MPa Ultimate Tensile Strength Research Articles

Developing a hybrid-built pre-hardened alloy steel for injection moulding tools using the laser powder bed fusion process

Hybrid additive-subtractive manufacturing has been adopted as a cost-effective alternative for manufacturing plastic injection moulding tools with conformal-cooled inserts created by fusing powder and wrought material. This article reports the development of a hybrid power-wrought pre-hardened alloy steel to supplement the current material choice for fabricating injection mould inserts using this advanced manufacturing strategy. In this study, MS1 (maraging 300) steel powder was additively deposited onto pre-machined wrought Nimax steel to form a hybrid alloy material. The mechanical and microstructural properties of the fusion-bonded interface were examined. Microstructural observation revealed a 280 μm thick interfacial region consisting of a homogenous mixing of powder and substrate materials. As a result of solid solution strengthening within the region, tensile tests established robust powder-substrate bonding with tensile ruptures occurring well away from the interface. The as-built hybrid-alloy steel possessed excellent mechanical properties, with 1200 MPa in ultimate tensile strength, 12.4 % in elongation at fracture and 39 HRC (Nimax)/42 HRC (MS1) in hardness. The overall results suggested that hybrid MS1-wrought Nimax steel is a suitable pre-hardened material for manufacturing durable and high-performance injection mould inserts as part of a cost-effective hybrid additive-subtractive manufacturing strategy.

Study on configuration design and microstructure optimization of quasi-continuous network structured (Ti3AlC2-Al3Ti)/2024Al

Configuration design and microstructure regulation are paramount strategies to surmount strength and ductility trade-offs in Aluminum Matrix Composites (AMCs). In this study, both methods were harnessed in fabricating, strengthening, and toughening quasi-continuous network structured (Ti3AlC2-Al3Ti)/2024Al composites: configuration design was applied through hot rolling, whereas microstructure regulation was facilitated via heat treatment. Hot rolling modified the network configuration and optimized the strain distribution by improving the matrix connectivity and the directional load-bearing capacity of the network structure. Subsequent heat treatment weakened grain orientation, gave full play to dynamic recrystallization and refined grains, and enhanced the dispersion of precipitates. Superior strength-ductility compatibility of 405 MPa (ultimate tensile strength), 242 MPa (tensile yield strength), and 12 % (elongation) was achieved, positioning it among the most competitive AMCs to date. Finite element analysis was employed for the in-situ monitoring of strain behaviors, elucidating the strengthening and toughening mechanisms.

ANN modeling and optimization of friction stir welding performance for AA6061 and AA5083 alloy joints

This research focused on the characteristics of the AA6061/AA5083 alloy joints which are fabricated by the friction stir welding (FSW) technique. The impact of FSW parameters such as tool tilt angle, pin depth, and tool geometry on the mechanical properties and fractographic characteristics were studied. Ultimate tensile strength (UTS), hardness (HBN), and specific wear rate (SWR) were examined for characterization while fractography analyses were done using scanning electron microscopy. Taguchi-Grey relational analysis (GRA) was employed to execute multicriteria optimization and recognize the best grouping of parameters. The optimized values attained from this analysis were 259.2 MPa for UTS, 94.9 HV for HBN, and 0.0819 m³/Nm for SWR. The analysis of variance (ANOVA) results derived from the GRA revealed that tool geometry exerted the most significant influence (39.79%) on output factors, followed by pin depth (24.90%) and tilt angle (24.26%). To enhance the predictive accuracy of the output responses, an artificial neural network (ANN) model was developed utilizing the Levenberg-Marquardt (LM) algorithm. The optimized ANN architecture, configured as (3–10–3), exhibited robust regression analysis outcomes, showcasing correlation coefficients ( R) of 0.99999, 0.99967, and 0.99994 for the training, validation, and test datasets. The overall R-value, computed at 0.99958, affirmed high conformity between experimental and predicted values.

