Addition Of Alloying Elements Research Articles

Effect on wetting properties of the Al-Ti system by the addition of different alloying elements

With lightweight and high-strength, Al-Ti composites have become one of the indispensable materials in the aerospace and automotive manufacturing fields. However, due to strong interfacial reactions, the traditional pure Al-Ti composites have been limited in practical applications. To better control the interfacial reaction between the reinforced phase and the matrix in the Al-Ti composites, in this paper, the effect on wetting behavior and interfacial properties of the Al-Ti system by the addition of different alloying elements (Si, Mg, Zn, Cu) in Al melt were systematically investigated using the sessile drop method. According to the results, adding Si, Mg, Zn, and Cu elements to the Al melt can increase the steady-state wetting angle to varying degrees at the end of the holding period compared to the pure Al-Ti wetting but still maintains good wettability. The Mg, Zn, and Cu elements ensure good wettability and simultaneously reduce the temperature required for wetting, providing novel ideas for preparing aluminum matrix composites. All the systems in this experiment are typical of reactive wetting. The system with added Si and Cu showed a clear interfacial layer at the Al-Ti interface, which was comparatively smooth, and both the original Al-Ti reaction at the interface and the dissolution of the Ti substrate are inhibited.

Gaining understanding of the effect of alloy composition on the properties of Ti–Cu–Mn–Al alloys

High performance cheaper Ti alloys can be developed based on the addition of several alloying elements, amongst which are Cu, Mn and Al. Studies are available in literature about binary and some ternary alloys based on the addition of these elements; however, no quaternary Ti–Cu–Mn–Al alloys were developed. Therefore, in this study quaternary Ti–Cu–Mn–Al alloys were manufactured via powder metallurgy to gain a better understanding of the effect of the alloy composition and the achievable mechanical performance. It is found that the selected quaternary Ti–Cu–Mn–Al alloys are characterised by a lamellar structure, which is progressively refined as the amount of alloying elements increases, and precipitation of the Ti2Cu intermetallic occurs if the Cu content is high enough. The amount of residual porosity increases and changes morphology as more thermal energy is invested in the diffusion of the alloying elements. In terms of mechanical behaviour, the quaternary Ti–Cu–Mn–Al alloys undergo both elastic and plastic deformation upon tensile loading. Strength and hardness linearly increase and the ductility monotonically decreases, which is the result of the compromise between the amount of residual porosity and the several strengthening mechanisms brought about by the actual total amount of alloying elements added.

Effect of Mo and Cr on the Microstructure and Properties of Low-Alloy Wear-Resistant Steels.

Low-alloy wear-resistant steel often requires the addition of trace alloy elements to enhance its performance while also considering the cost-effectiveness of production. In order to comparatively analyze the strengthening mechanisms of Mo and Cr elements and further explore economically feasible production processes, we designed two types of low-alloy wear-resistant steels, based on C-Mn series wear-resistant steels, with individually added Mo and Cr elements, comparing and investigating the roles of the alloying elements Mo and Cr in low-alloy wear-resistant steels. Utilizing JMatPro software to calculate Continuous Cooling Transformation (CCT) curves, conducting thermal simulation quenching experiments using a Gleeble-3800 thermal simulator, and employing equipment such as a metallographic microscope, transmission electron microscope, and tensile testing machine, this study comparatively investigated the influence of Mo and Cr on the microstructural transformation and mechanical properties of low-alloy wear-resistant steels under different cooling rates. The results indicate that the addition of the Mo element in low-alloy wear-resistant steel can effectively suppress the transformation of ferrite and pearlite, reduce the martensitic transformation temperature, and lower the critical cooling rate for complete martensitic transformation, thereby promoting martensitic transformation. Adding Cr elements can reduce the austenite transformation zone, decrease the rate of austenite formation, and promote the occurrence of low-temperature phase transformation. Additionally, Mo has a better effect on improving the toughness of low-temperature impact, and Cr has a more significant improvement in strength and hardness. The critical cooling rates of C-Mn-Mo steel and C-Mn-Cr steel for complete martensitic transition are 13 °C/s and 24 °C/s, respectively. With the increase in the cooling rate, the martensitic tissues of the two experimental steels gradually refined, and the characteristics of the slats gradually appeared. In comparison, the C-Mn-Mo steel displays a higher dislocation density, accompanied by dislocation entanglement phenomena, and contains a small amount of residual austenite, while granular ε-carbides are clearly precipitated in the C-Mn-Cr steel. The C-Mn-Mo steel achieves its best performance at a cooling rate of 25 °C/s, whereas the C-Mn-Cr steel only needs to increase the cooling rate to 35 °C/s to attain a similar comprehensive performance to the C-Mn-Mo steel.

