Kinds Of Alloys Research Articles

Tuning Cr-rich nanoprecipitation and heterogeneous structure in equiatomic CrFeNi medium-entropy stainless alloys

High-/medium-entropy stainless alloys (HESAs/MESAs) are a new kind of alloys with great potential to combine excellent properties from high-/medium-entropy alloys (HEAs/MEAs) and stainless steels. A CrFeNi MESA was chosen to investigate its microstructures and mechanical behaviors. After homogenization, the strength and ductility of CrFeNi MESAs with single-phase face-centered-cubic (fcc) structure were higher compared with those of Fe100−x–yCrxNiy austenitic stainless steels. Cr-rich body-centered-cubic (bcc) precipitates and heterogeneous structure were introduced by cold rolling and annealing at 800 °C. Rolling at 700 °C results in higher dislocation density and the occurrence of lamellar Cr-rich bcc precipitates. High-density dislocations and fcc grains with heterogeneous structure, together with Cr-rich bcc precipitates, contribute to a yield strength improvement of about 50 MPa, and appreciable tensile yield strength of ~ 540 MPa and fracture strain of ~ 20% are obtained. It reveals that not only compositional variations but also grain size and phase structure tuning can be utilized for achieving desired mechanical properties.

Remarkable Cryogenic Strengthening and Toughening in Nano-Coherent CoCrFeNiTi <sub>0.2</sub> High-Entropy Alloys via Energetically-Tuning Polymorphous Precipitates

In the present work, three kinds of precipitates with different morphologies, structures, sizes, and volume fractions were obtained via energetically-tuning the microstructures of the nano-precipitated CoCrFeNiTi0.2 high-entropy alloy (HEA). Subjected to the heavy cold rolling immediately after homogeneous precipitation, L12 structured spherical nano-particles with an average size of 16.5 nm rapidly grow into 200 nm-sized spherical ones due to Ostwald ripening. On the other hand, superfluous mechanical energy storage energetically facilitates the phase transformation from spherical L12 to rod-shaped D024 structures for initially formed nano-precipitates. Besides, some other newly formed nano-precipitates with an average size of 6.5 nm are available, originating from heavily plastically deformed-induced nucleated sites. Multi-scale precipitates interact with dislocations in different ways. The strengthening provided by dislocations cutting through smaller nano-particles and bypassing grown ones account for 57.7% and 42.3% of precipitation strengthening, respectively, while rod-shaped precipitates can act as equivalent interfaces to hinder dislocation movement. Their synergistic effect has achieved remarkable strengthening and toughening. Specially, dislocation slips dominate at 298 K, while stacking faults (SFs) assist plastic deformation at 77 K. Compared with 298 K, the yield strength (YS) and ultimate tensile strength (UTS) of the current HEAs at 77 K are increased by 38.9% and 38.2% to 1 GPa and 1.5 GPa, respectively, and the tensile strain is slightly increased to 35% instead of loss, realizing excellent strength and plasticity combination. Theoretically established strengthening models agree well room-temperature and cryogenic yield strengths experimentally. Moreover, the tensile elongation is effectively predicted by the Whitehouse-Clyne model. This strengthening strategy of energetically-tuning polymorphous precipitates provides the basic guidance to develop high-performance nano-precipitated alloys. The current strengthening and plasticity models can be employed to well predict the mechanical properties of such kinds of alloys at cryogenic temperatures.

Residual stress investigation on Ti-48Al-2Cr-2Nb samples produced by Electron Beam Melting process

Ti-48Al-2Cr-2Nb (Ti-48-2-2) is an intermetallic alloy belonging to a family of gamma-TiAl intermetallic alloys that are attracting significant attention. Electron Beam Melting (EBM) process is today the only manufacturing process that allows effective production of parts made by these kinds of alloys. Proper process control avoids high temperatures in the surrounding areas that may generate significant residual stresses that could cause micro-cracks. In this paper, an investigation on the residual stress state on Ti-48-2-2 parts is carried out using the hole drilling method. In particular, the influence of EBM process parameters is evaluated in order to understand the effects of the residual stresses on part integrity.

