Investigation on hot deformation behavior of Waspaloy Amir Amiri a , Stefania Bruschi b , Mohammad Hossein Sadeghi a,n , Paolo Bariani b a Department of Mechanical Engineering, Tarbiat Modares University, 14115-111 Tehran, Iran b Department of Industrial Engineering, University of Padova, Via Venezia 1, 35131 Padova, Italy article info Article history: Received 18 September 2012 Received in revised form 3 November 2012 Accepted 5 November 2012 Available online 16 November 2012 Keywords: Waspaloy Hot deformation Processing map Nickel based superalloys Microstructural analysis abstract The hot deformation behavior of the Waspaloy was investigated by means of hot compression tests, metallographic observations and processing map at temperature between 950 1C and 1150 1C, strain rate between 0.01 s 1 and 10 s 1 under strain of 0.8. The processing map was developed on the basis of experimental data, showing variations of the efficiency of power dissipation related to temperature and strain rate at constant strain. The processing map shows one stable domain, in which the dynamic recrystallization is the dominating microstructural phenomenon, and one instable domain. The results of interpretation of flow stress curves and processing map were verified by microstructural observa- tions. The efficiency peak of the processing map is 0.37 at the temperature of 1150 1C and the strain rate of 10 s 1 .The stable domain is within the temperature range between 1050 1C and 1150 1C and strain rate between 0.01 s 1 and 10 s 1 , and leads to recrystallized and equiaxed microstructure. The grain size in this domain increases at increasing temperature or decreasing strain rate. The instability domain is within the temperature range between 950 1C and 1000 1C and strain rate between 0.01 s 1 and 10 s 1 (the temperature of 1000 1C and strain rate of 0.01 s 1 is excluded). In this domain, the instability can be observed in terms of fracture, shear bands, flow localization, intergranular and triple junction cracking. & 2012 Elsevier B.V. All rights reserved. 1. Introduction Waspaloy is a widely used wrought nickel-based superalloy for gas turbine discs, rings, and blades [1], which exhibits sufficiently high temperature creep, fatigue, and oxidation resis- tance properties for operating at temperatures up to around 700 1C [2]. The alloy high-temperature strength is derived mainly from precipitates of the Ni 3 (Al,Ti) phase (g 0 , ordered L1 2 structure), which are embedded within the disordered face centered cubic matrix (g phase) [3]. Furthermore, solid solution strengthening elements, e.g. molybdenum, cobalt and chromium, have a minor high-temperature strength effect. The addition of carbon to the alloy composition promotes the formation of carbides in the form of MC and M 23 C 6 along grain boundaries, which enhance the creep resistance of the alloy through grain boundary pinning [4]. To ensure the required product properties for each specific application, the Waspaloy is usually forged and heat-treated to achieve a proper microstructure; in particular, two types of micro- structures are of interest: (1) a microstructure with a grain size of ASTM 10 to 14 for high tensile strength, resistance to crack nucleation in low-cycle fatigue, and ductility; or (2) a microstructure with a grain size of ASTM 4 to 8 required for creep strength and resistance to crack propagation [5]. Since the obtainable microstruc- ture is strictly dependent on the deformation process parameters, it is necessary to have a complete knowledge of the hot working behavior, heat treatment and microstructure evolution. A literature survey shows some studies on the mechanical and microstructural behavior of Waspaloy during hot deformation. Guimaraes and Jonas [6] studied the Waspaloy recrystallization behavior in a temperature range between 870 1C and 1220 1C, and a strain rate range between 10 4 s 1 and 1 s 1 . They reported that below 950 1C the restoration phenomenon is the dynamic recovery, and from 1000 1C to 1220 1C at strain rates between 5.0  10 4 s 1 and 9.3  10 2 s 1 dynamic recrystallization is observed after the strain of 0.4. Yield drops occurred while testing Waspaloy from 1050 1C to 1150 1C attributed to short range ordering of the g 0 forming elements. Shen et al. [5] developed a model to predict the evolution of the Waspaloy microstructure during thermo-mechanical processing in terms of dynamic recrystallization, metadynamic recrystallization, and grain growth phenomena. They found similarities between the hot-working response of Waspaloy and that of C–Mn steels. These include the Avrami dependence of the recrystallization kinetics on strain for dynamic recrystallization or time for metadynamic recrys- tallization; moreover, the effect of as-preheated grain size, imposed Contents lists available at SciVerse ScienceDirect journal homepage: www.elsevier.com/locate/msea Materials Science & Engineering A 0921-5093/$ - see front matter & 2012 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.msea.2012.11.024 n Corresponding author. Tel./fax: þ98 21 82883359. E-mail addresses: amir.amiri.80@gmail.com (A. Amiri), sadeghim@modares.ac.ir (M.H. Sadeghi). Materials Science & Engineering A 562 (2013) 77–82