Enhancing tensile properties of polymer‐based triply periodic minimal surface metamaterial structures: Investigating the impact of post‐curing time and layer thickness via response surface methodology

AbstractThis research aims to explore the influence of post‐curing time and layer thickness on the tensile characteristics of various triply periodic minimal surface (TPMS) structures produced by mask stereolithography (MSLA). The study determined the best post‐curing duration, layer thickness, and TPMS lattice type to improve ultimate tensile strength (UTS) and absorbed energy. To experimentally evaluate the tensile characteristics, a dog bone‐shaped specimen was utilized. Three distinct TPMS structures, Gyroid (G), Neovius (N), and Diamond (D), were present in the test region. After investigating many process factors with response surface methodology (RSM), optimization methods are applied to find their best printing procedure. The work shows the novel use of RSM to optimize post‐curing and printing parameters on TPMS structure mechanical properties during manufacturing. According to the optimization results, the biggest factor affecting UTS is layer thickness, while the most significant factor increasing energy is curing time. The optimal operating parameters for MSLA printing based on the optimization results are a layer thickness of 0.05 mm, a post‐curing period of 40 min, and a lattice type of N. The optimum responses corresponding to the optimum parameters were determined as 7.16 MPa for UTS and 18.16 J for energy.Highlights Optimized the production process parameters of TPMS geometries. Compared TPMS structures for mechanical performance. Identified optimal input parameters to improve UTS and energy absorption. Conducted comprehensive experimental evaluations to validate the optimization.

Tension fracture delamination analysis on a hot rolled Nb-bearing high-strength steel for vehicle wheel application

A comparative analysis was conducted on post-tensile specimens with and without delamination to investigate the causes of tensile delamination in hot rolled steel with a 600 MPa ultimate tensile strength (UTS) for automotive wheel applications. The tensile specimens were sampled from the hot rolled coils in the transverse direction per ASTM A370 standards, and Tensile tests were performed at room temperature with a constant crosshead speed of 0.5 mm/min. The results indicate that normal segregation is not the sole factor contributing to delamination; rather, the presence of Nb lumps within the central segregation area increased the susceptibility to tensile delamination. The statistical analysis indicates that there is a more intense presence of Nb lumps in specimens with tension delamination, tension delamination will occur during specimen stretching when there are Nb lumps with an average size greater than 6.5 μm and a quantity greater than 3 in the central segregation region. Meanwhile, the sources of lumps are also analyzed indicates that these Nb lumps originate from the ferroniobium alloy added during BOF tapping and ladle refining.

Wire-arc additive manufacturing of Mg-Gd-Y-Zn-Zr alloy: Microstructure and mechanical properties

Mg-Gd-Y-Zn-Zr alloy is an essential high strength weight ratio material in the aerospace field. It has been fabricated gradually using wire-arc additive manufacturing (WAAM), a key integrated preparation technology for large-scale parts. In this investigation, a Mg-9.4Gd-3.3Y-1.75Zn-0.38Zr (wt.%) alloy was prepared by WAAM based in the cold metal transfer (CMT) process. Investigations were conducted into the microstructural evolution and mechanical properties during the solution and aging heat treatment. With an average grain size of 18.30 ± 9.89 μm, the as-deposited Mg-Gd-Y-Zn-Zr alloy is mainly composed of α-Mg matrix, (Mg,Zn)3(Gd,Y) eutectic phase, RE-rich particles, and rare-earth (RE) segregation zone. Following a 12-h heat treatment at 500 °C, the average grain size of the α-Mg matrix showed no appreciable changes. The α-Mg matrix also dissolved the (Mg, Zn)3(Gd, Y) phases, which led to the production of long period stacking ordered (LPSO) phases and the disappearance of the RE-segregation zone. The appearance of the nanoscale β′ phase following aging heat treatment. The deposited alloys had the following tensile properties: 196.5 ± 24 MPa for ultimate tensile strength (UTS), 157.2 ± 14 MPa for yield strength (YS), and 2.08 ± 0.8% for elongation (EL). The formation of LSPO phase can improve the ductility while the formation of nanoscale β′ phase can improve the strength of Mg-Gd-Y-Zn-Zr alloy. Thus, after heat treatment at 500 °C for 12 h, the alloy's EL rose to 9.27 ± 0.94%. After further aging heat treatment for 225 °C at 24h, the alloy's YS rose to 234±3 MPa and its EL was 4.56 ± 0.25%.

Controlling Mechanical Properties of Medical-Grade Scaffolds through Electrospinning Parameter Selection.

