Research Status of Weldability of Low Expansion Superalloy

3 is called 2 welding hot crack formation mechanism influencing factors and preventive measures and other aspects of systematic introduction, the expansion of high-temperature alloy welding 4 open the welding test microstructure analysis and numerical simulation combined to be able to from the metallurgical and mechanical aspects More clearly understand the formation mechanism of cracks and the influence of various factors. Finalize a reasonable welding process and effectively prevent welding. 1. Introduction Low-expansion high-temperature alloys, unique properties of high-strength and low-expansion coefficients, good cold and heat fatigue Performance, heat shock resistance and high pressure resistance to hydrogen embrittlement. Since the beginning of the research and development of low expansion high temperature gold in the 1970s, there have been more than a dozen types of low expansion high temperature alloys, and are widely used in the aerospace industry.

The low-expansion high-temperature alloys used in the aviation industry are mainly used for turbine engine casing, turbine outer rings, and strict bee-poor imperfections, and other components and gas losses. Improve engine thrust and efficiency. The United States, the 56300 and the engine are large, using this type of helium to achieve engine quality in the aerospace industry to use these alloys to manufacture spacecraft and rocket engine main combustion chamber turbopumps and nozzles and other parts.

The application of low-expansion high-temperature alloys inevitably involves the research of the welding process, and the application range of the new material is limited, and it may cause reheat cracks and fatigue cracks to cause the product to be scrapped. Even laying a serious threat to the safe flight of the aircraft. Therefore, the study on the weldability of low-expansion high-temperature alloys and the influencing factors and control measures of the formation mechanism of welding cracks can not only enrich the welding crack theory, but also have important significance for improving the reliability and safety of aerospace engines.

Research in this field has received increasing attention from people and it has received the date of receiving the document 199905 Guo Shaoqing. Born in 19 years. Doctor. Mainly engaged in the control of welding thermal cracks and residual deformation Numerical simulation of welding thermal processes Research and development of the work 2 Low-expansion high-temperature alloy composition characteristics and weldability Low-expansion high-temperature alloys can be roughly divided into a category to go to a low-temperature alloy, which Including 17 903 and Qiaozhou, 1 and domestic, 03. Based on such alloys, adding other elements such as Hexa reinforcement. The first category is to drop 1 low-expansion Shang Wen alloy, which includes, 907 and take 3 and production; 907, in order to improve the anti-acceleration product boundary, brittleness, limit the content of 1 in the alloy 1 mass fraction, properly increased He content. The first category is 31 low expansion high, 909. This type of alloy is a modification of the low-expansion superalloy, which has the same basic composition and only increases the content by 3%. The last category is the low-expansion high-temperature anti-oxidation alloys. The existing low-expansion high-temperature alloys for corpses and the 909 have relatively few studies. The liquefaction cracks in the heat-affected zone at 907 pings have been systematically studied. On the other hand, the research and development of 09 solderability has not been reported yet.

1 and so on using punctiform and small variable constraints test and D. The results of the seven-seven joints show that these alloys are phase-sensitive to the liquefaction cracks in the heat-affected zone and the cracks in the joints. The 903(1) and their crack-sensitive parts are much higher than the 300-series austenitic stainless steels. Crack susceptibility. According to reports in the literature, the microcracking of the Intumescent Alloy 1 is more severe than that of the crystallized cracks in the soldering zone.

3 Weld seam crystal cracks The low-expansion superalloy's weld crystal crack susceptibility results from the converging process, the segregation of grain boundary and solidification substructure boundaries, and finally the formation of low-melting eutectic from the increased level of the final eutectic liquid phase. The decrease in the number and solidification temperature has an important influence, and thus also determines the sensitivity of the alloy to crystal cracks.

