A study was carried out on the effects of processing and composition on the structure and properties of P/M EP741NP type alloys. The objectives of this study were to understand the role of Hf in a P/M superalloy conta...A study was carried out on the effects of processing and composition on the structure and properties of P/M EP741NP type alloys. The objectives of this study were to understand the role of Hf in a P/M superalloy containing high niobium used in aircraft engines and to determine the effects of extrusion and forging the powders as contrasted to HIPing （hot isostatic pressing） only. Two alloys of the P/M EP741NP composition were atomized： one alloy contained 0.26%Hfand the other was Hf free. After the as-atomized powders from both alloys were characterized, the powders were extruded into billets, forged and heat treated. After each process, the microstructures were characterized by SEM and the phases were extracted and identified by X-ray diffraction. The presence of Hf in the residues was probed by EDS （energy dispersive spectroscopy）. The alloys were given the published Russian heat treatment as well as a more conventional heat treatment more typical of western powder alloys. Tensile, creep and stress rupture mechanical property tests were run. Results of the structural behavior of the alloys after each processing step will be presented and discussed. The role of the Hfon the mechanical properties will be discussed.展开更多
High temperature oxidation behaviors of FGH96 P/M superaUoy have been studied in air at temperatures ranging from 600 to 1000℃. By means of isothermal oxidation testing, X-ray diffraction, SEM （scanning electron mic...High temperature oxidation behaviors of FGH96 P/M superaUoy have been studied in air at temperatures ranging from 600 to 1000℃. By means of isothermal oxidation testing, X-ray diffraction, SEM （scanning electron microscopy）, and EDS （energy dispersive X-ray spectroscopy） analyses, the oxidation kinetics as well as the composition and morphology of scales were investigated. Thermodynamic calculations were used to explain the oxidation mechanism. The results showed that as the oxidation temperature increased, the oxidation rate, the scale thickness, and scale spallation increased. FGH96 P/M superalloy exhibits good oxidation resistance at temperature below 800℃. The oxidation kinetics follows an approximately parabolic rate law, and the oxide layer was mainly composed of Cr2O3 TiO2 and a little amount of NiCr2O4. The oxidation is controlled by the transmission of chromium. titanium, and oxygen through the oxide scale.展开更多
In situ fatigue tests in special designed SEM were conducted to trace the whole process of crack initiation and propagation fill to fracture in mckel-base P/M superalloy seeded inclusions. The experimental results sho...In situ fatigue tests in special designed SEM were conducted to trace the whole process of crack initiation and propagation fill to fracture in mckel-base P/M superalloy seeded inclusions. The experimental results show that non-metallic inclusions can induce crack initiation. When the inclusion size is larger than the critical one, the crack can propagate as the main crack that induces the specimen to fracture. As a result, the LCF life of the specimen decreases.展开更多
The low-cycle fatigue behavior of powder metallurgy Rene95 alloy containing surface inclusions was investigated by in-situ observation with scanning electron microscopy （SEM）. The process of fatigue crack initiation...The low-cycle fatigue behavior of powder metallurgy Rene95 alloy containing surface inclusions was investigated by in-situ observation with scanning electron microscopy （SEM）. The process of fatigue crack initiation and early stage of propagation behavior indicates that fatigue crack mainly occurs at the interface between the inclusion and the matrix. The effect of inclusion on the fatigue crack initiation and the early stage of crack growth was very obvious. The fatigue crack growth path in the matrix is similar to the shape of inclusion made on the basis of fatigue fracture image analysis. The empiric relation between the surface and inside crack growth length, near a surface inclusion, can be expressed. Therefore, the fatigue crack growth rate or life of P/M Rene95 alloy including the inclusions can be evaluated on the basis of the measurable surface crack length parameter. In addition, the effect of two inclusions on the fatigue crack initiation behavior was investigated by the in-situ observation with SEM.展开更多
A special designed experiment was conducted for observing crack initiation and growth in P/M Rene95 superalloy under tension-tension loading by self-made SEM in-situ fatigue loading stag. Several alumina inclusion par...A special designed experiment was conducted for observing crack initiation and growth in P/M Rene95 superalloy under tension-tension loading by self-made SEM in-situ fatigue loading stag. Several alumina inclusion particles exposed at the specimen surface were observed carefully. During fatigue test inclusions led to cracks initiation. The cracks can be formed by two mechanisms. Generally, the cracks nucleated at the interface between inclusion and matrix. Sometimes, cracks were also formed inside the inclusion. As the increase of cycles, some cracks at the interface between inclusion and matrix broadened and propagated along the direction about 45 degrees to the loading axis. On the other hand, the cracks inside the inclusion propagated in the inclusion and towards matrix.展开更多
