Nb-rich Phase Research Articles

Thermal stability of (HfCo)90(NbMo)10 and (HfCo)75(NbMo)25 refractory high entropy alloys with a bcc + B2 structure

The effect of long-term (700 h) annealing at 1000 °С on the structure and mechanical properties of the as-cast (HfCo)90(NbMo)10 and (HfCo)75(NbMo)25 (in at.%) refractory high entropy alloys was examined. The as-cast alloys consisted of a mixture of (Nb, Mo)-rich bcc and (Hf, Co)-rich B2 phases with bcc / B2 ratios close to NbMo / HfСo ratios. Annealing did not result in the formation of additional phases, which agreed with the Thermo-Calc predictions. However, annealing led to the formation of (i) B2 / bcc nanoprecipitates inside the initial bcc / B2 phases and (ii) separate Nb-rich and Mo-rich bcc phases. Annealing also caused significant strengthening of the alloys; for example, the room-temperature yield strength of the (HfCo)90(NbMo)10 alloy increased from 640 to 1340 MPa. Hardening was induced by the bcc nanoprecipitates in the B2 phase according to the Orowan mechanism. The results obtained suggest novel routes for the development of refractory high entropy alloys with a stable bcc + B2 structure.

Formation of Zr-rich BCC phase and its relation on the hydrogen storage properties of TiVNbZr high entropy alloy

Due to the large difference in atomic size between Zr and Nb, TiVNbZr high entropy alloy possesses greater lattice distortion. The change of Zr content can affect the stability of hydrides, which can have an important impact on the hydrogen storage performance. In order to explore the effect of Zr/Nb on hydrogen storage properties, Ti32.5V27.5Nb40-xZrx (x = 7.5, 10, 12.5, 15) high entropy alloys composed of BCC phase are designed. It is found that with the increase of Zr/Nb, the dendritic microstructures first disappear and then gradually become coarse. The Zr-rich BCC phase and the Nb-rich BCC phase appear in the interdendritic and dendritic regions, respectively. Ti32.5V27.5Nb25Zr15 shows excellent activation performance, which is related to the Zr-rich BCC phase with the most catalytic phase on the surface. The hydrogen storage performance of low Zr/Nb composition is better at low temperature, and that of high Zr/Nb composition becomes better after rising to high temperature. This is because with the change of Zr/Nb, low temperature can promote the hydrogen absorption reaction and high temperature can increase the diffusion rate of hydrogen atoms in the interstitial positions of the alloy. Ti32.5V27.5Nb32.5Zr7.5 achieves the best hydrogen absorption capacity of 1.71 wt % at 150 °C. All components undergo a transition from the BCC phase to the FCC phase during the hydrogen absorption process, and then change to a single-phase BCC structure after dehydrogenation. With the increase of Zr content, the first step desorption temperature raises in turn, owing to the stronger thermal stability of hydride.

Effects of Cu and Nb on martensite hardening and transformation-induced plastic deformation behavior of maraging TRIP-aided steel

Martensite hardening and transformation-induced plastic deformation (TRIP) are crucial to the mechanical properties of steels. In this study, maraging TRIP-aided steel was developed. The addition of Cu and Nb can effectively promote transformation-induced plastic deformation, this is due to the characteristic of the alternating combination of soft and hard phases. In contrast, the addition of Nb has a more significant effect on martensite hardening, which can be attributed to the smaller effect of Nb on the martensite transformation start temperature (Ms). The multi-phase structure and precipitation strengthening, lead to the ultimate tensile strength and elongation of the maraging TRIP-aided steel is ∼1300 MPa and ∼24%, respectively. It was found that the prior austenite formed a continuous network surrounding bainite and martensite. The high-density dislocations in bainite and martensite increased the hardness. In addition, the metastable austenite phase was transformed into the martensite phase, and a heterostructure with the alternating distribution of bainite/austenite was formed during deformation. The refinement of grains effectively reduced the concentration of stress. Massive nanometer-scaled precipitates were formed in Nb-containing steel after peak aging, and the co-precipitation of Nb-rich and Mo-rich phases occurred in the steel. The large-sized Laves-Fe2(Nb, Mo) effectively enhanced the strength of steel, and the fine and dense Ni3Ti was beneficial to the simultaneous improvement of strength and plasticity. Therefore, the jointed mechanisms of martensite hardening, and the TRIP effect improved the strength while retaining good plasticity.

