Plastic Toughness Research Articles

Research Progress on Laser Cladding Alloying and Composite Processing of Steel Materials

Laser cladding technology is a reliable and efficient surface modification technology, which has been widely used in surface alloying and composite processing of steel materials. Firstly, the characteristics of laser cladding technology were introduced, and the effects of process control and the material system on the geometric shape, size, microstructure, and properties of cladding coating were analyzed by summarizing the research results of laser cladding on steel surfaces. The results show that with the increase of laser power, the dilution rate and width of the cladding coating increase, and the grain becomes coarse. Thus, the wear resistance deteriorates. Compared with alloy cladding coating, composite cladding coating exhibits better wear and corrosion resistance, but the plastic toughness is worse than alloy cladding coating. The research progress of surface alloying and composite processing of steel worldwide was analyzed from various aspects. Current results suggest that laser cladding alloying and compounding can enhance the wear resistance and corrosion resistance of steel materials. Based on the summary of the current research results, the development prospect and planning of laser cladding technology in the field of surface alloying and composite processing of steel are further pointed out.

Effect of Secondary-Phase Precipitation on Mechanical Properties and Corrosion Resistance of 00Cr27Ni7Mo5N Hyper-Duplex Stainless Steel during Solution Treatment.

In this work, the effect of secondary-phase precipitation on the microstructure, mechanical properties, and corrosion resistance of 00Cr27Ni7Mo5N hyper-duplex stainless steel (HDSS) during solution treatment was investigated. The results reveal that σ-phase precipitates at the interface between the α and γ phase when the solution treatment temperature is lower than 1070 °C. It is not only brittle, but also prone to create a Cr-depleted zone, which significantly deteriorates the mechanical properties and corrosion resistance. With the increase in the solution treatment temperature, the volume fraction of ferrite gradually increases. The yield strength and tensile strength increase slightly, but the elongation decreases. At the same time, the impact toughness shows a trend of first increasing and then decreasing. When the solution treatment temperature is higher than 1130 °C, Cr2N precipitates in the ferrite. The precipitation of Cr2N causes a decrease in the plastic toughness, but it does not deteriorate the mechanical properties as significantly as the σ phase. However, it can also cause the formation of a Cr-depleted zone that significantly decreases the corrosion resistance. There is no secondary-phase precipitation in the sample after solution treatment at 1100 °C, which shows the best mechanical properties and corrosion resistance.

Role of multiple mid-temperature tempering on mechanical properties and wear behavior of carburized steel under complex service conditions

Tempering is a necessary heat treatment process to ensure that the surface of the carburized material has adequate strength and the core has sufficient toughness. In this work, the carburized layer was tempered several times at medium temperature (400–440 °C) and the effect of tempering temperature, and number of times on microstructure, plastic toughness, and wear properties in complex environments was investigated in detail. The modified layers of the tempered samples were characterized by martensite, carbide, and a small amount of residual austenite. Primarily, the results show that the maximum ultimate tensile strength (UST, 1441 MPa) and elongation (11.4 %) were obtained with 3 times tempering at 400 °C. Simultaneously, the least erosion wear rate (0.61 mg/g) was obtained for 400 °C 3-times tempered specimens. Then, under dry friction conditions, the friction coefficients of the 3-times tempered were inferior to those of the 5-times tempered samples. In the subsurface layer, the 420 °C 3-times tempered samples had the minimum wear rate (1.73 × 10−15 m3N−1 m−1). Nevertheless, the friction coefficient under oil lubrication is dramatically lower compared to the dry friction coefficient. Finally, the medium temperature multiple tempering ensured a well-balance of wear resistance and plastic toughness.

