Microstructure Of Superalloy Research Articles

Effect of laser/ultrasonic shock peening on the microstructure and mechanical properties of Nickel-based superalloys prepared by Powder Bed Fusion Laser Beam (PBF-LB)

Effect of laser/ultrasonic shock peening on the microstructure and mechanical properties of Nickel-based superalloys prepared by Powder Bed Fusion Laser Beam (PBF-LB)

Effect of withdrawal rate on the microstructure and static recrystallization behavior of Ni-based single crystal superalloy

Effect of withdrawal rate on the microstructure and static recrystallization behavior of Ni-based single crystal superalloy

Effects of ultrasonic shot peening process on the microstructure and mechanical properties of nickel-based superalloys formed by selective laser melting

Effects of ultrasonic shot peening process on the microstructure and mechanical properties of nickel-based superalloys formed by selective laser melting

Effect of Protective Coating Layer and Overlapping Factor on the Microstructure and Mechanical Properties of Rene-80 Ni-Based Superalloy in Laser Shock Peening Process

Effect of Protective Coating Layer and Overlapping Factor on the Microstructure and Mechanical Properties of Rene-80 Ni-Based Superalloy in Laser Shock Peening Process

The Effect of Shot Blasting Abrasive Particles on the Microstructure of Thermal Barrier Coatings Containing Ni-Based Superalloy

Grit particles remaining on the substrate surface after grit blasting are generally considered to impair the thermal performance of thermal barrier coatings (TBCs). However, the specific mechanisms by which these particles degrade the multilayer structure of TBCs during thermal cycling have not yet been fully elucidated. In this study, the superalloy substrate was grit-blasted using various processing parameters, followed by the deposition of thermal barrier coatings (TBCs) consisting of a metallic bond coat (BC) and a ceramic top coat (TC). After thermal shock tests, local thinning or discontinuities in the thermally grown oxide (TGO) layer were observed in TBCs where large grit particles were embedded at the BC/substrate interface. Moreover, cracks originated at the concave positions of the TGO layer and propagated vertically towards BC; these cracks may be associated with additional stress imposed by the foreign grit particles during thermal cycling. At the BC/substrate interface, crack origins were observed in the vicinity of large grit particles (~50 μm).

Effect of carbon content on the microstructure and stress rupture properties of a 4th-generation nickel-based single crystal superalloy

The balance between the stress rupture properties and castability of a 4th-generation Ni-based single crystal superalloy can be achieved by addition of appropriate carbon content. In this work, the effects of carbon content on the microstructure and stress rupture properties of a 4th-generation Ni-based single crystal superalloy were investigated in detail. The results showed that minor carbon addition could aggravate the dendrite segregation, while the addition of carbon had no obvious effect on the rafting and distortion of γ′ phase during stress rupture deformation. At 760 °C/810 MPa and 1100 °C/210 MPa, the stress rupture lives of the three experimental alloys initially increased and subsequently decreased with the increasing carbon content. However, under condition of 1140 °C/137 MPa, the increased carbon content resulted in the reduction of the stress rupture lives of alloy. It was discovered that minor carbon elements addition (0.045 wt%) can promote formation of interfacial dislocation networks and improve creep resistance at high temperatures. At intermediate temperature, the introduction of carbon could reduce the stacking fault (SF) energy of γ matrix, thus facilitating the formation of SFs in γ matrix. The M6Cgranular carbides precipitated at high temperature, which was considered to be beneficial to stress rupture properties.

Microstructure and Fatigue Behavior of PM-HIPed Ni-Based Superalloys and Martensitic Tool Steels: A Review

Hot isostatic pressing (HIP) is a near-net shape powder metallurgy (PM) technique, which has emerged as an efficient technique, offering precise control over the microstructure and properties of materials, particularly in high-performance alloys. This technology finds applications across a wide range of industries, such as aerospace, automotive, marine, oil and gas, medical, and tooling. This paper provides an overview of powder metallurgy and hot isostatic pressing, covering their principles, process parameters, and applications. Additionally, it conducts an analysis of PM-HIPed alloys, focusing on their microstructure and fatigue behavior to illustrate their potential in diverse engineering applications. Specifically, this paper focuses on nickel-based superalloys and martensitic tool steels. The diverse microstructural characteristics of these alloys provide valuable insights into the PM-HIP-induced fatigue defects and properties.