Effects of composite binder phase on microstructure and mechanical properties of ultrafine‐grained cemented carbides

AbstractIn order to develop a new high‐performance binder phase, four different alloys Co‐Ni‐Fe, Co‐Ni‐Cr, Co‐Ni‐Nb, and AlCoCrNiNb0.5 were used as a binder in cemented carbides. The room‐temperature mechanical properties and high‐temperature flexural strength of cemented carbides were studied. The results show that the optimal mechanical properties for the WC‐8(Co‐Ni‐Fe, Co‐Ni‐Cr, Co‐Ni‐Nb, and AlCoCrNiNb0.5) can be obtained at the sintering temperatures of 1200°C, 1350°C, 1350°C, and 1300°C, respectively. Compared with cemented carbides with Co as binder phase, the hardness of the four kinds of alloys is increased, the WC grain size becomes finer, but the fracture toughness is slightly decreased. When the temperature is under 600°C, there is no visible oxidation of the four kinds of cemented carbides, and their bending strengths are basically not reduced. When the temperature increased from 600°C to 900°C, the WC‐8(Co‐Ni‐Nb) and WC‐8(Co‐Ni‐Fe) samples present the better high‐temperature bending resistance compared with the WC‐8(Co‐Ni‐Cr) and WC‐8AlCoCrNiNb0.5 samples, with respective decrease in bending strength of 11.7% and 7.3%.

The effect of configurational entropy on mechanical properties of single BCC structural refractory high-entropy alloys systems

In the study of high-entropy alloys (HEAs), due to the enormous adjustment space of the content (5–35 at.%) of each principal element, the yield strength at room temperature (RT) of the alloys are basically difficult to estimate. Five kinds of Nb-Mo-Ta-W HEAs with the same component elements but in different contents were fabricated by vacuum arc melting (VAM). The crystal structures of five kinds of alloys are all single-phase solid solutions of BCC structure. The grain sizes of each alloy are about ~150 μm and the substructures within the grain are typical dendritic. The calculated yield strength through solid solution strengthening (SSS) model by Senkov is in certain agreement with the experimental yield strength of five alloys. In our study, the concept of configurational entropy is brought in to optimize the model. In comparison with the calculated yield strength of original model, the variation trend curve of the optimized model was in better agreement with that in experiment. Moreover, the optimized SSS model has a certain universality to predict the mechanical properties in other refractory HEAs system with a single BCC structure composed of W, Nb, Mo, Ta, Zr, Hf, Ti, V element. This conclusion provides a theoretical basis for the design of chemical contents of BCC structural refractory HEAs systems.

CO2 cryogenic milling of Inconel 718: cutting forces and tool wear

Machining Inconel 718 alloy is a challenge due to its low machinability. This thermal resistant alloy combines high strength even at high temperatures with strain hardening tendency that causes high forces and extreme cutting temperatures during the machining. These issues force industries to achieve suitable machining processes to deal with this kind of alloys and the high worldwide competitiveness. Nevertheless, environmental considerations must to be taken into account due to growing environmental concerns. In the work here presented, cryogenic cooling with external MQL lubrication (CryoMQL) working along with CO2 as internal coolant is proposed for milling Inconel 718 with the aim of not only improving from a technical point of view but also environmental. This technique was compared with other lubricooling techniques. The results show that internal CryoMQL improves tool life by 57% in comparison with emulsion coolant, achieving 120% if it is compared with MQL in stand-alone mode.

Response of microstructure and hardening to deuterium ion irradiation inV-4Cr-4Ti-1.8Y-0.4Ti3SiC2 and V-4Cr-4Ti alloy

