EFFECT OF P，S AND Si ON THE SOLIDIFICATION，SEGREGATION，MICROSTRUCTURE AND MECHANICAL PROPERTIES IN Fe－Ni BASE SUPERALLOYS

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Effect of Magnesium and Cerium Microelement on Microstructures and Mechanical Properties of K465 Nickel-Base Superalloy

0.02%(mass fraction) Mg and 0.02% Ce were added into nickel-base superalloy, K465, in order to study their effect on microstructures and mechanical properties. The results showed that without addition of Mg and Ce, the grain boundaries was flat, the MC carbide precipitate was noncontinuous with particle shape. With 0.02% Mg addition the MC carbide tended to have tiny granular and blocky morphology, while it had a cursive script-like morphology with 0.02% Ce addition. It was also shown that without any addition of Mg and Ce, the room temperature properties, average tensile strength (σb) and yield strength (σ0.2) were 960 and 790 MPa, the creep rupture life under the condition of 1248 K, 230 MPa was 28.1 h. With the addition of 0.02% Mg, the room temperature properties, average tensile strength and yield strength had a certain enhancement, the creep rupture life (1248 K, 230 MPa) was up to 66.7 h. When the Ce addition was 0.02%, average tensile strength and yield strength were up to 1020～1030 MPa and 855～885 MPa, respectively, but the average elongation percentage fell down to 3.0%, only reaching the required value. The most expressive thing was that the creep rupture life (1248 K, 230 MPa) was only 17.25～18.77 h, far below the required value.

Effect of carbon on microstructure and mechanical properties of DD99 single crystal superalloy

The effects of carbon on the microstructure and mechanical properties of DD99 single crystal superalloy were investigated. The results show that stress rupture life of DD99 alloy possesses peak value at carbon content of 0.03%(mass fraction). As carbon addition is greater than 0.03%, the stress-rupture life decreases with the increase of carbon content. The tensile strength and yield strength of DD99 alloy reach peak value at 0.08% carbon and 760℃. On the contrary, the tensile strength and yield strength have minimal values at 0.08% carbon and 900℃. The tensile ductility of DD99 alloy basically decreases with the increase of carbon content at 760℃or 900℃. The amount of carbides greatly increases with the addition of carbon content. Dislocation moving is retarded by carbides so that dislocation networks are apt to form, which has an important role on the mechanical properties in DD99 single crystal superalloy.

Mechanical properties and microstructure changes after long-term aging at 700℃ for a nickel-base superalloy

Mechanical properties and microstructure changes have been investigated on a new nickel-base superalloy after long-term aging at 700℃. It is found that the major precipitates of the tested alloy are MC, M23C6, M6C and γ' in the course of long-term aging at 700℃. The carbides maintain good thermal stability with the aging time up to 5008 h. The growth rate of gamma prime precipitates is relatively high in the early aging period and then slows down. The coarsening behavior of gamma prime follows a diffusion-controlled growth procedure. The room temperature Rockwell hardness of the alloy aged at 700℃ increases slightly at the initial stage of aging, but it decreases with the prolonged time. It mainly depends on the size of gamma prime. In comparison with Nimonic lloy 263, the new alloy characterizes with higher tensile and stress-rupture strengths at high temperatures. The new nickel-base superalloy offers a combination of microstructure stability, strength, ductility and toughness at 700℃.

Effect of cooling rate on microstructure,microsegregation and mechanical properties of cast Ni-based superalloy K417G

The effects of different solidification rates after pouring on the microstructures,microsegregation and mechanical properties of cast superalloy K417 G were investigated.Scheil-model was applied to calculate the temperature range of solidification.The casting mould with different casting runners was designed to obtain three different cooling rates.The microstructures were observed and the microsegregation was investigated.Also,high temperature tensile test was performed at 900?C and stress rupture test was performed at 950?C with the stress of 235 MPa.The results showed that the secondary dendrite arm spacing,microsegregation,the size and volume fraction of γ'phase and the size of γ/γ'eutectic increased with decreasing cooling rate,but the volume fraction of γ/γ' eutectic decreased.In the cooling rate range of 1.42?C s^(-1)–0.84?C s^(-1),the cast micro-porosities and carbides varied little,while the volume fraction and size of phase and γ/γ' eutectic played a decisive role on mechanical properties.The specimen with the slowest cooling rate of 0.84?C s^(-1) showed the best comprehensive mechanical properties.