Thermal Cycling Performance of Heterogeneous Solder Ball Joints with Sn-3.0Ag-0.5Cu and Sn-0.75Cu(-Ni,Bi) Solder Ball Composition for BGA Package

Sn-3.0Ag-0.5Cu (SAC305) is one of the most commonly used Pb-free solder composition nowadays. A minor alloying element addition can improve mechanical properties and thermal reliability of the solder joint. Minor amount of Bithmuth (Bi) or Nickel (Ni) addition can improve mechanical properties of solder by solid solution strengthening, or ensure the structural stability of the intermetalllic compounds. Also, low melting temperature solder with Bithmuth can reduce the cost of soldering process and keep components from deterioration. In this study, reliability of heterogeneous and homogeneous solder joint in the ball-grid-array (BGA) package solder joint were investigated. Using Sn-3.0Ag-0.5Cu (SAC305) solder paste and two kinds of solder balls, we have investigated which combination of solder joint improves the thermo-mechanical reliability. SAC305 and SCN (Sn-0.75Cu-Ni,Bi) balls were used for homogeneous and hetrogeneous joints. Solder balls were attached in BGA package. To examine the solder joint reliability, thermal cycling test was conducted after reflow soldering. Shear strength measurement and cross-sectional analysis of the BGA package solder joints were carried out before and after 2000 cycles of the test. The shear strength of homogeneous solder joint decreased to 68.2% and heterogeneous decreased to 43.5%. The cross-sectional analysis using scanning electorn microscopy (SEM) and electorn back-scattered diffraction (EBSD) showed the (Ni,Cu)<sub>6</sub>Sn<sub>5</sub> and Cu<sub>6</sub>Sn<sub>5</sub> IMCs which were generated in the solder joint, and the crack propagated longer in the homogeneous solder joint of SAC305 after the thermal cycling test. IPFM showed the grain refinement effect of the SCN solder joint after thermal cycling. The minor addition of Bi had played a role as dislocation pinning site and became to equiaxied grain, so that the lifetime of heterogeneous SCN solder joint was superior than that of the SAC305.

Evaluating the microstructural formation in Mo added Ti6Al4V alloy fabricated by direct energy deposition using a laser-stop strategy

The microstructure formation in the Ti64 alloy with the addition of different alloying elements is extensively researched to enhance the mechanical properties of the alloy, especially fabricated using additive manufacturing processes. In this work, the effect of Mo (0, 1, 2, 4 wt%) addition on the microstructure and mechanical properties of the direct energy deposited (DED) Ti64 alloy was evaluated in detail. As the Mo content increases, a remarkable refinement in the α-laths morphology was observed, with the average width decreasing from ∼1.12 μm to ∼0.39 μm, and an anomalous increase in the volume fraction of the α phase was noted in the Ti64–1Mo alloy. Further increase of the Mo content results in the attenuation of the variant dominance of the α-laths until virtually eliminated. Notice that the tensile strength and elongation increased by 7.3% and 37.5% with 1 wt% addition of Mo, respectively. A Laser-Stop (LS) strategy was employed to preserve the formed metastable phases during the DED process. Such LS strategy provides necessary insights into microstructural evolution and elucidates the mechanisms behind the formation of a refined microstructure and in turn its mechanical properties.

