Microstructure Behavior Research Articles

The Microstructure, Mechanical Properties, and Precipitation Behavior of 1000 MPa Grade GEN3 Steel after Various Quenching Processes

This study examines the microstructure, mechanical properties, and precipitation behavior of 1000 MPa grade GEN3 steel when subjected to various quenching processes, with a focus on the quench and partition (Q&P) technique. The Q&P-treated samples achieved 1300 MPa tensile strength and demonstrated superior yield strength, attributed to their refined substructure and their large amounts of precipitates. The quenched samples exhibited the thinnest martensite laths due to the highest martensite volume. Despite the as-annealed samples having the smallest grain size, the Q&P treatment resulted in optimal microstructural refinement results and a high dislocation density, reaching 1.15 × 1015 m−2. Analysis of the precipitates revealed the presence of V8C7, M7C3, M2C, and Ti(C, N) across various heat treatments. The application of the McCall–Boyd method and the Ashby–Orowan correction model indicated that quench and tempered (Q&T) samples contained the largest volume of fine precipitates, contributing to their high yield strengths. These findings offer valuable insights for optimizing heat treatment processes to develop advanced high-strength steels for industrial applications.

Microstructure, mechanical properties, and deformation behaviour of LPBF 316L via post-heat treatment

ABSTRACT The study focused on analysing the changes in dislocation density and elemental segregation at cellular substructures, as well as the transformation of nano-oxide inclusions at different post-treatment temperatures, and their impacts on the strengthening mechanisms of 316L processed by laser powder bed fusion (LPBF). Additionally, through quasi in-situ tensile experiments, the plastic deformation and fracture behaviours of LPBF 316L after annealing at 900 °C were studied, revealing the reasons behind its high ductility. The results indicated that with increasing annealing temperatures, the nano-oxide inclusions coarsened and their density decreased due to the Ostwald ripening mechanism. The coarsened oxide particles act as barriers to moving dislocations and grain boundaries, thereby prolonging the recovery and recrystallization processes. This resulted in cellular substructures exhibiting high thermal stability. Consequently, the ultimate tensile strength of LPBF 316L after annealing at 900 °C is 651 MPa, with a total elongation of 62.3%, surpassing other studies.

Effect of microstructure variation induced by processing on corrosion behavior of Zr-Sn-Nb alloy

In order to investigate the effect of microstructure variation induced by processing on corrosion behavior of zirconium alloys, Zr-Sn-Nb alloy original plates were processed by rolling and annealing, and the microstructure and corrosion behavior of both original plates and processed plates were analyzed. It was found that after the original plates were processed, the recrystallized microstructure in original plates was transformed to stress-relieved microstructure in processed plates, with second phase particles ripening. When exposed to pure water and water containing H3BO3 and LiOH, the original plates have better corrosion property than the processed plates, and the corrosion transition of the processed plates happened earlier than that of the original plates. The grain structure differences of original plates and processed plates have two aspects of influence on oxide cracking and corrosion transition. Firstly, there were more defects in processed plates which results in smaller grains and larger grain boundary areas in oxide. Secondly, the strength of processed plates is higher, and this will lead to less stress accommodation of the growing oxide by plastic deformation of the matrix, and higher stress in oxide layer formed during the corrosion process. Both factors caused more cracks in the oxide layer of processed plates, leading to earlier corrosion transition and decreasing corrosion property. Second phase particles and their surroundings are susceptible to cracks during corrosion process, and may become the original source of cracks. However, second phase particle ripening was not closely related to decreasing corrosion property of processed plates.

