Plastic Toughness Research Articles

Study on the effect of rare earth elements La, Ce, Y and Sc doping on the mechanical properties of aluminum–lithium alloys

In this paper, the effects of rare earth elements La, Ce, Sc, and Y on the bond strength of the aluminum–lithium alloy δ’ (Al3Li)/Al interface are investigated using first-principles calculations. The results show that the interfacial energy decreases after substitutional doping of Al atoms on both sides of the interface by rare earth elements, respectively, with values ranging from −2.0664 eV/Å2 to −1.9720 eV/Å2. The interfacial energy decreased by 2.0841 eV/Å2 and 2.0709 eV/Å2 when Ce and Sc elements replaced Al in the matrix, respectively. Uniaxial interfacial tensile simulations of Al/ Al3Li showed that the strain elongation of the material increased from 24 % to 42 % for the pure interface after doping with Sc elements at the interface. The same tensile tests yielded a maximum elongation at break of 3.25 % for Al-Li alloy after artificial aging at 0.6 % Sc content. Observation of the microstructure of the materials before and after rare earth doping using TEM reveals that the content of nanoscale Al3(Sc, Li) composite particles increases with the increase of Sc content after artificial aging at 185 °C for 10 h. Moreover, the presence of Al3Sc refines the precipitated phase of the alloy and improves the plastic toughness of the material.

Dispersion, solid solution, and covalent bond coupled to strengthen K4169/TiAl composite brazed joints: First-principles and experimental perspective

Ni/TiAl composite brazed joints could significantly reduce the aircraft's weight. However, low interfacial adhesion, coarse and brittle-hard intermetallic compounds (IMCs) seriously limited the application of Ni/TiAl composite joints in the next generation of aerospace applications. So enhanced K4169/TiAl composite joints were investigated by vacuum brazed with (Ni53.33Cr20B16.67Si10/Zr25Ti18.75Ta12.5Ni25Cu18.75) composite filler metal (CFM) designed based on cluster-plus-glue-atom model. The shear strength of the joint reached 485 MPa, comparable to the 491 MPa of TiAl substrate. The flat and brittle-hard diffusion reaction layer between Zones I and II was eliminated, simultaneously generating CrB4 dispersion strengthening due to the CFM developed with the interfacial solid-liquid space-time hysteresis effect. In Zones II and III, IMCs all transformed into Niss(Cr,Fe)[0–88], Niss(Ti, Al)[004], and Niss(Zr,Si)[11–2] of circular and oval shapes through isothermal solidification. Meanwhile, the residual stresses and hardness were distributed in reticulated cladding characteristics. Thereby, lattice distortion led to solid solution strengthening and increased plastic toughness through crack termination and bridging mechanisms, which inhibited dislocations from plugging and crack propagation. Various interfaces in Zone Ⅳ were regulated into semi- and coherent interfaces. Ni3(Ti,Al)/(Ni,Ti,Al) and (Ni,Ti,Al)/AlNi2Ti were composed of higher interfacial bonding energy (2.771 J/m2, 2.547 J/m2) and Ni-Ni covalent bonds. Interfacial covalent bonding and large interfacial bonding energy coupling strengthened Zone IV. Consequently, cracks initiated at the (Ni,Ti,Al)[013]/Ti3Al[010] and expanded rapidly into TiAl substrate. Therefore, applying this method to design CFMs and regulate the phase, grain morphology, and interface's fine structure could provide new pathways for dissimilar hard-to-join metals.

First Principles Calculation of the Effect of Cu Doping on the Mechanical and Thermodynamic Properties of Au-2.0Ni Solder.