Electrochemical corrosion behavior in sulfuric acid solution and dry sliding friction and wear properties of laser-cladded CoCrFeNiNbx high entropy alloy coatings

316 stainless steel (SS) was coated with CoCrFeNiNbx (x: atomic ratio, x = 0, 0.1, 0.2, and 0.3) high entropy alloy coatings (HEACs) by laser cladding (LC). The impacts of Nb content on the phase composition, microstructure, microhardness, wear resistance and corrosion properties of CoCrFeNi based HEACs were examined. Different from the canonical dendritic (DR) - interdendritic (ID) microstructure presented by the other three HEACs, the ID of Nb0.3 HEACs also existed nanoscale Nb-rich Laves phase composed of NbNi and NbCo. The inclusion of Nb significantly reduced the average grain size of CoCrFeNi based HEACs from 59.43 μm to 11.38 μm. It also greatly diminished the formation of high angle grain boundaries (HAGBs), increasing the percentage of low angle grain boundaries (LAGBs) from 31 % to 61 %. The microhardness of Nb-containing HEACs was significantly promoted due to the solid solution strengthening and fine grain strengthening caused by large size Nb atoms. Affected by Laves phase with high coordination number and space filling ratio and higher proportion of LAGBs, the microhardness of Nb0.3 HEAC was even as high as 530 HV. The increase in Nb concentration also strengthened the HEACs' resistance to wear. Nb0, Nb0.1, Nb0.2, and Nb0.3 HEACs had corresponding specific wear rates of 0.36, 0.32, 0.23, and 0.20 mm3/Nm. Unlike 316 SS, Nb0 and Nb0.1 HEACs, which had both adhesive wear and abrasive wear, Nb0.2 and Nb0.3 HEACs were mainly wear by abrasive wear. The corrosion behavior of CoCrFeNiNbx HEACs in 0.5 M H2SO4 solution was similar to 316 SS, but the corrosion resistance was stronger than 316 SS. Nb0.3 HEAC with the Ecorr of −164 mV and Icorr of 6.40 × 10−7 A/cm2 showed the best acid corrosion resistance, which could be attributed to the stable and dense passivation film on its surface. Distinct from the intergranular corrosion of other coatings, the corrosion of Nb0.3 HEAC mainly occurred in DR, because the FCC phase acted as the anode site in it when FCC and Laves phase co-existed.

Modified heat treatment and related microstructure-mechanical property evolution of arc melting additively manufactured GH4169 Ni-based superalloy

GH4169 Ni-based superalloy was prepared by wire arc additive manufacturing (WAAM) in this study. Similar to the microstructure of other additive manufactured superalloys, the additively manufactured GH4169 alloy suffered from a high-volume fraction of Laves phase, which is detrimental to the alloy’s mechanical properties. To solve this problem, two different post heat-treatment approaches were selected to improve the tensile properties at both room and elevated temperatures, which are the one with solution treatment temperature at 950 °C and the modified one with solution treatment at 1150 °C, respectively. Detailed phase analysis during different heat treatment processes was conducted using both scanning and transmission electron microscopes. Comparative tensile tests were also conducted at both room temperature and 650 °C to analyze the role of the different microstructures on the deformation responses of the prepared samples. By increasing the solution treatment temperature from 950° to 1150°C, the volume fraction of Nb-rich Laves phase dramatically decreased, and the previously Laves-phase-trapped Nb contributed to the formation of the strengthening γ″ phase. As a result, the tensile strength of this modified treated alloy is significantly improved at both room and elevated temperatures. Additionally, due to lower volume fraction of the Laves phase, the elongation of the modified treated alloy at room temperature is improved by ∼35%. These findings provided new insights into the post-heat treatment approaches of the WAAM Ni-based superalloy.

Sequence of phase transformations in metastable β Zr–12Nb alloy studied in situ by HEXRD and complementary techniques

Phase transformations in a metastable beta Zr–12Nb alloy were investigated by high-energy X-ray diffraction (HEXRD) measured simultaneously with thermal expansion in situ during linear heating from room temperature to 800 °C. Complementary in-situ methods of electrical resistance and differential scanning calorimetry, which were performed using the same heating conditions as in the HEXRD experiment, provided additional information on the transformation sequence occurring in the Zr–12Nb alloy. Two bcc phases with a different lattice parameter, βZr and βNb, were observed in the investigated temperature range and identified using the phase diagram of the Zr–Nb system. In the initial solution-treated condition, metastable βZr phase and athermal ω particles are present in the material. At about 300 °C, Nb-rich βNb phase starts to form in the material and the original βZr phase gradually disappears. Ex-situ observations of the microstructure using transmission electron microscopy revealed a cuboidal shape of the ω particles, which is related to a relatively large misfit between the ω and β phases. At 560 °C, ω solvus was observed, identified by an abrupt dissolution of ω particles which was followed by growth of the α phase.