Electrospinning (ES) is a versatile process mode for creating fibrous materials with various structures that have broad applications ranging from regenerative medicine to tissue engineering and surgical mesh implants. The recent commercialization of this technology for implant use has driven the use of resorbable electrospun products. Resorbable electrospun meshes offer great promise as temporary implants that can utilize the layer upon layer method of additive manufacturing to incorporate porosity as a function of process parameters into a scaffold structure. The interconnected porosity and feature size known to ES have previously been observed to hold great potential for simulating the natural cellular environment of soft tissue. This microstructure, proper degradation kinetics, and mechanical properties combine to provide the design basis for artificial tissue structures that could aid in not only wound healing but also true tissue engineering and regenerative medicine. While current advancement in the field is understood to be limited by material properties, the importance of optimizing mechanical properties with currently available materials should not be overlooked. This work investigated the process parameter effects and interactions that control the structure-property relationship for a range of medical-grade aliphatic polyester materials with a range of intrinsic properties. An ε-caprolactone homopolymer (PCL), l-lactide homopolymer (PLLA), and Lactoflex, a copolymer with intermediate properties relative to the homopolymers, were characterized before, during, and after the additive manufacturing process. The interacting effects of process parameters, distance to collector, and dispensing rate were shown to produce variable-density, nonwoven scaffold structures. The resorbable mesh scaffolds of PLLA, PCL, and Lactoflex demonstrated a broad range of mechanical properties (approximately 1-10 MPa ultimate tensile strength and 5-390 MPa tensile modulus). Postprocessing of scaffolds demonstrated removal of solvents and preservation of micrometer-sized features. Resorbable polymers and electrospinning can produce scaffold materials with excellent features and offer tremendous potential in the field of implantable resorbable devices.

Unveiling the Characteristics of ER70S-6 low Carbon Steel Alloy Produced by wire arc Additive Manufacturing at Different Travel Speeds

AbstractWire Arc Additive Manufacturing (WAAM) produces metal components with crucial properties dependent on process parameters. Understanding the effects of these parameters on microstructure and mechanical properties is vital for optimizing WAAM. This study investigated the impact of varying travel speeds (TS) on the microstructure and mechanical properties of low carbon steel ER70S-6 alloy produced by WAAM process. The hypothesis centred on the impact of different TS values on heat input (HI) and cooling rates, and the subsequent effects on the resulting microstructure and mechanical properties of the deposited material. ER70S-6 alloy was deposited at three different TS: 120, 150, and 180 mm/min. Microstructure and mechanical properties (microhardness, tensile strength, elongation) were evaluated for each TS condition. Distinct microstructures were observed in the deposited samples, influenced by cooling rates at different TS. Distinct microstructures emerged in different regions of the deposits due to varying cooling rates at different TS. Higher TS (180 mm/min) significantly reduced pores and cracks while enhancing yield strength (YS) and ultimate tensile strength (UTS) up to 25.2 ± 0.77% elongation and 502.3 ± 3.17 MPa UTS, respectively. However, UTS remained slightly lower (93%) than the catalogued value for ER70S-6 (540 MPa), indicating a mild softening effect. TS significantly influenced the microstructure and mechanical properties of WAAM-produced ER70S-6 alloy. This study provides key insights into optimizing WAAM parameters for low carbon steel, paving the way for improved component production for diverse industrial applications.

Minimizing Porosity in 17-4 PH Stainless Steel Compacts in a Modified Powder Metallurgical Process

Nowadays, powder-based manufacturing processes are recognized as cost-efficient methods frequently employed for producing parts with intricate shapes and tight tolerances in large quantities. However, like any manufacturing method, powder-based technologies also have several disadvantages. One of the most significant issues lies in the degree of porosity. By modifying the morphology of the gas-atomized spherical 17-4PH stainless steel powder via prior ball milling and then raising both the pressure of cold compaction (1.6 GPa) and sintering temperature (1275 °C), the porosity could be reduced considerably. In our novel powder metallurgical (PM) experimental process, an exceptionally high green density of 92% could be reached by employing die wall lubrication instead of internal lubrication and utilizing induction heating for rapid sintering. After sintering (at temperatures of 1200, 1250, and 1275 °C), the samples aged in the H900 condition were then mechanically tested (Charpy impact, HV hardness, and tensile tests) as a function of porosity. Sintering at 1275 °C for one hour enabled porosity reduction to below 4%, resulting in 1200 MPa yield strength and 1350 MPa ultimate tensile strength with significant (16%) fracture strain. These values are comparable to those of the same alloy products fabricated via ingot metallurgy (IM) or additive manufacturing (AM).