To meet the demands for high-temperature performance and lightweight materials in aerospace engineering, the Au-Ni solder is often utilized for joining dissimilar materials, such as Ti3Al-based alloys and Ni-based high-temperature alloys. However, the interaction between Ti and Ni can lead to the formation of brittle phases, like Ti2Ni, TiNi, and TiNi3, which diminish the mechanical properties of the joint and increase the risk of crack formation during the welding process. Cu doping has been shown to enhance the mechanical properties and high-temperature stability of the Au-Ni brazed joint's central area. Due to the difficulty in accurately controlling the solid solution content of Cu in the Au-Ni alloy, along with the high cost of Au, traditional experimental trial-and-error methods are insufficient for the development of Au-based solders. In this study, first principles calculations based on density functional theory were employed to analyze the effect of Cu content on the stability of the Au-2.0Ni-xCu (x = 0, 0.25, 0.5, 0.75, 1.0, 1.25 wt%) alloy phase structure. The thermal properties of the alloy were determined using Gibbs software fitting. The results indicate that the Au-2.0Ni-0.25Cu alloy exhibits the highest plastic toughness (B/G = 5.601, ν = 0.416, Cauchy pressure = 73.676 GPa) and a hardness of 1.17 GPa, which is 80% higher than that of Au-2.0Ni. This alloy balances excellent strength and plastic toughness, meeting the mechanical performance requirements of brazed joints. The constant pressure specific heat capacity (Cp) of the Au-2.0Ni-xCu alloy is higher than that of Au-2.0Ni and increases with Cu content. At 1000 K, the Cp of the Au-2.0Ni-0.25Cu alloy is 35.606 J·mol-1·K-1, which is 5.88% higher than that of Au-2.0Ni. The higher Cp contributes to enhanced high-temperature stability. Moreover, the linear expansion coefficient (CTE) of the Au-2.0Ni-0.25Cu alloy at 1000 K is 8.76 × 10-5·K-1, only 0.68% higher than Au-2.0Ni. The lower CTE helps to reduce the risk of solder damage caused by thermal stress. Therefore, the Au-2.0Ni-0.25Cu alloy is more suitable for brazing applications in high-temperature environments due to its excellent mechanical properties and thermal stability. This study provides a theoretical basis for the performance optimization and engineering application of the Au-2.0Ni-xCu alloy as a gold-based solder.

A new Ti–Al–Cr–Mo–Zr titanium alloy welding wire: Stability, microstructure and mechanical properties

In order to improve the plasticity of titanium alloy welded joints, relevant scholars currently focus primarily on studying the mechanism of action of alloying elements Mo and V, such as reducing the phase transition temperature of the welded seam and ensuring a certain amount of β phase residue in the welded seam. In addition to improving the stability and strengthening ability of titanium alloy welded joint, it can also maintain a certain degree of plasticity of the welded joint. However, the poor impact toughness is still the key problem that restricts its long-term stable service in the harsh environment. Our work designed and developed a new Ti–Al–Cr–Mo–Zr solid welding wire, with the synergistic effect of Al, Cr, Mo and Zr, the welded seam microstructure and grain can be refined while ensuring the enough stiffness of the welding wire and its flatness during wire feeding into the designated working area. It ensures good wetting and spreading flow performance of the liquid molten pool metal in the welding process, so better welded seam formation can be obtained. The relative contents of α′ martensite and β phase in the welded seam are 76.79% and 23.21%, respectively. The residual β phase is interspersed between the α′ martensite of the slats. The β phase provides a path for the plastic deformation of the welded joint, making it easier for dislocation slip to pass the β/α′ interface. At the same time, more dislocation slip channels and a small number of fine twins can be found in the interior of α′ martensite, which can ensure the strength while taking into account the toughness. After testing, it is found that the average tensile strength of welded joints is 901 MPa, which is close to 95% of the base metal (BM), the average post-fracture elongation of welded joints is 21%, and the impact toughness value at room temperature is distributed between 25 J and 33 J, which meets the requirements of the synergistic effect of welded joint strength and plastic toughness. It is suitable for long-term stable service of Ti64 titanium alloy welding structure under harsh working conditions.

