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.

/pdf/the-effect-of-strain-distribution-on-microstructural-ut3ackkqif.pdf

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.

/pdf/production-of-net-shape-static-parts-by-direct-hiping-of-2d5dglu75p.pdf

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

Process for preparing a nickel-based superalloy part by powder metallurgy: - manufacture of a superalloy with the composition 18 % ≤ Cr ≤ 24 %; 6 % ≤ Mo ≤ 10 %; 2.5 % ≤ Nb ≤ 5 %; traces ≤ Fe ≤ 10 %; traces ≤ Al ≤ 1 %; 0.5 % ≤ Ti ≤ 2.5 %; traces ≤ B ≤ 0,01 %; traces ≤ Mn ≤ 0.35 %; traces ≤ Si ≤ 0.2 %; traces ≤ C ≤ 0.05 %; traces ≤ Co ≤ 2 %; traces ≤ Ta ≤ 0.5 %; traces ≤ Mg ≤ 0.05 %; traces ≤ P ≤ 0.015 %; traces ≤ S ≤ 0.01 %; the rest being nickel and impurities; - atomisation of a molten mass of said superalloy in order to obtain a powder; - screening of said powder; - introduction of the powder into a container; - closure of and application of a vacuum to the container; - densification of the powder and the container by pressurizing them both in order to obtain an ingot or a billet; - hot forming of said ingot or said billet; The densification process is carried out at 500 to 1500 bar, at a temperature at which the fraction by volume of liquid phase in the superalloy is between 0.5 and 10 %, the temperature and the pressure being maintained for 3 to 16 h, and the forging being carried out without intermediate heat treatment after the densification of the powder. A hot formed part thus produced.

Process for preparing a nickel-based superalloy part and part thus prepared

L'invention concerne essentiellement l'utilisation d'un acier faiblement allie, sensiblement sans nickel, non-inoxydable, pour la fabrication d'au moins la surface d'un article destine a etre mis en contact avec le titane ou un alliage de titane, ainsi qu'un procede de fabrication d'au moins la surface d'un tel article.L'invention concerne notamment l'utilisation de cet alliage pour la fabrication d'au moins la surface en contact de moule de mise en forme a chaud a l'etat solide d'alliages a base de titane ou d'alliage de titane, ou pour la fabrication d'au moins la surface en contact d'outillages pour la densification ou le formage d'alliages massifs ou de poudres de titane ou d'alliage de titane. L'invention permet la realisation d'articles destines a etre mis en contact avec le titane ou un alliage de titane.

Surface en contact avec le titane ou un alliage de titane

The invention mainly concerns the use of a weakly alloyed steel, substantially nickel-free, non-stainless, for making at least one surface of an article designed to be contacted with titanium or a titanium alloy, as well as a method for making at least the surface of such an article In particular, the invention concerns the use of said alloy for making at least the contact surface of a mould for hot forming in solid state titanium-based alloys or titanium alloy, or for making at least the contact surface of tools for densifying or forming solid alloys or powders of titanium or of titanium alloy The invention also enables the manufacture of articles designed to be in contact with titanium or a titanium alloy

Gérard Raisson

Papers

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

Process for preparing a nickel-based superalloy part and part thus prepared

Surface en contact avec le titane ou un alliage de titane

Titanium or titanium alloy contacting surface