RU2806938C1 - METHOD FOR SELECTIVE LASER SINTERING OF MEDIUM-ENTROPY ALLOY OF Fe-Co-Ni-Cr-C SYSTEM - Google Patents

Abstract

FIELD: powder metallurgy of alloys.

SUBSTANCE: invention relates to the modes of producing products using additive technologies, to the production of parts using selective laser sintering with complex geometry from a medium-entropy alloy of the Fe-Co-Ni-Cr-C system, which can be used in low-temperature conditions. The method of selective laser sintering of a medium-entropy alloy of the Fe-Co-Ni-Cr-C system involves using as a starting material a powder of a medium-entropy alloy Fe₆₅(CoNi)₂₅Cr_9.5C_0.5 with the following ratio of components in atomic percent (at.%): 65 iron, 12.5 cobalt, 12.5 nickel, 9.5 chromium, 0.5 carbon, the formation of a product from which is carried out on a steel substrate, and the direction of laser movement when fusing each subsequent layer changes by 67°. The distance between the tracks and the thickness of the applied layer according to the simulation results are 50 mcm and 30 mcm, respectively. The product is formed using the following process parameters: beam power - 200-250 W, scanning speed 1600-2200 mm/s, while the pore volume fraction of the finished samples ranges from 0.1% to 0.3%.

EFFECT: method is provided for selective laser sintering of a medium-entropy alloy of the Fe-Co-Ni-Cr-C system, which has a structure with a pore volume fraction not exceeding 0.1% to 0.3% and high mechanical properties of the alloy.

1 cl, 1 tbl, 2 ex

Description

The invention relates to the field of powder metallurgy of alloys, namely to modes of producing products using additive technologies, to the production of parts using selective laser sintering with complex geometry from a medium-entropy alloy of the Fe-Co-Ni-Cr-C system, which can be used in low-temperature conditions.

The main advantages of additive manufacturing methods for creating metal parts, compared to conventional synthesis and molding processes, are their ability to produce complex, customized parts in a short time frame, albeit in relatively small quantities, resulting in weight savings critical to productivity or in case of repair of expensive metal parts, etc. [E. Povolyaeva, D. Shaysultanov et al., Mechanical Behavior of a Medium-Entropy Fe65(CoNi)25Cr9.5C0.5 Alloy Produced by Selective Laser Melting, Materials, 2023, 16(8), DOI: 10.3390/ma16083193]. Basically, many alloys produced by additive technologies have already been widely studied, for example alloys based on Ti, Ni, Fe, Al and Mg [D. Gu et al., Laser additive manufacturing of metallic components: materials, processes and mechanisms, Int. Mater. (2012), p. 133-164; D. Herzog et al. Emmelmann, Additive manufacturing of metals, Acta Mater. 117 (2016), p. 371-392]. Recently, close attention has been paid to high- and medium-entropy alloys produced by additive technologies [T. Deb Roy et al., Additive manufacturing of metallic components - Process, structure and properties, Progress in Materials Science 92 (2018) 112-224.]. Variations in structures and properties can be achieved using additive manufacturing, and this is also true for traditional manufacturing methods. However, high- and medium-entropy alloys during additive manufacturing are subjected to temperature-time ranges that are very different from those encountered in conventional manufacturing technologies, so the combination of microstructures and properties will also differ. It has recently been proven that additive manufacturing has the potential to produce high- and medium-entropy alloys that would have better structures and properties superior to analogues. High- and medium-entropy alloys are alloys that contain at least 5 elements, and the amount of each of them should not exceed 35 at% and should not be less than 5 at. % [Cantor, B., Chang, I.T.H., Knight, P. & Vincent, A.J.B. Microstructural development in equiatomic multicomponent alloys. Mater. Sci. Eng. A 375-377, 213-218 (2004)]. Such alloys are characterized by increased mixing entropy values compared to traditional multicomponent alloys. High-entropy alloys are allocated to a special group, since the processes of structure and phase formation in them, as well as the diffusion mobility of atoms, the mechanism for the formation of mechanical properties and thermal stability differ significantly from similar processes in traditional alloys. High- and medium-entropy alloys obtained by traditional methods, consisting of components such as Fe, Co, Cr, Ni, have long been one of the most widely studied classes; such materials have a number of exceptional mechanical properties, including cryogenic ones. Thus, for both science and industry, this class is of great interest in achieving their high-quality production using additive manufacturing methods, namely selective laser sintering. Selective laser sintering is an additive manufacturing method that involves sintering fine powder (usually metal) material using a laser [Carl R. Deckard. US Patent 4863538 A "Method and apparatus for producing parts by selective sintering" (English) (September 5, 1989)]. For some multicomponent materials, optimal methods of selective laser sintering have already been identified, but these methods are mainly suitable for producing powders and wires from high- and medium-entropy alloys.