Influence of WC particle size and morphology on the performance of NiCu-based composite coatings deposited by laser direct energy deposition

NiCu alloys are commonly utilized due to their outstanding plasticity, toughness, corrosion resistance, and thermal conductivity. Nevertheless, their limited hardness and wear resistance have hindered their further development. In this study, 24CrNiMo alloy brake disc was coated with NiCu-based composite coatings containing different sizes and shapes of tungsten carbide, in order to investigate the effects of tungsten carbide particle characteristics on the microstructure, microhardness and wear resistance of Nickel‑copper composite coating. The results show that the microstructure of the coatings was minimally affected by the size and morphology of the WC particles, while non-spherical WC particles exhibited superior uniformity within the coatings. In terms of microhardness, smaller WC particles demonstrated a more consistent distribution. The ball-disk wear tests revealed that coatings with larger WC particles displayed better wear resistance in sizes, while those with non-spherical WC particles exhibited excellent resistance to wear in morphologies. Additionally, in abrasive wear tests, composite coatings containing spherical WC particles demonstrated superior wear resistance compared to those containing non-spherical WC particles. The diverse wear resistance observed in different wear experiments among the various WC coatings can be attributed primarily to differences in the distribution and preparation methods of the WC particles. Consequently, these findings hold significant promise for the practical application of NiCu-based composite coatings in industry.

Microstructure and mechanical property of CoCrFeNiAlxMn(1-x) dual-phase gradient high-entropy alloy coatings prepared by laser cladding

High-entropy alloy (HEAs), known for their balanced strength and ductility, are promising candidates for impact wear-resistant applications. In this study, CoCrFeNiAlxMn(1-x)(x = 0, 0.2, 0.8, 1.0) dual-phase gradient coatings with a layered structure were prepared using laser cladding technology to explore the microstructure evolution, tensile properties and fracture mechanism of gradient coating. As the Al content increased, the single-phase face-centered cubic (FCC) HEA coatings transitioned to dual-phase of FCC+ body-centered cubic (BCC) solid-solution, and finally to a single BCC phase. The remarkable improvement of microhardness is attributed to the dominance of the BCC phase and the impeding effect of the second phase particles on dislocation movement. The gradient coating exhibited a gradual change in internal element composition, microhardness, and structure along the depth direction, with the highest hardness value reaching 530 HV. Compared with the minimum tensile strength (69.03 MPa) and the minimum elongation (0.14 %) of single-layer coating, the gradient coatings exhibited a balance of high tensile strength and good plastic toughness, with a tensile strength of 597 MPa and an elongation of 4.08 %. Fracture analysis indicated a transition from ductile to brittle fracture in single-layer coatings as x values increased. The double-layer and four-layer gradient coatings displayed a mixed mode of brittle and plastic fracture. The study provides valuable insights into the design and fabrication of HEA gradient coatings, offering a novel approach to enhance the durability and performance of laser-clad coatings for various applications.

Study on depth weakening of reinforced concrete piles cutting by abrasive waterjets under submerged conditions

In order to improve the efficiency and safety of shield machine cutting reinforced concrete piles, abrasive waterjets (AWJs) assisted mechanical combined cutting technology is considered a feasible solution. However, the water-rich flooding environment will cause the cutting performance of AWJs to weaken, which brings great challenges to the application of this technology. In order to analyze the influence of submerged conditions on the cutting performance of AWJs, the cross-sectional morphology of reinforced concrete piles cut by AWJs is explored using indoor experiments, and the weakening law of pile foundation cutting depth is revealed. The results show that the submerged environment greatly weakens the cutting ability, and the average cutting depth is reduced by about 20.0%. Rebar materials are more difficult to remove due to their high strength and strong plastic toughness, which is the root reason of the difficulty in cutting off piles. As the cutting times increases, the cutting depth discount factor initially decreases rapidly before stabilizing. At 380 MPa, the cutting depth discount factor remains stable at 0.49, while at 280 MPa, it stabilizes at 0.62. The findings presented in this paper can provide guidance and suggestions on waterjet parameters for AWJs assisted shield machine pile breaking. HIGHLIGHTS The cross-sectional change rules of reinforced concrete pile foundation cut by abrasive waterjets is clarified. The depth weakening effect of pile foundations cut by abrasive waterjets under submerged conditions is revealed. The cutting depth discount factor for rebars is established.

Effect of Cyclic Ice Plug Deformation on Microstructure and Mechanical Behaviors of Nuclear-Grade Low-Carbon Tubular Steel.