903 weld metal solidification with brain dendrites 6 and 0 segregated in 7 dendrite, his Chiou segregation in the interdendritic region, the end of solidification is 7MCftKGH, 4j; jmAiaiC7feiH.jjjU a small amount of 138 phase generation, weld metal is not The study of the microcracking 909 solidification behavior shows that the alloy solidifies at about 98%. Convergence with the final generation. The 71 types of co-product components. This difference in solidification eutectic will inevitably affect the sensitivity of the weld crystal cracks 907903,768 eutectic composition increased. According to the content of fermented grains, 8 analysis data, such as 1 agricultural method, calculated 17 high, including about Australia, Tanzania, negotiations, and the formation of carbides, will progress to reduce the end of solidification 7, the formation of eutectic components. However, there is not a linear relationship between the susceptibility to crystal cracking of the 900 series alloy and the amount of eutectic liquid phase. There is a critical amount of liquid phase at which grain boundaries are exactly wet. Below this critical value, the addition of liquid phase will promote the wetting of the grain boundary and thus increase the cracking tendency. Above this critical value, the addition of liquid phase will result in the healing of the sipes, which is beneficial. The variable detention test shows that the content of the +5 7909 crack sensitivity is greater than colfA03fHIncoloy907, JMljitfyi; Mjit low liquid crystalline phase critical position of crack healing 13

The solidification and weldability of the high-temperature alloys during the determination of the alloy constituents in the solidification hall for the development of the microstructure and the interfacial cracking susceptibility between the steps described 1 initial solidification 17, during which the interdendritic liquid phase enriches he and the , 2 eutectic reaction 7+, 3 solidification with hypo-eutectic reaction 7+, end. Addition, but also in the initial 7 condensation stage, the degree interval strongly sounded. With Sakura, 7+he, the reaction temperature increases, thus reducing the temperature interval during the initial 7 solidification phase. In the base alloy, add more than 0.052 mass fraction, the same as below. Significantly increase the resistance to crystal cracking. Only when the fly content is lower than 210, the inclusion test is added to the base alloy when it is higher than 0.12, and the vomiting is improved by 1 to prevent the formation of low and 70%. The reaction can improve the cracking of the crystal in the mixing zone. Resistance 9.

4 Your Microcracks 4.1 Mechanism of Formation The formation of continuous or semicontinuous liquid depletion in the grain boundaries rich in 3 and 0 is the main cause of 12 microcracks. If the liquid phase disperses the holes in the corpse boundary in a departed form, it will not cause the melting of the grain boundary caused by local compositional changes caused by the segregation of microscopically related to the formation of liquid film on the 1 grain boundary. The liquefaction of components such as initial carbide carbonitride boride sulfides causes the accumulation of 7-phase product boundary solute when the grain boundary forming liquid migrates from the product boundary; The diffusion along the crucible 1 continuously enters the judgment 25, and the lanthanum liquid phase penetrates from the fusion zone to the 1 inward along the 7-phase grain boundary.

In the above mechanisms, the liquefaction of components has received more recognition and research, and others' researches believe that in 906, 1 is from the liquid phase 909, its source is rich, and 3 is 68 phase and or, the phase is hunger. Sub-liquefaction and other research progress 1.1. . 90312 liquid phase mainly produced in the grain boundary on the original with a carbide river phosphide and fine carbide components liquefied micro-crack sensitive 1 and 1 product boundary liquid phase number 1 bamboo Guan, with his +3 content, plus, liquid phase, plus, crack sensitivities also increased solitary alone 1 and other researchers found that the solidification mode of the supersaturated liquid film on the grain boundary has an important impact on the formation of microcracks 44 When the grain boundary liquid film is solidified by the solidification method similar to the fusion zone, the 7-tree nucleation grows up and then enters the end of the 7-busy carbide twinning reaction, eventually causing a large number of microcracks; when the grain boundary liquid film is liquid When the film is allowed to solidify. Liquid desorption dissolves the 7-matrix in front of it and deposits 7 of the solid solution behind it. The solid solution in the liquid film reduces supersaturation by the transport of solute in the liquid film. A 21-to-1 spectacle reduces the total solidification temperature range, avoiding The low melting point of the grain boundary liquid phase ends the eutectic reaction, thus reducing the occurrence of microcracks.

