Nickel Superalloy Research Articles

On the formation of pileups during nano-scratching of Inconel 718 produced using additive manufacturing

The objective of this work is to understand the role of microstructure on pileup formation during nano-scratching of additively manufactured nickel superalloy, Inconel 718 (IN718). Scratches with median depths of ∼50 nm were made on as-received and solution annealed IN718 under the action of small normal forces using a spheroconical diamond indenter. The surface profiles of these scratches were then quantified using atomic force microscopy. The as-received IN718 showed a positive correlation between pileup height, and scratch depth. In contrast, the solution annealed IN718 specimen exhibited a negative correlation between pileup height, and scratch depth. Analysis of this observation involved experimental quantification of microstructure using electron back scatter diffraction, quantitative atomic force microscopy, in addition to complementary finite element simulations. Following analysis, we propose that this switchover originates due to differences in strength, hardening, and deformation localization characteristics of as-received and solution annealed IN718.

A new approach to protect and extend longevity of the thermal barrier coating by an impermeable layer of silicon nitride

AbstractA sample representation of a gas turbine engine blade, consisting of a nickel superalloy substrate with a deposited thermal barrier coating (TBC), was covered with silicon nitride, Si3N4, as an impermeable layer using plasma enhanced chemical vapor deposition (PECVD). The silicon nitride layer was used to seal the topcoat of yttria‐stabilized zirconia (YSZ) surface of the TBC to mitigate calcium–magnesium–aluminum–silicon oxide (CMAS) attack. CMAS testing was carried out on the covered and uncovered surfaces by melting a ratio of 25 mg/cm2 of CMAS powder onto the surface of each sample in a furnace at 1100°C for 1 h. The conformal surface reaction of the sealed layer confirmed no cracking or delamination at high temperatures. Scanning electron microscopy (SEM) micrographs confirmed that the surface of YSZ was successfully sealed. The new coating of silicon nitride was shown to be a viable solution and technique to significantly block CMAS infiltration in porous thermal barrier coatings.

High temperature shear and thermal aging behavior of dissimilar transient liquid phase bonded Hastelloy X to Ni3Al intermetallic compound

Nickel super alloys and intermetallic compounds (IMCs) are candidate as strategic materials for turbine industry, because of its excellent high temperature properties. In this study, mechanical properties and thermal aging behavior (post thermal exposure) of the transient liquid phase (TLP) bonds between Hastelloy X to Ni3Al IMC at temperature range of 800–900 °C were investigated. The microstructure and fracture surfaces of the joints were examined by optical and scanning electron microscopes as well as XRD analysis. The optimum joint bonding strength was achieved for the sample treated at 1100 °C–180 min equaling to 355 ± 4.5 MPa. XRD patterns of semi-cleavage fracture surfaces revealed nickel solid solution matrix containing BNi3 and Ni3Si compounds generated at ASZ/ISA interface. The ultimate tensile strength reaches 36.5 ± 1 and 20.5 ± 1 MPa at temperatures of 800 °C and 900 °C, respectively. Fracture occurred in the IMC substrates for both temperatures were due to shrinkage porosity during solidification of IMC and mismatch of crystal lattice constants with the matrix. The thermal aging process at 900 °C for 50–500 h had a minor effect on the joint microstructure but generated TCP phases in the Hastelloy X.

A first-principles study on the early-stage corrosion of a NiWNb alloy in a chloride salt environment

In this work a representative nickel superalloy, Ni70W20Nb10, was investigated in the presence of chlorine to quantify its early-stage dissolution behavior. Surface structures were generated from a bulk configuration sampled in equilibrium using a multi-cell Monte Carlo method for phase prediction. The predicted solid-phase at 800∘C was Ni72W19Nb9 in a body-centered tetragonal crystal structure closely resembling the Ni4W structure. Chlorine adsorption onto the energetically favored (110) surface showed preference to niobium which acted as a trapping sink on the top surface of the slab model. Our findings suggested that niobium and tungsten enhanced the corrosion resistance of nickel as their presence created regions that were thermodynamically preferred by the incoming chlorine and less susceptible to chlorine-facilitated dissolution from the alloy. Nickel, niobium, and tungsten resisted chlorine-induced dissolution from the surface model up to a 1/3 monolayer coverage of chlorine indicating that all constituents of this alloy possessed superior resistance to localized surface degradation such as corrosive pitting. Further analysis and comparisons between the corrosion resistance of the three metallic species was performed. This work may provide insights that aid in the development of improved structural materials for molten salt reactors.