This study subjected nuclear-grade 20# pipeline steel to cyclic freeze-thaw ice plugging tests, simulating the plastic deformation experienced by pipes during ice plug removal procedures. Subsequently, the dislocation morphology and mechanical properties of the specimens post cyclic ice plugging were examined. The cyclic ice plugging process led to an increase in the dislocation density within the specimens. After 20 and 40 cycles of ice plugging, the internal dislocation structures evolved from individual dislocation lines and dislocation tangles to high-density dislocation walls and dislocation cells. These high-density dislocation walls and cells hindered dislocation motion, giving rise to strain hardening phenomena, thereby resulting in increased strength and hardness of the specimens with an increasing number of ice plugging cycles. In addition, a large stress field was generated around the dislocation buildup, which reduced the pipe material's plastic toughness. The findings elucidate the effects of cyclic ice plugging on the microstructure and properties of nuclear-grade 20# pipeline steel, aiming to provide a theoretical basis for the safe and stable application of ice plugging technology in nuclear piping systems.

Effect of energy distribution on laser cleaning quality of 30Cr3 ultra-high strength steel

30Cr3 is a novel ultra-high strength steel (UHSS) with excellent strength and plastic toughness, which has been mainly used in aerospace shells and stressed parts. Currently, there is still a lack of systematic research and comprehensive evaluation on the laser cleaning of this particular material. In this study, a nanosecond pulsed laser was employed for the cleaning process. First, the energy distribution model was derived, the influence of the spatial and temporal distribution of laser energy on the cleaning quality was discussed, and the cleaning experiment was conducted. The results showed that a laser energy density of 15 J/cm2, combined with the beam overlap rate 52% in the x-direction and 61% in the y-direction, can effectively remove the oxide layer and thoroughly expose the natural metal matrix. Then, under the optimum parameters, the oxygen content decreased from 22.3% to 3.4%, the Fe content increased from 54.5 to 83.4%, the Fe3+ peak disappeared in the X-ray photoelectron spectroscopy (XPS), a remelted layer of only 1 μm was observed. Last, the roughness was slightly reduced from 3.573 μm to 2.985 μm, the hardness was restored to the original hardness level of the substrate (∼260 HV), and the electron back scatter diffraction (EBSD) showed that the structure hardly changed after cleaning, the grain size was comparable to that of the matrix. These findings indicated that laser cleaning can effectively remove the oxide layer of 30Cr3 UHSS without damaging the properties of the base material, which has promising application in the cleaning of UHSS.

Multi-pass butt welding of thick TA5 titanium-alloy plates by MIG: Microstructure and properties

A 35 mm-thick TA5 titanium alloy plate was successfully joined by metal inert-gas (MIG) welding. The welded joints were analyzed in a more integrated and comprehensive manner. The joint microstructure was analyzed by OM, SEM, EBSD, and TEM. Mechanical properties were analyzed by tensile, impact, and microhardness tests. The corrosion resistance of the joints was determined by FeCl3 immersion corrosion. Experimental results showed that the mechanical properties and corrosion resistance of the fusion zone (FZ) were poorer than those of the base material (BM). The mechanical properties of the welded joints were related to the acicular grains in the FZ. The 260 A joints showed relatively good mechanical properties. With increased welding current, the proportion and size of the acicular grains increased, and the strength of the joint increased, but the plastic toughness decreased. When the welding current was too small, anisotropy occurred in the FZmiddle, which affected the mechanical properties of the joints. The corrosion resistance of the FZ was lower than that of the BM, and the corrosion resistance of the three groups of joints decreased in the order 300 A > 230 A > 260 A.The welding current affected the corrosion resistance of the FZ by influencing the grain size of the FZ, the frequency of the HAGBs, and the GND density.