Characterizations of the B2-Ni-Al(B) ordered alloy produced by high-energy mechanical alloying process: microstructure and thermal behaviors

Characterizations of the B2-Ni-Al(B) ordered alloy produced by high-energy mechanical alloying process: microstructure and thermal behaviors

Effect of element N on microstructure and tribological properties of CoCrFeNiV alloy at severe temperature

In this study, CoCrFeNiV non-equiatomic high entropy alloys (HEAs) with varying N content were prepared using vacuum hot-press sintering. The effects of N content on the alloy's microstructure, mechanical properties, and tribological behavior at different temperatures were investigated. The results indicate that the N-added alloys primarily maintain an FCC phase. With increasing N content, the σ phase in the alloy gradually decreases, while the VN content increases, leading to grain refinement. This results in a 10.7 % increase in hardness, a 9 % increase in compression strength, and a 56 % increase in compression deformation. Below 400 °C, the primary wear mechanisms are adhesive wear, spalling wear, and slight oxidative wear, while above 600 °C, oxidative wear dominates. The addition of N reduced the wear rates of the alloy by 33.8 %, 8.1 %, and 31.3 % at RT, 200 °C, and 600 °C, respectively, and decreases the coefficient of friction at all temperatures. In summary, N addition improves the alloy's tribological performance at various temperatures.

Effect of I-phase formation on hydrogen embrittlement behaviour of as-cast Mg-8 wt%Li based alloys

By performing microstructural characterization, tensile testing and failure analysis, the effects of electrochemical H-charging on microstructure and mechanical behaviour of two as-cast Mg-8Li (in wt%) based alloys were investigated and compared. Due to the in-situ formation of I-phase, the failure elongation ratio for Mg-8Li-6Zn-1Y alloy was 31.2 % and its hydrogen embrittlement (HE) susceptibility was about 1/4 that of Mg-8Li alloy after H-charging for 24 h. Moreover, the preferential location of H-induced pores transferred from two matrix phases to I-phase/matrix eutectic pockets due to the preferential H absorption of I-phase, resulting in the higher HE resistance of Mg-8Li-6Zn-1Y alloy.

Effect of ZrC particle on microstructure and corrosion behavior of CoCrNi medium-entropy alloy fabricated by powder plasma arc cladding

Medium-entropy alloys (MEAs) show significant potential as corrosion-resistant coatings. However, their industrial applications are limited by fabrication challenges and low efficiency. This study synthesized CoCrNi(ZrC)x MEA coatings using powder plasma arc cladding (PPAC) technology. The CoCrNi(ZrC)x MEAs consist of columnar and equiaxed grains. Incorporating ZrC refines the grain structure, achieving maximum refinement at x = 3. This refinement enhances the coating hardness by approximately 40 % (from 165 ± 3.36 to 229 ± 4.83 HV0.1), mainly due to Hall-Petch strengthening, solid solution effects, and grain boundary and dispersion strengthening. In 3.5 wt% NaCl solution, corrosion resistance was notably improved, as evidenced by a substantial decline in corrosion pits and an 81 % (from 4.52 to 0.86 μA/cm²) reduction in icorr. This enhancement is primarily due to ZrC reducing the exposed surface area of the coating and providing protection through localized Cr segregation at anodic sites. This study is the first to introduce ZrC ceramic particles into CoCrNi MEAs, advancing the development of corrosion-resistant coatings.

Fabrication, Microstructure and Plasma Resistance Behavior of Y-Al-Si-O (YAS) Glass-Ceramics Coated on Alumina Ceramics.

This study investigates the fabrication, microstructural characteristics and plasma resistance of Y-Al-Si-O (YAS) glass-ceramics coated on alumina ceramics. YAS frits were initially prepared using a melt-quenching method, then homogenously milled and coated onto alumina ceramics. The melt-coating process was conducted at 1650 °C for 1 h. The composition and microstructure of the glass frits and coatings were thoroughly characterized using X-ray diffraction, scanning electron microscopy, and energy-dispersive X-ray spectroscopy. These analyses revealed a dense microstructure with a polycrystalline structure predominantly composed of Y3Al5O12 (YAG) phase and a minor phase of Y2Si2O7. The YAS coatings on alumina revealed a dense layer with strong adhesion to the substrate. Subsequently, the coatings underwent C4F6/Ar/O2 plasma treatment for 1 h. Plasma exposure tests demonstrated that the YAS-coated alumina exhibited significantly better etching resistance compared to uncoated alumina, with minimal surface damage observed on the YAS coating, confirming its protective properties against plasma. The superior plasma resistance of YAS coatings is attributed to the predominance of its YAG phase. This research offers a more stable and cost-efficient solution for protecting ceramics in demanding plasma environments.

