| Inconel 718 nickel-base superalloy has been promoted vigorously in chemical machinery,metallurgy and other fields because of its high temperature resistance,oxidation resistance and good mechanical properties at high temperature.The manufacturing cost of superalloy parts is high,so periodic inspection and repair become necessary measures to prolong their service life.On account of low heat input and small deformation,laser cladding technology has a good metallurgical combination with the substrate,and display a good foreground of application in solving the repair problems of high value-added parts.In view of above-mentioned reasons,combined the cladding properties requirements of high-temperature failure parts,this thesis investigated the influence of cladding properties of inconel 718 nickel-base superalloy with austenitic stainless steel 2Cr25Ni20 as substrate under different processing parameters.The processing optimization method of laser cladding inconel 718 nickel-base superalloy was proposed,and the evolution law of microstructure of cladding layer under different cladding strategies was found.The properties control strategy of cladding layer for inconel 718 nickel-base superalloy was pointed out,and the method for predicting and suppressing cracks of stacked multilayer to cladding layer was proposed.The results can provide a theoretical basis for laser cladding on inconel 718 nickel-base superalloy,promote the development of laser cladding technology for high value-added parts under high temperature conditions and has great significance in serving regional economic green manufacturing.This research mainly includes the following parts:1.Study on the laser cladding processing of inconel 718 nickel-base superalloy.The forming characteristics of inconel 718 nickel-base superalloy were analyzed by the requirements of cladding properties of high-temperature failure parts.The influence of laser power,scanning speed,powder feeding amount,spot diameter and cladding substrate temperature on the hardness,wear and friction coefficient of cladding layer were studied,and the optimal coordination relationship of processing parameters was obtained.The results showed that the change of microhardness was greatly affected by the temperature of substrate.For improving the microhardness of the cladding layer,the laser power and scanning speed played a dominant role.To the wear properties,the substrate temperature was a key influence factor on friction coefficient,while laser power and scanning speed were still influence the reducing wear rate predominantly.In the study of processing optimization,the three-dimensional transient model was established for the coaxial feeding laser cladding of inconel 718 nickel-base superalloy,the relation between the simplified cladding layer of geometrical morphology and the processing parameters was deduced through the heat balance principle,the effective powder utilization rate measured by existing experimental equipment was taken as the basic parameter,the laws between the processing parameters and geometrical morphology was obtained.Furthermore,the processing was optimized by numerical simulation with four factors and four levels orthogonal experiment design and the properties influenced by various processing parameters,the optimal processing parameter was obtained when the laser power was 1400 W,scanning speed was 10mm/s,powder feeding capacity was 1.8 r/min and spot diameter was 2mm.The above results provided experimental basis for subsequent research on microstructure evolution of different cladding strategies.2.Study on structure evolution of laser cladding technology for inconel 718nickel-base superalloy.The microstructure evolution of laser cladding for inconel 718nickel-base superalloy under different processing parameters was studied,and the influence of laser power,scanning speed,powder feeding amount and spot diameter on the forming coefficient of cladding layer and the microstructure defects of cladding was revealed.In the experiment of lap rate at 20%-50%,the surface flatness of cladding layer was improved with the increase of lap rate,and the content of element Nb in Laves phase decreased from 10.77%to 8.45%.It showed that the increase of lap ratio can improve the segregation of element Nb in the cladding layer within the scope of the experimental parameters.In the multi-channel cladding experiment under different substrate temperatures,SEM,EDS and XRD were used to analyze the grain size,element distribution and phase,it was found that when the substrate was heated at200?,the surface grain size was the smallest,and Fe,Cr,Ni and Nb elements were the most evenly distributed in the interface region,but no new phase was found in the four groups of compared experiments,which showed that the improvement of mechanical properties was due to grain refinement and uniform distribution of elements.In the study on the microstructure change law of cladding layer in curved surface,it was found that when the space Angle was controlled at 0-15°,the effect of spot control was the best,the dendrite size of the cladding layer was uniform,and the dendrite space was10-15?m,and the cracks,pores and unmelted particles can be found in the cladding layer when the space Angle was increased.In the study of crack evolution,it was found that the precipitated phase of laser cladding for cladding layer of inconel 718nickel-base superalloy was Laves phase and a small amount of carbide.After binarization treatment,the volume content of Laves phase at the bottom,middle and top of the cladding layer was 4.50%,15.15%and 6.40%,respectively.Therefore,cracks were easy to occur in the middle of the cladding layer.In addition,the cooling rate was directly related to the element segregation of cladding layer for inconel 718 nickel-base superalloy and the formation of low melting point eutectic Laves,and the segregation of element Nb is negatively related to the cooling rate.The above results provided a theoretical basis for subsequent properties control.3.Study on properties control of cladding layer on the laser cladding for inconel718 nickel-base superalloy.To improve the cladding layer properties of laser cladding for inconel 718 nickel-base superalloy with high-temperature failure parts,the laser remelting power,ultrasonic power and aging mechanism of heat treatment were used as variables to control the properties of the cladding layer by the method of laser remelting,ultrasonic vibration and heat treatment.Through the high temperature tensile test at650?,it was found that the cladding sample controlled by laser remelting method has the best tensile strength at high temperature,which was 720.96 Mpa.The wear resistance of the sample controlled by laser remelting method was found to be the lowest,which was 2.2013×10-6g·N-1·m-1.Numerical calculation was used to evaluate the control ability of the three methods,and the optimal method was laser remelting.BP neural network topology training structure was built with processing parameters(laser power,scanning speed,overlapping rate)as the input,the visual tracking technology was used to get the cladding layer surface crack index for output,and trained the cladding sample data from the orthogonal experiment to determine the mapping relationship between processing parameters and the index of cladding layer surface crack.The BP neural network algorithm optimized by genetic algorithm GA improved the prediction accuracy of cracks in cladding layer of inconel 718 nickel-base superalloy by more than 3 times.According to the above study,the composite technology of laser remelting which heating the substrate to 200? can suppress the cracks in the cladding layer of laser cladding for inconel 718 nickel-base superalloy,and provide effective technical support for the properties control to the cladding layer of laser cladding for nickel-based superalloy IN718 with high-temperature failure parts. |
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