Microstructure evolution and crack propagation mechanism during laser lap welding of Ti6Al4V and DP780 steel with CoCrNi powder

Joining steel and Ti alloys is important for aerospace applications. However, the brittle intermetallic compounds (IMCs) formed during welding of steel and Ti alloys are prone to cracks, which limit the preparation of high-strength steel/Ti joints. In this work, CoCrNi powder was used as an intermediate alloy to reduce the tendency of these brittle phases to produce cracks. The addition of this CoCrNi powder ensured that good quality joints were obtained and no cracks were observed. Three elements of CoCrNi are capable of infinite solid solution with Fe, so the alloy powder does not form a large amount of brittle IMCs with Fe by laser melting. A region of Fe-Ti IMCs formed at the steel/Ti interface due to the mixing of Fe and Ti. Moreover, the diffusion of CoCrNi from the melt pool into the Fe-Ti IMC interface layer reduced the interface layer brittleness, decreased the interface layer cracking tendency and improved joint performance. The plastic toughness of the interface layer of Fe-Ti compounds significantly improved after the addition of Co, Cr, and Ni alloying elements, which fully demonstrated the effectiveness of CoCrNi powder incorporation.

A surface modification of polylactic acid composites for additive manufacturing with modified chopped carbon fiber and modified nano‐hydroxyapatite

AbstractPolylactic acid (PLA) composites parts obtained by fused deposition modeling (FDM) three‐dimensional (3D) printing have obvious fusion interfaces. The printed parts have low strength and poor plastic toughness, limiting their application in clinical degradable load‐bearing implants. In this article, first, the nano‐hydroxyapatite (n‐HA) was modified by PLA to obtain a core‐shell structure with PLA coating. The micron chopped carbon fiber (CF) was modified by nitric acid to obtain a rich oxygen‐containing functional group structure. Second, the above two modified materials of n‐HA and CF were coated on the surface of the PLA filament by ultrasonic impregnation to obtain the PLA/n‐HA/CF composite filament. Finally, tensile samples were manufactured by FDM 3D printing with the PLA/n‐HA/CF composite filament, and the tensile test was conducted. The results show that the surface‐modified n‐HA particles form a regular spherical core‐shell structure with good dispersibility. It can be combined with a matrix of PLA filament by the PLA coating layer, while a silane coupling agent combines the PLA coating layer and the core of n‐HA. The modified chopped CF treated with 68% nitric acid for 6 h has an ideal etch pits with moderate depth and distribution producing firm combination with the PLA matrix. The surface of modified chopped CF has abundant –COOH and –OH functional groups. It can be combined with a matrix of PLA filament through an esterification reaction. Among all the tensile samples, PLA_5% n‐HA_6% CF, with 5% modified n‐HA and 6% modified chopped CF, respectively, improves the bonding strength between the fused interfaces with the two reinforcement materials well‐distributed in the fuse interface area.

Friction and wear characteristics of in-situ Cr+(Cr,Al)2O3 composite coating fabricated by plasma spraying

The [Cr+(Cr, Al)2O3] nanocomposite coating was synthesized in situ by reactive plasma spraying Al–Cr2O3–Al2O3 composite powder, and its friction and wear properties were studied at room temperature. Studies have shown that the microstructure and structure of the composite coating can be optimized by adding a certain amount of additives (aAl2O3+bCr2O3). The metallic Cr particles distributed in the matrix can significantly hinder the crack propagation. The eutectic composite coatings all below 10 nm show the best plastic toughness and friction and wear properties. The microhardness reaches 1899HV0.3, and the wear resistance is 3.28 times that of the Al2O3 ceramic coating. The wear mechanism is fatigue wear and slight adhesion wear.