Effect of heat treatment on microstructure and high temperature tensile properties of cast nickel-base superalloy with high W, Mo and Nb contents

The microstructural features and high temperature tensile properties of M963 superalloy at as cast, as solutioned and as aged conditions were investigated in detail. The results show that the solution treatment at 1?220?℃ for 4?h, AC causes an increase in high temperature yield strength but a drastic drop in high temperature ductility due to the precipitation of both the secondary carbide M 6C along grain boundaries and at the interdendritic regions and very fine γ ′ particles in the dendrite cores. Aging treatment following the solution treatment can improve the high temperature tensile properties of M963 superalloy due to the coarsing of the γ′ precipitate. One stage aging at 850?℃ for 16?h following the solution treatment causes an increase in both strength and ductility of alloy M963, and two stage aging of 1?089?℃ / 2?h, AC plus 850?℃ / 16?h, AC following the solution treatment further increases the ductility of alloy M963 but slightly decreases its strength.

Effect of Phosphorus on Microstructure and High Temperature Properties of a Cast Ni-base Superalloy

Effect of phosphorus on the microstructure and high temperature properties of a cast Ni-base superalloy M963 has been investigated. SEM observation and EDS analysis showed that P was mostly enriched in the interdendritic region, and the P-rich phase was formed in the front position of finally solidified eutectics in high P doped alloys. It was found that the P-rich phase, as preferred initiation and propagation site of cracks, could aggravate the fracture process at high temperature in high P doped alloys. Consequently, high P addition would reduce remarkably the ductility and creep life of M963 superalloy at high temperature.

MICROSTRUCTURE AND MECHANICAL PROPERTIES OF NOVEL 718 SUPERALLOY

Recently, a novel 718 superalloy with remarkable structural stability at 680℃ has been designed and fabricated by CISRI (Central Iron and Steel Research Institute) etc. Phase identification of novel 718 alloy under the above-mentioned heat-treatment condition was performed using optical microscopy (OM), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). Results show that the novel 718 alloy has outstanding structural stability at 680℃. The novel 718 alloy possess excellent structural stability and good mechanical properties, which is attributed to ?’-phase strengthening and also to the specific sandwich structure of the γ’ + γ’’ strengthening phase.

MICROSTRUCTURE AND MECHANICAL PROPERTIES OF Fe-Ni-Co-BASE SUPERALLOY AFTER LONGTERM AGING AT 650℃

The microstructure and mechanical properties of a Ni-Fe-Co base superalloy with lowthermal expansion coefficient after aging at 650℃ for 200,500,1000 and 2000 h have beeninvestigated.It was found that they are stable at 650℃.This alloy is believed to.fill the re-quirements for long time service to aircraft engine.

Effects of returns on composition,microstructure and mechanical properties of GH4169 superalloy

To recycle the returned alloy effectively, effects of returns proportion on alloy composition, microstructure and compression properties of superalloy GH4169 were studied by means of scanning electron microscopy(SEM), energy dispersive spectroscopy(EDS) and thermal-mechanical simulator. The results show that returns addition has no significant effect on the main alloy elements content and the principle precipitates, but increases the volume fraction of Al_2O_3 inclusions, resulting in the increase of oxygen level of GH4169 alloy. Returns addition does not change the elastic and plastic deformation process at room temperature or at 1,150 °C, but high returns proportion GH4169 alloy shows improved compression strength and yield strength. The alloy with 100% returns shows a maximum compression strength 1,153.45 MPa at room temperature, while the alloy with 80% returns has a maximum value 69.3 MPa at 1,150 °C. Returns addition increases fluctuation range and reduces the stability of yield strength and compression strength of GH4169 alloy at room temperature. It is noted that the volume fraction and the size of Al_2O_3, and the fraction of Laves phase reach their maximum values in the GH4169 alloy with 60% returns, which exhibits maximum yield strength of 516.65 MPa at room temperature and 62.17 MPa at 1,150 °C.