Development of Highly Machinable Ti Alloy with Exceptional Tensile Properties by Er Alloying Element Addition

This study demonstrates that the addition of the rare earth element Erbium (Er) significantly enhances the machinability and tensile properties of titanium (Ti). Pure Ti alloys and Er-added Ti alloys with 0.5-1.1 wt.% Er content were prepared, and their microstructure, machinability, and tensile properties were compared. Two different types of Er secondary phase particles were identified in the microstructure: pure Er and Er-oxide. The amounts of these particles increased with higher Er content. The machinability of the Eradded Ti alloys was significantly improved due to the ability of Er secondary particles to cut machining chips or absorb heat from localized deformation within the Ti matrix. In addition, Er-added Ti alloys exhibited higher strength than pure Ti. The strength enhancement was attributed to grain refinement induced by the Er element. Er secondary phase particles reduced the β grain size during solidification, and they also served as preferential sites for α nucleation during the β → α phase transformation, resulting in a refined microstructure. In addition, the Er secondary phase contributed to the strength enhancement through the well-known precipitation strengthening mechanism. Although ductility decreased with higher Er content due to the increased amount of Er secondary phase particles, 0.5 wt.% Er-added Ti showed no such degradation; its ductility was comparable to that of pure Ti. Er-oxidation was expected to reduce oxygen content within the Ti matrix, enhancing intrinsic Ti ductility; this effect offset the adverse impact on ductility caused by the Er secondary phase particles. Above 0.5 wt.% Er, the adverse effects caused by the Er secondary phase particles overwhelmed the beneficial effect caused by the reduction in oxygen content. The present findings will contribute significantly to the development of highly machinable Ti alloys with superior tensile properties.

Enhancement of mechanical properties and oxidation resistance of TiAl alloy with addition of Nb and Mo alloying elements

In this study, small button-shaped ingots were prepared by a non-self-consuming vacuum arc melting method. The effect of the content of Nb and Mo elements on the microstructure, mechanical properties and oxidation resistance of TiAl alloys were investigated. The as-cast TiAl alloy presented laminar microstructure. When only adding Nb element, a small amount of β phase was distributed in the form of dots at the grain boundaries of α2/γ lamellar structure. When adding both Mo and Nb, the precipitated β phase started to precipitate in lines inside the α2/γ lamellar structure. The microhardness of the alloy increased with the increasing Nb and Mo content. The compressive strength of the alloys increased firstly with the increasing Nb content and decreased when the content of Nb exceeded 7 wt%. However, with the addition of Mo, the compressive strength of the alloys decreased drastically. The optimal compressive strength of the alloy, i.e. 2250 MPa, was obtained with 5 wt% Nb and 5 wt% Mo addition. The oxidation resistance of the alloys were enhanced with the addition of Nb and Mo elements and the TiAl–5Nb–5Mo alloy also showed the best oxidation resistance at 800 °C.

Insights into the design of oxidation-resistant Mg alloy by alloying with rare-earth elements

The strategy of rare-earth elements addition into Mg alloys has been successfully developed and applied to enhance the mechanical performance and corrosion resistance of Mg alloys. Although this strategy has also been applied to enhance their high-temperature oxidation resistance, the mechanistic understanding of the beneficial effects remains elusive. Here, the oxidation of Mg–4Nd and Mg-4Nd–1Y alloys in Ar–20%O2 at 500 °C was studied and compared. It was found that even though a continuous layer of Nd2O3 did not form, the Nd addition could still enhance the oxidation tolerance of Mg–4Nd alloy by facilitating the generation of a more continuous and intact oxide scale and working as oxygen sinks to delay the violent oxidation of Mg. The formation of a continuous Y2O3 layer on Mg-4Nd–1Y alloy suggests that Y was more capable of facilitating the external oxidation due to its much faster diffusion rate in Mg matrix than that of Nd. However, the Nd addition could decrease the critical content of Y necessary for the oxidation transition from internal to external because of the synergistic effect of the Nd and Y addition. The dissolution of the thermal unstable Mg12Nd precipitates resulted in a localized increase of Nd content, accelerating the oxidation by increasing the preferential oxidation of Nd. Hence, in the design of oxidation-resistant Mg alloys, the addition of RE elements with faster diffusion rate and the addition of multiple alloy elements are preferred. In addition, the number of thermal unstable precipitates needs to be strictly controlled.