Effect of graphene on microstructure, strain hardening and corrosion behaviour of dual phase Mg-Li matrix processed through liquid metallurgy route

The significance of this study lies in the potential enhancement of magnesium (Mg)-based materials through the addition of graphene, aiming to improve their mechanical properties and corrosion resistance. This research investigates the development of graphene-Mg composites, employing a liquid metallurgy route to fabricate a dual-phase structured Mg-8Li composite. Mg-Li dual-phase composites are of interest due to their lightweight nature and promising mechanical properties, making them suitable for applications in aerospace, automotive, and structural engineering. Graphene was incorporated into the Mg matrix at varying percentages (0.2, 0.4 and 0.6 wt.%), and the resulting materials were subjected to microstructural, mechanical, and corrosion analyses. Microstructural characterization results reveals that the increase in graphene content results in decrement in grain size of α-Mg and β-Li up to ∼33 and ∼11.5% respectively. Likewise, additions of graphene improvise tensile and yield strength of base matrix up to ∼47 and ∼44% respectively. Strain hardening exponent (n) values of base material decrease from 0.21 to 0.17 with respect to graphene addition which confirms the effect of graphene that acts as effective barrier to slip that decreases the deformation. Corrosion analysis revealed a decrease in corrosion rate and increased pitting resistance with the addition of graphene, indicating improved corrosion resistance. Electrochemical impedance spectroscopy results depict that the composite with 0.4 wt.% graphene exhibits larger semi conducting loop with higher charge transfer resistance ( Rct) value of 128 Ω cm2.

Consequences of repeated hyperbaric hydrogen exposures on mechanical properties and microstructure of polyamide 11

The objective was to evaluate the impact of repeated exposure to hyperbaric hydrogen (90 MPa; 30 °C) and pressure release on the microstructure and mechanical behavior of PA11. Samples were analyzed after 1, 2, 5 and 10 cycles, by SAXS, WAXS, DMA, DSC, and a series of mechanical tests with variable triaxiality ratio. The most visible change in the residual state after desorption was a stiffening of the amorphous phase. It mainly originated from the first cycle, especially the first pressurization. The crystalline phase was slightly affected and no evidence of nano-voiding was brought in the residual state up to 10 cycles. Similar analyses were conducted during the first cycle's desorption transient. They showed a reversible plasticizing effect and a trend of nano-voiding vanishing after desorption but might promote damage upon further triaxial loading.

The effect of various Sn and Ca equal proportional addition on the microstructure, mechanical behavior and corrosion performance of Mg alloys

In the present study, the effects of various Sn and Ca equal proportional addition (0.3:0.1, 0.6:0.2, 1.2:0.4, wt%) on the microstructure, mechanical properties and corrosion behavior of Mg-Sn-Ca alloys were systematically investigated. With the increase of Sn and Ca content, microstructure uniformity of the Mg-Sn-Ca alloy was improved, the average grain size was refined (from 34.4 μm to 21.62 μm, 13.47 μm), and more CaMgSn phases were generated (from 0.39 % to 1.64 %, 4.53 %). With increasing Sn and Ca content, the tensile yield strength (TYS) and ultimate tensile strength (UTS) of Mg-Sn-Ca alloys were gradually increased (TYS: from 91.8 MPa to 98.24 and 125.05 MPa; UTS: from 187.48 MPa to 190.73 and 214.58 MPa), mainly due to the contribution of grain refinement. The electrochemical tests revealed that the corrosion resistance of the Mg-Sn-Ca alloy initially decreases and then increases with the increase of Sn and Ca contents. The hydrogen evolution volume of Mg-0.3Sn-0.1Ca alloy was 41.91 mL cm−2, and the corrosion current density was −1.54 × 10−3 A/cm2. As for Mg-0.6Sn-0.2Ca alloy, deteriorated corrosion resistance compared to the Mg-0.3Sn-0.1Ca alloy was mainly ascribed to the micro-galvanic corrosion between the CaMgSn phase and Mg-matrix. The Mg-1.2Sn-0.4Ca alloy had the best corrosion resistance, with the lowest hydrogen evolution volume of 34.09 mL cm−2 and a minimum current density of −1.15×10−3 mA cm−2, its high corrosion resistance could be attributed to the grain refinement and homogenous distributed CaMgSn phase and more generated Ca(OH)2 product film with dense-structure.

