Grain size characterization of nickel alloy 718 with optimized metallographic sample preparation route followed by a novel etching technique
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S. Saha
Shuvra Saha studied Metallurgical Engineering at RWTH Aachen University and currently working as a Materials Engineer in Materials R&D at Baker Hughes. In addition to his research activities in the field metallography, material testing and development, his work focuses on failure analysis of metallic components.
and
G. Wiese
Gabriela Wiese studied material science at Otto-von-Guericke-University in Magdeburg (Germany). She has been working at Baker Hughes INTEQ GmbH since 1992 in Celle as Materials Scientist, Lab Manager and Trainer for Materials Tester. Her main fields of work: material characterization and failure analysis on tools for oil-and-gas industry and geothermal applications.
Abstract
A suitable etching technique can distinguish the appearance of microscopic features such as grain boundaries (GBs), annealing twins (TBs), and precipitates, unlike nonmetallic inclusions, voids, and microcracks, which are visible in as-polished conditions. The difficulties arise when a semi-automatic or automatic grain size (GS) analyzer detects the TBs in addition to GBs concurrently. This study introduces a novel etching technique that has selectively highlighted the GBs without or faintly emphasizing TBs in heat-treated additively manufactured (AM) and wrought nickel alloy 718, respectively. The authors then measured the GS using the comparison and intercept procedure (lineal and Abrams three-circle) according to ASTM E112-2013. Moreover, the comparative study identified the comparison procedure as the most effective approach based on accuracy, post-processing, and time consumption. However, it had limitations in terms of precision and applicability. In contrast, the intercept procedure emerged as the preferred choice for higher accuracy demands.
Kurzfassung
Mit einer geeigneten Ätzmethode lassen sich mikroskopische Merkmale, wie z. B. Korngrenzen (KG), Zwillingsgrenzen (ZG) und Ausscheidungen, voneinander unterscheiden, ganz im Gegensatz zu nicht-metallischen Einschlüssen, Hohlräumen und Mikrorissen, die erst im polierten Zustand sichtbar werden. Schwierigkeiten entstehen, wenn bei der automatischen oder halbautomatischen Korngrößenbestimmung sowohl Zwillingsgrenzen als auch normale Korngrenzen identifiziert werden. Die vorliegende Untersuchung stellt eine neuartige Ätzmethode vor, mit der in einer wärmebehandelten additiv hergestellten (AM, additively manufactured) bzw. als Knetlegierung vorliegenden Nickel-Legierung 718 die Korngrenzen selektiv hervorgehoben werden und Zwillingsgrenzen gar nicht oder nur schwach erscheinen. Im Anschluss erfolgte die Korngrößenbestimmung mithilfe der Vergleichs- und Linienschnittverfahren (mit geraden Schnittlinien nach Heyn sowie kreisförmigen Schnittlinien nach Abrams) gemäß ASTM E112-2013. Im Rahmen dieser vergleichenden Studie wurde außerdem festgestellt, dass das Vergleichsverfahren den effektivsten Ansatz in Bezug auf Genauigkeit, Nachbearbeitungs- und Zeitaufwand darstellt, wobei der Methode bei Präzision and Anwendbarkeit Grenzen gesetzt sind. Bei höheren Anforderungen an die Genauigkeit ist daher das Linienschnittverfahren die erste Wahl.
About the authors
Shuvra Saha studied Metallurgical Engineering at RWTH Aachen University and currently working as a Materials Engineer in Materials R&D at Baker Hughes. In addition to his research activities in the field metallography, material testing and development, his work focuses on failure analysis of metallic components.
Gabriela Wiese studied material science at Otto-von-Guericke-University in Magdeburg (Germany). She has been working at Baker Hughes INTEQ GmbH since 1992 in Celle as Materials Scientist, Lab Manager and Trainer for Materials Tester. Her main fields of work: material characterization and failure analysis on tools for oil-and-gas industry and geothermal applications.
References / Literatur
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Articles in the same Issue
- Contents
- Editorial
- Editorial
- Microstructural characteristics and mechanical properties of WAAM components
- Grain size characterization of nickel alloy 718 with optimized metallographic sample preparation route followed by a novel etching technique
- High-resolution microscopy of biofilm and bacteria on titanium implants
- Failure Analysis
- Failure analysis of LCF cracked medium-voltage switch bellows
- Picture of the Month
- Picture of the Month
- News
- News
- Meeting Diary
- Meeting Diary
Articles in the same Issue
- Contents
- Editorial
- Editorial
- Microstructural characteristics and mechanical properties of WAAM components
- Grain size characterization of nickel alloy 718 with optimized metallographic sample preparation route followed by a novel etching technique
- High-resolution microscopy of biofilm and bacteria on titanium implants
- Failure Analysis
- Failure analysis of LCF cracked medium-voltage switch bellows
- Picture of the Month
- Picture of the Month
- News
- News
- Meeting Diary
- Meeting Diary
