The paper reports on the fabrication and mechanical properties of Ni3Al based alloy, which represents the most
frequently used basic composition of nickel based intermetallic alloys for high temperature applications. The structure
of the alloy was controlled through directional solidifi cation. The samples had a multi-phase microstructure.
The directionally solidifi ed specimens were subjected to tensile tests with concurrent measurement of acoustic
emission (AE). The specimens exhibited considerable room temperature ductility before fracture. During tensile
testing an intensive AE was observed.Web of Science52331230

Chmelík, František

Kursa, Miroslav

Malcharcziková, Jitka

Pešička, Josef

Pohludka, Martin

DSpace at VSB Technical University of Ostrava

309METALURGIJA 52 (2013) 3, 309-312J. MALCHARCZIKOVÁ, F. CHMELÍK, J. PEŠIČKA, M. KURSA, M. POHLUDKANON-ALLOYED Ni3Al BASED ALLOYS – PREPARATION AND EVALUATION OF MECHANICAL PROPERTIESReceived – Prispjelo: 2012-09-12Accepted – Prihvaćeno: 2012-12-26Original Scientifi c Paper – Izvorni znanstveni radISSN 0543-5846METABK 52(3) 309-312 (2013)UDC – UDK 669.2:539.4.:534.6=111J. Malcharcziková, M. Kursa, M. Pohludka RMSTC, Faculty of Metal-lurgy and Materials Engineering, VŠB-TU Ostrava, Czech RepublicJ. Pešička, F. Chmelík Department of Physics of Materials, Charles Uni-versity in Prague, Czech RepublicThe paper reports on the fabrication and mechanical properties of Ni3Al based alloy, which represents the most frequently used basic composition of nickel based intermetallic alloys for high temperature applications. The struc-ture of the alloy was controlled through directional solidifi cation. The samples had a multi-phase microstructure. The directionally solidifi ed specimens were subjected to tensile tests with concurrent measurement of acoustic emission (AE). The specimens exhibited considerable room temperature ductility before fracture. During tensile testing an intensive AE was observed.Key words: Ni3Al based alloys, directional solidifi cation, tensile test, acoustic emission, fractureINTRODUCTIONFavourable properties of inter-metallic compounds enable their use in demanding environments, especially at elevated and high temperatures in oxidizing atmos-phere. Nickel or Ni3Al based alloys can be used for me-chanical joining of high temperature parts, such as in-sert bolts in the combustion chamber of the gas turbine [1, 2]. Practical applications of these materials are so far severely limited by their considerable brittleness. Struc-ture of these alloys may be favourably inﬂ uenced by addition of suitable alloying elements, by heat treatment and directional solidiﬁ cation [3]. Mechanical properties of these materials depend on the volume fraction, distri-bution, size and morphology of the γ’-precipitates [4, 5]. Their microstructure consists of a high volume frac-tion of γ’–strengthening precipitates (70 %) coherently merged in a γ (Ni-based solid solution) matrix [6]. For steam power plants that operate at temperatures of 700 °C and higher, nickel-base alloys have been devel-oped. In order to achieve desirable creep properties of these alloys further strengthening through solid solution or precipitation strengthening is needed.Solid solution strengthening is achieved by addition of Mo, Fe, W, Ta, Cr and Co [7, 8]. The additions of Ti and Al are necessary to improve the yield and creep strength of Ni3Al based alloys through precipitation strengthening by the γ’ particles.FABRICATION OF MATERIALBinary Ni3Al based alloy with 22 at.