Competitive Fracture Mechanism and Microstructure‐Related Life Assessment of GH4169 Superalloy in High and Very High Cycle Fatigue Regimes

ABSTRACTHigh and very high cycle fatigue tests were performed to examine the microstructure and fracture mechanism of GH4169 superalloy in combination with techniques including electron‐backscatter diffraction (EBSD). Fractographic analysis revealed that surface failures are induced by surface flaws, whereas internal failures are caused by pores, facets, and inclusions. The three‐dimensional observation shows that fracture surfaces exhibit an irregular texture due to crystallographic mismatch of grains and plastic deformation at the crack tip. Based on EBSD analysis, Euler angles exhibited a complex geometry of grain orientation at the crack tip area, hindering crack propagation as evidenced by lower values of the Schmid factor and misorientation at the crack tip. Furthermore, the threshold values of small and long cracks decrease, whereas the transformation sizes from small to long crack growth increase from surface to internal failure. Finally, a novel microstructure defect‐based life prediction model is established, and the predicted results demonstrate a close resemblance to experimental outcomes.

Microstructure and high temperature tribological behavior of nickel-based superalloy with addition of revert

The recycling of revert plays a crucial role in cost-efficiency and green manufacturing of superalloy. In this study, optical microscopy, scanning electron microscopy coupled with energy dispersive spectroscopy, tensile test, and tribological analysis were employed to investigate the microstructure, mechanical properties, and tribological behaviors of vacuum induction melted superalloys of 100% original material (Sample 1) and 40% original material + 60% revert (Sample 2). Dry sliding tests were conducted at 300 and 730 °C. The addition of revert promotes microstructure refinement, hardness increase, and carbide formation, at the cost of 18.5% ductility loss. During the high-temperature dry sliding process, abrasive, adhesive, and oxidative wear mechanisms were observed on the contact surfaces. Sample 2 exhibited a lower wear rate and coefficient of friction at both 300 and 730 °C. Additionally, a more continuous and wear-resistant tribolayer was formed on the wear track of Sample 2, effectively mitigating matrix oxidation compared to Sample 1. At 730 °C, a thick tribolayer developed on the wear surface of Sample 2, characterized by a hard and wear-resistant glaze layer on the outermost surface. The continuous sliding induced matrix heating, which facilitates recrystallization in the subsurface of Sample 2, induced by increased inclusions and carbides from the revert. The analysis of wear debris further illustrated the variations of wear mechanism at different temperatures. These findings are meaningful for understanding the high-temperature behavior of superalloys and optimizing alloy recycling process.

Microstructural evolution of GH4079 superalloy during hot deformation and heat treatment

Through hot compression and subsequent heat treatment experiments on GH4079 superalloy, the influence of different hot deformation and heat treatment conditions on the evolution of GH4079 superalloy microstructure was studied. The evolution of grains and γ′ phases under different thermomechanical conditions was investigated. The results indicate that at deformation temperatures above 1100 °C and strain rates ranging from 0.01 to 0.1 s−1, the primary mechanism of dynamic softening in the alloy is discontinuous dynamic recrystallization (DDRX). When the deformation temperature is below 1100 °C and strain rates range from 0.01 to 0.1 s−1, both continuous dynamic recrystallization (CDRX) and DDRX are the main dynamic softening mechanisms. Due to high strain energy accumulation, the samples deformed at lower temperatures (below 1100 °C) and then solution-treated at 1120 °C for 8 h exhibit significant increases in recrystallization volume fraction and recrystallization grain size. Conversely, the samples deformed at higher temperatures (above 1100 °C) and then solution-treated at 1120 °C for 8 h show minimal changes in recrystallization volume fraction and recrystallization grain size. After solution treatment at 1140 °C, the grain size of the alloy significantly increases. The samples deformed at higher strain rates exhibit the evolution of fine γ′ phases into elongated rod shapes during solution treatment, while larger γ′ phases undergo splitting processes.