Mechanical properties, corrosion behavior, and in vitro and in vivo biocompatibility of hot-extruded Zn-5RE (RE = Y, Ho, and Er) alloys for biodegradable bone-fixation applications

Biodegradable Zn alloys have significant application potential for hard-tissue implantation devices owing to their suitable degradation behavior and favorable biocompatibility. Nonetheless, pure Zn and its alloys in the as-cast state are mechanically instable and low in strength, which restricts their clinical applicability. Here, we report the exceptional mechanical, corrosion, and biocompatibility properties of hot-extruded Zn-5RE (wt.%, RE = rare earth of Y; or Ho; or Er) alloys intended for use in biodegradable bone substitutes. The microstructural characteristics, mechanical behavior, corrosion resistance, cytocompatibility, osteogenic differentiation, and capacity of osteogenesis in vivo of the Zn-5RE alloys are comparatively investigated. The Zn-5Y alloy demonstrates the best tensile properties, encompassing a 138 MPa tensile yield strength, a 302 MPa ultimate tensile strength, and 63% elongation, while the Zn-5Ho alloy shows the highest compression yield strength of 260 MPa and Vickers hardness of 104 HV. The Zn-5Er alloy shows a 126 MPa tensile yield strength, a 279 MPa ultimate tensile strength, 52% elongation, a 196 MPa compression yield strength, and a 101 HV Vickers microhardness. Further, the Zn-5Er alloy has a 130 µm per year corrosion rate in electrochemical tests and a 26 µm per year degradation rate in immersion tests, which is the lowest among the tested alloys. It also has the best in vitro osteogenic differentiation ability and capacity for osteogenesis and osteointegration in vivo after implantation in rat femurs among the Zn-5RE alloys, indicating promising potential in load-bearing biodegradable internal bone-fixation applications. Statement of significanceThis work reports the exceptional mechanical, corrosion, and biocompatibility properties of hot-extruded (HE) Zn-5 wt.%–rare earth (Zn-5RE) alloys using single yttrium (Y), holmium (Ho), and erbium (Er) alloying for biodegradable bone-implant applications. Our findings demonstrate that the HE Zn-5Er alloy showed σuts of 279 MPa, tensile yield strength of 126 MPa, elongation of 51.6%, compression yield strength of 196 MPa, and microhardness of 101.2 HV. Further, HE Zn-5Er showed the lowest electrochemical corrosion rate of 130 µm/y and lowest degradation rate of 26 µm/y, and the highest in vitro osteogenic differentiation ability, in vivo osteogenesis, and osteointegration ability after implantation in rat femurs among the Zn-5RE alloys, indicating promising potential in load-bearing biodegradable internal bone-fixation applications.

Developing novel multifunctional protective clothes for disabled individuals using bio-based electrospun nanofibrous membranes

A novel kind of protective apparel for handicapped persons has been created with bio-based electrospun nanofibrous (NFs) membranes. Hydrophobic membranes with fine polylactic acid (PLA) NFs had a smooth, bead-less structure with an average diameter of 950 nm. The hydrophilic layer has a similar pattern but a smaller fiber diameter dispersion and an average diameter of 750 nm. The silica nanoparticle-modified super-hydrophobic top layer (contact angle, ~153°) repels water and keeps the user dry. Super-hydrophilic silver nanoparticles in the fabric's bottom layer react with perspiration to kill microorganisms. The fabric's porosity (avg. 1.2–1.5 μm) allows for breathability, while silica nanoparticles boost infrared radiation reflection, keeping users cool on hot days. The dual-layer textile has 4.9 MPa ultimate tensile strength and 68 % elongation compared to the membrane's super-hydrophobic and super-hydrophilic layers. Wearing protective clothes reduced hand temperature by 25 % in direct sunlight and 13 % in a sun simulator with 1 Sun. This fabric will work well for adult diapers, outdoor clothing, and disability accessories. Overall, the protective textiles may improve the quality of life for disabled and elderly people by providing usable textile items adapted to their needs.