Investigation on the microstructural evolution and corrosion behaviors of Zn-microalloyed Al-Cu-Li alloys

Zn microalloying made great contributions to microstructures evolution and performances enhancement. The effects of various contents of Zn on the precipitate microstructure, tensile property and corrosion behavior of Al-3.2Cu-1.5Li alloys with medium Cu/Li mass ratio were examined by tensile testing and corrosion measurement. Experimental results demonstrated that the tensile strength of the Zn microalloyed samples dropped slightly as the Zn content increased due to the number density of precipitates with minor size variation showed a downward trend within the grains. Corrosion testing revealed that the corrosion type of Zn microalloyed samples was primarily localized intragranular corrosion, slight intergranular corrosion and local pitting corrosion was also partially involved. The emergence of Zn element in grain boundary (GB) coarse (T1) phases and the suppressed precipitation of intragranular phases in the alloys with higher content Zn were found to reduce corrosion sensitivity with the increase of Zn content, which was ascribed to the decreased potential difference between the GB and adjacent matrix, and between the GB precipitates and precipitation free zone (PFZ).

An Overview on Additive Manufacturing of Duplex Stainless Steels: Microstructure, Mechanical Properties, Corrosion Resistance, Postheat Treatment, and Future Perspectives

Additive manufacturing (AM) is a cutting‐edge technique for constructing intricate components with unique microstructural features and strength comparable to wrought alloys. Due to their exceptional corrosion resistance and mechanical properties, duplex stainless steels (DSS) are used in a wide range of critical applications. Over the past several years, a substantial body of research has been conducted on the AM of DSS. In‐depth knowledge is required to understand the complete benefits of the AM process. This review overviews the AM‐processed DSS parts based on process‐specific microstructural changes, mechanical behavior, electrochemical performance, and postheat treatment processes based on the classifications of directed energy deposition and powder bed fusion AM techniques along with future perspectives. Major challenges in AM of DSS are optimizing the austenite–ferrite fractions and controlling the formations of deleterious phases. This review will be extensively useful to researchers and industries working in the AM of DSS.

Study on the Effect of Pressure on the Microstructure, Mechanical Properties, and Impact Wear Behavior of Mn-Cr-Ni-Mo Alloyed Steel Fabricated by Squeeze Casting

ZG25MnCrNiMo steel samples were prepared by squeeze casting under pressure ranging from 0 to 150 MPa. The effects of pressure on the microstructure, low-temperature toughness, hardness, and impact wear performance of the prepared steels were experimentally investigated. The experimental results indicated that the samples fabricated under pressure exhibited finer grains and a significant ferrite content compared to those produced without pressure. Furthermore, the secondary dendrite arm spacing of the sample produced at 150 MPa decreased by 45.3%, and the ferrite content increased by 39.1% in comparison to the unpressurized sample. The low-temperature impact toughness of the steel at −40 °C initially increased and then decreased as the pressure varied from 0 MPa to 150 MPa. And the toughness achieved an optimal value at a pressure of 30 MPa, which was 65.4% greater than that of gravity casting (0 MPa), while the hardness decreased by only 6.17%. With a further increase in pressure, the impact work decreased linearly while the hardness increased slightly. Impact fracture analysis revealed that the fracture of the steel produced without pressure exhibited a quasi-cleavage morphology. The samples prepared by squeeze casting under 30 MPa still exhibited a large number of fine dimples even at −40 °C, indicative of ductile fracture. In addition, the impact wear performance of the steels displayed a trend of initially decreasing and subsequently increasing across the pressure range of 0–150 MPa. The wear resistance of samples prepared without pressure and at 30 MPa was superior to that at 60 MPa, and the wear resistance deteriorated when the pressure increased to 60 MPa, after which it exhibited an upward trend as the pressure continued to rise. The wear mechanisms of the samples predominantly consisted of impact wear, adhesive wear, and minimal abrasive wear, along with notable occurrences of plastic removal, furrows, and spalling.