Effect of wall thickness on the microstructure and properties of a fourth-generation single crystal superalloy

This study investigated the effect of various thicknesses (0.3–1.5 mm) on the as-cast and heat-treated microstructures of the fourth-generation single crystal superalloy. The microstructures and fracture characteristics of samples with various thicknesses were analyzed after high-temperature stress rupture tests at 1100 ℃/137 MPa. The results showed that as the alloy thickness increased from 0.3 mm to 1.5 mm, the degree of segregation between dendritic core and inter-dendritic significantly increased. The increased segregation was attributed to the slower solidification rate of the 1.5 mm-thick sample compared to the 0.3 mm-thick sample. Lower solidification rates and higher degrees of dendritic segregation enhanced the area fraction of eutectics, the primary dendrite arm spacing (PDAS), the and area fraction of pores. After stress rupture tests, the rupture life of the alloy increased from 81 h to 333 h. It was observed that in the 0.3 mm-thick sample, microcracks initiated at the surface and extended into the matrix. On the contrary, as for the 1.5 mm-thick sample, microcracks initiated at the matrix and propagated towards the surface. To evaluate the influence of oxidation, interrupted stress rupture tests were conducted in air atmosphere to investigate the thickness debit effect. Surface oxidation led to the initiation of microcracks on the surface and change the morphology and area fraction of the internal γ′ phase, as well as the effective load-bearing area of the samples. TEM and EBSD were employed to characterize the deformation characteristics of samples with various thicknesses, and the influence of thickness on deformation mechanisms was discussed as well.

Research status on the effect of energy density on the forming microstructure and properties of nickel-based superalloys for laser additive manufacturing

Abstract Nickel-based superalloys have excellent high-temperature mechanical properties, corrosion resistance and oxidation resistance, and strong machinability. It is widely used in aerospace, submarine and shipbuilding, petrochemical, electronic industry and other industries. However, there are still challenges in the popularization and application of nickel-based superalloys for alloy components with complex structures and extremely harsh working conditions. In this paper, the research status of the influence of energy density on the microstructure and properties of laser additive fabrication of nickel-based superalloys at home and abroad is reviewed. The influence of energy density on the microstructure evolution behavior and mechanical properties improvement effect of laser additive manufacturing nickel-based superalloys is summarized. The mechanism of energy density was discussed from the perspectives of microstructure evolution and macroscopic performance change. Based on the individual effects and synergistic effects of each process parameter, the influence of laser energy density on dendrite growth, phase precipitation characteristics, element distribution and porosity defect control effect of nickel-based superalloy was expounded, as well as the influence mechanism on microhardness, wear resistance and residual stress. Finally, the energy density optimization and development prospect of laser additive fabrication of nickel-based superalloys are prospected.

Effect of ultrasonic micro-forging on the microstructure and properties of GH4169 superalloy deposited by laser direct energy deposition

Nickel-based superalloys prepared by laser direct energy deposition (DED) still suffer from microstructure, elemental segregation, and unstable strength, which cannot meet the service requirements and severely limit the application and development of DED-prepared superalloy parts. In this paper, GH4169 specimens with high density and free of defects were prepared by ultrasonic micro-forging assisted laser direct energy deposition (UMT-DED) method. The effects of UMT on the dendritic structure, elemental segregation, and precipitation phases of the alloys prepared by UMT-DED, as well as the densities, hardness, and tensile properties at room and high temperatures were investigated. The contribution of the strengthening mechanism to the yield strength was estimated. The grain refinement mechanism and the deformation mechanism of the Laves phase in GH4169 were discussed. The results show that UMT achieves grain refinement by forming fine crystal strips between the layers. The proportion of fine grain areas increased from 5.9 % to 33.3 %. The plastic deformation introduced by UMT provides external work for dislocation movement to break and fracture part of the Laves phase during plastic deformation, with dislocation cutting of the Laves phase being the main deformation mechanism. The residual stresses was transformed into residual compressive stress. The tensile strength, yield strength, and elongation of the specimens at 25 °C were increased by 4.23 %, 6.42 %, and 23.67 % respectively.

