel. When the laser scanning direction is vertical to optimal growth direction, the orientation of cladding layer is consistent with that of substrate. If a bigger deviation exists between vertical direction and optimal growth direction within the longitudinal section plane of cladding layer, the tendency of stray grains would be great.In the laser repairing processing of groove in SX alloy with [001] orientation, the groove angle will affect neither the fact that dendrites grow along the optimal growth direction, nor that the orientation of cladding layer is consistent with that of substrate. However,the bigger the groove angle is,the bigger the stray grain tendency near the sidewall is.In the laser repairing process of the SX blade root, the growth direction of dendrites in the corner of laser molten pool become uncertain, and reducing heat input can benefit to the narrowing of this area. The EBSD results illustrates that there existed large quantity of subboundary due to both optimal growth direction, but the orientation of solidification zone stay the same with that of substrate.?' phase(Ni3(Al, Ti)) in the substrate is in the shape of square. Through the SEM photograph of the heat affected zone(HAZ) of multilayer multipass laser repairing area, it is found that some of ?' phases have fuzzy boundaries, and aren't in fixed shapes, which is due to the solid solution under the effect of multiple thermal cycle. TEM results show that,in the laser solidification morphology of DD6,? ' phases are square and exist in a large number, and have size range of 20-40 nm.