Effect of Solutionizing Heat Treatment on Microstructure and Mechanical Behavior of Additively Manufactured Medium Gamma Prime Nickel Superalloy

Effect of Solutionizing Heat Treatment on Microstructure and Mechanical Behavior of Additively Manufactured Medium Gamma Prime Nickel Superalloy

Effects of high-energy laser peening followed by pre-hot corrosion on stress relaxation, microhardness, and fatigue life and strength of single-crystal nickel CMSX-4® superalloy

This study investigated the stress relaxation and fatigue life and strength of laser-peened single-crystal nickel superalloy specimens compared to unpeened and shot-peened specimens following hot corrosion exposure and then fatigue testing. The specimens were treated by conventional laser peening and a new cyclic laser peening plus thermal microstructure engineering process. The latter treatment supports the benefit of a unique process involving application of layers of laser peening using high energy with large footprint spots combined with interspersed cyclic annealing. Stress measurements by slitting showed the plastic penetration depth of laser peening exceeded shot peening by a factor of 24. Unpeened and peened specimens were exposed to sulphate corrosives at 700 °C for 300 h and then fatigue tested. Tests of five non-laser-peened specimens all failed in low-cycle fatigue regime, whereas three identically tested laser-peened specimens all achieved multi-million-cycle runout without failure, indicating fully consistent large benefit for life by laser peening. Additional tests also showed fatigue strength improvement of 2:1 by laser peening. Residual stress measurements post hot-corrosion exposure and fatigue testing showed notable 5 mm depth retention of residual eigenstress in a laser-peened specimen.

Correction: Tools for the Assessment of the Laser Printability of Nickel Superalloys

Correction: Tools for the Assessment of the Laser Printability of Nickel Superalloys

Influence of Near-Surface Severe Plastic Deformation on the Corrosion Behavior of GTD-111 Nickel Superalloy in Hydrofluoric Acid Solution

High-energy shot peening (HESP) as a common near-surface severe plastic deformation (NS-SPD) was used to create a severely deformed surface with ultrafine grains and dense crystallographic defects (e.g., grain boundaries, dislocations, and twins) on GTD-111 Ni superalloy. The fluoride-induced corrosion performance of HESPed GTD-111 and its solution-annealed counterpart is comparatively studied using immersion tests, grazing-incidence x-ray diffraction analysis, electrochemical techniques, and glow discharge optical emission spectroscopy (GDOES). As supported by the immersion tests and electrochemical measurements, HESPed GTD-111 exhibits corrosion film with higher resistance and lower passivity current density at the expense of a higher initial corrosion rate. Both samples suffer pitting corrosion; however, the solution-annealed one shows deeper and larger pits. The dense distribution of crystallographic defects on the surface of the HESPed sample significantly increases the diffusion of alloying elements to the corrosion front. The GDOES depth profiles reveal that (i) a thicker corrosion film with a higher contribution of alloying elements (namely, Cr, Ti, Co, and Al) is developed on the HESPed sample, and (ii) the corrosion films formed on the solution-annealed and HESPed samples consist of an outer F-rich part and an inner O-rich region. The protective mechanism of NS-SPD is discussed by a physical model.