Abstract Deuterium implantation with 60 keV was carried out in V-4Cr-4Ti-1.8Y-0.4Ti3SiC2 alloy prepared via MA-HIP method and V-4Cr-4Ti alloys prepared by VAR. Dispersion particles, Ti-rich precipitates and irradiation-induced dislocation loops are studied using TEM. Micro-hardness and radiation-hardening are measured using Nano-indenter. The dissolving of additional Ti3SiC2 particles and the formation of Y2O3, (Ti, Si) C and Y2 (Ti, Si) 2O7 particles are observed in V-4Cr-4Ti-1.8Y-0.4Ti3SiC2 alloy. Ti-rich precipitates in both alloys prefer to grow along M direction, where the precipitates/matrix interfaces have minimum distortion energy. Ti-rich precipitates in V-4Cr-4Ti-1.8Y-0.4Ti3SiC2 alloy is much smaller. Although the mean size and density of dislocation loops is similar in both kinds of alloy, V-4Cr-4Ti-1.8Y-0.4Ti3SiC2 alloy has a much lower radiation-hardening. TEM results show that Ti-rich precipitates in V-4Cr-4Ti-1.8Y-0.4Ti3SiC2 alloy grow up after irradiation, while the size of precipitates decrease in V-4Cr-4Ti alloy. The calculation results based on Orowan mechanism show that the size evolution of Ti-rich precipitates is the dominant factor for the different behavior of two alloy on radiation-hardening.

Superior Slurry Erosion Behavior of a Casting NiCoCrFeNb0.45 Eutectic High Entropy Alloy

The flow passage components in hydraulic machinery will be eroded rapidly when running in sand water. The wear resistance of materials commonly used in hydraulic machinery needs to be improved to prevent the failure of hydraulic machinery. New wear-resistant materials are urgently needed to improve the service life of hydraulic machinery. Eutectic high entropy alloy (EHEA) is a new kind of alloys with in situ lamellar structure. NiCoCrFeNb0.45 EHEA has combined excellent strength and toughness. In this study, slurry erosion tests of NiCoCrFeNb0.45 EHEA were carried out with different impact angles and impact velocities using a rotary jet erosion test apparatus. The NiCoCrFeNb0.45 EHEA exhibited significant slurry erosion resistance compared with medium carbon steel 1045 and stainless steel 04Cr13Ni5Mo. The erosion rate of EHEA is much slower. Compared with medium carbon steel and stainless steel, the erosion of EHEA is completed via the accumulation and removal of platelets after plowing and work hardening, accompanied by partial micro-cutting.

Co-Reduction Behavior of Ce (III), Al (III) and Ga (III) on a W Electrode: An Exploration for Liquid Binary Al-Ga Cathode

It is well known that searching for electrode materials with high Ln/An separation efficiency in molten salt based electrorefining has been a big challenge. Both Al and Ga have exhibited excellent performance, respectively, for the Ln/An separation based on molten salt electrolysis. Therefore, in this work, the electrochemical behavior of Ce (III) on the binary Al-Ga alloy electrode was systematically explored by co-reduction of Ce (III), Al (III) and Ga (III) on a W electrode. The results showed that different kinds of alloys are formed on the surface of W electrode. In addition, several typical Ga-Ce and Al-Ga-Ce intermetallic compounds were obtained by potentiostatic electrolysis and the deposited products were characterized by X-ray diffraction (XRD) and Scanning Electron Microscopy (SEM) with Energy Dispersive Spectroscopy (EDS). It was found that ternary intermetallic compound Al2Ga2Ce and binary Ga2Ce and Ga6Ce were identified. Acknowledgments The work was financially supported by the National Natural Science foundation of China (11675044, 21790373, 21876034 and 11875116), and the International Exchange Program of Harbin Engineering University for Innovation−oriented Talents Cultivation.

