Elsevier

Materials Science and Engineering: A

Volume 591, 3 January 2014, Pages 183-192
Materials Science and Engineering: A

Hot deformation behavior and processing map of a typical Ni-based superalloy

https://doi.org/10.1016/j.msea.2013.09.049Get rights and content

Abstract

The hot compressive deformation behaviors of a typical Ni-based superalloy are investigated over wide ranges of forming temperature and strain rate. Based on the experimental data, the efficiencies of power dissipation and instability parameters are evaluated and processing maps are developed to optimize the hot working processing. The microstructures of the studied Ni-based superalloy are analyzed to correlate with the processing maps. It can be found that the flow stress is sensitive to the forming temperature and strain rate. With the increase of forming temperature or the decrease of strain rate, the flow stress significantly decreases. The changes of instability domains may be related to the adiabatic shear bands and the evolution of δ phase(Ni3Nb) during the hot formation. Three optimum hot deformation domains for different forming processes (ingot cogging, conventional die forging and isothermal die forging) are identified, which are validated by the microstructural features and adiabatic shear bands. The optimum window for the ingot cogging processing is identified as the temperature range of 1010–1040 °C and strain rate range of 0.1–1 s−1. The temperature range of 980–1040 °C and strain rate range of 0.01–0.1 s−1can be selected for the conventional die forging. Additionally, the optimum hot working domain for the isothermal die forging is 1010–1040 °C and near/below 0.001 s−1.

Introduction

During hot forming processes, material flow behaviors are very complex. The hardening and softening mechanisms are both significantly affected by the thermo-mechanical parameters, such as forming temperature, deformation degree, and strain rate [1], [2]. Generally, there are several types of metallurgical phenomena during the hot deformation, such as the dynamic recrystallization (DRX) [3], [4], [5], [6], [7], [8], [9], [10], [11], [12], [13], [14], [15], [16], [17], metadynamic recrystallization (MDRX) [8], [9], [10], [11], [12] and static recrystallization (SDRX) [13], [14], [15], [16], [17], which result in the complex microstructural evolution in alloys. In order to obtain the optimum hot working process, a good understanding of hot deformation behaviors, kinetics of metallurgical transformation and processing maps is very important for the designers of metal forming processes [18], [19].

Dynamic material modeling (DMM) aims to correlate the constitutive behavior with microstructural evolution, flow instability and hot workability. Base on the dynamic material model (DMM), the processing map was developed by Prasad et al. [20]. Processing maps are useful to identify the deformation temperature–strain rate windows for hot working. In recent years, some investigators have developed processing maps to optimize the hot working processing for some typical metals or alloys [21], [22], [23], [24], [25], [26], [27], [28], [29], [30], [31], [32], [33], [34], [35], [36], [37], [38], [39], [40], [41]. Samantaray et al. [21] optimized the hot working parameters for the modified 9Cr–1Mo (P91) steel by the dynamic materials model. Also, Samantaray et al. [22] studied the processing parameters of a nitrogen enhanced 316L(N) stainless steel based on the high-temperature flow behavior and microstructural evolution, and the optimum window for the hot deformation were identified as 1350–1423 K and 0.001–0.05 s−1 with peak efficiency of 50% and activation energy of 150 kJ/mol. El Mehtedi et al. [23] studied the high temperature workability of a 1%C–1.5%Cr steel by means of torsion experiments carried out between 1125 and 1000 °C. Momeni and Dehghani et al. [24], [25] characterized the hot deformation behaviors of 410 martensitic and 2205 austenite–ferrite duplex stainless steels using constitutive equations and processing maps. Abbasia and Momeni [26] studied the hot workability of Fe–29Ni–17Co alloy by the mechanical testing and microstructural observations, and established the processing maps for the studied material. Based on the experimental data, the processing maps of 42CrMo steel were developed, and the validity was proved by the microstructural features [27]. Lin et al. [28] studied the flow behavior and microstructural evolution of a typical Al–Zn–Mg–Cu alloy, and identified the optimum hot working domain as 623–723 K and 0.001–0.05 s−1. Rajamuthamilselvan and Ramanathan et al. [29] developed the processing map for 7075 Al/20% SiCp composite, and the relationship between microstructure and hot workability were investigated through microstructural observations. Senthilkumar et al. [30] developed the processing map of the Al-based nanocomposite by the dynamic materials model (DMM), and different deformation mechanisms such as the dynamic recrystallization (DRX), dynamic recovery and flow localization were validated by the manifestation of many microstructural features after hot deformation. The optimum hot working parameters for Al6063/0.75Al2O3/0.75Y2O3 nano-composite were identified, and the flow instability characteristics were validated by processing maps and micrographs [31]. Quan et al. [32], [33] discussed the optimum hot working parameters for the as-extruded 42CrMo high-strength steel and 3Cr20Ni10W2 heat-resistant alloy, which were validated by DRX refined microstructures without any wedge crack. Liu et al. [34] and Han et al. [35] developed the processing maps for the as-cast 6Mo superaustenitic stainless steel and 20Cr–25Ni superaustenitic stainless steel, respectively, and the optimized processing parameters were obtained. Additionally, the processing maps were developed for Mg–Zn–Cu–Zr magnesium alloy [36], DC cast Al–15%Si alloy [37], PM TiAl alloy [38], Al–Cu–Mg alloys microalloyed [39], SiC particles reinforced metal matrix composites [40], and AISI 4340 steel [41].