Plasticity of the Nb-rich μ-Co7Nb6 phase at room temperature and 600°C

The µ phase is a common precipitation phase in superalloys and it exists in a wide composition and temperature range. As such, we study the influences of composition and temperature on its plasticity by micropillar compression tests and transmission electron microscopy. The micropillars of the μ-Co7Nb6 phase deform plastically by basal slip at room temperature and 600 °C. At room temperature, the Co-49Nb and Co-52Nb micropillars show high yield stresses and an abrupt large strain burst at the onset of yielding regardless of orientation, whereas the Co-54Nb micropillars oriented for basal slip yield at much lower stresses and show intermittent small strain bursts during plastic deformation. While the Co-49Nb micropillars deform by full dislocation slip on the basal plane at room temperature, the Co-54Nb micropillars deform by partial dislocation slip on the basal plane. At 600 °C, the Co-49Nb micropillars oriented for basal slip show stable and continuous plasticity and their critical resolved shear stresses decrease dramatically. In contrast to the full dislocation slip at room temperature, the plastic deformation of the Co-49Nb micropillars occurs via partial dislocation slip on the basal plane at 600 °C. Based on the geometric γ-surfaces for all potential basal slip planes, we explore where and why the glide of full and partial dislocations on the basal plane occurs in the μ-Co7Nb6 phase.

Quantitative and Qualitative Assessment of As-Cast Microstructure and Microporosity of γ-γ′ Co-based Superalloys

The γ-γ′ Co-based alloys have attracted extensive attention as a new class of materials for high temperature applications. The work is focused on quantitative and qualitative microstructural characterization of selected γ-γ′ type Co-based superalloys obtained by gravity casting. The four Co-based alloys were prepared via vacuum induction melting. The microstructure was analyzed by means of light microscopy and scanning electron microscopy. The microstructural parameters such as porosity and secondary dendrite arm spacing (SDAS) were evaluated by image analysis. The new Co-based superalloys are characterized by proper as-cast microstructure owing to low SDAS and limited microporosity. The values of secondary dendrite arm spacing are comparable for all alloys. The W-free alloys containing Mo and Nb exhibit substantially lower shrinkage porosity compared to those of Co–Al–W and Co–Ni–Al–W. Due to crystallization of Mo and Nb rich phases at lower temperatures, these alloys are characterized by higher solidification range.

Effect of Zr on growth kinetics, microstructure and microtexture of Nb3Sn by bronze technique

We have experimentally studied a systematic quantitative effect of Zr on the factors influencing the critical current density of Nb3Sn, such as growth kinetics, microstructure and microtexture using a diffusion couple method. The Nb3Sn phase develops in the interdiffusion zone of the Cu(Sn)/Nb diffusion couple. For the Zr-alloyed diffusion couples, a two-phase mixture of Zr-containing Nb3Sn and sub-micron β-(Nb,Zr) solid solution second-phase develops. The growth kinetics of Zr-containing Nb3Sn is higher than the Zr-free Nb3Sn phase. Enhancement of growth kinetics is attributed to an increase in the diffusion flux of the Sn atoms along the grain boundaries of Nb3Sn owing to grain refinement. The Zr-free Nb3Sn phase has a weak crystallographic texture. On the other hand, the Zr-containing Nb3Sn phase develops not only with a strong crystallographic texture, but also has similar texture component as that of the adjacent Nb-rich parent phase.

Weldability of Nickel/Aluminum Dissimilar Materials Laser Welding Part I: Microstructure Development, Solidification Behavior and Mechanical Properties of Polycrystalline Nickel-based Superalloy