Influence of Various Alloying Element Additions on Microstructure and Magnetic and Mechanical Properties and Corrosion Behavior of Cast Fe–Ga–Z Shape Memory Alloys

Fe–Ga alloys are attractive materials where high mechanical strength, toughness, ductility, and large low-field magnetostriction combine to give unique properties. Adding alloying elements is an effective method to further enhance these properties. In order to integrate these alloys into the operating environments, e.g., micro-robots and magnetic actuators, the corrosion behavior should be addressed. This work analyzed the microstructure, magnetization, hardness, and corrosion properties of Fe81Ga19−xZx (X = 5 at.% of Ni, Mn, or Ti, and 2 at.% Al; separately) alloys. X-ray diffraction (XRD), scanning electron microscope-electron (SEM), vibrating sample magnetometer (VSM), Vickers hardness (HV), and a potentiostat were used for characterization. XRD revealed that the prominent peak belongs to the bcc disorder A2 phase and a small peak for the cubic order L12 phase. Fe–Ga–Al alloy got the maximum Ms value, while Fe–Ga–Mn alloy gained the lowest one. However, the Mr and Hc properties for Fe–Ga alloy were distinctly improved by adding Al but slightly affected by doping Mn. Addition of Ti achieved the highest hardness, followed by Ni, Mn, and Al. The microstructure of the different alloys significantly influenced their corrosion behavior. Fe–Ga–Mn alloy with the fine globular grain structure showed the lowest corrosion rate (C R = 0.03 mm/year), whereas Fe–Ga–Al alloy with the coarse longitudinal grains exhibited the highest corrosion rate (C R = 0.19 mm/year).

Machine learning approach for predicting the fracture toughness of Nb[sbnd]Si based alloys

Machine learning based data analysis was used to quantitatively examine the effects of constituent elements on the room-temperature fracture toughness of NbSi based alloys. Correlation between the room-temperature fracture toughness and alloying elements was analyzed using the machine learning model developed in this study based on the collected NbSi based alloy data. In addition, using a reasonably trained data analysis approach, the accuracies of several machine learning algorithms were compared to determine the specific machine learning algorithm with showing the highest accuracy. The results of the correlation analysis between the input and output features coincided with widely accepted facts regarding the effects of alloying elements additions on the room-temperature fracture toughness of NbSi based alloys. It was confirmed that the random forest algorithm outperformed other three representative machine learning algorithms.

MICROSTRUCTURE EVOLUTION AND HARDNESS IMPROVEMENT OF GRAY CAST IRON BY ADDITION OF FeSiMg FOLLOWED BY FLAME HARDENING PROCESS

The addition of magnesium alloy elements followed by a flame-hardening process will change the phase configuration in gray cast iron. This study aims to investigate changes in microstructure and hardness due to these two processes. The addition of magnesium is conducted by adding FeSiMg as a carrier for magnesium. Metallographic examination to observe changes in microstructure was carried out using a Scanning Electron Microscope (SEM) and Energy-Dispersive X-ray Spectroscopy (EDS). The formed phase is examined by X-Ray Diffraction testing. The hardness test was carried out using the Vickers technique on the surface of the gray cast iron, the nodular cast iron, and the flame-hardened nodular cast iron. Whilst for flame-hardened nodular cast iron, the Vickers technique was also conducted on a cross-section. The addition of the FeSiMg compound changed flake graphite into spherical graphite with increased hardness from 130 VHN to 313.22 VHN. The flame-hardening process in nodular cast iron results in the formation of a martensite phase and the disappearance of graphite on the surface of the material. The hardness on the surface of the material due to the flame-hardening process increased by 82.4% compared to the substrate.