Out-of-Pile Performances of Zr-Sn-Nb-Fe Alloys for PWR Fuel Cladding

The safety and reliability of Pressure Water Reactors (PWRs) is closely related to the performances of zirconium (Zr) alloy as fuel rod cladding material. Zr-Sn-Nb-Fe series alloys are one of the important directions for continuous improvement of zirconium alloys for high burn-up fuel element claddings. Two new zirconium alloys, N1(Zr-0.5Sn-0.15Nb-0.5Fe-0.25V) and N2(Zr-0.2Sn-1.3Nb-0.1Fe-0.05V) have been developed to use as advanced PWR fuel rod cladding materials through the studies of the corrosion behavior of Zr-Sn-Nb-Fe Alloys, the composition optimization, the preparation of claddings and the out-of-pile performances and in-pile tests of new zirconium alloys. The results are obtained by out-of-pile performance tests of two Zr alloy claddings. Transmission Electron Microscopy (TEM) results shown that fine and uniform distribution of β-Nb and/or ZrFeV(Nb) particles could lead to excellent out-of-pile corrosion resistance. Autoclave testing in 360 °C/18.6 MPa pure water, 60 °C/18.6 MPa/70 ppm Li+ aqueous solution and 360 °C/18.6 MPa/1000 ppm B3+/3.5 ppm Li+ aqueous solution indicated that both of N1 and N2 alloys possessed better corrosion resistance than Zr-4 alloy. The hydrogen uptake results of two kinds of alloys from corrosion reactions under various corrosion conditions showed hydrogen uptake increased with the exposure time or oxide thickness, and hydrogen uptake rate of the new alloys after long-term corrosion are lower than Zr-4. Moreover, the new alloys have demonstrated superior or similar out-of-pile tensile, burst and creep properties relative to Zr-4.

A comparison study on wear characteristics of Ni-based, Co-based and Fe-based alloys for heated hot stamping tools manufactured by surfacing technology

To meet the demanding requirement of ultra-high-strength steel parts with tailored properties, heated hot stamping tools are becoming widely used. However, due to severe working conditions, wear on tool surface is serious. Therefore, the service life of heated hot stamping tools is limited. In this paper, with the purpose of improving the service life of heated hot stamping tools, we aim to find a suitable alloy with better wear-resistant properties to manufacture heated hot stamping tools by surfacing technology. Thus, wear comparison tests between SDCM steel and specimens made of Ni-based, Co-based and Fe-based alloys were conducted under 500 °C and 180 N normal load to determine which kind of alloy has the best wear-resistant properties. Specifically, the mechanical properties, worn volume, worn morphologies and wear mechanisms of test materials were investigated. The results indicate that the Fe-based alloy has the highest compressive yield strength and hardness, but the Co-based alloy has the lowest worn volume, which is 0.49 mm3 at 20 min and 0.70 mm3 at 90 min. And there is no obvious positive relationship between the mechanical properties and the wear-resistant properties of the test materials under the test conditions. The common wear characteristic of the four test materials is that their main wear mechanisms are oxidation wear. The Co-based alloy has the moderate mechanical properties, and its wear mechanisms are oxidation wear and adhesive wear; thus, shear tearing, material transfer and severe abrasive wear are avoided, and the oxide layers adhere to its worn surface instead of spalling. Therefore, the Co-based alloy manifests the best wear-resistant properties and is chosen as the surfacing materials for heated hot stamping tools.

Microstructure and mechanical properties of oxide dispersion strengthened FeCoNi concentrated solid solution alloys

Microstructure and mechanical properties of two kinds of oxide dispersion strengthened concentrated solid solution alloys (CSAs), FeCoNi-1.5Y2O3 (FCNY) and FeCoNi-1.2Ti-1.5Y2O3 (FCNTY), are studied through a comparing investigation with FeCoNi (FCN) CSAs. All these alloys are fabricated by mechanical alloying, spark plasma sintering, hot rolling and annealing treatment. For three kinds of alloys, both the as-milled powders and bulk materials are of single face-centered cubic structure. Electron backscattered diffraction results reveal that the texture transformation is suppressed during the hot rolling process because the movement of grain boundaries is hindered by the oxide particles. Compared with FCN CSAs, grains are refined by 43% and 47% for FCNY and FCNTY CSAs, respectively. Nano-sized Y2O3 (monoclinic structure) and Y2Ti2O7 (pyrochlore structure) particles are uniformly distributed in FCNY and FCNTY CSAs, respectively. Both Y2O3 and Y2Ti2O7 particles show a semi-coherent relationship with the matrix. Yield strength of FCN, FCNY and FCNTY CSAs is 559, 981 and 1050 MPa, respectively. Theoretical calculations illustrate that high strength of FCNY and FCNTY CSAs comes from refined grains and high-density nano-sized oxide particles.