Experimental study of processing γ-TiAl by blasting erosion arc machining

γ-TiAl alloy is an ideal material for aerospace components due to its low density, high specific strength and outstanding oxidation resistance at high temperature. However, γ-TiAl is difficult to cut because of its high temperature strength, poor plastic toughness as well as low thermal conductivity. Blasting Erosion Arc Machining (BEAM) has an excellent performance in processing difficult-to-cut materials such as nickel-based superalloy and titanium alloy. Thermal machining model simulated in COMSOL Multiphysics shows the feasibility of processing γ-TiAl by BEAM. Machining experiments are designed to study the effects of different machining parameters (open circuit voltage, electrode diameter, cutting depth) on the machining performance. The experimental results show that the maximum material removal rate can reach up to 4,484.9 mm3/min, the tool wear ratio being 2.74%, and the surface roughness Sa is 74.14 μm, when the peak current is 400 A. Material removal rate is mainly affected by cutting depth. Tool wear ratio is mainly affected by electrode diameter. Surface quality is sensitive to all three parameters. Suitable processing parameters should be selected when different processing objectives are pursued. Considering the recasting cutting depth (< 50 μm) and residual stress influence depth (about 400 μm) after BEAM, it is recommended to reserve at least 500 μm thickness allowance for subsequent processing.

Effect of Aluminum on Microstructure and Mechanical Properties of Weld Metal of Q960 Steel

High-strength low-alloy (HSLA) steel is used in important steel structural members because of its strength and plastic toughness. Q960 steel is HSLA steel obtained by adding an appropriate amount of alloy elements and quenching and tempering treatment on the basis of ordinary low-carbon steel. This kind of steel has strong hardenability due to the alloy elements added. Cold cracks, embrittlement and softening of the heat-affected zone easily occur after welding. In particular, the low-temperature impact toughness cannot meet the requirements and limits its use. In this paper, self-shielded welding is used to adjust the content of aluminum in flux-cored wire. The relationship between weld metal (WM) microstructure and strength and properties was studied by tensile test and impact test, and the influence mechanism of Al content on weld metal microstructure and properties was analyzed. The results show that when the content of Al is 0.21%, the impact energy at 0 °C~−60 °C is the best, the tensile strength can reach 1035 MPA and the number of pores is small. The size of inclusions in WM is mostly less than 1.0 μm Al2O3 spherical oxide. It can become the center of acicular ferrite (AF) and increase the nucleation probability. However, with the increase of Al content, large irregular AlN inclusions are produced, which reduces the tensile strength and impact energy of the welded joint.

Effect of Reversed Austenite on Mechanical Properties of ZG06Cr13Ni4Mo Repair Welded Joint

In this work, gas tungsten arc welding (GTAW) was used to repair ZG06Cr13Ni4Mo martensitic stainless steel. Repair welding occurred either once or twice. The changes in the microstructure and properties of the repair welded joints were characterized by optical microscope (OM), scanning electron microscope (SEM), electron backscattering diffraction (EBSD), tensile and impact tests. The effects of reversed austenite in repair welded joints on microstructure and mechanical properties were studied. The results show that the microstructure of the welded joint after repair welding consists of a large amount of martensite (M) and a small amount of reversed austenite (A), and the reversed austenite is distributed at the boundary of martensite lath in fine strips. With the increase in the number of welding repairs, the content of reversed austenite in the welded joint increases. The microstructure in the repair welded joints is gradually refined, the microstructure in the once and twice repaired joints is 45.2% and 65.1% finer than that in the casting base metal, respectively. The reversed austenite presented in the repair welded joints decreases the tensile strength by 4.8% and 6.7%, increases the yield strength by 21.3% and 26.4%, and increases the elongation by 25% and 56%, respectively, compared with the casting base metal. In addition, the reversed austenite mainly nucleates and grows at the boundary of lath martensite. The refinement of the martensite structure was due to the generation of reversed austenite and the refinement of original austenite grain by the welding thermal cycle. After repair welding, the reverse austenite appeared in the repair welded joints and the tensile strength decreased slightly, but the plastic toughness was significantly improved, which was conducive to the subsequent service process.

