Effect of Ru on stress rupture properties of nickel-based single crystal superalloy at high temperature

Two experimental single crystal superalloys, Ru-free alloy and Ru-containing alloy with [001] orientation, other alloying element contents being basically kept same, were cast in the directionally solidified furnace. The effect of Ru on the stress rupture properties of the single crystal superalloy was investigated at （980 ℃, 250 MPa）, （1100 ℃, 140 MPa） and （1120 ℃, 140 MPa）. The results show that Ru can enhance high temperature stress rupture properties of single crystal superalloy. The improvement effect of Ru addition on stress rupture properties decreases with increasing test temperature. The γ′ coarsening and rafting directionally are observed in Ru-free alloy and Ru-containing alloy after stress rupture test. Needle shaped TCP phases precipitated in both of alloys after stress rupture test at （1100 ℃, 140 MPa） and （1120 ℃, 140 MPa） and no TCP phase was observed in both of alloys after stress rupture test （980 ℃, 250 MPa）. The precipitate volume fraction of TCP phases is significantly decreased by the addition of Ru. At last, the relationship between the microstructure change with Ru addition and improvement of stress rupture properties was discussed.

Effect of Phosphorus on Stress Rupture Properties of GH4133 Ni-Base Superalloy

The effect of phosphorus on the stress rupture property of GH4133 alloy has been investigated and is compared with that of IN718 alloy. The GH4133 alloy is crept by dislocation movement. Phosphorus has a tendency to prolong the rupture life of some wrought superalloys by inhibiting the dislocation movement. If the phosphorus addition is too high, its effect on impairing the grain boundary cohesion overwhelms that on inhibiting the dislocation movement, and the life of the GH4133 alloy can be shortened. The two functions of inhibiting the dislocation movement and impairing the grain boundary cohesion determine that the optimum phosphorus content in the GH4133 alloy is around 0.011 wt pet. Phosphorus exhibits a greater effect on prolonging the rupture life of IN718 alloy than that of GH4133 alloy. The two alloys are crept by different mechanisms. The intergranular phosphorus-bearing phase is precipitated in the IN718 alloy, while not in the GH4133 alloy. The precipitation of the phosphorus bearing phase can balance the phosphorus segregation at the grain boundaries and allows a more remarkable effect of phosphorus on extending the rupture life of IN718 alloy.

Effect of γ' formation and strengthening elements on microstructures and stress rupture property of single crystal super-alloys

An investigation was carried out to study the effects of γ' formation and strengthening elements (Al, Ti and Ta) on the microstructure and stress rupture properties of nickel base single crystal super-alloys.The results show that with the increase of γ' formation and strengthening elements, the percentage of γ-γ' eutectic and the misfit degree of γ/γ' increases.Detailed microstructural analysis revealed that with the increase of γ' forming element content, the morphology of γ' changed from spherical to cubic, then irregular shape; and the size of γ' increases gradually.Excessive γ' formation and strengthening elements will lead to the precipitation of μ phase during stress rupture tests.The alloy with 5wt.%Al, 1wt.%Ti and 6wt.%Ta has the best stress rupture property.

EFFECT OF HEAT TREATMENT ON INTERMEDIATE TEMPERATURE STRESS RUPTURE PROPERTIES OF ALLOY K403

The standard heat treatment of cast nickel base superalloy K403 is the solid solution treatment of 1210℃/4h, air cooling. It is very difficult to meet the requirements of Aviation Standard HB5155, in which the stress rupture life at 750℃ and 645MPa is longer than 50h. The results showed that the intermediate temperature stress rupture properties impaired by treatment of 1210℃/4h were due to precipitation of too small γ′ phase(<0.2μm) in grains and absence of the secondary carbides at grain boundaries. Microstructure containing the intergranular M6C carbides with envelope of γ′ and the residual coarse γ′ was obtained by means of 1180℃/4h treatment, therefore the stress rupture life was obviously increased to meet the demand of HB5155. The effect of γ′ size was also discussed from the view point of deformation mechanism in this paper.

