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 present work, powder metallurgy (PM) Ti-6Al-4V alloy was produced by hot isostatic pressing (HIPing) from gas atomized powder. Various HIPing conditions and heat treatments were used to investigate the heat response of PM Ti-6Al-4V alloy. The results show that the optimization of HIPing parameters is temperature from 920 to 940 degrees C, pressure over 120 MPa and holding for 3 h. The microstructure of powder compact changes significantly after different heat treatments, while there was no obvious difference in tensile properties. Temperature induced porosity (TIP) in powder compact occurred after annealing at 930 degrees C for 1 h plus aging. The TIP has no obvious effects on tensile, impact, and fracture toughness properties of powder compact, but the TIP has an adverse effect on fatigue property, especially at shorter fatigue lives. In order to eliminate the TIP in powder compact, several probable solutions were suggested for the application of titanium powder components. (C) 2015 Elsevier B.V. All rights reserved.

Microstructural evolution and mechanical properties of powder metallurgy Ti-6Al-4V alloy based on heat response

An advanced powder metallurgy (P/M) nickel-base superalloy envisaged for aerospace applications is realized through hot isostatic pressing (HIPing) of inert gas atomized powder. Extensive characterization of the microstructural features at different scales by employing optical microscopy, SEM-EBSD and transmission electron microscopy (TEM) divulged multi-modal distribution of γʹ precipitates within austenitic γ-FCC matrix phase in the as-HIPed condition. Investigation of prior particle boundary precipitates (PPBs) through TEM and Electron Probe Micro Analysis (EPMA) techniques revealed the dominance of metallic oxides and MC type carbides. The suitability of the advanced P/M superalloy for realizing near-net shape components by Direct-HIPing for short duration aeroengine rotating components is assessed by evaluating the room temperature and elevated temperature tensile behaviour as well as stress-rupture life in the service temperature regimes. The yield strength and the ultimate tensile strength of the present alloy at 650 °C are found to be 850 MPa and 1275 MPa respectively combined with 28% of ductility which is comparable to those of the similar class of superalloys in service. On the other hand, the as-HIPed superalloy exhibited minimum 1000 h of stress rupture life around service temperatures and bettered the stress rupture life of wrought superalloy IN718 alloy showing its potential for fabrication of near-net shape components for aerospace applications.

Microstructure and mechanical behaviour of an advanced powder metallurgy nickel base superalloy processed through hot isostatic pressing route for aerospace applications

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

The effect of cooling rates from temperatures above the γ′ solvus on the microstructure of a new nickel-based powder metallurgy superalloy

Industrial production of critical parts in aero engine by PM is now more than 30 years old. During this period, evolution of design principles and better evaluation of the impact of cleanliness has led to an evolution of metallurgy (grades and microstructure) and processes. The basis of this evolution will be presented and illustrated by examples taken from companies worldwide.

Gérard Raisson

Papers

Evolution of PM nickel base superalloy processes and products