A high strength high γ ′ fraction nickel-based superalloy powder RR 1000 has been hot isotatically pressed (HIPed) at different temperatures. Microstructural analysis and assessment of the tensile properties were performed on these samples. It was found that HIP led to the formation of (Hf,Zr)O 2 particles on prior particle boundaries (PPBs) which were not present in the as-received powder. It is suggested that the oxides are formed by the diffusion of Hf and Zr from the interior of powder particles to the particle surfaces where oxygen level is usually high. When different HIP temperatures were used, no obvious effect on oxide size and distribution was observed but there was an effect on the microstructure and tensile properties. Thus, HIPing at super-solvus temperatures reduced the density of PPBs over the density observed in samples HIPed at sub-solvus temperatures by making grains within the original powder particles grow beyond the precipitates on PPBs, resulting in larger grains with serrated boundaries. Slow cooling from HIPing temperatures also led to the formation of irregular-shaped γ ′. The 0.2% yield strengths at room temperature and at 700 °C were found to decrease with increase of HIP temperature but the high temperature ultimate tensile strengths and elongation increased considerably. Increasing HIPing temperature from sub-solvus to super-solvus temperatures also led to the transition of fracture mode from interparticle debonding to transgranular fracture mode.

Influence of hot isostatic pressing temperature on microstructure and tensile properties of a nickel-based superalloy powder

Influence of heat treatment on microstructure and tensile behavior of a hot isostatically pressed nickel-based superalloy

Inconel 718 powders have been hot-isostatic-pressed (HIPed) at representative temperatures to investigate the variations in microstructure, tensile properties and tensile fracture mode of the powder compact. Microstructure of the powder compacts were characterized by optical microscopy (OM), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and so on. The results showed that the interdendritic precipitates inherited from the powders were partially retained in the powder compacts when the powders were HIPed at or below 1210 °C but were eliminated when HIPed at and above 1260 °C. The grain size uniformity of the powder compacts first increases and then decreases with increasing HIPing temperature. Prior particle boundaries (PPBs) were observed in the powder compacts HIPed at and below 1260 °C but was eliminated when HIPed at 1275 °C. The PPBs were decorated with carbide particles, the amount of the carbide particles at the PPBs decreases with increasing HIPing temperature. Most of the PPBs were pinned by the carbide particles in the compacts HIPed at 1140 °C. When the HIPing temperature was increased to 1210 °C and 1260 °C, a large number of PPBs de-pinned and moved beyond the pinning carbide particles, leading to grain growth and leaving carbide particles at the site of the original PPBs within the new grains. With increasing HIPing temperature, the 0.2% yield strength of the powder compacts at 650 °C decreases, the tensile elongation increases, and the tensile fracture mode changed from inter-particle dominant fracture to fully dimple ductile fracture.

Influences of hot-isostatic-pressing temperature on microstructure, tensile properties and tensile fracture mode of Inconel 718 powder compact

In the current study, the effect of strain distribution in a simple forging geometry on the propensity for recrystallization, and its impact on mechanical properties has been investigated in a newly developed experimental nickel-based superalloy. The new alloy was produced via a Powder Metallurgy (PM) route and was subsequently Hot Isostatic Processed (HIP), isothermally forged, and heat treated to produce a coarse grain microstructure with average grain size of 23–32 μm. The alloy was examined by means of Electron Back-Scatter Diffraction (EBSD) to characterise the microstructural features such as grain orientation and morphology, grain boundary characteristics and the identification of potential Prior Particle Boundaries (PPBs) throughout each stage of the processing route. Results at the central region of the cross-section plane parallel to the loading direction showed significant microstructural differences across the forging depth. This microstructural variation was found to be highly dependent on the value of local strain imparted during forging such that areas of low effective strain showed partial recrystallisation and a necklace grain structure was observed following heat treatment. Meanwhile, a fully recrystallised microstructure with no PPBs was observed in the areas of high strain values, in the central region of the forging.

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The Effect of Strain Distribution on Microstructural Developments during Forging in a Newly Developed Nickel Base Superalloy

A new hot-isostatic-pressing (HIPing) scheme, which consists of a short time holding above the solidus and a long time annealing below the incipient temperature of Laves phase, has been proposed for Inconel 718 powder to avoid the formation of prior particle boundaries (PPBs). The powder metallurgy Inconel 718 compacted with the above HIPing scheme is free of PPBs, features transgranular ductile fracture mode during tensile tests, and possesses a stress rupture life that is much longer than that of the wrought alloy.

Preparation of hot-isostatic-pressed powder metallurgy superalloy Inconel 718 free of prior particle boundaries

In order to reduce costs and increase the operating temperatures in aero-turboengines and space propulsion systems, net-shape or near net-shape production processes have been developed for static parts through HIPing (Hot Isostatic Pressing) of nickel base superalloys prealloyed powders. The presented results hereafter are related to the manufacturing processes and the mechanical properties (tensile, creep and LCF) characterisation. The effects of net shape surfaces and of surface conditioning have been investigated too. Examples of actual parts (CFM56 turbine casing and Vulcain rocket engine gas generator) illustrate the presentation. This study has confirmed the interest of this production route and future potential for development.

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Production of net-shape static parts by direct HIPing of nickel base superalloy prealloyed powders

A support for a bearing that guides a shaft in a turbomachine is disclosed The support includes an annular part made of a shape memory material which retains an initial shape when the load applied to it remains below a threshold value and which deforms, absorbing energy when the applied load becomes at least equal to the threshold value The annular part is capable of reverting at least approximately to its initial shape when the applied load drops back below the threshold value

Turbomachine shaft guidance

The support (56) has thin blades (58) made of a shape memory material e.g. superelastic material. The blades retain an initial shape, when a load applied to the blades remains below a threshold value, where the load is an imbalance load resulting from ingestion of a foreign body e.g. bird. The blades are deformed by absorbing mechanical energy generated by the load, when the applied load is equal to the threshold value. The blades revert to its initial shape, when the applied load again drops below the threshold value.

Guiding of a shaft in a turbomachine

PROBLEM TO BE SOLVED: To provide a support for a bearing to guide a shaft in a turbomachine SOLUTION: The support (56) for a bearing (28) is fixed to a casing (32) to guide a shaft (24) in a turbomachine (10) The support includes an annular part (58) made of a shape memory material which retains an initial shape when the load applied to it remains below the threshold and which deforms, absorbing energy when the applied load becomes at least equal to the threshold This annular part (58) reverts at least approximately to its initial shape when the applied load drops back below the threshold COPYRIGHT: (C)2009,JPO&INPIT

Guiding shaft in turbomachine

Support (56) de palier (28) fixe a un carter (32) pour le guidage d'un arbre (24) dans une turbomachine (10), caracterise en ce qu'il comprend une partie annulaire (58) realisee dans un materiau du type a memoire de forme qui conserve une forme initiale, quand la charge qui lui est appliquee reste inferieure a une valeur seuil et qui se deforme en absorbant de l'energie quand la charge appliquee devient au moins egale a la valeur seuil, cette partie annulaire (58) etant capable de reprendre au moins approximativement sa forme initiale quand la charge appliquee redevient inferieure a la valeur seuil.

Jean Marc Rongvaux

Papers

Production of net-shape static parts by direct HIPing of nickel base superalloy prealloyed powders

Turbomachine shaft guidance

Guiding of a shaft in a turbomachine

Guiding shaft in turbomachine

Guidage d'un arbre dans une turbomachine