Microstructure and phase investigation of FeCrAl-Y2O3 ODS steels with different Ti and V contents

FeCrAl-based steels are considered promising materials for high-temperature nuclear applications. Over the past years, various compositions have been studied to assess their mechanical properties, structural integrity, and radiation damage resistance. However, the microstructure and phase composition of FeCrAl-ODS steels with the addition of different alloying elements are less commonly studied than pure FeCrAl alloys. The paper presents a novel research path for developing FeCrAl matrix ODS steels with Y2O3, Ti, and V additions. The materials synthesis consisted of mechanical alloying of pure metallic components with yttrium oxide in a planetary ball mill under an argon atmosphere. Titanium was added in the amount of 1.0 wt.% to both samples, while 0.5 wt.% of vanadium was added to one sample to verify its impact on the structural stability and hardness. The spark plasma sintering (SPS) technique was used to consolidate the powders. Afterward, the microstructure, chemical composition, phase composition, and hardness were assessed using SEM-EDS, EBSD, TEM-EDS, XRD, XRF, Nanoindentation, and Vickers microhardness. The experimental data reveal rather homogeneous powders after mechanical alloying and dense bulk samples after SPS. The microstructure observations show oxide particles and carbides on the grain boundaries and inside grains of the bcc matrix, which suggests elevated radiation damage resistance. The presence of nanoscale oxide particles (15–50 nm) in the matrix could significantly reduce the impact of aging embrittlement at high temperatures by affecting the chromium diffusion pathways in the ODS steel matrix. The addition of vanadium leads to an improvement of hardness to 4.83±0.43 GPa compared to 3.78±0.34 GPa for the sample without vanadium. Presented experimental results are promising in terms of research and development of FeCr and Al-based ODS materials tailored to operate under harsh conditions in generation IV fission reactors and fusion reactors.

Comparison on structural andmagnetic properties of FeCoNi medium entropy alloy, FeCoNiAl and FeCoNiAlTi high entropy alloys

In the present study, we investigated the effect of configurational entropy on the phase evolution and magnetic properties of medium and high-entropy alloys. Three different, FeCoNi medium entropy alloys (MEA), FeCoNiAl, and FeCoNiAlTi high entropy alloys (HEAs) were synthesized through the mechanical alloying technique (MA). XRD analysis revealed the formation of the single fcc phase structure for FeCoNi MEA. The mixture of bcc and fcc phase is formed forFeCoNiAl HEA. However, for FeCoNiAlTi HEA the mixture of fcc, and bcc phases, along with a minor fraction of intermetallic R-phase is confirmed through the fitting of XRD data. The magnetic properties of FeCoNi MEA changed drastically by adding Al and Al, Tiwith Fe, Co, Ni as alloying elements for the formation of HEAs. The values of saturation magnetization (Ms) and coercivity (Hc) for FeCoNi MEA are 133.7 emu/g and 26.1 Oe, respectively. For FeCoNiAl HEA, the value of Ms decreased to 85.4 emu/g, and Hc increased to 74.2 Oe. However, for FeCoNiAlTiHEA, the value of Ms is reduced to 52.50 emu/g, and Hc increased to 90.55Oe. The present study clearly shows that the addition of different alloying elements significantly impacts the phase formation and the magnetic behavior of the MEA and HEAs.