The formation mechanism of microcracks can be attributed to the fact that the rapid thermal cycle of the welding process can promote the liquefaction of the components of the precipitates in some alloy systems, and form a grain boundary liquid film in the portion of the solid phase below. Rapid cooling limits the diffusion of solute from the grain boundary liquid phase to the matrix, thus expanding its solidification range. At the same time, the liquid phase does not reduce the supersaturation by the liquid membrane migration LM and avoids the formation of a final low eutectic liquid phase before the crack formation. When the local thermal stress becomes tensile, there is a liquefied crack in the grain boundary liquid film. In addition, the liquid phase adsorbs phosphorus to the grain boundary, reducing the solid-liquid interface can weaken the grain boundary bond and exacerbate the microcracks. The straight grain boundary channels are conducive to liquid phase spreading and crack growth, reducing the driving force for generation 1 and adding microcrack sensitivities. 141 4.2. Factors Affecting The heat treatment regime and initial microstructure have an important influence on the tendency of microcracks. Usually solution treatment is conducive to the solid solution of impurities to reduce the grain boundary accumulation of impurities, while the aging treatment is just to make the impurity solubility in the lowest valley, so the material sensitive to 1 liquefaction cracks should generally be welded in the solution state. However, Shi Changji and others replied that the 1907 electron beam welding research found that when the solution was in the solution state before welding, it was prone to occur, liquefaction cracks, and the state of Guluo was in the state of aging before welding, but there was no 1B crack, and this still required improvement. Test study analysis.

Influence of initial microstructure of 903 alloy on perspiration microcracks. The study found that a large number of micro-cracks occur in specimens consisting mainly of coarse, warm-processed grains, while only few micro-cracks appear in the fine grains of the week. The uniform grain boundary curvature of the fine product is large, which is favorable to occur, thereby reducing the tendency of 12 micro cracks. Increasing the proportion of fine recrystallized grains around the coarse temperature-processed grains can reduce microcracks. In addition, we also systematically investigated the effects of the heat treatment system on microcracking of the microstructure 1 for the cast alloy 718 system. It was found that the order of crack susceptibility in different heat treatment conditions was homogenization + aging 010, homogenization homogenization, paleosolular dissolution 0 5.1. The change in crack sensitivity was closely related to the precipitation of grain boundary 1;

In order to reduce the occurrence of 2 microcracks, 1 et al. also investigated the effect of electric house beam welding parameters on the microcracks and quantitatively determined the relationship between microcrack sensitivity and welding parameters and weld pool shape.

Aspect ratio. For electric wide beam working distance. For Tun wide beam current. To accelerate the voltage for the welding speed.

This equation shows that the heating input, ie increasing the beam current 1 and decreasing, can reduce the crack. The elliptical weld pool reduces crack tipping compared to a teardrop weld pool. Afterwards. In other terms, the optimization of the beam welding parameters across the 903 electron beam was performed, and the influence of the electron beam current focusing current and electron beam amplitude on the 12 microcracks in the form of a regression equation was revealed. However, the regression equation is applicable to 903, Shi Changkai and others pay factory; the research of 907 shows that the increase of line energy and high temperature residence time and the increase of heating and cooling speed will aggravate the liquefaction of components and increase crack susceptibility. Different rules of the relationship with the above equations. This may be due to differences in the composition of the two alloys.

1 It was found that when the crack behavior was compared with the penetration depth ratio of the maximum width of the weld measured by the cross-section of the weld, the total length of the crack decreased with the increase in the size of the household, and was found in the milk. When the value of the household is more than 1.6, cracks are eliminated. The high welding speed was deduced by the authors by reducing the number of dead bodies by 1 body. Electron beam swing and preheat can affect the shape of the weld puddle and the amount of thermal stress generated. Reducing the occurrence of microcracks 1. Analyze the effect of welding speed on the temperature profile and the time profile of the off 2 temperature in combination with the thermal cycle of the blasting. The research found that low welding speed can cause the decrease of liquid film thickness to increase the elliptical shape of the molten pool and reduce the thermal stress, and reduce the tendency of micro-cracks to flash. 1 5 Quantitative study on weldability of low-expansion superalloy Weld cracks The occurrence of 12 microcracks depends not only on the formation of a low melting point eutectic and a boundary liquid film, but also on the effect of stress or strain on the liquid film. In order to predict the susceptibility of a given welding condition 1 alloy crack, it is necessary to simulate the evolution of the microstructure and stress-strain development centered on the condensing process and grain boundary liquefaction of the weld seam.