Microstructure and properties of laser cladding coating at the end of L415/316L bimetal composite pipe

This article attempts to use the laser cladding to realize the metallurgical combination of the ends of L415/316L bimetal mechanical lined pipe. For the convenience of the tests on mechanical properties, two kinds of nickel-based alloy powders, self-fluxing alloy powder (SFAP) and non-self-fluxing alloy powder (NSFAP), were cladded on substrate L415 sheet. The microstructure of two cladding coatings was analyzed by optical microscopy (OM) and scanning electron microscopy (SEM), electron backscattered diffraction (EBSD), and the mechanical properties and corrosion resistance of two cladding coatings were determined. The results show that two cladding coatings do meet the requirements of both low hardness and high corrosion resistance, and that two cladding coatings which mainly contain γ-Ni solid solution are composed of planar dendrites, cell dendrites, columnar dendrites and equiaxed dendrites. In addition, SFAP coating exhibits high tensile strength and low toughness, showing that SFAP coating is brittle. However, NSFAP coating exhibits good plastic toughness, high tensile strength and excellent impact Charpy energy, and excellent bending performance. SFAP coating is a quasi-cleavage fracture, which is a brittle fracture. The fracture of NSFAP coating is composed of a large number of dimples, which is a ductile fracture. Considering the three aspects of microstructure, chemical composition, and mechanical and corrosion properties, NSFAP is suitable for laser cladding at the end of mechanically lined bimetal pipe.

Effects of Isothermal Temperature on Microstructure and Properties for N80 Oil Pipe Steel

Some key temperature parameters in the process of controlled rolling and controlled cooling of N80 grade oil casing steel were simulated by heat treatment method, and the effects of different isothermal temperatures on the microstructure and mechanical properties of N80 grade oil casing steel were studied. The results show that when the isothermal temperature increases from 500 °C to 550 °C, the influence of different microstructure volume and grain size is not obvious; when the temperature reaches 600 °C, the ferrite grain coarsens obviously, the volume fraction of ferrite increases obviously, and the volume fraction of pearlite and bainite decreases obviously. In addition, when the isothermal temperature increases from 500 °C to 550 °C, the yield strength and tensile strength of the test steel increase slightly, and the plastic toughness increases obviously; but when the temperature increases to 600 °C, the yield strength and tensile strength of the test steel decrease obviously, and the plastic toughness continues to increase. The optimum isothermal treatment temperature of test steel is 550 °C.

A review of coextruded wood–plastic composites

AbstractWood–plastic composites (WPCs) are increasingly broadly applied composites that combine the merits of wood and plastics, such as the renewable, degradable, lightweight, and low‐cost characteristics of wood, and the thermoplasticity, hydrophobicity, and toughness of plastics. However, WPCs also display the disadvantages of the two main components including hydrophilicity and flammability of wood, and weathering degradability, flammability, and thermal expansion of plastics. Coextruded WPCs (Co‐WPCs) are multilayer composites in which regular WPCs are coated with a protective shell layer through coextrusion. The core–shell structure of Co‐WPCs provides a way to overcome the shortcomings of WPCs by modifications specific to the composite surfaces. This review summarizes the studies of Co‐WPCs in terms of their mechanical properties, moisture absorption, weathering, flame resistance, and dimensional stability. It also presents expectations for the further development of Co‐WPCs.

Structure and magnetic properties of spinodal decomposed Cu60Ni20Fe10Co10 ribbons with hard magnetism

The spinodal decomposed Cu-Ni-Fe alloy can possess both hard magnetic properties and excellent plastic toughness, corrosion resistance, and cold workability. Cu60Ni20Fe10Co10 ribbons are prepared by melt-spinning and annealing methods, and their phase composition, microstructure, and magnetic properties are studied. The results show that the as-spun ribbons are composed of equiaxed grains. Through the decomposition of γ → γ1 + γ2 inside the grains, the spinodal structure is formed, which endows the ribbons with the hard-magnetic properties. Also, the maximum coercivity of 679.3 ± 149.1 Oe and saturation magnetization of 72.0 ± 2.7 emu/g are obtained in the ribbons annealed at 435 °C for 30 min and 835 °C for 30 min, respectively. The shape anisotropy of γ1 and γ2, the concentration of Fe, Co, Ni in the γ2 phase, and the content of the α phase are the main factors to determine the magnetic properties. At the same time, the corresponding microstructure evolution models are proposed.