Preparing a dilute Mg-Mn-Zn alloy with ultra-high strength by coupling extrusion and forging at low temperatures

In this work, a Mg-1.0Mn-1.0Zn (wt.%) alloy with ultra-high strength was prepared by extrusion at 438 K and forging at 453 K. High tensile yield strength of 373 MPa and ultimate tensile strength of 417 MPa were realized with only 2 wt% low-cost alloying element additions, resulting from the closed combination of ultrafine dynamic recrystallized grains, high-density dislocations, nanoscale precipitates and strong texture. It is believed that such a low-temperature deformation method can be widely used to fabricate other low-alloyed Mg alloys with ultra-high strength in industrial fields.

Role of Al and Mg alloying elements on corrosion behavior of zinc alloy‐coated steel substrates in 0.1 M NaCl solution

AbstractThe corrosion behavior and corrosion products of three zinc alloy‐coated steel substrates with different Al and Mg contents such as hot‐dip galvanized steel (HDG), Zn–Al‐coated steel (ZA), and Zn–Al–Mg‐coated steel (ZM) substrates were investigated during 168 h of immersion in 0.1 M NaCl solution. The characteristics and morphology of corrosion products on all the substrates formed during exposure to electrolyte solution were observed by X‐ray diffraction, X‐ray photoelectron spectroscopy, and scanning electron microscopy/energy‐dispersive X‐ray spectroscopy. Their electrochemical behavior was investigated by open‐circuit potential, polarization curves, and electrochemical impedance spectroscopy. The addition of Al and Mg alloying elements affected the corrosion mechanism as well as the anticorrosion properties. The main crystalline corrosion products on the HDG surface were simonkolleite and zincite, while the ZnAl hydrotalcite was identified as the main corrosion product on ZA and ZM surfaces. The corrosion resistance of ZA and ZM substrates was improved compared to the HDG substrate due to the enhanced adhesion of the corrosion product layer.

980 MPa Grade Low-Alloy Carbide-Free Bainitic Steel Obtained by Dynamic Continuous Cooling Transformation

The addition of high-content alloying elements and the unbefitting process make carbide-free bainite steel difficult in industrial production. Thus, we adopted a dynamic continuous cooling process for developing the high-strength cold-rolled low-alloy carbide-free bainitic steels in this study. The influence of cooling rates on the microstructure and mechanical properties was investigated by dilatometry, scanning electron microscopy (SEM), X-ray diffraction (XRD), electron backscatter diffraction (EBSD), and tensile tests. The results show that the bainitic ferrite plates were refined by decreasing the cooling rate, and more austenite was retained in the steel with a medium cooling rate. Both the TRIP effect and the refined bainitic ferrite plate contribute to the good strength–ductility match. Consequently, the propitious microstructure adjustment is critical for developing 980 MPa carbide-free bainitic steel.

Effects of Ageing in Disinfectant Solution on the Corrosion Resistance and Antimicrobial Behavior of Copper Alloys.

This work studies two copper-based alloys as potential antimicrobial weapons for sectors where surface hygiene is essential. Effects of different alloying elements addition at the same Cu content (92.5% by weight) on the corrosion resistance and the antibacterial performance of two copper alloys were studied in an aerated disinfectant solution (0.25% v/v Aniosurf Premium (D)) by electrochemical corrosion, X-ray photoelectron spectroscopy (XPS), time-of-flight secondary ion mass spectroscopy (ToF-SIMS) and antibacterial tests. Results showed that the nature of the alloying elements had a clear influence on the corrosion resistance and antibacterial performance. Electrochemical impedance results and surface analyses demonstrate the presence of organic compounds bound on the substrate and that a film covers part of the total active surface and may act as a protective barrier by preventing the interaction between metal and solution, decreasing the antimicrobial performance of copper-based materials. Low zinc and silicon contents in copper alloys allows for better aging behavior in D solution while maintaining good antibacterial performance. The XPS and ToF-SIMS results indicated that artificial aging in disinfectant enhanced Cu enrichment in the organic film formed, which could effectively stimulate the release of Cu ions from the surface.