For example, patent RU 2759347 (publication date November 12, 2021) describes a multicomponent wire for producing a high-entropy AlCoCrFeNi alloy. The invention relates to the creation of a multicomponent wire intended for wire-arc additive manufacturing, and can be used to produce layer-by-layer surfacing of a high-entropy alloy with the composition AlCoCrFeNi. The multicomponent wire contains an aluminum core of round cross-section and two wires of round cross-section with a diameter of no more than 0.4 mm, one of which is a chromium-nickel wire X20N80, and the other is a wire made of precision alloy 29NK. All cores are twisted in a spiral to obtain a multi-component wire diameter of no more than 1 mm, while the aluminum content in aluminum wire is 99.95%, and its diameter is no more than 0.5 mm. The wire provides a high-entropy alloy with high mechanical properties. However, there are no specific data on mechanical properties in the description.

Patent RU 2762897 (publication date December 23, 2021) describes a method for producing high-entropy alloy carbide powder with spherical particles. The invention relates to powder metallurgy and processing of non-ferrous metals and can be used in additive technologies to create high-quality final products of complex shape and in the production of ceramic products. Take 4-6 initial elemental powders from the series Ti, V, Zr, Nb, Hf, Ta, W, Mo with a purity of at least 99.5% in an equiatomic ratio and mix them in a gravitational mixer in air. The resulting mixture is placed in a planetary mill or attritor with the addition of a grinding agent - ethanol, isopropanol or polymethyl methacrylate, and grinding balls with a diameter of 5-15 mm, with a mass ratio of the mixture to grinding balls (1:10)-(1:40), respectively. After this, mechanical alloying is carried out for 1-50 hours in an argon atmosphere at a rotation speed of the main disk of the planetary mill of 100-400 rpm and its glasses - 100-1200 rpm or with a rotation speed of the attritor agitator of 100-600 rpm. The formed high-entropy alloy, homogeneous in chemical composition, is dried in a vacuum at 90-130°C for 1-2 hours, cooled in air to ambient temperature and separated from the grinding balls. Next, fractions 15-63 and 63-125 microns are separated from the powder. Then they undergo low-temperature plasma spheroidization and carbidization, using a plasma jet of argon-acetylene mixture, which is a plasma-forming gas, as the working atmosphere. The resulting melt drops are cooled in a stream of carrier gas, which is argon. The formed particles of ultra-high-temperature high-entropy carbide powder have a spherical or round shape with a shape factor of no more than 1.6 and a size of 20-120 microns, characterized by high fluidity and zero porosity. The disadvantage of the patent is the narrow focus on the use of the powder; there is also not enough information that the parts obtained from this powder actually have a set of high functional and mechanical properties, as the authors claim.

Patent RU 2751498 (publication date July 14, 2021) describes a method for producing powdered hard magnetic alloys based on the Fe-Cr-Co system. The invention relates to a method for producing powdered hard magnetic alloys based on the Fe-Cr-Co system of hard magnetic alloys. The initial powder mixture containing iron, chromium and cobalt is prepared by melting metal ingots of iron, chromium and cobalt in an atomizer and gas atomization of the melt to obtain a spherical powder. From the resulting spherical powder, spherical powder with a dispersion of no more than 80 microns and a spherical powder with a dispersion of more than 80 microns are isolated, which is subjected to jet grinding to obtain fragmented powder with a dispersion of no more than 80 microns. Then the resulting spherical and fragmentation powders with a dispersion of no more than 80 microns are mixed. Consolidation of the prepared initial powder mixture is carried out by selective laser fusion. Spherical powder with a dispersion of no more than 80 microns is mixed with fragmentation powder with a dispersion of no more than 80 microns in proportions of 1:1 or 4:1. It is possible to obtain magnetically hard powders from alloys of the Fe-Cr-Co system with a yield of a usable product of more than 90% and the possibility of using the resulting powders in additive manufacturing. The disadvantage of the invention is that the description does not contain information about the porosity of the obtained alloy samples.