Transformation-assisted hydrogen desorption during deformation in steels: Examples of α′- and ε-Martensite

Hydrogen desorption behavior associated with γ-α′ and γ-ε martensitic transformation during tensile tests is investigated in four kinds of alloys with different austenite stabilities. Remarkable deformation-induced hydrogen desorption is detected not only as a result of the γ-α′ martensitic transformation, but also because of the γ-ε martensitic transformation, and the amount of desorbed hydrogen from transformed α′ martensite is more than that of transformed ε martensite. This suggests that the solubility of hydrogen in the ε phase is higher than that in the α′ martensite but lower than that in austenite.

A first-principles phase field method for quantitatively predicting multi-composition phase separation without thermodynamic empirical parameter

To design tailored materials, it is highly desirable to predict microstructures of alloys without empirical parameter. Phase field models (PFMs) rely on parameters adjusted to match experimental information, while first-principles methods cannot directly treat the typical length scale of 10 μm. Combining density functional theory, cluster expansion theory and potential renormalization theory, we derive the free energy as a function of compositions and construct a parameter-free PFM, which can predict microstructures in high-temperature regions of alloy phase diagrams. Applying this method to Ni-Al alloys at 1027 °C, we succeed in reproducing evolution of microstructures as a function of only compositions without thermodynamic empirical parameter. The resulting patterns including cuboidal shaped precipitations are in excellent agreement with the experimental microstructures in each region of the Ni-Al phase diagram. Our method is in principle applicable to any kind of alloys as a reliable theoretical tool to predict microstructures of new materials.

Co-reduction behaviors of Ce (III), Al (III) and Ga (III) on a W electrode: An exploration for liquid binary Al-Ga cathode

Both Al and Ga have exhibited excellent performance, respectively, for the An/Ln separation based on molten salt electrolysis, and the Al-Ga composite cathode may have superior properties. Therefore, in this work, the electrochemical behaviors of Ce (III) on the binary Al-Ga electrode were systematically explored by co-reduction of Ce (III), Al (III) and Ga (III) on a W electrode. A new oxidation signal of Al2Ga2Ce ternary intermetallic compound was successfully detected. In addition, for comparison, the co-reduction behaviors of Ce (III) with Al (III) and Ce (III) with Ga (III) on an inert tungsten electrode were also investigated. The results showed that different kinds of alloys are formed on the surface of W electrode. Finally, several typical Ga-Ce and Al-Ga-Ce intermetallic compounds were obtained by potentiostatic electrolysis and the deposited products were characterized by X-ray diffraction (XRD) and Scanning Electron Microscopy (SEM) with Energy Dispersive Spectroscopy (EDS).

Hot cracking susceptibility of commercial filler metals for Alloy 617 by Varestraint test. Study of hot cracking of Alloy 617 in multipass welds

ABSTRACT Solidification cracking and liquation cracking susceptibility of four kinds of alloy 617 commercial filler metals were evaluated by Varestraint test, in order to clarify a fundamental effect of each solute element in the alloy. Fracture surface of cracking in alloy 617 multipass welds by GTA welding exhibited a possibility of occurrence of both solidification cracking and liquation cracking. Brittle temperature ranges (BTR) of the liquation cracking at each alloy were almost same, however the BTRs of solidification cracking indicated significant difference. Complex carbide composed carbon, titanium and niobium was formed in the weld metal in the case of the smallest BTR for the solidification cracking, in other words alloy 617 including a lot of titanium and niobium indicated a good susceptibility for the solidification cracking. Numerical simulation of solidification segregation of alloy 617 was carried out to reveal the solidification behaviour at terminal stage of the alloy. The solidification segregation analysis suggested that solidification cracking susceptibility was attributed to the carbide formation depending on the solidification segregation of carbon, titanium and niobium. In the alloy containing titanium and niobium, the carbide formation occurred at the terminal stage of the solidification. Therefore, solidification completed temperature increased because the amount of carbon in residual liquid decreased after the carbide formation.

The thermodynamic analytical models for steady-state of continuous drive friction welding based on the maximum entropy production principle

An analytical model was developed based on the thermodynamic theory of Onsager-Ziegler maximum entropy production principle (OZ-MEPP) and the relevant dynamic laws, and used for characterizing the steady-state system of the severe plastic deformation (SPD) produced by continuous drive friction welding (CDFW) without any pre-assumed or measured response parameters. The accuracy and universality of the model were verified by the CDFW experiments of eight kinds of alloys, the results of which indicated that the model could precisely predict the temperature, axial shortening rate, welding power. Moreover, the coefficient of friction, traditionally regarded as an empirical parameter, could be forecasted too.