Microstructure and Mechanical Properties of Spray Deposited Ni-based Superalloys

Three kinds of superalloys were prepared by spray deposited process. The analysis results of microstructures and mechanical properties indicate that the spray deposited preforms with higher integral densification and the oxygen content in each kind of superalloy was very low. The microstructures are consisted of fine grain without dendritic equi-axed. The spray deposited superalloys possessed good ductility. The forging experiment displays that even though the once deformation of spray deposited GH742 alloy more than 60%, the crack can not be found. Meanwhile, the mechanical properties of spray deposited superalloys are significantly increased.

Effect of boron addition on the microstructure and mechanical properties of K4750 nickel-based superalloy

The effect of boron addition at 0,0.007 wt.% and 0.010 wt.% on the microstructure and mechanical properties of K4750 nickel-based superalloy was studied.The microstructure of the as-cast and heat-treated alloys was analyzed by SEM,EPMA,SIMS and TEM.Lamellar M_(5) B_(3)-type borides were observed in boroncontaining as-cast alloys.After the full heat treatment,boron atoms released from the decomposition of M_(5) B_(3) borides were segregated at grain boundaries,which inhibited the growth and agglomeration of M_(23)C_(6) carbides.Therefore,the M_(23)C_(6) carbides along grain boundaries were granular in boron-containing alloys,while those were continuous in boron-free alloys.The mechanical prope rty analysis indicated that the addition of bo ron significantly improved the tensile ductility at room tempe rature and stress rupture properties at 750℃/430 MPa of K4750 alloy.The low tensile ductility at room temperature of 0 B alloy was attributed to continuous M_(23)C_(6) carbides leaded to stress concentration,which provided a favorable location for crack nucleation and propagation.The improvement of the stress rupture properties of boron-containing alloys was the result of the combination of boron segregation increased the cohesion of grain boundaries and granular M_(23)C_(6) carbides suppressed the link-up and extension of micro-cracks.

Microstructure and mechanical property of MIM 418 superalloy

In this study, the influence of hot isostatic pressing(HIP) process on the 418 alloy produced by metal injection molding(MIM) technique(named as MIM 418)was investigated based on the characteristic analysis of 418 alloy powder. And comparison analysis of the microstructure and mechanical property between the MIM 418 and as-cast 418 alloys was performed by scanning electron microscopy(SEM), energy-dispersive spectroscopy(EDS),and X-ray diffraction(XRD). The results show that MIM418 alloy exhibits fine grain(~30 μm) and uniform microstructure. The defects existing in MIM 418 alloy formed during sintering process can be eliminated through HIP treatment, and the relative density increases from97.0 % to 99.5 %. The mechanical property can be improved significantly because of the elimination of defects, and the tensile strength and elongation are1,271 MPa and 16.8 %, respectively, which are increased by 34.5 % and 180 % compared with K418 alloy after solution heat treatment.

Effects of the Solution Treatment on Microstructural Evolution, Mechanical Properties, and Fracture Mechanism of Nickel-Based GH4099 Superalloy