Study on the room temperature compression deformation mechanism and microstructural evolution of Mg-Gd-Y-Zr alloy

This study explores the dynamic impact deformation mechanisms of Mg-Gd-Y-Zr alloys, specifically focusing on the influence of varying Gd content. Using metallographic observation, SEM, EDS, XRD, EBSD, and TEM, along with hardness and room-temperature compression tests, the research investigates the effects of Gd content on the microstructure, mechanical properties, and deformation behaviors of as-cast Mg-(x)Gd-3Y-0.5Zr (x = 6.5/7.5/8.5) alloys.The results show that increasing Gd content reduces grain size and increases the volume fraction of the non-equilibrium eutectic phase Mg24(Gd,Y)5, though with smaller phase dimensions. These alloys exhibit excellent compressive properties at room temperature, with the highest compression deformation rate of 27.8 % observed at 6.5 % Gd and the maximum compressive strength of 401 MPa recorded at 8.5 % Gd, surpassing some high-Gd-content cast and extruded alloys.At lower Gd content, basal slip and tensile twinning are the primary deformation mechanisms. As Gd content increases, these mechanisms evolve to include prismatic slip and compressive twinning. The fracture mode transitions from predominantly ductile to a combination of ductile and brittle features, with an increase in brittle cleavage at higher Gd levels.

Effect of cold work level on the crack propagation behaviour of 316LN stainless steel in high-temperature pressurized water

We investigated the microstructure, mechanical properties, and stress corrosion cracking (SCC) propagation behaviour of 316LN austenitic stainless steel with various cold work (CW) levels. CW increased the crack growth rate of 316LN. The stress corrosion crack growth rate (SCCGR) for 316LN with 5% CW was approximately 6.52% higher than that of the solution-annealed state; 10%, 20%, and 30% CW resulted in 1.20, 3.18, and 6.10 times higher SCCGRs, respectively. A larger residual strain and proliferation of slip bands via cold deformation augmented the SCCGR. The SCC propagation mechanism of 316LN changed with increasing CW levels owing to slip bands.

Tailoring the Crystalline structures and mechanical properties of IN718 alloy repaired by wire-fed electron beam directed energy deposition through a custom-designed heat treatment process

Wire-fed electron beam directed energy deposition (EB-DED) is a cost-effective technique for repairing damaged metal components. However, a large number of Laves phases precipitated in the deposited zone impair the mechanical properties of the repaired IN718 alloy parts. This study investigated the microstructural evolution and mechanical properties of IN718 alloy repaired by EB-DED, emphasizing a custom-designed heat treatment combining homogenization and double aging to enhance deformation coordination. Two homogenization durations, 15 min (HA15) and 60 min (HA60), were tested. The research utilized advanced characterization techniques, including scanning electron microscopy, electron backscatter diffraction, transmission electron microscopy, and digital image correlation, to analyze microstructural evolution and deformation behavior. These findings revealed that, in the as-repaired condition, the deposited zone exhibited columnar grains with inter-dendritic Laves phase, while the substrate zone contained equiaxed grains and δ phase precipitation at the grain boundaries. Post-HA treatment led to the dissolution of Laves and δ phases and the precipitation of γ'/γ'' strengthening phases. Furthermore, the HA60-repaired sample showed recrystallization in the deposited zone, markedly improving plastic deformation uniformity. Tensile tests exhibited that the HA samples achieved yield strength and elongation matching wrought standards, with ultimate tensile strength reaching 95 % of wrought values. This work presents a novel method for achieving high-quality repair in IN718 alloy, advancing the potential for broader industrial applications.