Study on the grain development and dislocation evolution from dynamic to post-dynamic stage in IN718Plus superalloy; the role of second-phase

The introduction of hexagonal η-Ni3(Al,Ti)0.5Nb0.5 phase can refine and homogenize the microstructure of IN718Plus superalloy during hot working, but produces more complicated recrystallization behavior associated with second-phase modified structural mechanisms. Derived from this perspective, the role of η phase on recrystallization mechanisms and grain development from dynamic deformation to post-dynamic dwell was systematically investigated. The results indicated that η phase delayed the throughout recrystallization procedure and grain development. During dynamic deformation, boundary η inhibited discontinuous dynamic recrystallization via preventing the bulging of original grain boundaries, while intragranular lamellar η promoted heterogeneous strain concentration, stimulated random dislocations for continuous dynamic recrystallization and dislocation walls for banded dislocation substructures, which limited recrystallization occurrence in dynamic stage. During post-dynamic dwell, boundary η dissolution increased the nucleation sites for discontinuous static recrystallization, and η phase restricted grain boundary migration to provide abundant nucleation sites for continuous static recrystallization (CSRX). The banded dislocation substructures slowly evolved into subgrains to further form banded CSRX grains, which reduced grain size during early post-dynamic stage. After fully recrystallization, the residual η protected the small grains and impeded grain growth, meanwhile controlled the grain distribution. As a result, η phase induced sluggish dislocation evolution and recrystallization nucleation, consequently suppressed grain development and obtained the more homogeneous and fine grain configuration.

Grain size assessment using EBSD on heterogeneous additively manufactured microstructures

Abstract Grain microstructures are important for a whole range of materials properties. With the widespread use of additive manufacturing (AM), current standards for grain boundary evaluation, such as ASTM E2627-13, may not be fit for purpose due to their microstructural complexity. They are notoriously anisotropic across a range of length scales due to the non-equilibrium nature of the solidification process and the tracking of the heat source. In this work we examine the grain microstructure of a nickel superalloy produced by laser powder bed AM by electron back scatter diffraction. We find that the guidelines provided by the ASTM E2627-13 are not suitable for such heterogeneous and anisotropic materials and some modified guidelines are provided on the field of view and EBSD step size that should be used to characterise such materials.

Microstructure and properties of K648 superalloy additively manufactured by extreme high-speed laser metal deposition

Microstructure and properties of K648 superalloy additively manufactured by extreme high-speed laser metal deposition

Comparative study on microstructure, mechanical and high temperature oxidation resistant behaviors of SLM IN718 superalloy before and after heat treatment

The microstructure, phase transformation behavior, heat treatment effects, and their impacts on the mechanical properties and high-temperature oxidation resistance of IN718 nickel-based superalloy processed by selective laser melting (SLM) both before and after heat treatment was systematically investigated. The heat treatment process involved a two-step aging at 720 °C for 8 h plus 620 °C for 10 h with a controlled slow cooling rate of 10 °C/min. Through the comprehensive use of scanning electron microscopy (SEM), X-ray diffraction (XRD), electron backscattering diffraction (EBSD), and transmission electron microscopy (TEM), the evolution of the microstructure and its mechanism of influence on material properties were revealed. The study identified the formation of γ phase, γ′ phase, γ'' phase, δ phase, and Laves phase during the SLM forming process. Heat treatment played a key role in improving the microstructure and properties of the SLM-processed alloy, with experimental results showing that the mechanical performance and high-temperature oxidation resistance were significantly enhanced after heat treatment. Specifically, the material after heat treatment exhibited a yield strength of 1472 MPa, a tensile strength of 1608 MPa, and an elongation of 9.2%, which represented increases of 76.5%, 38.4%, and 16.5% respectively, compared to the as-printed alloy. Moreover, the oxidation resistance at 1000 °C of the heat-treated samples improved significantly, with weight loss reduced from −0.17 mg/cm2 before heat treatment to −0.15 mg/cm2. Microstructural analysis further indicated that heat treatment optimized the crystal orientation, promoted the formation of more precipitated phases and reduced defects, thereby enhancing the overall performance of the material. This work provides significant scientific insights into understanding and optimizing the IN718 nickel-based superalloy processed by SLM, demonstrating the crucial role of heat treatment in improving its microstructure and properties.