% of Al, were used for determination of mechanical characteristics and characterisation of fracture behaviour. The alloy was melted in corundum crucible in a vacuum induction furnace and cast into graphite moulds. Chemical com-position of the samples was checked by the optical emission spectroscopy method. The samples were sub-jected to directional solidiﬁ cation in a two-zone furnace. The samples were melted in a corundum tube with spe-ciﬁ c apex angle. Temperature of the melt was optimised on the basis of numerous preliminary measurements and temperature gradient in liquid at the solid-liquid in-terface was within the interval of 70 - 90 °C·cm-1. Two solidiﬁ cation rates (rDS) were applied, i.e. 50 and 20 mm·hod-1 (Table 1). After directional solidiﬁ cation the samples had a multi-phase microstructure formed main-ly by Ni3Al (γ‘) phase and two phase regions composed of the γ‘ precipitates embed in the γ matrix. The pre-cipitation of very ﬁ ne γ‘ particles was observed in the γ channels separating the γ‘ particles.EXPERIMENTALShort tensile specimens with a length of 55 mm and gauge diameter of 5 mm were prepared by lathe-turning from directionally solidiﬁ ed samples. The strain rate was approximately 1,33x10-3 s-1 for all tested specimens. Table 1 gives the measured values of offset 0,2 % ten-sile yield stress (Rp0.2), ultimate tensile strength (Rm) and tensile strain until the fracture.Figure 1 shows stress-strain curves of the samples No. 1 and No. 2. Acoustic emission (AE) was measured by the four-channel commercial facility instrument Table 1 Obtained mechanical characteristicsSpecimen No. rDS / mm/h Rp0.2 / MPa Rm / MPa Tensile strain / -1 20 164 451 1,422 50 172 487 1,41310  METALURGIJA 52 (2013) 3, 309-312J. MALCHARCZIKOVÁ et al.: NON-ALLOYED Ni3Al BASED ALLOYS – PREPARATION AND EVALUATION…DAKEL IPL. This device enables a continuous data ac-quisition and subsequent analysis of signals. Two-threshold detection was used in accordance with the ASTM standard, which enables a simple amplitude dis-crimination of signals. For all tested specimens the total ampliﬁ cation of 40 dB was used. Dynamic range of the A/D converter was 0-2 400 mV. The ﬁ rst threshold level was set to 15 % of this range and the result was the count rate dNC1/dt. The second threshold level was set to 30 % of the full range for registration of the AE sig-nals with high amplitude. The result was the count rate dNC2/dt. The AE signal was measured by a miniaturized piezoceramic AE transducer MICRO 2006 working in the frequency range from 100 to 600 kHz. An intensive AE was observed with characteristic dependence on time and correlation with individual stages of deforma-tion (Figures 2 and 3).EVALUATION OF MEASUREMENT RESULTSDeformation curves of the specimens 1 and 2 are very similar. The deformation curves are smooth with considerable deformation strengthening. The shape of the curves resembles the strengthening curve of single crystals. The AE response in the specimen 1 up to strain of about 0,4 corresponds to prevailing plastic deforma-tion. Afterwards the material gets damaged. A distinct AE response of discontinuous character can be seen in Fig. 2, when formation of cracks occurs. AE disappears at strain of approx. 0,7 and it reappears only close to the rupture. As a result of failure processes immediately af-ter plastic deformation a drop on the deformation curve is observed at the strain of about 0,8 (Figure 2). The specimen 2 has also high ductility. We assume that plas-tic deformation dominates up to the strain of 0,5, but the deformation may be of a non-homogeneous character.As soon as the failure processes appear, the charac-ter of the curve corresponds to crack formation. In the speciment 2 a drop was also observed on the deforma-tion curve at the strain of about 1,1. This drop appeared later than in the specimen 1 and failure processes take place mainly at the ﬁ nal stage of deformation (Fig. 3). TRIP steels show also similar type of failure, where ad-ditional strengthening of material takes place. In this case, however, material shows signiﬁ cantly higher val-ues of Rp0.2 at room temperature [9].Figures 4-7 show fracture surfaces. Fracture surface of the specimen 1 has elliptic shape (Figure 4). It is formed by several plane areas, which are mutually in-clined in such a manner that the fracture surface is con-cave above the sample cross-section. The entire fracture surface exhibits transcrystalline plastic fracture with dimple-like morphology (Figure 5). For comparison, the wrought alloy Nimonic 80A shows mainly brittle fracture with ductile areas at the edges of the specimen [1]. The fracture surface of the specimen 2 has mostly planar character. This planarity is disrupted at two plac-es at the edge by a distinct step. Cross-section of the specimen is also elliptic (Figure 6). Also by this sample, the entire fracture surface exhibits again character of transcrystalline plastic fracture of dimple-like type (Fig-ure 7). This type of fracture corresponds to multiphase structure with high proportion of regions with two phase γ /γ‘ microstructure.CONCLUSIONSMechanical characteristics and fracture behaviour of directionally solidiﬁ ed Ni3Al based alloy with 22 at.