Interfacial evolution in Cr/Mo-coated Zr alloys near the Mo-Zr eutectoid temperature

This study investigates the interfacial evolution of Cr/Mo-coated Zr alloys near the Mo-Zr eutectoid temperature, from the viewpoints of microstructure and chemical composition and with the joint application of XRD, TEM and EDS analyses. The experimental findings highlight significant changes in microstructure and diffusion behavior associated with the Mo-Zr eutectoid reaction. In the as-fabricated specimen, it is noted that introducing a Mo-intermediate layer results in the formation of an amorphous Cr layer at the Cr/Mo interface. In the case of the annealing temperature below the Mo-Zr eutectoid reaction, Mo interlayer effectively impedes the diffusion between Cr and Zr, thereby suppressing the formation of intermetallic compounds. However, the diffusion barrier function of Mo interlayer deteriorates when the temperature exceeds the eutectoid point, with the presence of four distinct diffusion zones, including α-Zr, β-Zr, the intermetallic compound Zr(Mo,Cr,Fe)₂, and the Mo layer containing fine Zr(Mo,Cr,Fe)2 particles. These findings underscore the critical role of Mo-interlayer in influencing the structural stability and intermetallic compound formation in Cr/Mo-coated Zr alloys, not only at the temperature regime around the eutectic reaction, but also at the temperature regime around the eutectoid reaction, which is of great necessity for the practical applications of accident tolerant fuel cladding under high temperature environment.

Supportless lattice structure of 316L stainless steel fabricated by material extrusion additive manufacturing: Effect of relative density on physical, microstructural and mechanical behaviour

Studies on lattice structures fabricated by material extrusion additive manufacturing for metal, leveraging the advantages of additive manufacturing, are limited. In this work, by varying the number of unit cells, the effects of density on the macro- and microstructure, and on the physical and mechanical properties of 316L stainless steel fabricated by our in-house developed 316L metal-filled filament were investigated. Utilising our in-house developed 316L metal-filled filament, supportless octet-truss lattice specimens with relative density ranging from 16 % to 55 % were successfully fabricated. The relative density increased with the number of unit cells, compressive strength, Young's modulus, and energy absorption, consistent with the Gibson-Ashby's porous material model. Stretch-dominated behaviour was observed in the 2 × 2 × 2 and 3 × 3 × 3 unit cells, while the 4 × 4 × 4 and 5 × 5 × 5 units exhibited bending-dominated behaviour. The deformation behaviour was well simulated by finite element analysis with the core-shell structure. The successful fabrication of supportless lattice structures highlights their potential for manufacturing lightweight materials and their future application.

Stress-strain curve estimation from micropillar compression with transverse contraction effect

The Focused Ion Beam (FIB) technique and the associated compression testing capabilities provide versatile access to understanding the microstructural behaviour of materials. Among many objectives, determining the stress-strain relationship from experimental or numerical force-displacement data remains a fundamental challenge. However, for micropillers under compression, the inside deformation constraint is complex like in components and the transformation of a measured force-displacement curve into an accurate uniaxial stress-strain curve is not straightforward. In this context, in a previous numerical based analysis for perfect volume constancy or incompressibility the determination of reliable and accurate stress-strain curves from nonlinear load-deformation curves of micropillers was already verified. In the case of transverse contractions, however, numerical simulations of micropillers provide unexpected force-displacement behaviour, i.e. their force-displacement curves are almost superimposing and are very close to the force-displacements for incompressibility. This effect implies, that transverse contraction would have no contributions in micropillar compression. In contrast, independent simulations using a single finite element accurately explore the true uniaxial stress-strain behaviour for the whole range of transverse contractions. These are considered as the reference behaviour and are also treated by an analytical expression. With the presented new stress-strain estimation approach, including transverse contraction, any force-displacement curve from a micropillar under compression can be stepwise corrected. The first step of the new stress-strain curve estimation method, including transverse contraction, is carried out in the same way as in the preceding analysis for incompressibility, followed by further steps to obtain the final true stress-strain curve. Although the presented numerical analysis is exemplarily performed for the behaviour of fused silica, but the stress-strain approach is in the same manner generally applicable for a material behaviour with other stress-strain curves. The assumption behind is isotropic and nonlinear material behaviour.