Effects of phase transition temperature and preheating on residual stress in multi-pass & multi-layer laser metal deposition

To investigate the influences of phase transition temperature and preheating on the residual stress of multi-layer and multi-pass laser metal deposition (LMD), the multi-layer and multi-pass LMD, with and without preheating, were performed using five kinds of alloy with different phase transition features, and their residual stresses were measured using the hole drilling method. A finite-element (FE) model incorporating the phase transition was developed based on experimentally obtained physical property data. The results demonstrated that the low-temperature solid phase transition has a tensile stress relaxation effect, which leads to the formation of a compressive stress area. This relaxation effect was observed to decrease with the increase of the phase transition temperature. The high-temperature solid phase transition has no significant tensile stress relaxation effect during the multi-layer and multi-pass LMD process, which is different from the single track LMD. when the solid phase transition temperature is low, the preheating can improve the uniformity of the stress field only to a certain extent. However, when the preheating increases the lowest temperature of the thermal cycle and makes it higher than the starting point temperature of the solid phase transition, the tensile stress relaxation effect of the solid phase transition can be brought into full play.

High Cycle Fatigue Performance of Inconel 718 Alloys with Different Strengths at Room Temperature

In this paper, the high cycle fatigue performance of solid solution state and aged Inconel 718 superalloys was studied at room temperature. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were used to analyze the original structural features and fatigue deformation features of two kinds of alloys. SEM, laser scanning confocal microscopy, and electron backscatter diffraction (EBSD) were used to analyze the secondary fracture features of the fatigue fracture morphology and fatigue fracture profile. The results showed that the aging treatment significantly affected the strength and plasticity of the alloy, which in turn affected the fatigue performance of the alloy. After the aging treatment, the yield strength σs and the tensile strength σb of the Inconel 718 alloy increased by 152% and 65.9%, respectively, compared with those of the solid solution state, but the rate of elongation δ and rate of contraction in the cross-section area φ decreased by 63.7% and 52.3%, respectively. The fatigue limit of the aged state was lower than that of the solid solution state by 6.3%. The quadratic function relationship between the high cycle fatigue limit σ−1 and the tensile strength σb of the Inconel 718 superalloy at room temperature was σ−1 = σb · (0.869−3.67 × 10−4 · σb). An analysis of the fatigue fracture mechanism showed that the fatigue fractures before and after aging were all initiated in the grains oriented relatively unfavorably on the surface of the sample, with a mixture of intergranular and transgranular propagation after the transgranular propagation of several grains. The higher plasticity of the solid solution state Inconel 718 alloy resulted in a large number of slip deformation zones under high cycle fatigue loads, and the plastic deformation was relatively uniform. The lengths of the secondary fractures were as high as 120 μm, which formed the single-source plastic fatigue fracture that promoted an increase in the fatigue limit. After aging treatment, the higher strength of the Inconel 718 alloy made dislocation slip difficult under high cycle fatigue loads, and the plasticity compatible deformation capability was poor. When local dislocations slipped to the intragranular γ” phase, γ’ phase, or interfaces with nonmetallic compounds (NMCs), plugging occurred. The degree of stress concentration increased, causing the initiation of fatigue fracture; the secondary fracture was approximately 20 μm. Brittle cleavage due to multiple sources significantly reduced the fatigue limit.

Correlation between microstructure, thermal parameters and mechanical properties of a directionally solidified Al-1%wt Mn alloy

This works aims to study the mechanical properties of a Al-1%wt Mn alloy directionally solidified under unsteady-state conditions. The as-cast microstructure was analysed by measuring the cellular spacing, and the mechanical properties were obtained through Vickers microhardness and tensile strength tests. The correlation between the mechanical results and the as-cast microstructure was fundamental to imply a relation between the solidification thermal parameters and the rolling process in which this kind of alloy is submitted to afterwards.