Grain growth, mechanical properties, and fracture mechanism of nickel-based GH4099 superalloy are investigated using heat treatments, tensile tests, optical microscopy (OM), and scanning electron microscopy (SEM) with energy dispersive X-ray spectroscopy (EDS). The OM observation shows that the matrix grains (γ-grains) undergo an apparent growth during the solution treatment. The grain size diameter increases from 100 to 174 μm when the solution temperature rises from 1100℃ to 1160℃ for 30 min. When the holding time increases from 15 to 60 min at 1140℃, the grain size diameter increases from 140 to 176 μm, indicating that the γ-grain growth is more sensitive to temperature than time. Standard deviation, Sv, and the grain size distribution are utilized to characterize the microstructural uniformity. To predict the grain size more accurately, we develop the grain growth kinetics and find that the growth index is close to 5. The yield strength (Rp0.2), tensile strength (Rm), and ductility (Af) are also measured. It is found that the effect decreases in the order cooling rate, solution temperature, time. Rp0.2 reduces by 47% with the increase in the cooling rate from 1℃ to 8000℃/min, while both strength and ductility exhibit little changes with time. The SEM results show that the fracture surfaces have typical mixed brittle and ductile characteristics when specimens are subjected to water quenching and air cooling. However, a complete brittle fracture occurs under furnace cooling conditions. The EDS analysis indicates that the brittle γ' (Ni3Ti) phase precipitates around the γ-grain boundary during the slow cooling process, which is the main factor yielding the complete brittle fracture. Finally, the optimal solution treatment scheme for the GH4099 superalloy is proposed—a temperature of 1140℃ for 30 min followed by air cooling.

Effects of Varying Copper Content on the Microstructure and Mechanical Properties of FeCoNiCu_(x)

Five sets of high entropy alloys(HEAs)FeCoNiCu_(x)(x=0.5,1.0,1.5,2.0,2.5)were produced by vacuum induction smelting.The effects of Cu content on the microstructure and mechanical properties of the alloys were interrogated by X-ray diffractometer(XRD),field scanning electron microscope(FESEM)and tensile mechanical test.The result shows that the HEAs form single FCC solid solution phase.With the increase of Cu content,the diffraction peak first deviated to the right and then shifted to the left.The alloys changed from equiaxed crystal structure to refined dendritic crystal structure,as Cu content increased.A large number of Cu atoms are isolated in the inter-crystalline region.The tensile mechanical tests show that with the increase of Cu content,the ultimate tensile strength first increased and then decreased.When x is 2.0,the ultimate tensile strength reaches a maximum of 473 MPa,the percent elongation is 43.0%,and the fracture presents ductile behaviour.

Effect of ultrasonic micro-forging treatment on microstructure and mechanical properties of GH3039 superalloy processed by directed energy deposition

In this work,ultrasonic micro-forging treatment(UMFT)was introduced to achieve homogeneous microstructure,reduce defects and improve mechanical properties of GH3039 superalloy cladding layer processed by directed energy deposition(DED).The microstructure,defects and mechanical properties of the cladding layers treated by UMFT with different ultrasonic powers(UIPs)were investigated.Results revealed a gradient structure as equiaxed grains distributed at the top,a columnar-to-equiaxed transition(CET)region that mixed of columnar dendrites and equiaxed grains distributed at the middle and columnar dendrites at the bottom of the cladding layer was formed.After UMFT,the proportion of equiaxed grains was increased,the average size of equiaxed grains was refined to 10μm from 16μm,the orientation of grains was more uniform and the phases enriched of Al,Ti,C,Nb and Mo were precipitated.The grain refinement can be attributed to the fracture of columnar dendrites induced by the ultrasonic vibration during solidification.Besides,the porosity of the cladding layer was reduced after UMFT.The microhardness of the cladding layers exhibited a depth-dependent gradient at the top region.The microhardness of the top surface was the highest and showed an increasing trend with the increase of UIP.The microhardness of different grain morphologies exhibited no substantial difference.However,due to grain refinement and precipitation of strengthening phase induced by UMFT,the microhadness of some local locations were improved.These results indicated UMFT has a significant effect on improving the microstructure,defects and mechanical properties of the deposited cladding layer.

Microstructure and stress rupture properties of polycrystal and directionally solidified castings of nickel-based superalloys

A new directionally solidified Ni-based superalloy DZ24,which is a modification of K24 alloy without rare and expensive elemental additions,such as Ta and Hf,was studied in this paper.The microstructure and stress rupture properties of conventionally cast and directionally solidified superalloys were comparatively analyzed.It is indicated that the microstructure of K24 alloy is composed of γ,γ′,γ/γ′ eutectics and MC carbides.Compared with the microstructure of K24 polycrystalline alloy,γ/γ′ eutectic completely dissolves into the γ matrix,the fine and regular γ′ phase reprecipitates,and MC carbides decompose to M6C/M23C6 carbides after heat treatment in DZ24 alloy.The rupture life of DZ24 alloy is two times longer than that of K24 alloy.The more homogeneous the size of γ′ precipitate,the longer the rupture life.The coarsening and rafting behaviors of γ′ precipitates are observed in DZ24 alloy after the stress-rupture test.