Influence of thermal exposure on microstructure and stress rupture properties of a new Re-containing single crystal Ni-based superalloy

In this study, the long-term thermal microstructural stability and related stress rupture lives of a new Re-containing Ni-based single-crystal superalloy, DD11, were investigated after high-temperature exposure for different lengths of time. The results show that the γ' precipitates retained a cuboidal morphology and the γ' size increased after short thermal exposure for 50 h at 1,070℃. As the thermal exposure time was prolonged to 500 h, the cuboidal γ' gradually changed into irregular raft-like morphology due to particles coalescence, and the morphology of the microstructure was almost unchanged after further thermal exposure up to 3,000 h. The stress rupture experiments at 1,070℃ and a tensile stress of 140 MPa showed that the rupture lives increased significantly after thermal exposure for 50 h and dropped dramatically with increasing exposure time up to 500 h but decreased slowly after exposure for more than 500 h. These results imply that stress rupture properties did not decrease when the γ' remained cuboidal but degraded to different extents during the γ' coarsening process. The coarsening of the γ' precipitates and change in morphology were regarded as the main factors leading to the degradation of the stress rupture lives. This study provides fundamental information on the high-temperature longterm microstructural stability and mechanical performance, which will be of great help for DD11 alloy optimization and engineering aeroengine applications.

Effect of boron addition on the microstructure and stress-rupture properties of directionally solidified superalloys

This study is focused on the effect of boron addition, in the range of 0.0007wt% to 0.03wt%, on the microstructure and stress-rupture properties of a directionally solidified superalloy. With increasing boron content in the as-cast alloys, there is an increase in the fraction of the γ′/γ eutectic and block borides precipitate around the γ′/γ eutectic. At a high boron content of 0.03wt%, there is precipitation of lamellar borides. Upon heat treatment, fine block borides tend to precipitate at grain boundaries with increasing boron content. Overall, the rupture life of the directionally solidified superalloy is significantly improved with the addition of nominal content of boron. However, the rupture life decreases when the boron content exceeds 0.03wt%.

Effect of Nb content on microstructure stability and stress rupture properties of single crystal superalloy containing Re and Ru

Three experimental single crystal superalloys with 0%Nb,0.5%Nb,1.0%Nb were cast in the directionally solidified furnace,while other alloying element contents were basically kept unchanged.The effect of Nb on the microstructure,stability at1100°C and stress rupture properties at 1070°C and 160 MPa of the single crystal superalloy were investigated.The experiment results show that the primary dendrite arm spacing decreases and the volume fraction ofγ/γ′eutectic of the alloy increases with the increase of Nb content in the as-cast microstructures.The size ofγ′phase particles becomes small and uniform and the cubic shape does not obviously change with the increase of Nb content.The precipitating rate and volume fraction of TCP phases increase significantly with the increase of Nb content in the process of long term aging at 1100°C.The stress rupture lives increase and elongation decreases with increasing Nb content at 1070°C/160 MPa.At last,the relationship between the microstructures stability,stress rupture properties of the alloy and Nb content is discussed based on JMat Pro software and the lastest relevant database for single crystal superalloy.

Effect of anisotropy on microstructure and high temperature stress rupture properties of Ni_3Al base single crystal alloy

The effect of anisotropy on microstructure and high temperature stress rupture property of Ni3Al base single crystal alloy was investigated. The single crystal specimens were produced by screw selection crystal method. The microstructures were examined by OM, SEM, TEM and X-ray EDS techniques. The stress rupture tests were carried out in air by constant load creep machines under 1 100℃and 130 MPa. The experimental results show that the dendrites preferential orientation deviates certain angles to heat flow orientation, and the secondary arms occur for different crystallographic orientations. The single crystal alloy with different orientations shows obvious anisotropy during tensile stress rupture tests under 1 100℃and 130 MPa. The <111> orientation specimen has the best stress rupture life of 211 h. The high ductility at 1 100℃of the <001> orientation specimen may be attributed to the most multiple equivalent slip systems.

Effect of dendrite arm spacing and the γ' phase size on stress rupture properties of Ni_3Al-base single crystal superalloy IC6SX

The effect of dendrite arm spacing and the size of γ' phase on stress rupture properties of as-cast Ni3Al-based single crystal superalloy IC6SX was studied.It has been found that the stress rupture properties were affected by dendrite arm spacing and the size of γ' phase significantly,i.e.,the stress rupture lives of as-cast specimens under the test condition of 1100°C/120 MPa were significantly increased from about 10 h to 31 h with decreasing dendrite arm spacing and the size of γ' phase from 3.0 μm and 1.6 μm to 1.3 μm and 0.8 μm,respectively.The creep cracks generated easily in the brittle Y-NiMo phase.Then the cracks gradually mergered and grew up during creep,and finally led to specimens fracture.The orientated coarsening of γ' phase has been found in the stress ruptured specimens,due to the elements diffusion.However,the γ' phase did not form the integrated structure during the short periods of 10-31 h as the creep tests lasted.