Strengthening additively manufactured Inconel 718 through in-situ formation of nanocarbides and silicides

We report additive manufacturing (AM) of a nickel superalloy metallic matrix composite (Ni-MMC) using laser powder bed fusion (LPBF). Nanoceramic-containing composite powders were prepared by high-speed blender declustering and ball milling of as-received SiC nanowires (2 vol%) and Inconel 718 alloy powders, which produced a homogeneous decoration of SiC on the surfaces of Inconel particles. Analysis of the as-printed specimens revealed the dissolution of SiC nanowires during laser melting, leading to the in-situ formation of Nb- and Ti-based silicide and carbide nanoparticles. These in-situ formed nanoparticles resulted in a more desirable solidification microstructure of the AM Inconel 718 with fewer printing defects (cracks and pores) and slightly refined grain sizes. Mechanical characterization of the as-printed Ni-MMCs revealed notable increases in hardness, yield strength (by 16%), and ultimate tensile strength (σUTS, by 12%) compared to the reference samples without SiC addition. After heat treatment, the same composite samples displayed a 10% higher σUTS compared to identically treated unreinforced material while maintaining ∼14% total tensile elongation. We believe this in-situ precipitate formation presents a simple and effective method for strengthening additively manufactured high-temperature materials that could be used in the increasingly harsh environments in energy and propulsion applications.

Phase decompositions of Gd2Zr2O7 + 8YSZ TBC systems under the condition of long-term high-temperature oxidation

The article presents the results of research related to the assessment of the phase composition of two-phase TBC systems based on gadolinium zirconate GZO and a conventional zirconium oxide modified by the yttrium oxide 8YSZ. The coatings were made on a nickel superalloy of IN 625 type with a NiCrAlY base bond coat. The technique of atmospheric plasma spray was used for coatings depositions. Three types of composite coatings, made of a mixture of base powders with the proportion of components 25–75, 50–50 and 75–25, were evaluated. The thickness of the ceramic layers was approximately 300 μm. The TBC systems were then subjected to high temperature oxidation at 1100 °C for up to 2000 h in air. Changes in phase composition were evaluated by the XRD method after 48, 175, 500, 1000 and 2000 h of exposure. Detailed microstructural studies with the use of scanning microscopy methods were performed after 2000 h. The GZO + 8YSZ composite coatings were found to be characterized by high susceptibility to changes in phase composition, which is related to the formation of new zirconate phases with a lower content of gadolinium oxide (in the case of zirconates) and phases based on zirconium oxide with a higher content of gadolinium oxide. The observed changes are diffusive and take place predominantly within the GZO phase. Additional structural effects observed during SEM studies are the phenomena of the formation of a network of numerous small voids in the GZO phase, which suggests the course of nonequilibrium diffusion processes. Furthermore, a high concentration of nickel oxide and a slightly lower concentration of chromium oxide were found in the ceramic layer.

Wear mechanism, subsurface structure and nanomechanical properties of additive manufactured Inconel nickel (IN718) alloy

Inconel nickel (IN718) superalloy is a cutting-edge material for high temperature applications owing to its superior mechanical properties in both cryogenic and high temperatures. Although the selective laser melting (SLM) processed IN718 superalloy has extraordinary properties, the tribological behavior of this new class of material is unclear. This study aims to explore the tribological behavior and subsurface mechanical properties of SLMed IN718 superalloy with the aid of nanomechanical and structural characterization techniques. The worn subsurface structure was revealed against the mechanical properties of the material using the ball-on-disk contact sliding test. Structural analysis confirmed that the SLMed IN718 superalloy consisted of Fe, Ni, Cr, Nb and Mo elements. EBSD analysis showed that a mixture of equiaxed and columnar grains emerged in <001>, <101> and <111> of SLMed IN718 superalloy. In-situ wear track investigations using 3D profilometer integrated tribometer revealed that its width and depth significantly increased with applied sliding load. Severe abrasive wear occurred at a low load. Under a high load, however, frictional heating brought about plastic deformation and led to increase wear in absence of any significant subsurface damages. The plastic deformation also generated shear-bands in the immediate subsurface and refined the grain structure, which significantly increased the nanohardness and elastic modulus of the deformed material layer.

