PM Nickel Base Research Articles

Effect of Ta Content on High Temperature Creep Deformation Behaviors and Properties of PM Nickel Base Superalloys

Effect of Ta Content on High Temperature Creep Deformation Behaviors and Properties of PM Nickel Base Superalloys

Novel powder packing theory with bimodal particle size distribution-application in superalloy

Powder packing behavior plays an important role in determining sintering ability of powder and the resultant performance of materials. In this study, a novel powder packing theory with bimodal particle size distribution is proposed by considering the loosening effect, wall effect and wedging effect. This theory is applied in PM nickel base superalloy by using mixture of coarse particles and fine particles. Microstructures of alloy sintered by vacuum hot pressing (HP) are observed by optical microscope (OM) and electron backscatter diffraction (EBSD). The prediction result by this theory is in good agreement with the experimental results. The enhanced sintering ability of powder containing appropriate fractions of coarse particle and fine particle is ascribed to the filling of fine particles to the voids between coarse particles, which enhanced the density of sample after sintering. Tensile behavior and the fracture morphology of alloys with various particle distributions are analyzed in details, suggesting the higher reliability of the present theory.

Plastic Flow and Microstructure Evolution during Thermomechanical Processing of a PM Nickel-Base Superalloy

Plastic flow and microstructure evolution during sub- and supersolvus forging and subsequent supersolvus heat treatment of the powder-metallurgy superalloy LSHR (low-solvus, high-refractory) were investigated to develop an understanding of methods that can be used to obtain a moderately coarse gamma grain size under well-controlled conditions. To this end, isothermal, hot compression tests were conducted over broad ranges of temperature [(1144 K to 1450 K) 871 °C to 1177 °C] and constant true strain rate (0.0005 to 10 s−1). At low temperatures, deformation was generally characterized by flow softening and dynamic recrystallization that led to a decrease in grain size. At high subsolvus temperatures and low strain rates, steady-state flow or flow hardening was observed. These latter behaviors were ascribed to superplastic deformation and microstructure evolution characterized by a constant grain size or concomitant dynamic grain growth, respectively. During supersolvus heat treatment following subsolvus deformation, increases in grain size whose magnitude was a function of the prior deformation conditions were noted. A transition in flow behavior from superplastic to nonsuperplastic and the development during forging at a high subsolvus temperature of a wide (possibly bi- or multimodal) gamma-grain-size distribution having some large grains led to a substantially coarser grain size during supersolvus annealing in comparison to that produced under all other forging conditions.

Hot Deformation Behaviors and Microstructure Evolution in a New PM Nickel-Base Superalloy

The hot deformation behaviors and the effect of flow stress on the microstructure were investigated for the as-HIPed and as-extruded materials in a new PM nickel-base superalloy. Under most test conditions, the as-extruded material exhibits superplastic flow because of grain growth corresponding to work hardening during deformation process, activation energy for deformation of which is 211 kJ/mol. However, activation energy of deformation for the as-HIPed material is 717 kJ/mol, because grain size is refined due to dynamic recrystallization, the reason being considered to be associated with the initial microstructure before the deformation. Based on the results of compression tests, two constitutive equations for the two materials were established using the mathematical regression; these will provide the valuable helps for predicting and controlling the deformed microstructure as well as optimizing hot-working process.

Discs of medium alloyed PM nickel base alloy : G.Genrikh et al. (All-Russia Inst. of Light Alloys (VILS), Moscow, Russia.)

Discs of medium alloyed PM nickel base alloy : G.Genrikh et al. (All-Russia Inst. of Light Alloys (VILS), Moscow, Russia.)

Model of viscoplastic behaviour of a PM nickel base superalloy at 650 °c : V. Aubourg et al. (University of Dayton, Dayton, Ohio, USA)

Model of viscoplastic behaviour of a PM nickel base superalloy at 650 °c : V. Aubourg et al. (University of Dayton, Dayton, Ohio, USA)

PM nickel-base superalloy dual-property disks produced by superplastic forging

A manufacturing process for dual-structured turbine disks made from PM nickel-base superalloys has been specially developed. The disks are composed of two metals: AF115, which has superior stress rupture properties, was used in the rim region, and TMP-3, which has good tensile properties and a low cycle-fatigue life, was used in the bore region. A 400mm diameter dual-property disk was successfully produced through double-stepped HIP treatment and superplastic forging, in which gas atomized powders composed of the above alloys were consolidated into a well-designed preformed structure. After heat treatment, the microstructure of the product was very fine and homogeneous in the bore region, and coarse grains were obtained in the rim region. The mechanical properties were of such high quality as to enable practical use as a turbine disk.

Effect of Boron on the Structure and Properties of a PM Nickel Base Superalloy

Effect of Boron on the Structure and Properties of a PM Nickel Base Superalloy

Effect of Minor Chemistry Variations on the Structural and Mechanical Behaviour of a PM Nickel Base Superalloy

Addition of 0.7% Hf to a heavily alloyed low carbon Ni base PM superalloy has been found to significantly reduce the alloy solidus in contrast to another chemisty variant free of Hf but with increased alloying. The Hf-bearing alloy showed major microstructural changes with increase in HIPing temperature. Reduction in C to < 0.02% severely affected its elevated temperature strength. The Hf-free alloy containing 0.03% C offered a good combination of tensile and stress rupture properties after a suitable heat treatment.

Sigma phase formation in conventional and PM nickel-base superalloys

AbstractAgeing treatments of up to 5000 h at 705–980°C have been carried out on five chemically modified nickelbase superalloys based on Astroloy (No. I), MAR-M432 (No.2), IN-100 (No.3), PAI0l(No. 4), and AF-2-IDA (No.5). The kinetics and morphology of a-phase formation were examined in two unstable heats (Alloys 3 and 5) processed by powder metallurgy methods and by conventional casting and extrusion procedures. The morphologies of σ were similar in both forms of a given alloy; however, σ precipitation occurred sooner in the powder metallurgyform of Alloy 3 than in the cast and extruded form. Numerical methods based on electron-vacancy concepts predicted σ formation correctly when experimentally determined γ-phase (austenite) compositions were used. Standard methods for computing γ and γ′ contents and compositions were unsuccessful with these modified alloys, and therefore a new regression equation was developed for γ′ contents using a 71 alloy data base. Using this new equation, more accurate γ and γ′ c...

Grain coarsening of PM nickel-base superalloy by critical strain annealing

Critical strain annealing has been investigated for the of development of coarse grain structures in PM Astroloy. The need for this type of treatment arises because normal grain coarsening is severely retarded by carbides in the prior particle boundaries (PPBs). It was found that a strain of ∼ 2.2% produced coarse grain structures (∼ 360 μm) on subsequent annealing for 2 h at 1250°C. Smaller amounts of deformation could also initiate the nucleation of recrystallization but here the driving force was insufficient to cause the migration of the recrystallization front through the PPBs, resulting in no increase in grain size beyond the size of the prior powder particles.