Due to its excellent mechanical, physical and anticorrosion properties, Ni-based superalloys are widely used in the critical parts of aeroengine. It is well known that Ni-based superalloys are generally kind of precipitation strengthen alloys. Due to the narrow forming temperature range, great deformation resistance and complex microstructures of Ni-based superalloys, some investigations have been carried out to understand the effects of processing parameters on the hot deformation behavior and microstructural evolution [42], [43], [44], [45], [46], [47], [48], [49], [50], [51], [52], [53]. Dehghan et al. [45] studied the constitutive modeling and microstructural evolution of hot compressed A286 iron-base superalloy. Wang et al. [46] investigated the hot deformation behavior and processing maps of X-750 Ni-based superalloy, and the optimum processing parameters for the hot working were identified as 1000–1050 °C and 0.1–1 s−1. Sui et al. [47] constructed the processing maps for GH4169 superalloy, and found that the adiabatic shear bands appear under low deformation temperature and high strain rate. Wang et al. [48] studied the hot compressive behaviors of Inconel 718 superalloy, and found that the δ phase (Ni3Nb) can stimulate the dynamic recrystallization. Wang et al. [49] studied the effect of δ phase on the strain rate sensitivity exponent, strain hardening exponent and microstructure evaluation during hot deformation of Inconel 718. Ning et al. [50] studied the flow behavior and constitutive model for Ni–20.0Cr–2.5Ti–1.5Nb–1.0Al superalloy compressed below γ′-transus temperature. Etaati and Dehghani [51] studied the hot deformation behavior of Ni–42.5Ti–7.5Cu alloy. Wu et al. [52] studied the hot deformation characteristics and established the strain-dependent constitutive analysis of Inconel 600 superalloy. Guo et al. [53] studied the hot deformation behavior and developed the processing maps of Inconel 690 superalloy. Although a number of investigations have been conducted to the hot deformation behavior of superalloy, further investigations should be carried out to optimize the forming processing parameters and control the microstructures of the Ni-based superalloy.

In this study, the hot deformation behaviors of a typical Ni-based superalloy with δ phase (Ni3Nb) are investigated by isothermal compression tests under wide ranges of forming temperature and strain rate. The effects of forming temperature, strain rate and strain on the flow behaviors are discussed. Based on the dynamic material modeling (DDM), the processing maps of the studied Ni-based superalloy are constructed to optimize the hot working domains. In addition, the microstructural evolution is analyzed to validate the established processing maps of the studied Ni-based superalloy.

Section snippets

Materials and experiments

The chemical compositions (wt%) of the studied Ni-based superalloy are shown in Table 1. The metastable body-centered tetragonal coherent precipitate γ(Ni3Nb) and the face-centered cubic coherent precipitate γ(Ni3Al) are the main strengthening phases. Furthermore, γ phase is the major strengthening phase which may transform to δ phase (Ni3Nb) in the dynamic equilibrium [54]. Cylindrical specimens with diameter of 8 mm and a height of 12 mm were machined from the wrought billets. In order to

True strain–true stress curves

Fig. 2 shows the true stress–strain curves of the studied Ni-based superalloy under the tested conditions. Obviously, the flow stress increases sharply until a peak stress in the early deformation stage, which results from the work hardening caused by the dislocation generation and multiplication. Due to the low stacking fault energy, the dynamic recovery for the studied Ni-based superalloy proceeds slowly. The increase of dislocation density leads to the occurrence of dynamic recrystallization

Conclusions

The high temperature deformation behaviors of the studied Ni-based superalloy are investigated over wide ranges of forming temperature and strain rate. Based on the experimental data, the processing maps are constructed. Some important conclusions can be made as follows:

  • (1)

    The effects of the forming temperature and strain rate on the flow stress are significant. Increasing the forming temperature or decreasing the strain rate can decrease the flow stress.

  • (2)

    The values of power dissipation efficiency

Acknowledgments

This work was supported by National Natural Science Foundation of China (Grant no. 51375502), Program for the 973 program (Grant no. 2013CB035801), and Sheng-hua Yu-ying Program of Central South University, China. The authors are thankful to Prof. Yan Wang (Central South University) for her technical assistance and useful discussions for this work.

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