Superior shear strength subject to the regulation of plastic toughness in K4169 alloy/TiAl intermetallic joints vacuum brazed with gradient composite amorphous filler metals

The concept of gradient composite amorphous filler metal (GAFM) was utilized to solve the scientific problem of low strength caused by excessive Ti-containing brittle-hard intermetallic compounds (IMCs) generated in Ni/TiAl brazed joints through interfacial hysteresis reaction. Based on the cluster-plus-glue-atom model, the GAFMs (Zr25Ti21.25Ni25Cu18.75/Zr31.25-XVXCu50Ni18.75) were designed for vacuum brazing of K4169 alloy with TiAl intermetallic. And the shear strength of the joint brazed with (Ti21.25Zr25Ni25Cu18.75/Zr25V6.25Cu50Ni18.75) GAFM reached 344 MPa. The relation between grain boundary, solution, dislocation and strength was established. The cracks initiated from the (Ti,Zr)(Ni,Cu)+(Cr,Fe,Ni) brittle-hard phase and the plastic-tough phase (Zr,Ti)(Ni,Cu) interface in Zone II with (Ti21.25Zr25Ni25Cu18.75/Zr31.25-XVXCu50Ni18.75) GAFMs at 1040 °C/10 min, and then extended to the (Ti,Zr)(Al,Ni,Cu)3[010]/(Ti,Zr)(Ni,Cu,Al)3[0-10] non-coherent interface. To regulate the distribution of the plastic-tough phase in Zone II, raising brazing temperature could promote the dissolution of Zone I into Zone II. The addition of V to the GAFMs, εG and εα mismatches increased and prompted the Niss[00-1]+TiAl[010] phase, (Cr,Fe,Ni)ss[00-1] phase with a-value lattice distortion of 21.38%, (Ni,Cr,Fe) and ZrNi3[0-2-1] grains refinement in Zone II, where KIC*/KIC>1, the brazed joint strengthening effect was enhanced. The columnar grains were transformed into grains with reticulated cladding characteristics. The percentage of substructured grains increased from 46.6% to 56.3%, and the percentage of HAGBs rose to 84.7%, which inhibited dislocation migration. Therefore, the ZrNi3 plastic-tough phase, prohibited the expansion of the major crack generated from the (Cr,Fe,Ni) brittle-hard phase. The major crack extended to the Ti(Ni,Cu,Al)3 [1–10]/Ti(Al,Cu,Ni)2[0-10] semi-coherent interface and then to the TiAl substrate, resulting in a zigzag crack expansion.

Electrospun nanofiber interleaving through double infusion method to induce pseudo‐ductile damage resistance response in carbon/epoxy composites

AbstractCarbon composites are susceptible to invisible damage development such as matrix cracking, fiber kinking, and interfacial debonding upon external transverse loading. These incipient damages may interact to evolve into life‐limiting delamination propagating both in in‐plane and transverse directions. This study addressed that by interleaving carbon/epoxy composites with electrospun nylon 6 nanofibers adopting a double infusion method. Damage resistance results showed that the optimum nanofiber areal weight (17.35 g/m2) offered a 27% improvement in specific total toughness. The emergence of pseudo‐ductility substantially enhanced the plastic toughness (46.15%) of interleaved composites. The load required for initial matrix cracking was 65.49% higher, and number of matrix cracking events was suppressed by 84.11% at the optimum areal weight of interleave. Fractography revealed frequent interlaminar crossings and delamination crack bridging as two major toughness mechanisms. Both the external damage area and delaminated area increased with increment in nanofiber areal weight.Highlights Electrospun nanofibre interleaved carbon/epoxy composites were fabricated through a double infusion method to characterize damage resistance. Acoustic data of matrix cracking was rationalized to show the effectiveness of nanofiber interleaves in suppressing this damage type. Microstructural factors and mechanisms contributing to the improved toughness of optimally interleaved composites were identified. External damage/delaminated areas of interleaved composites were correlated with nanofiber areal weights.