Weldability-related issues, including asymmetrical weld pool shape, γ phase multicomponent microstructure development, solidification behavior and mechanical properties, of γʹʹ precipitation-strengthened polycrystalline nickel-based superalloy are experimentally analyzed during keyhole laser welding repair. The crucial relationship between them provides weldability improvement opportunities and defect-free high quality weld for feasible aerospace materials laser processing. Attractive neck transition region of weld is more vulnerable to coarser dendrite than bottom part in the vicinity of fusion boundary, and this location is also liable to abundant Laves/γ eutectic phase formation because of heat and solute accumulation. The dominant chemical inhomogeneity brings about microstructure anomalies and irregular morphology to deteriorate hot cracking resistance. Because of thermometallurgical factors of selective alloying partition in the molten pool, partition-resistant Cr is chemically accumulated in dendrite core, while partition-susceptible Ti, Al, Mo and Nb are enriched in high-supersaturation interdendrite region, which consequently result in serious segregation and extensive Nb-rich intermetallic phase formation across solidification interface. Dendrite refinement and aggressive Laves/γ eutectic phase formation suppression are not simultaneously satisfied by low heat input under nonequilibrium solidification conditions. Therefore, mechanical properties are only partially improved by diffusion-limited microstructure refinement as result of phase instability. In other words, reductions of tensile strength and ductility are attributed to brittle Laves/γ eutectic phase formation during terminal stage of solidification. The severity of eutectic reaction thermodynamically depends on nail-shaped keyhole profile, solidification conditions and solute redistribution ahead of solid/liquid interface. Additionally, viable control of weld metallurgical and mechanical properties progressively encourages optimal combination of laser power and welding speed to interdendritically minimize disadvantages of eutectic phase formation by a variety of welding conditions optimization.

Microstructure evolution and hardness enhancement of LMD Inconel 718 multilayer in as-deposited and post heat treated: A comparative study

ABSTRACT This work aims to study the influence of heat treatment on the microstructure of laser metal deposited multi-layered Inconel 718 alloy. As-deposited samples were subjected to standard heat treatment, and the resulting microstructure and mechanical properties are studied. When observed under optical microscope and scanning electron microscope, the microstructure revealed microstructural homogenisation. In this case, the grain morphology shows that Nb-rich Laves phase in as-deposited sample is converted to small irregular granules in post heat treatment. The main finding of this study is that after heat treatment, the continuous bands of Nb-rich Laves phase are dissolved into small patches, as observed in elemental mapping through Energy Dispersive Spectroscopy. Also, Nb and Ti are distributed uniformly in the microstructure forming γ´ (Ni3Ti) and γ´´ (Ni3Nb) strengthening precipitates in Ni matrix. The precipitates developed has resulting in 50–60% higher hardness (419 HV) in the heat-treated sample compared to as-deposited sample.

Microstructural and mechanical characterization of pre-used SA 335 P91 super-heater pipe weldment used in 70 MW CFBC boilers

The enhanced SA 335 P91 steels are specially designed to be used in the super-heaters in thermal power plants which are commonly operated at an elevated temperature. The present study involves an analysis of microstructure and the tensile property of the used P91 tubular steel of such heat exchanger in as-received conditions. The joints were fabricated by gas tungsten arc welding (GTAW) and shielded metal arc welding (SMAW) by employing ErNiCrMo-3 and E9018 B9 fillers. The microstructure showed the presence of flakes of martensite, formation of Nb-rich phases with an unmixed zone in the interface of the weld followed by the columnar and equiaxed dendrites in the centre of the weld zone, while employing the ERNiCrMo-3 filler in GTAW. Whereas in SMA welding, no such unmixed zone was observed while employing E9018 B9 filler except the precipitation of carbides. The metallurgical and mechanical characterization of welded joints was performed by optical microscope, scanning electron microscopy with energy dispersive spectroscopy (EDS), hardness, toughness and tensile tests. From the SEM/EDS analysis in the fusion zone of joints inferred the uniform distribution of the element with Nb phases and oxide formation in the pre used P91 steel for both the weldments irrespective of the fillers employed. Alongside the hardness of the SMA weld zone showed a higher hardness by the precipitation of M23C6 and martensitic structure compared to the GTAW weld zone which is found to be lower owing to the presence of elements such as Mo, Nb, Al and C. In both the joints, the tensile failure occurred away from the fusion zone in the parent metal and SMAW joints imparted better strength than GTAW joints. The GTAW joints showed better toughness by ensuring the ductile mode of failure in fractography studies.

