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Hot Isostatic Pressing as an Advanced Processing Route for Fabrication and Post-treatment of Metallic Parts

A special issue of Materials (ISSN 1996-1944). This special issue belongs to the section "Metals and Alloys".

Deadline for manuscript submissions: closed (20 April 2022) | Viewed by 2699

Special Issue Editors


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Guest Editor
Department of Applied Science and Technology, Politecnico di Torino, C.so Duca degli Abruzzi 24, 10129 Turin, Italy
Interests: additive manufacturing (AM); hot isostatic pressing (HIP); Ni alloys; hot working tool steels; heat treatment; microstructure analysis
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E-Mail Website
Guest Editor
Department of Applied Science and Technology, Politecnico di Torino, C.so Duca degli Abruzzi 24, 10129 Turin, Italy
Interests: hot isostatic pressing; additive manufacturing; advanced steels; nickel-based alloys
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

The hot isostatic pressing (HIP) process was developed in 1955, and since then, it has undergone a radical process of renewing and developing. It was first used for cladding alloys for nuclear power production purposes. Today, HIP has gained renewed interest especially with the affirmation of the powder metallurgy near-net-shape HIP (NNSHIP) manufacturing processes and of the practice of HIP post-treating additive manufactured (AM) parts. Tailored cycles can be applied to a wide number of materials to obtain fully dense medium to big size components starting from loose powders or to eliminate the most significant flaws inherent in AM parts. Further achievements in cycle optimization are studied to enhance the reliability and performance of components operating in highly demanding environments. The application of these techniques is highly appealing especially for materials which are difficult to forge and to machine.

Apart from the clear technical achievements provided by HIP, new solutions in terms of HIP industrial equipment and of tooling for the NNSHIP process are currently introduced in the market to improve the manufacturing readiness level (MRL) of such fabrication routes and to reduce their related cost. Another topic of increasing interest is the development of reliable simulation models that help to design the tooling in NNSHIP, thus reducing the buy-to-fly index of this process.

The proposed Special Issue of Materials aims at presenting the latest efforts spent on the abovementioned topics. Contributions are particularly invited from, but not limited to, those who are involved in:

(i) Developing tailored HIP cycles for materials typically adopted for additive manufacturing, in particular (but not limited to) nickel-based superalloys, TiAl, or titanium-based alloys;

(ii) Understanding of microstructure evolutions due to HIP, for instance, recrystallization, second phase dissolution or grain boundary stability and of their impact towards mechanical properties;

(iii) Studying the effects of the high pressure levels on phase transformations in materials or of the implementation of thermal heat treatments during or immediately after the HIP cycle;

(iv) Developing simulation models regarding the single or multiple steps of near-net-shape HIP process (i.e., capsule filling and/or densification and/or microstructural evolutions during the cooling stage);

(v) Assessing eventual residual defects and shape stability of components after HIP and studying potential solutions for them;

(vi) Studying the interactions and modifications which can be activated by elemental diffusion at the interface between the powders and the capsule used to contain them in NNSHIP.

Prof. Dr. Daniele Ugues
Dr. Emilio Bassini
Guest Editors

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Keywords

  • near-net-shape hot isostatic pressing
  • recovery of defects structure
  • synergy between AM and HIP
  • metallurgical transformations
  • difficult to forge and to machine materials
  • demanding service performance
  • MRL
  • buy-to-fly

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Published Papers (1 paper)

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Research

19 pages, 6905 KiB  
Article
Thermal Mass Effect on the Solution Cooling Rate and on HIPped Astroloy Component Properties
by Unai Galech Napal, Miren Aristizabal Segarra, Borja Elguezabal Lazcano, Antonio Sivo and Iñigo Iturriza Zubillaga
Materials 2022, 15(4), 1434; https://doi.org/10.3390/ma15041434 - 15 Feb 2022
Cited by 3 | Viewed by 1766
Abstract
Astroloy is a Ni-based superalloy with high-volume fraction of γ′, which gives high temperature properties but reduces its forgeability. Therefore, powder metallurgy manufacturing processes such as Near Net Shape HIPping are the most suitable manufacturing technology for Astroloy. However, NNSHIP has its own [...] Read more.
Astroloy is a Ni-based superalloy with high-volume fraction of γ′, which gives high temperature properties but reduces its forgeability. Therefore, powder metallurgy manufacturing processes such as Near Net Shape HIPping are the most suitable manufacturing technology for Astroloy. However, NNSHIP has its own drawbacks, such as the formation of prior particle boundaries (PPBs), which usually tend to decrease material mechanical properties. The detrimental effect of PPBs can be reduced by optimizing the entire HIP processing route. Conventional HIP cycles have very low cooling rates, especially in big components from industry, and thus a series of post-heat treatments must be applied in order to achieve desirable microstructures and improve the mechanical properties. Standard heat treatments for Astroloy are long and tedious with several steps of solutioning, stabilization and precipitation. In this work, two main studies have been performed. First, the effect of the cooling rate after the solutioning treatment, which is driven by the materials’ thermal mass, on the Astroloy microstructure and mechanical properties was studied. Experimental analyses and simulation techniques have been used in the present work and it has been found that higher cooling rates after solutioning increase the density of tertiary γ′ precipitates by 85%, and their size decreases by 22%, which leads to an increase in hardness from 356 to 372 HB30. This hardness difference tends to reduce after subsequent standard heat treatment (HT) that homogenizes the microstructure. The second study shows the effect of different heat treatments on the microstructure and hardness of samples with two different thermal masses (can and cube). More than double the density of γ′ precipitates was found in small cubes in comparison with cans with a higher thermal mass. Therefore, the hardness in cubes is between 4 and 20 HB 30 higher than in large cans, depending on the applied HT. Full article
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