文摘A study was carried out on the effects of processing and composition on the structure and properties of P/M EP741NP type alloys. The objectives of this study were to understand the role of Hf in a P/M superalloy containing high niobium used in aircraft engines and to determine the effects of extrusion and forging the powders as contrasted to HIPing （hot isostatic pressing） only. Two alloys of the P/M EP741NP composition were atomized： one alloy contained 0.26%Hfand the other was Hf free. After the as-atomized powders from both alloys were characterized, the powders were extruded into billets, forged and heat treated. After each process, the microstructures were characterized by SEM and the phases were extracted and identified by X-ray diffraction. The presence of Hf in the residues was probed by EDS （energy dispersive spectroscopy）. The alloys were given the published Russian heat treatment as well as a more conventional heat treatment more typical of western powder alloys. Tensile, creep and stress rupture mechanical property tests were run. Results of the structural behavior of the alloys after each processing step will be presented and discussed. The role of the Hfon the mechanical properties will be discussed.
文摘High temperature oxidation behaviors of FGH96 P/M superaUoy have been studied in air at temperatures ranging from 600 to 1000℃. By means of isothermal oxidation testing, X-ray diffraction, SEM （scanning electron microscopy）, and EDS （energy dispersive X-ray spectroscopy） analyses, the oxidation kinetics as well as the composition and morphology of scales were investigated. Thermodynamic calculations were used to explain the oxidation mechanism. The results showed that as the oxidation temperature increased, the oxidation rate, the scale thickness, and scale spallation increased. FGH96 P/M superalloy exhibits good oxidation resistance at temperature below 800℃. The oxidation kinetics follows an approximately parabolic rate law, and the oxide layer was mainly composed of Cr2O3 TiO2 and a little amount of NiCr2O4. The oxidation is controlled by the transmission of chromium. titanium, and oxygen through the oxide scale.
文摘In situ fatigue tests in special designed SEM were conducted to trace the whole process of crack initiation and propagation fill to fracture in mckel-base P/M superalloy seeded inclusions. The experimental results show that non-metallic inclusions can induce crack initiation. When the inclusion size is larger than the critical one, the crack can propagate as the main crack that induces the specimen to fracture. As a result, the LCF life of the specimen decreases.
基金This work was financially supported by the National Natural Science Foundation of China (No. 50571047) and the National BasicResearch Program of China (No.2004CB619304).
文摘The low-cycle fatigue behavior of powder metallurgy Rene95 alloy containing surface inclusions was investigated by in-situ observation with scanning electron microscopy （SEM）. The process of fatigue crack initiation and early stage of propagation behavior indicates that fatigue crack mainly occurs at the interface between the inclusion and the matrix. The effect of inclusion on the fatigue crack initiation and the early stage of crack growth was very obvious. The fatigue crack growth path in the matrix is similar to the shape of inclusion made on the basis of fatigue fracture image analysis. The empiric relation between the surface and inside crack growth length, near a surface inclusion, can be expressed. Therefore, the fatigue crack growth rate or life of P/M Rene95 alloy including the inclusions can be evaluated on the basis of the measurable surface crack length parameter. In addition, the effect of two inclusions on the fatigue crack initiation behavior was investigated by the in-situ observation with SEM.
基金the National Natural Science Foundation of China, No. 59871007.]
文摘A special designed experiment was conducted for observing crack initiation and growth in P/M Rene95 superalloy under tension-tension loading by self-made SEM in-situ fatigue loading stag. Several alumina inclusion particles exposed at the specimen surface were observed carefully. During fatigue test inclusions led to cracks initiation. The cracks can be formed by two mechanisms. Generally, the cracks nucleated at the interface between inclusion and matrix. Sometimes, cracks were also formed inside the inclusion. As the increase of cycles, some cracks at the interface between inclusion and matrix broadened and propagated along the direction about 45 degrees to the loading axis. On the other hand, the cracks inside the inclusion propagated in the inclusion and towards matrix.