Machining-induced surface integrity and nanocrystalline surface layers in cryogenic finishing turning of Inconel 718

In this study, the effects of cryogenic and flood cooling on the surface integrity of Inconel 718 are investigated for face turning with four selected cutting speeds of 25, 50, 75 and 100 m/min. Surface integrity of machined samples was characterized in terms of surface morphology, sub-surface microstructure, microhardness, x-ray diffraction textures, and residual stresses. While the differences between cryogenic and flood cooling were relatively limited for the majority of surface integrity metrics, a substantially increased (+80% vs flood condition) nanolayer depth was observed at the highest cutting speed of 100 m/min with cryogenic cooling. Additionally, cryogenic cooling resulted in slightly improved surface roughness and slightly increased compressive residual stress, particularly at elevated cutting speeds. Nb-rich secondary phases were detected after machining for all conditions, however, cryogenic cooling and low cutting speed led to reduced mixing of these nanocrystalized phases in the recrystallized surface layer. Based on these observations a and qualitative model for surface generation and nanocrystallization under flood and cryogenic machining conditions was proposed. Overall, the effect of cryogenic cooling on nanolayer generation was most pronounced at elevated speeds, suggesting the potential for cryogenic cooling to allow for more aggressive, yet sustainable, processing strategies with improved surface integrity.

Strengthening and toughening effect of laser melting deposited Nb–16Si–20Ti–3Al with nano-ZrC additions

The phase composition, microstructure, and properties of Laser Melting Deposited (LMD) Nb–16Si–20Ti–3Al alloys with different nano-ZrC (0, 2.5, 5.0, 10.0 wt%) addition were detailed investigated in this study. Results showed that the LMDed Nb–16Si–20Ti–3Al alloy was composed Nb-based solid solution (Nbss) and Nb3Si. The addition of nano-ZrC promoted the decomposition of the Nb3Si phase and the eutectic transformation from Nb3Si to (Nbss+γ-Nb5Si3) eutectic structure. With the content of nano-ZrC increased from 2.5 wt% to 5.0 wt%, the (Nbss+γ-Nb5Si3) eutectic structure was significantly refined. Nb-rich TiC phase precipitated at the grain boundaries of (Nbss+γ-Nb5Si3) eutectic structure by the titanium in the alloy reacted with nano-ZrC additions. With the content of nano-ZrC increased to 10.0 wt%, coarse and irregular primary γ-Nb5Si3 phase and dendritic TiC were observed in the Nb–Si alloy. The fracture toughness was improved from 5.1 MPa m½ to 17.1 MPa m½ by adding an optimized amount of nano-ZrC (5.0 wt%) due to the refinement of (Nbss+γ-Nb5Si3) eutectic structure and dispersion distributed nano-ZrC in the alloys. The Nb–16Si–20Ti–3Al alloy with 5.0 wt% nano-ZrC addition has the maximum compressive strength of 1836 MPa and a compressive strain of 12.6%. The crack deflection seems an important toughening mechanism for Nb–16Si–20Ti–3Al alloys containing nano-ZrC. The fracture mode of each Nb–16Si–20Ti–3Al alloys with (0, 2.5, 5.0, 10.0 wt%) addition exhibited a brittle quasi cleavage fracture.

Effect of welding speed on microstructure and mechanical properties of selective laser melting Inconel 625 alloy laser welded joint

The Inconel 625 manufactured by SLM is limited in size and practical application requires advanced welding techniques to join them. In this paper, Inconel 625 fabricated by SLM was laser welded and the effect of welding speed on the microstructure of the joint was investigated. The microstructures were analyzed by SEM, EBSD and TEM. The fusion zone of the joint was mainly columnar dendrites, a large number of equiaxed crystals formed along with the fusion line, and nanoscale carbides and Nb-rich phases precipitated at the grain boundaries can be observed. With increasing welding speed, the grain size and the ratio of high angle grain boundary (HAGB) were decreased, and the tensile strength and elongation are improved. The tensile strength of joints exceeds 875 MPa, joint efficiency reaching 97.8%. Moreover, the elongation of joints is near 39.8%, reaching 94.8% of the base metal. In addition, the cause of softening of the fusion zone was explored， and The fracture method of the joint shows that it is ductile fracture. The material properties for selective laser melting fabrication meet the requirements of the application.

Precipitation Kinetics During Post-heat Treatment of an Additively Manufactured Ferritic Stainless Steel

The microstructure response of laser-powder bed fusion (L-PBF)-processed ferritic stainless steel (AISI 441) during post-heat treatments is studied in detail. Focus is on the precipitation kinetics of the Nb-rich phases: Laves (Fe2Nb) and the cubic carbo-nitride (NbC), as well as the grain structure evolution. The evolution of the precipitates is characterized using scanning and transmission electron microscopy (SEM and TEM) and the experimental results are used to calibrate precipitation kinetics simulations using the precipitation module (TC-PRISMA) within the Thermo-Calc Software package. The calculations reproduce the main trend for both the mean radii for the Laves phase and the NbC, and the amount of Laves phase, as a function of temperature. The calibrated model can be used to optimize the post-heat treatment of additively manufactured ferritic stainless steel components and offer a creator tool for process and structure linkages in an integrated computational materials engineering (ICME) framework for alloy and process development of additively manufactured ferritic steels.