% of Al were determined. The samples exhibited a multi-phase microstructure formed mainly by single Ni3Al (γ‘) phase and two phase regions containing γ‘ particles embed in the γ matrix. During tensile testing an inten-sive AE was observed, exhibiting direct correlation to various stages of deformation (plasticity and failure). Tensile curves were smooth with signiﬁ cant deforma-Figure 3 AE record - specimen No. 2Figure 1 Stress-strain curves of the specimen Nos. 1 and 2Figure 2 AE record - specimen No. 1Stress / MPaTime / sTime / sStress / MPaTime / sStress / MPa311METALURGIJA 52 (2013) 3, 309-312J. MALCHARCZIKOVÁ et al.: NON-ALLOYED Ni3Al BASED ALLOYS – PREPARATION AND EVALUATION…tion strengthening. The specimens showed unusually high room temperature ductility. Only transcrystalline plastic fracture with dimple-like morphology was ob-served on fracture surfaces. Dimple-like fracture corre-sponds approximately to the proportion of the γ/γ’ net-work in microstructure.ACKNOWLEDGEMENTThe presented results were obtained within the frame of solution of the project CZ.1.05/2.1.00/01.0040 “Re-gional materials science and technology centre” and the research project TA 01011128 “Research and develop-ment of centrifugal casting technology of the Ni-based intermetallic compounds”. The authors thank Mr. Ing. P. Dobroň, Ph.D. from Charles University in Prague for the execution of tensile tests.Figure 7 Fracture surface - specimen No. 2Figure 4 Fracture surface - specimen No. 1 Figure 5 Fracture surface - specimen No. 1Figure 6 Fracture surface - specimen No. 2REFERENCES[1] R. Sunulahpašić, M. Oruč, Effect of temperature on me-chanical properties and type of fracture of superalloys Ni-monic 80A, Metalurgija 50 (2011) 3, 155-158.[2] J. K. Wessel Handbook of Advanced Materials: Enabling New Designs. USA, A JOHN WILEY & SONS, INC., 2004, p. 645.[3] E. M. Schulson, Y. Xu, On the ductility of Ni3Al: effect of strain rate, environment and boron, Acta Mater., 45 (1997) 8, 3491-3494.[4] J. Lapin, M. Gebura, T. Pelachova, O. Bajana, Microstructu-re degradation of nickel base single crystal superalloy CMSX-4, In “18th Anniversary International Conference on Metallurgy and Materials (METAL)”, (2009), 304-310.[5] J. Lapin, M. Gebura, O. Bajana, T. Pelachova, Effect of size and volume fraction of cuboidal gamma’precipitates on me-chanical properties of single crystal nickel–based superalloy CMSX-4, Kovove Mater., 47 (2009) 3, 129-138.312  METALURGIJA 52 (2013) 3, 309-312J. MALCHARCZIKOVÁ et al.: NON-ALLOYED Ni3Al BASED ALLOYS – PREPARATION AND EVALUATION…[6] J. Cormier, P. Villechaise, X. Milhet, γ’-phase morphology of Ni-based single crystal superalloys as an indicator of the stress concentration in the vicinity of pores, Materials Science and Engineering A, 501 (2009) 1-2, 61-69.[7] A. Nagode, L. Kosec, B. Ule, G. Kosec, Review of creep resistant alloys for power plant application, Metalurgija 50 (2011) 1, 45-48.[8] J. Lapin, Effect of ageing on microstructure and mechani-cal behaviour of directionally solidiﬁ ed Ni3Al-based alloy. Intermetallics, 5 (1997) 8, 615-624.[9] M. Cagala, et al., Hot ductility of two high manganese ste-els, In “20th Anniversary International Conference on Me-tallurgy and Materials (METAL)” (2011), 510-516.Note:  The responsible translator for English language is B. Škandera, Informetal, Dobrá, Czech Republic

Non-alloyed Ni3Al based alloys – preparation and evaluation of mechanical properties

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Non-alloyed Ni3Al based alloys – preparation and evaluation of mechanical properties

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