Microstructure and properties of Ni-based VC and TiVC2 composite coatings fabricated in situ by laser direct deposition

Ni-based VC and TiVC2 composite coatings were prepared on the surface of worn brake discs by laser direct deposition, and the influence mechanism of trace TiC addition on the microstructure and performance of the coating was investigated. The microstructure of the coatings was analyzed by XRD, SEM, EDS, and TEM, which revealed the evolution mechanism of the microstructure during the laser deposition process. The friction wear performance was tested on friction wear equipment. The results showed that VC0.88 was formed by the in-situ reaction of C and V under the action of the laser, which presents dendritic morphology. After the addition of TiC particles, TiVC2 was further synthesized along the TiC particles in addition to dispersed VC0.88 in the coating. It can be seen that the addition of trace TiC particles inhibited the formation of VC0.88 dendrites and enhanced the plastic toughness of the coating. HRTEM calibration proved the existence of TiVC2 and Ni, and there was no obvious orientation relationship between the interface. The friction coefficients of Ni-based VC and Ni-based TiVC2 coatings with Al2O3 balls were 0.59 and 0.51 at room temperature, respectively. After 1.5 h of high-temperature wear at 300 °C and 600 °C, the distribution of wear marks shows a groove and high-temperature fatigue appearance. The TiC-doped coating has better wear properties than the base material and the original coating is expected to meet the requirements for brake discs.

Numerical simulation of the mold filling process of the brake lever for an electric multiple unit

The brake lever for an electric multiple unit (EMU) of a train is an important supporting component that directly affects the usability and safety of EMU. In this study, the mold filling, solidification, and shrinkage processes of the brake lever of the EMU were simulated using Anycasting software, and the distributions of the mold filling speed, mold filling temperature, and shrinkage defects were analyzed. The results show that the brake lever for the EMU exhibits casting defects such as shrinkage porosity and shrinkage cavities. To eliminate these casting defects, a chilled-iron process was developed; however, the appearance of cementite increased the brittleness of the castings, which deteriorated their strength and plastic toughness. Hence, a snap-chilling sheet process was designed to fabricate the brake lever for the EMU, and a numerical simulation of the process was performed using the Anycasting software. The shrinkage defects of the castings were effectively eliminated; simultaneously, the cementite disappeared, and the microstructure of the thick parts of the brake lever showed no obvious changes. The prepared brake lever satisfied the requirements of the EMU.

Effect of cooling rate on microstructure and crystallographic characters for Fe3O4 seam-free on J82B steel from 650 ​°C

Surface quality and tensile strength are required for the deep processing yield of high-carbon steel wires, particularly those with a cumulative reduction rate above 60 ​%. A systematic investigation was conducted to discern the influence mechanism of cooling rate on microstructure and crystallographic characteristics for the matrix from 650 ​°C. The results show that the microstructure of the sample cooled at 1.5 ​°C/s consists of a single pearlite, and the grain orientation is mainly the easy sliding crystal plane {101}. The retained austenite/martensite microstructure appears and grows with the cooling rate increasing to 4.5 and 7.5 ​°C/s. The grain orientation shifts from an easy slip {101} plane orientation to hard slip {001} and {111} plane orientations. The number of high-angle grain boundaries that inhibit crack expansion decreased. In addition, the number of twin boundaries in the austenite/martensite grains increased. An increase in the cooling rate increased the material hardness and decreased the plastic toughness. Therefore, the cooling rate of 1.5 ​°C/s from 650 ​°C might concurrently yield the optimal surface quality and the microstructure of the matrix during steel production.

Temperature dependence of surface microstructure of 316 L stainless steel exposed to low-energy hydrogen ion irradiation

The austenitic 316 L stainless steel (316LSS) is an important metal for nuclear installations due to its high strength, good plastic toughness and excellent corrosion resistance, and is commonly used as the plasma-facing and structural material. In this study, 316LSS samples are irradiated with low-energy hydrogen ions (35 eV) at the temperature of 400–1300 K to investigate the surface microstructure evolution. The experimental results show that the surface of 316LSS samples remains relatively smooth at 400 K and 600 K after irradiation. Significant surface roughening including spherical protrusions is formed on the surface at 800 K and 1100 K, and step-like streaks are observed at 1300 K. However, no drastic change in the surface morphology is observed in the separate annealing experiments at 800–1300 K. It has been shown that hydrogen ion irradiation mainly causes the surface microstructure evolution of 316LSS samples. After hydrogen plasma exposure, a large number of adatoms are first formed on the surface of 316LSS because of bubble growth. The adatoms then preferentially reach the defects by diffusion at certain temperatures, and aggregate into spherical protrusions with low surface energy. The qualitative simulation results show that the irradiation temperature affects the diffusion and aggregation of adatoms on the surface, and the radius of the spherical protrusions gradually increases due to the decrease of the surface binding energy and the increase of the irradiation fluence.

