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47PRODUCTION OF SPHERICAL MICROPOWDER OF THE HIGH-TEMPERATURE STRENGHT NiAl-BASED ALLOY USING COMBUSION SYNTHESIS AND THEIR APPLICATION IN THE SELECTIVE LASER
MELTING TECHNOLOGY
Yu. Yu. Kaplanskii*", E. A. Levashov", Zh. A. Sentyurina"^, P. A. Loginov",
A. V. Korotitskiy", and E. I. Patsera"
aNational University of Science and Technology MISiS, Moscow, 119049 Russia
bJSC Kompozit, Korolev, 141070 Russia *e-mail: [email protected]
DOI: 10.24411/9999-0014A-2019-10055
Currently, an increased attention is dedicated to the development of gas-turbine engines with enhanced performance via the application of novel heat-resistant materials and topologically optimized structures. Ones of the most prospective materials with high potential for application in the aerospace industry are NiAl-based heterophase alloys due to their high specific heat resistance, chemical stability, and creep resistance. Manufacturing of the heat-loaded parts (blades for rotors and impaler, burners, etc.) of gas-turbine engine from these particular alloys will increase its performance considerably. However, NiAl-based alloys are exceedingly brittle at room temperature (plasticity 3-6%), precluding their mechanical treatment and wide-scale industrial implementation. The technological breakthrough in the industrial implementation of NiAl-based alloys for aerospace industry will allow the creation of complex-shaped parts via additive manufacturing technologies. Currently, the most prospective additive manufacturing technology is selective laser melting (SLM) of powders of metals and alloys, which is being actively implemented at the advanced aerospace enterprises for the one-step manufacturing of complex-shaped parts. Implementation of this technology, however, requires spherical powders with close-cut and regulated particles size distribution (10-45 |m) and uniform chemical composition.
In this work, a universal technology for the production of chemically and structurally homogeneous NiAl-based spherical powders, based on the exothermic SHS reaction in mechanically activated mixture of the elemental powders. The developed technology includes the following operations: (1) preparation of the MA-mixtures in planetary ball mill (PBM);
(2) pressing of MA mixtures up to ~ 40% green body density; (3) SHS of the alloy in the water-cooled reactor under constant argon pressure (alloy is produced in a form of porous sinter cake);
(3) milling of the sinter cakes in jaw crusher and PBM to a particle size smaller than 100 |m;
(4) air separation of the target phase to 20-45 |m and (5) plasma-assisted spheroidization of SHS powder.
According to this technology, spherical powders of novel prospective heat-resistant alloy NiAl-12Cr-6Co-0.25Hf, at % (designated CompoNiAl-M5-3) 20-45 |m in size were produced [1]. The synthesized powders had a faceted shape and a bimodal distribution of particle size in the range of 10-87 |m at D50 = 47 |m, flowability of 38 s and low bulk density of 2.35 g/cm3. Relatively high flowability of SHS powders is a result of absence of submicron particles.
The research into the spheroidization of SHS powders was conducted on the plasma device with an electro-discharge DC plasmatron. Ar + 17 vol % H2 mixture was used as the plasma-forming gas. Investigation revealed that the optimal powder plasma treatment regime ensures the increase in the bulk density up to 3.95 g/cm3 and flowability up to 19 s due to the
XV International Symposium on Self-Propagating High-Temperature Synthesis
spheroidization of the particles. Spheroidization degree was up to 95% at particles size of 5-77 |im and D50 = 43.1 |im, with no satellite particles. According to the chemical analysis, the content of oxygen and nitrogen impurities was below 0.12 and 0.0017 wt %, respectively.
SEM, TEM, and EDS studies of the spherical powders (Fig. 1) revealed a dendritic grain structure with degraded Cr(Co)e eutectic along the grain boundaries, interspersed with strengthening Hf nanoparticles (< 100 nm). Dendritic cells were 1-6 |im in size. ICP-MS analysis of SHS powders before and after the spheroidization showed that the plasma treatment does not lead to the deviations in chemical composition.
Fig. 1. (a) Morphology and (b, c) microstructure of spheroidized SHS-powders of
ComoNiAl-M5-3alloy.
Spheroidized SHS powders with particle size of 20-45 |im were sintered by hot isostatic pressing (HIP) and selective laser melting (SLM). Optimal HIP regime provided a dense material with the following mechanical properties: tensile strength (ob) 2870 MPa; yield strength (00.2) 1131MPa; and plasticity (s) 16.87%. High-resolution TEM demonstrated that nano-sized particles of Ni2AlHf Heysler phase are formed along the grain boundaries and within the NiAl matrix, which is caused by a decrease in the interface energy. Hf nanoparticles were observed only within the a-Cr phase. SLM 280 installation (SLM Solution) was employed for the optimization of additive manufacturing of cubic samples and models of the blade of gasturbine engine with a residual porosity below 0.2% (Fig. 2). Subsequent HIP treatment of SLM samples ensured a further enhancement of mechanical properties.
Fig. 2. SLM model of the blades of gas-turbine engine made of spherical CompoNiAl-M5-3 powders.
Two CompoNiAl-M5-3 alloy specimens manufactured by HIP, SLM + HT (850°C for 2 h), and SLM + HT + HIP were subjected to the thermomechanical testing to ascertain the temperature and load limits for the sustainable performance of the alloy. Young's modulus and yield strength at 850 °C and a loading rate of ~ 0.01 s-1 were: 137.8 GPa and 455 MPa for HIP samples; 58 GPa and 334 MPa for SLM + HT samples; 75 GPa and 495 MPa for SLM + HT + HIP samples. Figure 3 reveals that the HIP of SLM samples ensures the considerable increase in the deformation resistance of the investigated NiAl-based alloy. Therefore, additional HIP treatment of complex-shaped SLM parts is necessary to reinforce the high-temperature strength of nickel aluminide-based alloys.
800
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600 650 700 750 800 850 900 9 50 1000 1050 1100 Temperature, °C
Fig. 3. Temperature dependence of the yield strength of CompoNiAl-M5-3 after HIP, SLM, and SLM+HIP.
The authors gratefully acknowledge support from Russian Science Foundation (project no. 19-79-10226).
1. Yu.Yu. Kaplanskii, A.V. Korotitskiy, E.A. Levashov, Zh.A. Sentyurina, P.A. Loginova, A.V. Samokhin, I.A. Logacheva, Microstructure and thermomechanical behavior of Heusler phase Ni2AlHf-strengthened NiAl-Cr(Co) alloy produced by HIP of plasma-spheroidized powder, Mater. Sci. Eng. A, 2018, vol. 729, pp. 398-410.