In a scientific article [E.A. Povolyaeva et al., Outstanding cryogenic strength-ductility properties of a cold-rolled medium-entropy TRIP Fe65(CoNi)25Cr9⋅5C0.5 alloy, Materials Science & Engineering A, Volume 836, 142720] a medium-entropy alloy based on the Fe system was studied -Co-Ni-Cr-C, obtained by the traditional method (vacuum arc melting). The alloy has a number of high cryogenic mechanical properties in the original and rolled states. However, the article does not contain data on the production of a medium-entropy alloy of the Fe-Co-Ni-Cr-C system using additive manufacturing methods, including selective laser sintering.

There is already a large amount of research in the field of synthesis of parts from alloys using additive technologies. At the same time, most of the regimes for producing medium-entropy alloys are still poorly studied or not studied at all.

The technical objective of the invention is to create a method for selective laser sintering of a medium-entropy alloy of the Fe-Co-Ni-Cr-C system, which has a structure with a pore volume fraction not exceeding 0.1% to 0.3% and high mechanical properties of the alloy.

Achieving the stated technical result is achieved by selective laser sintering of medium-entropy powder of an alloy of the Fe-Co-Ni-Cr-C system on a ProX DMP 200 installation in an argon atmosphere. Fe ₆₅ (CoNi) ₂₅ Cr _9.5 C _0.5 powder is used as the starting material, with the following ratio of components in atomic percent (at.%): 65 iron, 12.5 cobalt, 12.5 nickel, 9.5 chromium, 0.5 carbon. The product is formed on a steel substrate. The direction of laser movement when fusing each subsequent layer changes by 67°. The distance between the tracks and the thickness of the applied layer according to the simulation results are 50 μm and 30 μm, respectively. When forming the product, the following process parameters are used: beam power - 200-250 W, scanning speed 1600-2200 mm/s. Using an optical microscope, it was found that the pore volume fraction of the finished samples varies from 0.1% to 0.3%.

The technical result is that in the resulting samples, upon visual inspection, a defect-free surface is observed, there are no unmelted areas, cracks and pores. Using an optical microscope, it was found that the pore volume fraction of the finished samples varies from 0.1% to 0.3%. Microstructural analysis using a scanning electron microscope demonstrates a homogeneous single-phase structure of the medium-entropy alloy along all fusion axes. Tensile-to-break tests revealed high mechanical properties at room and cryogenic testing temperatures (Table 1).

The claimed invention meets the conditions of novelty and inventive step, since the production of a medium-entropy alloy of the Fe-Co-Ni-Cr-C system by selective laser sintering is not known from the prior art.

Compliance with the conditions of industrial applicability of the invention is confirmed by the following examples of implementation.

The preparation of the obtained experimental samples for studying the structure and properties of the resulting medium-entropy alloy of the Fe-Co-Ni-Cr-C system is carried out as follows: grinding on sandpaper with a gradual decrease in its grain size on LaboPol-5 grinding and polishing machines (StruersA/S) and electrolytic polishing in a solution of 90% CH3COOH and 10% HClO4 at a voltage of 29.5 V for 10-30 seconds at room temperature. An optical microscope (Olympus GX71) is used to study the structure of the alloy. To study the microstructure of the resulting alloys, a scanning (raster) electron microscope (FEI Quanta 600 FEG) is used; The shooting is carried out in the diffraction mode of back-reflected electrons at an accelerating voltage of 20-30 kV. Additional EBSD survey is carried out in electron backscattering diffraction mode at an accelerating voltage of 20-30 kV, survey step is 0.3 microns. EBSD data were analyzed using the TexSEM Laboratories system (TSL OIM Analysis 6).

Specimens for uniaxial tensile testing with working part dimensions of 16×3×1.5 mm are tested with an initial strain rate of 10 ^-3 s ^-1 at room (24°C) and cryogenic (-196°C) temperatures, not less than 3 samples until rupture. Tests are carried out on an Instron 5882 testing machine in an air atmosphere in accordance with GOST 1497-84 (ISO 6892-84, ST SEV 471-88). Metals. Tensile test methods.