Effect of power density on microstructure characterization and fatigue behavior of laser shock peened Rene-80 Ni-based superalloy

The microstructure plays a crucial role in determining the mechanical properties and performance of materials, particularly in high-strength alloys such as Rene-80. This study focuses on the microstructure characterization of Rene-80 nickel-based superalloy after undergoing Laser Shock Peening (LSP), an advanced surface treatment technique imparting beneficial residual stresses and improving fatigue life. The primary objective of this research is to investigate how varying power densities during the LSP process affect the microstructure of the Rene-80 superalloy. The power density in LSP is a critical parameter that influences the intensity of shock waves imparted onto the material’s surface, consequently impacting the microstructure. Through advanced microscopy techniques and analysis, the study explores the resulting microstructural changes, including surface roughness, dislocation density, and the presence of defects like dislocations and dislocation cells. These alterations are vital indicators of the material’s mechanical properties, such as tensile and fatigue strength. LSP samples were characterized using various techniques, including field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), atomic force microscopy (AFM), and X-ray diffraction (XRD) analysis. Additionally, the mechanical performance of the samples was assessed through low-cycle fatigue tests and tensile tests, both conducted before and after LSP treatment. The optimal power density for Laser Shock Peening is determined to be 2.5 HEL. At this power density, the shock wave generated does not create a molten layer on the surface but accumulates defects, resulting in maximum compressive residual stress at the surface. LSP induces intense plastic deformation in the sample, distorting γ’ precipitates. Higher power densities lead to the formation of cross-linked sets of slip bands, highlighting defect slip as the main mechanism of plastic deformation in the LSP process. Understanding these effects is essential for optimizing the LSP process parameters to achieve desired mechanical properties and enhance the performance and longevity of components made from Rene-80 nickel-based superalloy in high-stress applications. It was found that the fatigue life of the samples increased by 500% and optimizing the effect of power density on the LSP process led to an improvement in the fatigue life of the Rene 80 samples.

Molecular dynamics simulation of tensile properties of Nickel-based superalloy with temperature and Co

Ni(Nickel)-based superalloys are used as indispensable materials for turbine blades in aero-engines because of their excellent creep, fatigue and corrosion resistance. Co(Cobalt), as one of the new key elements in Ni-based superalloys, has attracted extensive attention in Ni-based superalloys field. However, the effect mechanism of Co on Ni-based superalloys is still controversial. To solve this problem, tensile properties and microstructure of Ni-based superalloys doped with or without Co (5 %) have been investigated through molecular dynamics simulation, and the joint impact of temperature and Co on the superalloy mechanical properties has also been analyzed. The findings indicate that 5 % Co doping reduces the yield stress, yield strain, and elastic modulus of the structure, while increasing the flow stress at 300 K–600 K; however, the advantage decreases at 900 K and disappears completely at 1200 K. This can be explained that Co doping leads to more slippage of stacking faults in the elastic stage and hinders the loop formation of dislocations at 300 K–600 K, while more Stair-rod dislocations occur in the plastic stage. These effects disappear at 900 K–1200 K.

Effects of annealing powder on microstructures and tensile properties of LPBF-processed Haynes230 superalloy

ABSTRACT This study reveals a novel understanding of the influence of annealing the feed powder, which alters the precipitate characteristics in the powder particles on the microstructure and mechanical properties of Haynes230 superalloy fabricated by laser powder bed fusion (LPBF) plus hot isostatic pressing (HIP) and solution treatment. Specifically, annealing Haynes230 superalloy powder at 1000°C for 1 h under vacuum resulted in the precipitation of M6C carbide instead of the typical M23C6 found in unannealed powder. The alloy fabricated by LPBF of the annealed powder plus HIP and heat treatment exhibited an increased number density of the carbide precipitates at grain boundaries, but a reduced number density of the intragranular carbide precipitates. Consequently, its ambient temperature tensile properties decreased clearly in terms of yield strength (406–383 MPa), ultimate tensile strength (936–841 MPa) and elongation to fracture (38.6% to 25%) compared to the alloy fabricated by LPBF of the as-received powder plus same post-print processing. However, the annealing of the feed powder had little effect on the tensile properties of the samples at 900°C. These findings underscore the significant impacts of feed powder microstructure on the mechanical properties of LPBF-processed superalloys.