First-principles calculation of phase stability and elastic properties of CrxMoNbTiV refractory high-entropy alloys

Compared with traditional alloys, high-entropy alloys (HEAs) have been widely studied because of their unique phase formation rules and excellent physical properties. This work used the first-principle calculation method to study the effect of Cr content on the phase formation, stability, and mechanical properties of MoNbTiV refractory HEAs (RHEAs). The structural model of CrxMoNbTiV (x = 0.00, 0.25, 0.50, …, 2.00) RHEAs was constructed by the virtual crystal approximation method. The structural model was geometrically optimized using the Cambridge Sequential Total Energy Package code, and the structures’ binding energy, enthalpy of formation, and elastic constants were calculated. The results show that the CrxMoNbTiV RHEAs can form a stable body-centered cubic structure, and the addition of Cr significantly impacts the lattice constant, elastic constant, plastic toughness, and elastic anisotropy of the alloy. At the same time, the three-dimensional surface map of Young’s modulus anisotropy is also drawn.

Study on Effect of Tempering Temperature on Microstructure and Properties of Super Martensitic Stainless Steel Welded Joints

The ultra-martensitic stainless steel ZG06Cr13Ni4Mo, due to its excellent corrosion resistance, good tensile property and excellent weldability, is widely used in many occasions of hydropower, thermal power, and nuclear power, especially as the preferred material for pump impeller. This type of steel has good weldability due to its low carbon content, but the low content of reversed austenite in the weld will lead to poor plastic toughness of the welded joint. The effect of different tempering processes on the microstructure transformation and mechanical properties of welded joints of ultra-martensitic stainless steel was studied. The 20 mm thick test plate was MIG welding and then tempered at 560 °C, 600 °C, and 640 °C for 2 h. The results show that after increasing tempering temperature, the microstructure gradually decreases from the base metal to the weld and gradually transforms from lath martensite to tempered sorbite; When tempering at 600 °C, the microstructure in the weld is the finest, and the size of grain size is 0.274 μm. The highest content of reversed austenite is 9.39%; In the welded joint, compared with the untempered joint, the hardness of the welded joint area decreases after tempering, and the tensile strength first decreases and then increases. The yield strength and elongation gradually increase.

Study on the Strength and Plastic Toughness Control Technology of Electron Beam Welding Joint of Titanium Alloy

Study on the Strength and Plastic Toughness Control Technology of Electron Beam Welding Joint of Titanium Alloy

Study on formability of duplex steel expansion pipe and its threaded joints

The threaded joint of equal well-diameter-expansion pipe is prone to fracture and leakage after expansion forming. The structural integrity and material selection of the expansion pipe threaded joint are the main difficulties. Taking dual-phase steel and other well-diameter expandable casings as the research object, a method combining finite element simulation and experimental verification is used to construct an enhanced constitutive model. Firstly, three kinds of reinforced constitutive models are constructed, and then finite element software is used for simulation, combined with experiments to analyze the axial length of the pipe, pipe wall thickness, thread clearance, material hardness, plastic toughness and microstructure. The results showed that after expansion the top and root of the threaded area of the tube after expansion have greatest change and the residual stress is relatively high. Microhardness and Charpy impact tests were carried out on the pipes before and after expansion to study the changes in hardness and toughness. It can be found that the toughness of the expansion pipe has decreased, and although the wall thickness will be reduced, the strength of the pipe will be significantly increased, which is the effect of work hardening. The topography of the crack surface is nearly identical over the entire range of expansion ratios considered in this study. In addition, the microstructure of the unexpanded and expanded tubes is similar, consisting of ferrite and austenite. This paper provides a theoretical reference for engineering practice.