Microstructures and properties of transient liquid phase diffusion bonded joints of Ni_3Al-base superalloy

An investigation of transient liquid phase (TLP) diffusion bonding of a Ni 3Al base directionally solidified superalloy, IC6 alloy, was presented. The interlayer alloy employed was Ni Mo Cr B powder alloy. The results show that the microstructure of the TLP diffusion bonded joints is a combination of γ solid solution (or a γ+γ′ structure) and borides. With the bonding time increasing, the quantity of the borides both in bonding seam and adjacent zones is gradually reduced, and the joint stress rupture property is improved. The obtained stress rupture property of the TLP bonded joints is on a level with the transverse property of IC6 base materials. [

Stress rupture properties and deformation mechanisms of K4750 alloy at the range of 650℃ to 800℃

The stress rupture properties and deform ation mechanism s of K4750 alloy at 650 ℃, 700 ℃, 750 ℃ and 800 ℃ were investigated. As the decrease of tem perature and stress, the stress rupture life gradually increased. A Larson-Miller Parameter (LMP) method was used for analyzing the stress rupture life under different conditions. The linear fitting formula between stress (σ) and LMP was derived as σ= 3166.455-119.969 ×LMP and the fitting coefficient w as 0.98. After testing, the dislocation configurations of all stress rupture samples w ere investigated by transm ission electron microscopy (TEM). The tem perature and stress had a significant impact on the deform ation m echanism, thereby affected the stress rupture life of K4750 alloy. As the increasing stress at a given tem perature, the deform ation m echanism gradually transform ed from Orowan looping to stacking fault shearing. Based on experim ental results, the threshold stress at 650 ℃, 700 ℃, 750 ℃ and 800 ℃ for the transition of deformation mechanism was estimated to be about 650 MPa, 530 MPa, 430 MPa and 350 MPa, respectively. Below the threshold stress,γ phase effectively hindered dislocation motion by Orowan looping mechanism, K4750 alloy had along stress rupture life. Slightly above the threshold stress, Orowan looping combining stacking fault shearing was the dom inant mechanism ,the stress rupture life decreased. As the further increase of stress, stacking fault shearing acted as the dominant deformation mechanism , the resistance to dislocation motion decreased rapidly, so the stress rupture life reduced significantly.

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 718alloy possess excellent structural stability and good mechanical properties,which is attributed to y-phase strengthening and also to the specific sandwich structure of theγ′+γ'strengthening phase.

Effects of Dendritic Orientation on Stress Rupture Properties of DD6 Single Crystal Superalloy

DD6 single crystal superalloy slabs were prepared with seed method in the direetionally solidified furnace with high temperature gradient. The transverse stress rupture properties and fracture hehaviour of the alloy at 760 ℃/758 MPa, 850 ℃/550 MPa and 980 ℃/250 MPa were investigated and compared with those of longitudinal specimens. The transverse stress rupture lives are corresponding with the longitudinal stress rupture lives at 760 ℃/758 MPa and 850 ℃/550 MPa. The transverse stress rupture lives are slightly less than the longitudinal stress rupture lives at 980 ℃/ 250 MPa. The fracture mechanism of the transverse stress rupture of the alloy at 760 ℃/758 MPa shows quasi-cleav- age mode and the fracture mechanism at 980 ℃/250 MPa shows dimple mode, while the fracture mechanism at 850 ℃/ 550 MPa shows quasi-cleavage and dimple mixture mode. At higher temperature and lower stress, the microeracks are easier to initiate and interconnect in the transverse specimen than those in longitudinal specimen because there are interdendritic regions perpendicular to the axis of stress.

Effect of Hf on Stress Rupture Properties of DD6 Single Crystal Superalloy After Long Term Aging

The specimens of the second generation single crystal superalloy DD6 with different Hf contents were prepared in the directionally solidified furnace with a high temperature gradient. The long term aging of the specimens after full heat treatment was performed at 1040℃for 800 h. The effect of Hf on the microstructure and stress rupture properties under 980℃/250 MPa of the alloy after long term aging was investigated. The results show that the γ＇ coarsening and rafting and no topologically close packed phase （TCP） are observed in the microstructures of DD6 alloy with different Hf contents after aged at 1 040℃ for 800 h. It indicates that DD6 alloy with different Hf contents all possesses good microstructure stability. With increasing Hf content the rupture life after long term aging turns shorter and the elongation represents the increasing first and decreasing afterwards. The fracture mechanism of the alloy with different Hf contents at 980℃/250 MPa all shows dimple model. The influence of the microstructures on the stress rupture properties of the alloy is also discussed.