Table 1 presents examples of the invention in comparison with the results of the mechanical properties of a medium-entropy alloy of the Fe-Co-Ni-Cr-C system obtained by selective laser sintering of a medium-entropy alloy of the Fe-Co-Ni-Cr-C system subjected to uniaxial tensile tests at room temperature equal to 24°C and cryogenic temperature equal to -196°C. Also, for comparison, the properties of a medium-entropy alloy of the Fe-Co-Ni-Cr-C system obtained by vacuum-arc alloying are presented [E.A. Povolyaeva et al., Outstanding cryogenic strength-ductility properties of a cold-rolled medium-entropy TRIP Fe65(CoNi)25Cr9⋅5C0.5 alloy, Materials Science & Engineering A, Volume 836, 142720].

Selective laser sintering of medium-entropy powder of an alloy of the Fe-Co-Ni-Cr-C system is carried out on a ProX DMP 200 installation in an argon atmosphere. Laser radiation is specified in the form of a circle with a diameter of 75 microns (beam size), with a uniform energy distribution, without a gradient from the center to the edge of the laser beam spot. The laser radiation power varies from 200 to 250 W in steps, the reflection coefficient is assumed to be 0.3. When simulating the movement of a laser beam, the displacement speed of the laser beam is set from 1600 mm/s to 2200 mm/s. To improve the quality of the workpieces, the direction of laser movement during fusion of each subsequent layer was changed by 67°.

Example 1.

The starting material is a powder of a medium-entropy alloy of the Fe-Co-Ni-Cr-C system with the following component ratio, at. %: 65 iron, 12.5 cobalt, 12.5 nickel, 9.5 chromium, 0.5 carbon. The product is formed on a steel substrate. The direction of laser movement when fusing each subsequent layer changes by 67°. The distance between the tracks and the thickness of the applied layer were chosen based on the simulation results to be 50 μm and 30 μm, respectively. When forming the product, the following process parameters are used: beam power - 200 W, scanning speed 1600 mm/s. Upon visual inspection, the resulting sample demonstrated a defect-free structure: no cracks or non-adhesions were detected, the volume fraction of pores did not exceed 0.1%. Microstructural analysis showed a homogeneous structure of the alloy along all fusion axes; Using uniaxial tensile tests to break, high levels of mechanical properties were discovered at room and cryogenic test temperatures.

Example 2.

The starting material is a powder of a medium-entropy alloy of the Fe-Co-Ni-Cr-C system with the following component ratio, at. %: 65 iron, 12.5 cobalt, 12.5 nickel, 9.5 chromium, 0.5 carbon. The product is formed on a steel substrate. The direction of laser movement when fusing each subsequent layer changes by 67°. The distance between the tracks and the thickness of the applied layer were selected based on the simulation results and are 50 µm and 30 µm, respectively. When forming the product, the following process parameters are used: beam power - 250 W, scanning speed 2200 mm/s. Upon visual inspection, the resulting sample demonstrated a defect-free structure: no cracks or non-adhesions were detected, the volume fraction of pores did not exceed 0.3%. Microstructural analysis showed a homogeneous structure of the alloy along all fusion axes; Using uniaxial tensile tests to break, high levels of mechanical properties were discovered at room and cryogenic test temperatures.

The claimed technical result is the creation of a method for selective laser sintering of a medium-entropy alloy of the Fe-Co-Ni-Cr-C system, which has a structure with a pore volume fraction not exceeding 0.1% to 0.3% and high mechanical properties of the alloy.

Claims (1)

A method for selective laser sintering of a medium-entropy alloy of the Fe-Co-Ni-Cr-C system, including the use of medium-entropy alloy powder Fe ₆₅ (CoNi) ₂₅ Cr _9.5 C _0.5 with the following component ratio in atomic percent (at. %) as the starting material: 65 iron, 12.5 cobalt, 12.5 nickel, 9.5 chromium, 0.5 carbon, while the direction of laser movement when fusing each subsequent layer changes by 67°, while the distance between the tracks and the thickness of the applied layer according to the simulation results are equal 50 µm and 30 µm, respectively, the formation of the product is carried out on a steel substrate using the following process parameters: beam power 200-250 W, scanning speed 1600-2200 mm/s, while the pore volume fraction of the finished samples ranges from 0.1% up to 0.3%.