Influence of Ru Content on Microstructural Stability and Stress Rupture Property of DD15 Alloy

A fourth generation single crystal(SC)nickel based cast superalloy DD15 with 1%Ru,3%Ru,5%Ru was prepared using vacuum induction single crystal furnace in order to optimize the properties and cost of DD15 alloy.The exposure experiment of three alloys was conducted at 1100℃for 1000 h.The stress rupture properties tests were performed at 1100℃temperature and 137 MPa pressure.The composition optimization of Ru element in DD15 alloy had been studied.It was found that the alloys with different Ru contents all consist of cuboidalγ′phase embedded coherent inγphase.Theγ′phase of the alloy all has a size of about 300-500 nm and a volume content of more than sixty percent.The dimension ofγ′precipitates is reduced and uniform with increase of Ru content.Ru element can reduce the distribution ratio of high melting point element,so the microstructural stability is enhanced with Ru content increasing.No topologically close-packed(TCP)phase precipitated in the 5%Ru alloy even after 1000 h exposure.The stress rupture life of the alloy is significantly improved as Ru content rising.The raft breadth decreases slightly as Ru content increases.The specimen with 1%Ru and 3%Ru exhibits the presence of TCP phases and without TCP phases precipitated in fracture specimen with 5%Ru.The density and integrity ofγ/γ′interfacial dislocation network increase as Ru content of the alloy rises.

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 High Temperature Stress Rupture Strength of Brazing Seam for Nickel-base Superalloy

In order to enhance the high-temperature stress rupture strength of brazing seam by heat treatment, it was diffusion treated, then solution heat treated, and finally aging treated. The microstructure of brazing seam especially morphology of gamma ' phase and boride was observed and the strength of brazing seam was measured in this process. The results show that heat treatment can enhance high-temperature stress rupture strength by improving the microstructure of brazing seam. The strength of brazing seam after solution heat treatment decreases in comparison with that only after diffusion treatment while aging treatment after solution heat treatment increases the strength of brazing seam.

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.

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.

The stress field and rupture feature in compound model containing typical cracks system and hard-inclusion

Aiming at the research on mechanical mechanism of hard-inclusion earthquake preparation model, in this paper,experimental and contrast research on stress field and rupture feature of hard-inclusion model has been made respectively, which contained en echelon and composite cracks systems in models, and was loaded under uniaxial compressive stress. The result shows that reverse en echelon and T-shape cracks systems in hard-inclusion are the favorable geological structures to trigger earthquakes.

Metallurgical Forensics: Investigating a Superheater Tube Failure in Industrial Process Plants

A metallurgical forensic investigation was conducted to determine the cause of a failed superheater tube. Analysis techniques by Visual Examination, Energy Dispersive X-ray Analysis, Mechanical Testing and Metallographic Investigation were conducted, together with a comparative study from an inlet elbow section that did not fail. The superheater tube suffered premature failure after being in service for about two years. It was concluded that the failed tube underwent overheating, corrosion-erosion, embrittlement, and eventual failure under its internal pressure by stress rupture. The analysis revealed intergranular cracks, window fracture features and spheroidization of pearlite with grain growth. A possible contribution to embrittlement was from copper. Follow-ups and recommendations were provided, as well as covering materials, inspection, and operational considerations.

Study on Stress Triggering During the Activity Process of the Jiashi Strong Earthquake Swarm

The Bachu-Jiashi earthquake of MS6.8 occurred on February 24,2003,about 20km from the southeast of the 1997～1998 Jiashi seismic region in Xinjiang,and its aftershocks are rich and strong.Did the 1997～1998 Jiashi strong earthquake swarm trigger the Bachu-Jiashi MS6.8 earthquake? The Atushi earthquake of MS6.7 occurred in 1996,and the 1997～1998 Jiashi strong earthquake swarm occurred about 70km from the Atushi earthquake 10 months later.Did the Atushi earthquake of M-S6.7 encourage the 1997～1998 Jiashi strong earthquake swarm? There were 9 earthquakes with M-S6.0 from 1996 to 1997 in the Jiashi seismic region,how did they act on each other? To answer the above questions,the article studies the triggering effect of the activity process of the whole Jiashi earthquake swarm from the 1996 Atushi earthquake of M-S6.7,the 1997～1998 Jiashi strong swarm to the 2003 Bachu-Jiashi earthquake of M-S6.8,and analyzes the seismicity characteristics around the Jiashi region.The results show that the 1996 Atushi earthquake of M-S6.7 encouraged the 1997～1998 Jiashi strong swarm to some extent,the accumulative Coulomb stress change from the previous M-6.0 earthquakes of the Jiashi strong swarm had certain triggering effects on the following M-6.0 events,and the Coulomb stress change converted from the Jiashi strong swarm strongly encouraged the 2003 Bachu-Jiashi earthquake with M-S6.8.