First-principles study of β-titanium alloy TiX (X=Al, Ni, Fe) for key parts of automobile engines

As we all know, titanium alloys have excellent comprehensive mechanical properties, such as high ductility, rigidity, and density, which are superior to aluminium alloys. However, due to their high price, titanium alloys have not been able to be used in automobile engine bodies, but on small engine components, such as titanium alloys have been well used in connecting rods, valves, engine exhaust systems and fasteners. This article uses a new alloy design concept to design a new beta titanium alloy, hoping that it may be applied to small parts of automobile engines. Based on the density functional theory, the first-principles calculation method was used to study the structure and stability, formation heat, binding energy and elastic properties of TiX (X = Al, Ni, Fe) β titanium alloy. The results show that these types of β titanium are structurally and mechanically stable. By using Voigt-Reuss-Hill (VRH), the theoretical elastic constants Cij, bulk elastic modulus B, shear modulus G, Young’s modulus E, Poisson’s ratio υ of these β titanium alloys are further obtained. The ductility and plastic toughness of these kinds of β titanium alloys are analysed, and the β titanium alloy system with excellent comprehensive performance is determined, which also provides a basis for the next element selection of the β titanium alloy system for automobile engines.

Effect of Different Molding Process on Mechanical Properties of 316L Stainless Steel

The effects of laser selective melting (SLM) and rolling on the mechanical properties of 316L stainless steel were studied. The morphology and fracture characteristics after impact were characterized by means of an optical microscope (OM) and scanning electron microscope (SEM), Meanwhile, tensile strength, hardness, and impact toughness are characterized. The results show that compared with the roll forming, the 316L stainless steel group formed by laser selective melting has surface holes, cracks and spheroidization, and the grains are smaller, the dimples are smaller and shallower, and the strength and hardness are higher than the roll forming. Plastic toughness is much lower than that of rolling.

Microstructure and mechanical properties of the IC10/GH3039 dissimilar electron beam welded joint

The dissimilar welded joint of GH3039 superalloy and IC10 single crystal Ni3Al-based superalloy was manufactured by electron beam welding, with no defects. The microstructure and mechanical properties were investigated systematically. The results indicated that the microstructure of welded joint was transformed from cellular crystals to columnar crystals and dendritic crystals. The microstructure texture in fusion zone showed strong local grain orientation and high angle grain orientation dominated. The dislocation structures existed in intergranular and intragranular, and the γʹ phases induced the dislocation accumulation. The welded joint possessed high plastic toughness to release stress through its deformation, preventing cracks from occurring. The microhardness of welded joint can averagely reach 288 HV and the tensile strength was 751 MPa, which is higher than that of the GH3039 base metal. The fractography of welded joint is ductile combined with brittle fracture in local area.

Systematically investigate mechanical and electrical properties of Bi2O2Se by Te atom substitution and compare it with homologue Bi2O2Te from first-principles calculations