Tribological Behavior of Titanium-Sintered Composites with Ring-Shaped TiN Dispersoids

The wide applicability of titanium (Ti) has prompted the analysis to improve its mechanical strength through the addition of different alloying elements. Among these, Ti materials with pre-mixed pure Ti and titanium nitride (TiN) powders as the starting materials have exhibited improved mechanical properties and tribological performance. In this study, the tribological properties of Ti matrix composites with ring-shaped TiN dispersoids were evaluated. The materials were fabricated from pre-mixed pure Ti powder and core–shell structured Ti–(N) powder, which were prepared by heat treatment at 1273 K under N2 gas. The tribological behavior of the Ti–TiN composites was studied by varying the applied load using a ball-on-disk wear test under oil lubrication conditions. The initial familiarity period of the Ti–TiN composites decreased. Subsequently, compared to the pure Ti specimen employed as a reference material, the friction coefficient was significantly lower and more stable. This is attributed to the ring-shaped, hard TiN dispersoids, which prevented the adhesion phenomenon and improved the oil film formability owing to the increase in microhardness and abrasive wear resistance of the nitrogen solid solution in the core region.

Effect of intercritical heat treatment on microstructure, nano-size precipitation and mechanical properties of Fe–Ni–Cu–Al low carbon steel

In recent years, the co-precipitation of nanoscale Cu and Ni–Al particles in Fe–Ni–Cu–Al low-carbon steel provide an extremely high strengthening increment while minimizing the addition of carbon and alloy elements, however, the toughness and plasticity dramatically decreased. This research focuses on the improvement of toughness and plasticity utilizing an intercritical (Quenching-Lamellarization-Aging (QLA)-type) heat treatment for Fe–Ni–Cu–Al steel. The microstructure and nanoparticles precipitation of Fe–Ni–Cu–Al steel were characterized by TEM, HRTEM and phase analysis after a QLA treatment. The results indicate that the multi-phase microstructure consisting of maraging martensite, intercritical ferrite and austenite reversion were obtained by QLA treatment. With decreasing intercritical quenching temperature between 820 °C and 660 °C, −80 °C V-type impact energy and plasticity of Fe–Ni–Cu–Al steel was obviously improved due to the formation of intercritical ferrite and austenite reversion. Meanwhile, the coarsening of Ni3Al particles were markedly accelerated because of Ni segregation in matrix and abundant Fe atoms for the substitution of Al atoms within Ni3Al particles. The strengthening mechanisms of Ni3Al particles in Fe–Ni–Cu–Al steel was mainly Orowan bypassing strengthening after QLA treatment, and the corresponding strengthening increment was calculated as 89% (214 MPa) at the intercritical quenching temperature of 720 °C, which was 17% (259 MPa) lower than the value of order strengthening obtained by 820 °C primary quenching. The combination of multi-phase microstructure and co-precipitation strengthening contributed to excellent mechanical properties (yield strength>1050 MPa at 20 °C, the elongation>13%, a Charpy impact toughness of >80 J at −80 °C) during the intercritical quenching temperature of 720 °C–780 °C.

Redistribution of substitutional alloying elements between α-Fe matrix and cementite after long-term tempering in a low alloying steel

ABSTRACT The partitioning behaviour of non-carbide forming elements (Si, Cu and Ni) and carbide forming elements (Mn and Mo) between α-Fe matrix and cementite (θ) after long-term tempering a quenched reactor pressure vessel (RPV) model steel has been studied by atom probe tomography (APT). It has demonstrated that a non-carbide forming element enriched layer near the interface of α/θ in the α-Fe matrix side is a common feature for tempered steels containing non-carbide forming element, which is widely accepted as the mechanism by which substitutional elements retard the coarsening of cementite. In addition, a carbide forming element enriched layer near the interface of α/θ in the cementite side, Si, Cu and Ni enriched clusters formed in the cementite and Mo2C carbide formed beside cementite were observed, and all this is taken as valuable mechanisms by which addition of substitutional alloying elements can increase tempering resistance of alloying steels.