A coupled model of the heat flow and material flow in the formation and solidification process was used. The microstructure evolution of the pseudo binary alloy was calculated using this model, and the factors that increased the liquid phase life of the instantaneous grain boundary were determined. This is important for predicting the liquefaction cracking susceptibility of alloy welding. 15. Afterwards, numerical simulation was used to study the variation of the microstructure of the welds of the 01 welds of the jaws. 25.2. Cooling of the beer using simulations. Velocity, and mouth, predicted the microstructure of the galvanic zone in the book (3).

The solute redistribution and tissue development in the consolidation process. The change of the ratio and composition of the liquid phase in the initial 17 and eutectic 7 + solidification phases was calculated under the condition of infinitely fast conditions of the matrix, 1. Ziji Chengziqi as the elementary system. The calculation results are superimposed on the pseudo-element 7 solidification phase, and the order of the solidification reaction and the total amount of the co-product components and their respective amounts are predicted. This simulation makes the quantitative understanding of the relationship between crystallographic cracks in the compositional microstructures of his test alloys become the initial welding process. The numerical simulation mainly focuses on the prediction of welding residual stress and deformation. 0.81 1. First, the numerical heat flow model microstructure model and mechanical model were combined first, and the residual stress and deformation of the microstructure evolution of the 608216 aluminum alloy hollow extrusion welding process were successfully predicted.

The numerical simulation of the stress-strain evolution in the welding process with regard to the formation conditions of the welding hot cracks is currently focused on the study of the crystallization cracks in the fusion zone in this respect. 3 and Chile have made useful explorations successively. 24. Feng Chile developed two modeling techniques for the simulation of solidification effects, introducing microscopic solidification kinetics and cell regeneration techniques. Afterwards, he used this model to quantitatively evaluate the central heat transfer rate of the three-grade test, through the structural stress location, revealed the complex stress development of the moving molten pool tail, and utilized 8; the internal stress evolution explained +1 test strips. 1 hot cracking plant cracking phenomenon. 2 The stress-strain study of liquefaction crack formation has not been reported.

6 Conclusion In general, the current research on the weldability of low-expansion superalloys mainly rests on the use of microscopic analysis methods and weldability tests to qualitatively investigate crack sensitivity from the metallurgical point of view. The study of the microstructure evolution and the numerical simulation of the stress and strain development in the welding process has just begun. In addition, it should be pointed out that high-energy-density welding methods such as electron beam welding and laser welding should be applied before precision manufacturing in the aerospace field. This type of welding heat source physical model is obviously different from ordinary fusion welding, and the thermal process also has different characteristics. Therefore, the numerical simulation of thermal process mechanics and microstructure evolution under high-energy-density welding conditions is more targeted and important. Only the combination of microstructure analysis and numerical simulation of the weldability test can be more clearly revealed in both metallurgy and mechanics. The formation mechanism of welding cracks in low-expansion superalloys and the influence of various factors are the guiding principles for the final formulation of the welding process and the effectiveness of preventing welding cracks. Zhang Shaowei. Development and Application of Low Expansion Superalloys . In the year of the outstanding correspondent of aviation manufacturing workers of the year, the correspondents of this publication gave great support to the editorial department in the work of drafting and advertising advertisements for group articles. The editorial department expresses its sincere gratitude for this, and gives the outstanding correspondents a glimpse of the future. I also hope that you will give more support and help to the publications.

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