In this paper, first-principles calculations based on density functional theory (DFT) were used to study the optimization of the mechanical and electrical properties of Bi2O2Se by equivalent Te atom substitution (Bi2O2Se1-XTeX (X = 0, 0.25, 0.50, 0.75, 1)). The structures of Te atom after equivalent substitution satisfy the mechanical stability, and can improve its plastic toughness. The minimum thermal conductivity (kmin) of Bi2O2Se1-XTeX (X = 0, 0.25, 0.50, 0.75, 1) determined by elastic constants are 0.398 (W/m k), 0.362 (W/m k), 0.332 (W/m k), 0.376 (W/m k), 0.36 (W/m k) and Debye-temperature (TD) are 287.0 K, 263.4 K, 245.9 K, 274.6 K, 266.7 K, respectively. The values indicate that the substitution of Te atoms can inhibit the heat transfer and reduce the atomic bonding force to improve the toughness. And the effect is best when the concentration of Te atom substitution reaches 0.5. The calculated energy band gaps (Eg) of Bi2O2Se1-XTeX (X = 0, 0.25, 0.50, 0.75, 1) are 0.85 eV, 0.52 eV, 0.18 eV, 0.11 eV and 0.23 eV, respectively. The Eg of Bi2O2Se and Bi2O2Te are consistent with the experimental results. Electronic structure analysis shows that Te atom substitution makes s-orbital and p-orbit hybridization stronger and Fermi level (EF) right shift, and then narrows the band gap. It is more directly reflected in the charge density difference and electron localization function (ELF) maps. The results show that the substitution of Te atom for Se atom in the Bi2O2Se can improve the mechanical and electrical properties, and then improve the actual conversion efficiency of thermoelectricity.

Experimental Research on Turning of Superalloy GH4169 under High Pressure Cooling Condition

Superalloy GH4169 possesses excellent high temperature strength, thermal stability, and thermal fatigue, and is widely used in aerospace and other fields. However, it is a typical difficult-to-cut material owing to its poor thermal conductivity, high plastic toughness, severe workpiece hardening, and difficult chip breaking. In this study, high pressure cooling was used for GH4169 cutting test. The effects of high pressure cooling on the cutting force, chip morphology, and tool wear were analyzed, which can provide technical support to achieve high efficiency turning of GH4169.

Dynamic mechanical response and weldability of high strength 7A62 aluminum alloy

The 7A62 as one kind of Al-Zn-Mg alloys is the highest strength weldable aluminum alloy currently. Plates and forgings of 7A62 alloy have been widely used in the defense system and main bearing parts of special vehicles. The microstructure, dynamic mechanical response and weldability of 7A62 aluminum alloy were investigated by OM, TEM, SHTB, DSC, microhardness and other tests. The morphology and mechanical test results showed that the 7A62 aluminum alloy strengthened by trans-scale precipitates had high strength, high hardness and good plastic toughness. The mechanical responses of the 7A62 aluminum alloy were found to be strain-rate sensitive and the dynamic response behavior was significantly higher than that of the 7A52 aluminum alloy through the SHTB test. In addition, for the as-welded 7A62 the tensile strength reached a scope of 260 MPa-305 MPa, which is considerably higher than the tensile properties reported when using ER5356. Because the weld of 7A62 alloy was free of macroscopic imperfections. The grains were highly equiaxed and homogeneous throughout the melting zone, showing smooth grain boundaries. Compared with 7A52, the lower melting point, low thermal enthalpy and low specific heat capacity of 7A62 alloy are more conducive to weld performed.

Microstructure and mechanical properties of low activation Fe–Ti–Cr–V–W multi-principal element alloys

Single-phase multi-principal element alloys can have low activation and rapid induced radioactive decay properties that make them ideal structural materials for the first wall/cladding structure of nuclear fusion reactors. The present work proposes the design of multi-principal element alloys consisting of low activation elements Fe, Ti, Cr, V, and W with both equiatomic and optimized compositions. The optimal composition of the multiple components is based on the formation of a single-phase solid solution with a minimal Gibbs free energy. The microstructures and mechanical properties of the alloys are investigated. The equiatomic alloy is observed to be composed of dendritic crystals consisting of a body-centered cubic (bcc) solid solution phase and a complex intermetallic compound, while the optimized alloy is composed of cellular dendritic crystals consisting of a single bcc solid solution phase in its as-cast state. Homogenization treatment is observed to reduce the fracture strength of the equiatomic alloy due to grain coarsening, although it has little effect on the hardness and other mechanical properties. However, homogenization increased the hardness and compressive yield strength of the optimized alloy to different degrees. The optimized alloy has better plastic toughness than the equiatomic alloy, which increases its workability and radiation resistance.