Effect of Cooling Rate on Microstructure and Mechanical Properties of K465 Superalloy

K465 superalloy,as a material for production of turbine nozzle,shows high mechanical properties as well as microstructure stability under critical and severe service conditions.The appropriate microstructure and strength of this alloy can be obtained by solid solution strengthening mechanism.Heat treatment parameters such as time and temperature of homogenization,partial solution and aging temperatures,and cooling rate from solid solution temperature affect the microstructure of the alloy.Among these parameters,cooling rate from solid solution temperature is the most effective.Therefore,the effect of cooling rate on microstructure and mechanical properties(tensile and stress properties) was investigated.For this purpose,three different cooling rates were applied to the cast K465 specimens subjected to solution treatment at 1 483 K for 4 h.Microstructures of the specimens then were studied using optical and electron microscopy.Also,tensile tests were performed at room temperature and stress rupture tests were performed under the condition of 1 248 K and 230 MPa.It was found that with increasing the cooling rate,the size of the γ' precipitates decreases and the mechanical properties of specimens increases.Also,it was found that the shape and volume fraction of primary γ' particles are largely influenced by the cooling rate after solution treatment at 1 483 K for 4 h.

Microstructures and mechanical properties of DZ125 directional solidified superalloy repaired by HIP technology

DZ125 directional solidified superalloys show excellent bearing temperature ability and creep resistance and have been widely used to manufacture the advanced aviation engine blades parts.However,the high temperatures and stresses for longtime service would cause a loss of mechanical properties and service life.In this paper,the damaged alloys were repaired using hot isostatic pressing combined with rejuvenation heat treatment technology,where the irregularγ'phases in damaged alloys are recovered to be cubic particles like original state and the creep cavities and casting porosities also reduce obviously compared with those in damaged state.The restorable alloys exhibit apparently higher tensile properties and hardness than the alloys in damaged state,which is close or even more than those of original alloy,and their elongation and rupture life can satisfy criterion completely.This method can be easily extent to repair other damaged superalloys.

Effect of solution cooling rate on the microstructure and creep deformation mechanism of a rhenium-free second-generation single crystal superalloy

Various cooling scenarios(water,oil,air and furnace)were employed to study the impacts of the solution cooling rate(SCR)on the microstructure and creep behavior of a novel single-crystal(SX)superalloy.The results showed that the cubic degree and size of theγphases were inversely proportional to the SCR.The creep life first increased and then dropped dramatically with a reduction in the SCR.The creep life of the sample cooled with air cooling(AC)was the highest,up to 144.90 h at 800℃/750 MPa and160.15 h at 1100℃/137 MPa.During creep at 800℃/750 MPa,the improved creep life of the AC sample was mainly attributed to the fine cubicγphases,which decreased the rate ofγ-phase coarsening and favoured plastic deformation by promoting the active movement of dislocations.The AC helped theγphases become rich in Al,Ti and Ta while depleted in Co and Cr,which enhanced its stacking fault energy,thus promoting the formation of dislocation locks.Meanwhile,the largest negative lattice misfit caused by AC induced denserγ/γinterface dislocation networks at 1100℃/137 MPa,which efficiently reduced the minimum creep rate.The calculated average dislocation spacing results indicated that the smallest density of excess dislocations corresponded to the AC sample,proving its greatest creep resistance.Interestingly,the size of the secondaryγphases first decreased and then increased sharply with decreasing SCR during creep at 1100℃/137 MPa,when fine secondaryγphases had a positive role in the blockage of dislocation movement in the matrix.Eventually,the comprehensive SCR effect was explored to provide more guidance in the design of Re-free SX superalloys.