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Superalloys-by-Design: Applications and Mechanics
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Superalloys-by-Design: Applications and Mechanics

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

Deadline for manuscript submissions: closed (20 October 2023) | Viewed by 2832

Special Issue Editors

Dr. Xuezhi Qin

E-Mail Website
Guest Editor
Institute of Metal Research, Chinese Academy of Sciences, Shenyang 110016, China
Interests: superalloys; chemical composition design; relationship among chemical composition, microstructure, and properties; thermal expansion behavior; damage assessment and life prediction of hot end components; superalloys for the hot end components of gas turbines; superalloys for nuclear reactors and reprocessing; superalloys for the petrochemical industry
Special Issues, Collections and Topics in MDPI journals
Prof. Dr. Lei Zheng

grade E-Mail Website
Guest Editor
School of Materials Science and Engineering, University of Science and Technology Beijing, Beijing 100083, China
Interests: design, research and application of superalloys
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

Superalloys are widely used in the aviation, navigation, power generation, and petrochemical industries because of their excellent high-temperature creep resistance, oxidation–corrosion resistance, and fatigue resistance.

Wrought superalloys include solid solution-strengthened and precipitation-strengthened alloys. The mechanical properties of the former mainly depend on grain size and solution strengthening, while the properties of the latter are determined by strengthening phases. The chemical composition, deformation process, and heat treatment are three key factors that determine the performance of the wrought superalloys that are often used as plates, strips, pipes/tubes, bars, discs, etc. Components that are very small or large in size are more suitably manufactured by wrought superalloys.

The development of solidification technology leads to the elimination of transverse or even all grain boundaries in the equiaxed alloys and accordingly results in the presence of directional solidification and single crystal alloys, markedly improving the mechanical properties of cast superalloys. In recent years, more and more refractory additions are being made in order to obtain a better strengthening effect in cast superalloys, which makes the matrix highly supersaturated and unstable, easily precipitating harmful TCP phases. Therefore, how to better balance the microstructural stability, mechanical properties, and service lifetime of cast superalloys using matching various element additions more reasonably is still a great challenge. Cast superalloys are generally employed in high-temperature and -stress environments with strong corrosion attacks, such as in the hot end parts of aeroengines and gas turbines.

This SI will focus on recent developments in design theory and in superalloy practices to determine better mechanical properties and a wider range of applications in various industrial fields. The articles presented in this SI will cover chemical composition, solidification/deformation technology, heat treatment, microstructure, mechanical properties, service lifetime, and the relationship between them, all of which are crucial for the design and application of superalloys.

Dr. Xuezhi Qin
Prof. Dr. Lei Zheng
Guest Editors

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Materials is an international peer-reviewed open access semimonthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2600 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

  • superalloys (e.g., Ni-based, Ni-Fe-based, Ni-Co-based, and Co-based superalloys)
  • solidification technology
  • deformation (e.g., forging, rolling and hot extrusion) technology
  • heat treatment
  • chemical composition
  • microstructures
  • mechanical properties
  • service lifetime
  • superalloy design
  • superalloy applications

Published Papers (2 papers)

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Research

11 pages, 26394 KiB  
Article
Microstructural Evolution and Mechanical Properties of a Ni-Based Alloy with High Boron Content for the Pre-Sintered Preform (PSP) Application
by Xiufang Gong, Yunsheng Wu, Zhenhuan Gao, Youbei Sun, Yingbo Guan, Xianjun Guan, Xuezhi Qin, Jieshan Hou and Lanzhang Zhou
Materials 2023, 16(23), 7483; https://doi.org/10.3390/ma16237483 - 2 Dec 2023
Viewed by 770
Abstract
The pre-sintered preform (PSP) is an advanced technology for repairing the Ni-based superalloy blade in a turbine. In general, boron is added to the Ni-based superalloys in small quantities (<0.1 wt.%) to increase boundary strength and cohesivity. Despite this, the effect of high [...] Read more.
The pre-sintered preform (PSP) is an advanced technology for repairing the Ni-based superalloy blade in a turbine. In general, boron is added to the Ni-based superalloys in small quantities (<0.1 wt.%) to increase boundary strength and cohesivity. Despite this, the effect of high B content (>1.0 wt.%) on the microstructure evolution and mechanical properties in Ni-based superalloys for the PSP application is rarely studied. The variety, composition and evolution of the precipitates during solution heat treatment in the alloy with high B content were determined by EBSD, EPMA and SEM. The results indicate that Cr, W and Mo-rich M5B3 type borides precipitate from the matrix and its area fraction reaches up to about 8%. The area fraction of boride decreases with the prolonging of solution time and the increase of temperature higher than 1120 °C. The borides nearly disappear after solution treatment at 1160 °C for 2 h. The redissolution of boride and eutectic results in the formation of B-rich area with low incipient melting (about 1189 °C). It can bond metallurgically with the blade under the melting point of the blade, which decreases the precipitation of harmful phases of the blade after PSP repairing. The microhardness within the grain in the PSP work-blank first decreases (lower than 1160 °C) and then increases (higher than 1185 °C) with the increase of solution heat treatment temperature due to the dissolving and precipitation of borides. The tensile strength of the combination of PSP work-blank and Mar-M247 matrix at room temperature after solution treatment is related to the area fraction of boride, incipient melting and the cohesion between PSP work-blank and Mar-M247 matrix. Full article
(This article belongs to the Special Issue Superalloys-by-Design: Applications and Mechanics)
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19 pages, 15480 KiB  
Article
Study on the Tribological Behavior and the Interaction between Friction and Oxidation of Graphite Reinforced by Impregnated Phosphate at High Temperatures
by Hao Cheng, Siyang Gao, Deli Duan, Shuai Yang, Weihai Xue, Bi Wu and Zhenguo Zhu
Materials 2023, 16(9), 3517; https://doi.org/10.3390/ma16093517 - 4 May 2023
Cited by 1 | Viewed by 1655
Abstract
The stability of the graphite seal device is a key factor for the normal operation of aero engines. However, conventional graphite exhibits poor comprehensive performance due to its porous structure, which limits its application at high temperatures. Therefore, in this paper, phosphate was [...] Read more.
The stability of the graphite seal device is a key factor for the normal operation of aero engines. However, conventional graphite exhibits poor comprehensive performance due to its porous structure, which limits its application at high temperatures. Therefore, in this paper, phosphate was used to impregnated graphite pores, and the interaction between the friction, wear, and oxidation of phosphate-impregnated graphite against superalloy at high temperatures was studied through pin-on-disk friction tests. The results revealed that the coefficient of friction (COF) of matrix graphite fluctuated greatly, from 0.07 to 0.17, in the range of 100 °C to 500 °C, while the COF of impregnated graphite was stable, at around 0.13, from 100 °C to 500 °C. The wear rates of the two types of graphite were close from 20 °C to 300 °C, while the wear rate of the impregnated graphite was significantly lower than that of the matrix graphite at higher temperatures, from 400 °C and 500 °C. The reason was that the impregnated phosphate reacted with graphite at a high temperature, forming the inert site which helped to inhibit the oxidation and maintain the mechanical properties of the impregnated graphite at high temperatures. In addition, the impregnated graphite could maintain better integrity of the contact surface and reduce the inclusion of large hard metal oxides, thus effectively reducing the abrasive wear of the disk. Therefore, the wear depth of the superalloy disk samples with impregnated graphite was significantly lower than that of the matrix graphite. The results promote the application of phosphate-impregnated graphite under the high temperature conditions of aero engines. Full article
(This article belongs to the Special Issue Superalloys-by-Design: Applications and Mechanics)
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