High-Temperature Wear Behavior of CoCr Matrix Coatings Reinforced by Niobium Element From Room Temperature to 1000 °C

Abstract The high-temperature wear resistant CoCr matrix coatings reinforced by the Nb element were fabricated on the Inconel 718 alloy by using the hot-pressed sintered method. The effects of Nb on the microstructure, hardness, and high-temperature tribological performance of coatings are also investigated in detail, and Nb content was further optimized. The tribological properties were investigated by using a ball-on-disk tribo-tester at 23 °C (room temperature), 200 °C, 400 °C, 600 °C, 800 °C, and 1000 °C. The results showed that the Nb element showed the solution strengthening effect and particle strengthening effect. The Nb greatly affected the tribological performance of the coatings. With the increase of Nb content, the wear-rate and friction coefficient initially decreased and then increased. There was a critical value of Nb content for the high-temperature wear behavior of coatings. The coating with 5.0 wt% Nb kept the best tribological properties compared with other specimens, and the wear resistance was 1.4–29 times as high as that of the substrate. It was attributed to the high hardness, high load-bearing capacity of the Nb-rich phases, and oxide lubricating film on the worn surfaces. The corresponding wear mechanism was discussed.

Influence of Al/Ti Ratio and Ta Concentration on the As-Cast Microstructure, Phase Composition, and Phase Transformation Temperatures of Lost-Wax Ni-Based Superalloy Castings.

The as-cast microstructure, alloying element segregation, solidification behavior, and thermal stability of model superalloys based on Inconel 740 with various Al/Ti ratios (0.7, 1.5, 3.4) and Ta (2.0, 3.0, 4.0 wt%) concentrations were investigated via ThermoCalc simulations, scanning and transmission electron microscopy, energy-dispersive X-ray spectroscopy, dilatometry, and differential scanning calorimetry. The solidification of the superalloys began with the formation of primary γ dendrites, followed by MC carbides. The type of subsequently formed phases depended on the superalloys’ initial Al/Ti ratio and Ta concentration. The results obtained from solidification simulations were compared to the obtained microstructures. For all castings, the dendritic regions consisted of fine γ′ precipitates, with their size mainly depending on the initial Al/Ti ratio, whereas in the interdendritic spaces, (Nb, Ta, Ti)C carbides and Nb-rich Laves phase precipitates were present. In high Al/Ti ratio superalloys, β-NiAl precipitates, strengthened by η and α-Cr phases, were observed. Based on dilatometric results, the dissolution of γ′ precipitates was accompanied by a substantial increase in the coefficient of thermal expansion. The end of the dilatation effect took place around the γ′ solvus temperature, as determined via calorimetry. Moreover, the bulk solidus temperature was preceded by the dissolution of the Laves phase, which may be accompanied by local melting.

Microstructural evolution and mechanical properties of Inconel 625 superalloy fabricated by pulsed microplasma rapid additive manufacturing

An innovative pulsed microplasma additive manufacturing (MPAM) system was proposed for fabricating thin-walled Inconel 625 superalloy parts to improve the deposition and heat efficiency of additive manufacturing (AM). During deposition, the heat accumulation from the microplasma was effectively controlled by adjusting the AM current, pulse length of the plasma arc, and scanning speed. Subsequently, the microstructural evolution and mechanical properties were characterized. The Inconel 625 thin-walled parts manufactured using pulsed microplasma rapid AM consisted of γ, γ″, δ, MC, and Laves phases; the latter exhibited a rod-like aggregation distribution. The microhardness ranged from 210.4 HV0.5 to 279 HV0.5, and the tensile strength was 834.77–855.61 MPa. Furthermore, the yield strength was 533.84–543.79 MPa, and the elongation was 31.34%. An Nb-rich phase fraction (31.4%) was observed in the middle region of the as-fabricated sample. Furthermore, the mechanical properties of Inconel 625 superalloy parts produced using pulsed MPAM satisfied the requirements for standard forged Inconel 625 components.

Plasticity of the Nb-Rich μ-Co7Nb6 Phase at Room Temperature and 600 °C

Plasticity of the Nb-Rich μ-Co7Nb6 Phase at Room Temperature and 600 °C