Tools for the Assessment of the Laser Printability of Nickel Superalloys

Tools for the Assessment of the Laser Printability of Nickel Superalloys

Emerging Functional Metals in Additive Manufacturing

Additive manufacturing (AM) is a disruptive technology which continues to challenge conventional manufacturing methods. New generations of materials for metal AM are sought to enable components with new functionalities and to save costs. However, many within the AM industry are primarily focused on metal alloys such as titanium alloys, cobalt alloys, nickel superalloys, aluminum alloys or stainless steels. This article presents a detailed overview of emerging non‐ferrous metals in the AM industry and their recent development. The potential and challenges of these materials and their adoption by AM are highlighted and compared to those of conventional materials. Furthermore, qualification pathways and supply issues for newly developed materials are discussed. This perspective is based on literature review and a thorough analysis of the metal AM industry.

Interaction of Exogenous Zirconia Nanophases with Tin in Nickel Superalloys

Interaction of Exogenous Zirconia Nanophases with Tin in Nickel Superalloys

Statistical Comparison of Creep-Rupture Lifetime Predictions of Single and Two-Step Aged Wrought Haynes 282 Alloy

AbstractThe paired and Welch's t-tests were used to determine if statistically significant differences exist between the predicted creep rupture life of single- and two-step aged wrought Haynes 282 nickel superalloy. Both tests indicated that there is no difference in the temperature range of 700–800 °C. These results provide a quantitative perspective to support the conclusions reached in previous publications that the creep rupture strengths of wrought single- and two-step aged Haynes 282 are very similar or the same. The lack of creep rupture data above 800 °C for two-step aged H282 precluded extending the statistical analysis above that temperature.

Assessment of surface integrity and hole quality in graphene-based NMQL Micro-drilling of ceramic-coated Nimonic 90 for gas turbine applications

Nickel-based superalloys have superior strength properties at higher temperature ranges and thus have become increasingly important in manufacturing gas turbine components for aerospace industry. However, the desire for a larger thrust-weight ratio has raised the typical operating temperature in a gas turbine; thus, thermal barrier coatings are essential. The present work compares the micro-drilling performance of ceramic-coated Nimonic 90 nickel superalloy under dry, flood and 0.5% graphene-based NMQL conditions. The biodegradable acid oil was used as a base oil, and the assessment comprised surface integrity in terms of surface roughness inside the hole and micro-crack formation and hole quality based on the diametrical overcut and taper ratio. Spindle speed (1000, 2000 and 3000 rpm) and feed rate (3, 6, and 9 μm/rev) were changed in three levels, and Taguchi L9 array was applied for the design and analysis of the experiments. Ti-Al-N coated tungsten carbide drill of diameter 700 μm was used, and Analysis of variance (ANOVA) revealed that spindle speed was the utmost important parameter impacting surface roughness, while speed and feed rate both influenced overcut and taper ratio. 0.5% Graphene-based NMQL lubrication condition significantly diminished the surface roughness by 52.67%, overcut by 46.86% and the taper ratio by 48.87% as compared to dry condition. Furthermore, in the NMQL condition, micro-crack development and ceramic layer damage were minimized, resulting in better surface integrity. In addition, burr development was minimized at the hole periphery, and tool wandering was not seen in the NMQL condition. Hence the hole quality was superior in NMQL conditions as compared to the dry and flood lubrication.

Effect of the Laser Cladding Parameters on the Crack Formation and Microstructure during Nickel Superalloy Gas Turbine Engines Repair

Cracking of nickel superalloys with a high content of γ’-phase remains an unresolved problem, including in technologies for repairing gas turbine engines blades. Laser cladding is a method of material deposition used to repair parts exposed to aggressive environment and surface wear. Cladding parameters have a high influence on cracking susceptibility nickel superalloys. Alloy ZhS32 has a high propensity for hot cracking when exposed to laser radiation. In this work, the study of the structural and phase features of ZhS32 alloy was carried out. A high tendency to form segregation of refractory elements and carbides in the intergranular areas was found. The features of the structure and phase composition of the material for different cladding parameters were studied. The main contribution of technological parameters to the formation of cracks is shown.