Effect of Heat Treatment on Microstructure and Stress Rupture Properties of a Ni–Mo–Cr–Fe Base Corrosion-Resistant Superalloy

The influences of heat treatment and test condition on the microstructure and stress rupture properties of a Ni–Mo–Cr–Fe base corrosion-resistant superalloy have been investigated in this paper. Optical microscope and scanning electron microscope were employed for the microstructure observation, and X-ray diffraction, electron probe micro-analyzer, and transmission electron microscope were used for phase determination. It was found that the grain size increased and the volume fractions of initial M_6C carbides decreased along with the increase in solution treatment temperature. When tested at 650 °C/320 MPa, the stress rupture lives decreased with the increase in solution treatment temperature, but the stress rupture lives increased slightly at first and then decreased for the samples solution heat treated at 1220 °C when tested at 700 °C/240 MPa. The elongations showed the descendent trends under these two conditions. The stress rupture life and elongation for the aged samples all showed a noticeable improvement at 650 °C/320 MPa, but there was no noticeable improvement at 700 °C/240 MPa. The reasons can be attributed to the grain size, test conditions, and the initial and secondary carbides.

Effects of Heat Treatment on Surface Recrystallization and Stress Rupture Properties of a Fourth-Generation Single-Crystal Superalloy after Grit Blasting

The specimens of a fourth-generation single-crystal superalloy were grit-blasted and heat-treated in vacuum at 1100, 1150, 1200, 1250 and 1300 °C for 4 h, respectively. Then, the microstructure and the stress rupture properties of the recrystallized alloy were investigated at 1150 °C/120 MPa. The results showed that a cellular recrystallization occurred in the surface layer after heating at 1100, 1150 and 1200 °C for 4 h. An equiaxed recrystallization formed as the specimen was heat-treated at 1300 °C for 4 h, while a mixed recrystallization occurred in the specimen heat-treated at 1250 °C for 4 h. The recrystallized depth clearly increased with a rise of the heat treatment temperature. The stress rupture life continuously decreased with a rise of the heat treatment temperature up to 1250 °C. Although the overall stress rupture life reduced to different degrees, the stress rupture life of specimen after heat treatment at 1300 °C was relatively high and intermediate between those of specimens treated at 1150 and 1200 °C. The fact that the stress rupture life reduced to different degrees after heat treatment can be attributed to the recrystallization of the surface layer and to the microstructure evolution of the interior of the specimen. The small γ’ phase precipitated again after heat treatment at 1300 °C for 4 h. So,the stress rupture life was relatively longer than that after heat treatment at 1200 or 1250 °C although the equiaxed recrystallization formed in the surface layer.

Microstructure evolution and stress rupture properties of K4750 alloys with various B contents during long-term aging

The relationship among B content,microstructure evolution and stress rupture properties of K4750 alloy during long-term aging were investigated.After aging at 800℃for 1000 h,the decomposition degree of MC carbides of K4750 alloys with 0 B,0.007 wt.%B and 0.010 wt.%B were basically identical,which indicated that B has no inhibition on MC carbide decomposition during long-term aging.The MC carbide decomposition was accompanied by the formation of M_(23)C_(6) carbides and a small number ofηphases,which was controlled by the outward diffusion of C and Ti combined with the inward diffusion of Ni and Cr from theγmatrix.In addition,M_(23)C_(6) carbides in boron-free alloy were in continuous chain and needle-likeηphases were precipitated near them,while M_(23)C_(6) carbides in boron-containing alloys remained in granular distribution and noηphases precipitation around them.Adding B could delay the agglomeration and coarsening of M_(23)C_(6) carbides during long-term aging,which was because the segregation of B at grain boundary retarded the diffusion of alloy elements,thus weakened the local fluctuation of chemical composition near grain boundary.The stress rupture samples of K4750 alloys with various B contents after aging at 800℃for 1000 h were tested at 750℃/380 MPa.The results indicated that the stress rupture properties of bo ron-containing alloys were significantly better than that of boron-free alloy,which could be attributed to the increase of grain boundary cohesion strength and the optimization of M_(23)C_(6) carbide distribution due to the addition of B.

