Techniques for microstructural characterization of powder-processed nickel-based superalloys Agnieszka M. Wusatowska-Sarnek *, Martin J. Blackburn, Mark Aindow Department of Metallurgy and Materials Engineering, Institute of Materials Science, University of Connecticut, Unit 3136, 97 N. Eagleville Rd., Storrs, CT 06269-3136, USA Received 4 April 2003; received in revised form 6 June 2003 Abstract Methods are described for sample preparation of polycrystalline Ni-based superalloys in order to perform a detailed microstructural characterization. Specific techniques for the precise definition of the various phases present are outlined and these are shown to be useful for the measurement of size, volume fractions and distribution. A number of optical, scanning and transmission microscopy techniques are used to provide the necessary information. # 2003 Elsevier B.V. All rights reserved. Keywords: Nickel-based superalloys; Metallography; Etchants; Microscopy 1. Introduction The evolution of high efficiency turbine engines has resulted in the extensive use of nickel-based superalloys to accommodate the ever-higher temperatures. Super- alloys appear to have deceptively straightforward struc- tures, but the details can be quite complex. The major phases are an ordered g? (Ni 3 Al type) phase, and a disordered solid-solution face-centered cubic g matrix. Carbides and borides occur as minor phases and, under certain conditions, the topologically close-packed (TCP) phases such as s, m, and Laves can also form. A number of extensive publications provide detailed information on the evolution of the particular phases and their effects on the properties [1  /3]. Nickel-based superalloy components can be produced as castings or wrought products made from ingot or powder metallurgy (P/M) pre-forms. Powder processing is typically employed for wrought parts made from alloys with high volume fractions of g? phase, as the process results in remarkable chemical and structural homogeneity, and the ability to produce very fine microstructures. These characteristics result in excellent strength and toughness properties over a wide range of temperatures. A number of microstructural features control the specific level of properties, and a detailed knowledge of the spatial distributions, morphologies, volume fractions and chemical constitutions of the phases is essential for the prediction of alloy perfor- mance. As part of the Accelerated Insertion of Materials DARPA project led by Pratt and Whitney a detailed characterization study was undertaken on the wrought P/M alloy IN100 to provide the underpinning for structural property models [4]. The objective of the present paper is to describe the methods that were employed during this extensive characterization. Although there is a considerable literature on metallographic and related techniques applied to superalloys, the information tends to be rather scattered and lacks detail. This compilation is intended to fill this gap. Techniques have been opti- mized for revealing the structural features in this particular alloy, however, applicability has been verified for other alloys from this class, such as Waspaloy, Udimet 700 and Udimet 720, and may have broader utility. * Corresponding author. Present address: Pratt and Whitney, 400 Main Street M/S 114-40, East Hartford, CT 06108, USA. Tel.:  /1- 860-565-074. E-mail address: agnieszka.wusatowska-sarnek@pw.utc.com (A.M. Wusatowska-Sarnek). Materials Science and Engineering A360 (2003) 390  /395 www.elsevier.com/locate/msea 0921-5093/03/$ - see front matter # 2003 Elsevier B.V. All rights reserved. doi:10.1016/S0921-5093(03)00498-2