Mechanical Properties of Structural Components in Hastelloy X Joints Brazed with Ni-Pd-Cr-B-Si Alloy.

The brazing of structural high-temperature-resistant nickel alloys is a predominant method in manufacturing jet engines in the aircraft industry. Ni-Cr-base brazing filler metals (BFMs) containing B and Si as the melting point depressants are used for this purpose. The presence of the latter can lead to the formation of brittle constituents in the joints, decreasing their strength, toughness and creep resistance. The structures of Hastelloy X nickel superalloy joints brazed with Palnicro 36M BFM are presented in this paper along with the mechanical properties of their particular phases as a function of brazing time. Indentation hardness, Martens hardness, reduced modulus and creep coefficient were measured using the instrumented indentation method. The elastic part of the indentation work was also calculated. Pd forms an unlimited solution with Ni, but its high content in BFM does not fundamentally change the general joint structure known from other Ni-superalloy-Ni-BFM systems. However, new Pd-containing phases are emerging. The hardest components were Ni-B and Cr-B boride phases and Pd-Ni-Si phase in MZ and the boundary of DAZ and BM. MZ reduces the plasticity of a joint to the highest extent. The hardness of particular parts in the joints and the elastic portion of the indentation work decreased with the increase in brazing time, while the reduced modulus of the indentation contact and indentation creep increased. The results of indentation creep measurements indicate that all structural components of the joints were less susceptible to creep than the parent material at room temperature.

Performance of eco-benign lubricating/cooling mediums in machining of superalloys: A comprehensive review from the perspective of Triple Bottom Line theory

Nickel, titanium, and cobalt-based superalloys are utilized in several engineering applications. The unique material properties, for instance, low thermal conductivity and high strength, make it a challenge to machine them easily. The utilization of appropriate lubricating technology is crucial for increasing the machinability of superalloys. Superalloys are frequently machined using mineral oils as lubricants. However, various biological and environmental issues could be caused by these mineral oils. To eliminate the harmful consequences, it's indeed necessary to switch to the use of environmentally friendly lubricants/coolants. Sustainable lubricating/cooling mediums use a minimum quantity of lubricants, liquid nitrogen, dry ice, vegetable oil, nanofluid and compressed air as a cutting fluid, which is thought to be environmentally beneficial and biodegradable. In this review paper, a comprehensive analysis of different eco-benign lubricating/cooling methods used in superalloy machining specifically for turning, milling, drilling, and grinding, etc. is presented. In comparison to traditional wet machining, it has been discovered that these methods produce significantly enhanced surface morphology and tool life, lower cutting temperatures, and cutting forces. The current paper also discusses the benefits and drawbacks of various lubrication/cooling strategies for enhancing superalloy machinability. Following that, for the first time, a review is conducted from the perspective of the Triple Bottom Line, demonstrating that the majority of previous surveys focus on the environmental and economic dimensions of lubrication/cooling techniques used in machining, so more emphasis should be put on the social dimension. In summary, this paper presents a detailed collection of information concerning eco-friendly lubrication/cooling systems that would assist new researchers in recognizing the latest progress as well as potential future research areas on the sustainability elements of superalloy machining.

Features of Permanent Joints of Titanium (α+β)-Alloys Obtained by Friction Stir Welding Using a Nickel Superalloy Tool

Titanium alloys are widely used in industry, especially (α+β)-alloys, among which Ti-6Al-4V alloy is the most popular one. Another common alloy that often appears in patents for titanium products is Ti-4Al-3Mo-1V. Here, we investigate welded joints of (α+β)-alloy Ti-4Al-3Mo-1V obtained by friction stir welding (FSW) using a working tool made of nickel-based heat-resistant alloy ZhS6U. In addition, welded joints of Ti-6Al-4V and Ti-4Al-3Mo-1V alloys with similar mechanical characteristics were considered. Mechanical tests showed that the obtained joints had a tensile strength greater than that of the base metal. This result was achieved in the welding mode where the axial load was varied during the welding process. X-ray diffraction analysis revealed a change in the phase structure of the welded joint.