Effect of Co on Microstructure and Stress Rupture Properties of K4750 Alloy

The effects of substituting Co for Fe on the microstructure and stress rupture properties of K4750 alloy were studied.The microstructure of the alloy without Co(K4750 alloy)and the alloy containing Co(K4750-Co alloy)were analyzed.Substitution of Co for Fe inhibited the decomposition of MC carbide and the precipitation ofηphase during long-term aging treatment.In K4750-Co alloy,the morphology of MC carbide at the grain boundary(GB)remained dispersed blocky shape and noηphase was observed after aging at 750℃ for 3000 h.However,in K4750 alloy,almost all the MC carbides at GBs broke down into granular M23C6 carbide and needle-likeηphase.The addition of cobalt could delay the decomposition of MC carbides,which accordingly restricted the elemental supply for the formation ofηphase.The stress rupture tests were conducted on two alloys at 750℃/430 MPa.When Co is substituted for Fe in K4750 alloy,the stress rupture life increased from 164.10 to 264.67 h after standard heat treatment.This was mainly attributed to increased concentration of Al,Ti and Nb inγ’phase in K4750-Co alloy,which further enhanced the strengthening effect ofγ’phase.After aging at 750℃ for 3000 h,substitution of Co for Fe can also cause the stress rupture life at 750℃/430 MPa to increase from 48.72 to 208.18 h.The reason was mainly because MC carbide degradation andηphase precipitation in K4750 alloy,which promoted the initiation and propagation of micro-crack during stress rupture testing.

Effects of cerium addition on the microstructure and stress rupture properties of a new nickel-based cast superalloy

The microstructure and stress rupture properties of a new nickel-based cast superalloy were investigated with the cerium(Ce)additions of 0,19,50,96,150,and 300 ppm,respectively.The results indicated that Ce was mainly found in M C and M 23 C 6 carbides,and it was also found to exist in the form of cerium-rich phases or inclusions.According to the microstructure evidence,Ce promoted the formation of M C carbides and aggravated the inhomogeneity of M 23 C 6 carbides along grain boundaries.It was also identi-fied that the average sizes of primary and secondaryγ’phases all decreased with the rising Ce content.The acceleration of Ti,Nb,and C segregations during solidification was attributed to the influence of cerium on the variation of carbides along grain boundaries.The stress rupture life experienced a signifi-cant drop as the Ce content increased from 19 to 300 ppm.Explorations showed that the degradation was mainly attributed to the severe degradation of M C carbides and the easily forming micro-voids around them caused by the Ce addition.In addition to that,the increments in the inhomogeneous distribution of M 23 C 6 carbides at grain boundaries and the accelerated coarsening rate ofγ’phases both induced the fracture under complex stress conditions.

Effect of grain boundary precipitates on the stress rupture properties of K4750 alloy after long-term aging at 750℃for 8000 h

In K4750 alloy,the evolution of grain boundary(GB)precipitates,including the degradation of blocky MC carbide particles and the precipitation of granular/needle-likeηphase particles,were observed after longterm aging(LA)at 750℃for 8000 h.During MC degradation,the Ti and C released from the MC carbide combined with Ni and Cr,respectively,in theγ’matrix to formη-Ni_(3)Ti phase and Cr-rich M_(23)C_(6)carbide.Large amounts of granularηphase precipitated at GBs and the needle-likeηphase grew gradually from GBs toward the grain interior.Because of the growth of theηphase through absorbingγ’phase,γ-depleted zones were formed around theηphase.The evolution of the MC carbide andηphase was primarily responsible for the decrease of the stress rupture life and the increase of elongation.After an LA sample was tested at 750℃and 360 MPa,the residual strain distribution was investigated by electron backscatter diffraction(EBSD).The results showed that the residual strain mainly distributed at GBs,especially in the region of MC degradation and at the edges ofηphases,which was closely related to the appearance of phase interfaces.Microvoids/cracks easily initiated at phase interfaces,then easily extended along theγ-depleted zones,thus the stress rupture life of LA samples was substantially shorter than that of samples subjected to the standard treatment.In particular,because of large amounts of fine degraded MC,granular M_(23)C_(6)and granularηphase particles distributed at GBs after 750℃/8000 h LA and microvoid/crack formation could be hindered by the formation of dimples,which led to an increase of elongation.