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 stabilizing treatment on microstructure and stress rupture properties of phosphorus microalloyed Inconel 706 alloy

The microstructure and stress rupture properties of Inconel 706 alloy microalloyed with phosphorus are examined under stabilizing and unstabilizing heat treatment conditions.It was found that applying the stabilizing treatment resulted in a 98% increment in the stress rupture life and a 215% increment in the elongation tested at 650℃/690 MPa for the alloy compared to that under the unstabilizing heat treatment condition.The stabilizing treatment led to the precipitation of rod-shaped and needle-shaped n phases at the grain boundaries.Morphologies of γ'-γ" co-precipitates in the grain interior were noncompact form and compact form for the alloy under unstabilizing and stabilizing heat treatment conditions,respectively.Based on the microstructure characterizations,the improvement of stress rupture properties by the stabilizing treatment was attributed to the precipitation of n phases at the grain boundaries,which can hinder cracks initiation and propagation and relieve the stress concentration.

Determination of multiaxial stress rupture criteria for creeping materials:A critical analysis of different approaches

Materials in engineering applications are rarely uniaxially-loaded.In reality,failures under multiaxial loading has been widely observed in engineering structures.The life prediction of a component under multiaxial stresses has long been a challenging issue,particularly for high temperature applications.To distinguish the mode of failure ranging from a maximum principal stress intergranular damage to von Mises effective stress rupture mode a multiaxial stress rupture criterion(MSRC)was originally proposed by Sdobyrev and then Hayhurst and Leckie(SHL MSRC).A multiaxial-factor,α,was developed as a result which was intended to be a material constant and differentiates the bias of the MSRC between maxi-mum principal stress and effective stress.The success of the SHL MSRC relies on accurately calibrating the value ofαto quantify the multiaxial response of the material/geometry combination.To find a more suitable approach for determining MSRC,the applicability of different methods are evaluated.Given that the resulting analysis of the various approaches can be affected by the creep failure mechanism,princi-ples in the determination of MSRC with and without using continuum damage mechanics approaches are recommended.The viability of uniaxial material parameters in correlating withαthrough the analysis of available data in literature is also presented.It is found that the increase of the uniaxial creep dam-age tolerance parameterλis accompanied bythe decreaseof theα-value,whichimplies thatthe creep ductility plays an important role in affecting the multiaxial rupture behavior of materials.

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.

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. [

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 and Zr Contents on Stress-rupture and Fatigue Crack Growth Rate Performances in FGH96PM Superalloy

Four experimental FGH96 alloys with various contents of Hf and Zr （0 and 0.04%, 0.3% and 0.04%, 0.6% and 0. 04%, 0. 3% and 0.06%, respectively） were produced using PREP （plasma rotating electrode process）＋ HIP （hot isostatic pressing） route. The unnotched and notched stress-rupture properties and fatigue crack growth rate （FCGR） of all the experimental alloys were investigated to study the effect of Hf and Zr. Relevant fracture morphol ogy and microstructure were observed by scanning electron microscopy and transmission electron microscopy. The results revealed that appropriate content of Hf could lengthen stress-rupture life, eliminate notch sensitivity and slo wer FCGR. Microstructure analysis showed that the amount of ＂f phase should be increased or decreased by adjusting Hf and Zr contents, and MC carbide and oxide coupled growth should be increased by adding Hf content, which caused oxycarbide to precipitate along grain boundary and strengthen the alloy. It was found that excessive Zr in Hf- containing FGH96 alloy had certain deleterious effects on stress-rupture property because there was strong Zr segre- gation at prior particle boundary, leaving a long chain of large-size oxides along the boundary. The optimal content of Hf and Zr in FGH96 alloy was 0.6% and 0. 04%, respectively.

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 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.

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.