Sc/Zr microalloying on strength-corrosion performance synergy of wire-arc directed energy deposited Al-Mg

ABSTRACT WADED Al-Mg and Al-Mg-Sc-Zr aluminium alloy thin-wall components were produced. Heat treatment (350°C aging for 4 h) was further conducted. The effects of Sc/Zr addition on porosity, microstructure, mechanical properties and corrosion behaviour were investigated. With Sc/Zr adding, pore area fraction decreased from 0.208 to 0.005% and grain size decreased from 84.34 to 19.54 μm. In WADED Al-Mg-Sc-Zr component, microstructure showed refined equiaxed grains. Mechanical properties were improved with 360 MPa ultimate tensile strength (UTS), 185 MPa yield strength, and 23.31% elongation. After heat treatment, UTS increased to 388 MPa with good ductility (22.53%) maintained. The grain refinement and Al3(Sc, Zr) particles were the key factors for mechanical property improvement. The corrosion behaviour was improved with introduced Sc/Zr and further optimised after heat treatment. The corrosion exhibited layered characteristics due to the distribution of primary Al3(Sc, Zr) while minor-size secondary Al3(Sc, Zr) along grain boundaries improved the corrosion behaviour.

Suppressing formation of microcracks in laser powder bed fusion manufactured AA6061 aluminum alloy by introducing mechanical alloyed Al-25at%Ti particles

A novel approach which incorporates mechanical alloyed Al-25at%Ti particles into an AA6061 aluminum alloy powder feedstock has been used to suppress pronounced hot cracking that normally occurs in laser powder bed fusion (LPBF) manufactured AA6061 alloy. Investigation of the microstructure and tensile properties of the Ti-modified AA6061 sample fabricated by LPBF confirms the effectiveness of this approach. The suppression of microcrack formation is associated with the transition of a coarse columnar structure to fine equiaxed structure facilitated by heterogeneous nucleation of the grains on Al3Ti nanoparticles. This crack-free microstructure also results in excellent tensile properties of 252 MPa in yield strength, 361 MPa in ultimate tensile strength, and 9.7 % in elongation to fracture.

Controlling of cellular substructure and its effect on mechanical properties of FeCoCrNiMo0.2 high entropy alloy fabricated by selective laser melting

Fine cellular substructures are typical microstructure feature of high entropy alloys (HEAs) produced via selective laser melting (SLM), playing a pivotal role in improving the mechanical properties. Nonetheless, the controlling of cellular substructure and its impact on the mechanical properties remains ambiguous. This study investigates the effect of energy densities on the cellular substructure evolution and mechanical properties of the FeCoCrNiMo0.2 HEA. It is found the increase in energy density causes a decrease in temperature gradient (G) and solidification rate (R) in molten pool, consequently leading to the increase of cellular substructure size and the intensification of Mo segregation at cellular substructure boundaries. The cellular substructure size (d) can be described by formula d=80(GR)−1/3, in which G and R can be obtained from discrete element method - computational fluid dynamics (DEM-CFD) simulation. The strength of the FeCoCrNiMo0.2 HEA is significantly affected by dislocation strengthening (σd) and segregation strengthening (σs), which are further determined by the cellular substructure size and the Mo segregation, respectively. The increase of cellular substructure size leads to the decrease of σd, while the intensification of Mo segregation results in the increase of σs. The competition between these two strengthening effects leads to an optimized and excellent tensile property of 707 MPa in yield strength, 947 MPa in ultimate tensile strength and 34 % in fracture elongation at a moderate energy density of 47 J/mm3. The findings provide guidance towards the advancement of high-performance high entropy alloys fabricated by SLM in terms of cellular substructure controlling.

A high strength and high electrical conductivity copper based composite enhanced by graphene and Al2O3 nanoparticles

The rapid development of electrical and electronic engineering requires to further surmount the trade-off between the electrical conductivity and strength of Cu matrix composite. In this study, the surface of Cu–Al2O3 powder is selective for carbon sources, and only α-naphthol can prepare graphene. Graphene and Al2O3 particles are simultaneously incorporated into Cu matrix by hot-press sintering Cu–Al2O3 powders by internal oxidation coated with in-situ grown graphene. This composite exhibits a good combination of strength and conductivity (600 MPa of ultimate tensile strength and 81.7 % IACS of electrical conductivity) due to synergistic effect of graphene and Al2O3 particles. This composite fabricated by such synergistic more effectively retains the microstructure induced by plastic deformation during the cold-rolling process. Both graphene and Al2O3 particles uniformly distribute in Cu matrix. Coherent Al2O3 particles and graphene in situ grown can be well enhance to Orowan looping mechanism effect, and the addition of graphene in Cu matrix composite with Al2O3 particles can improve dislocation strengthening and dispersion strengthening at the same time. Our study provides an effective route to achieve simultaneously high strength and conductivity of Cu matrix composites.

Improving ductility in dual-phase FeNi2Al medium-entropy alloy through rapid solidification-induced expansion of Interface transition zones

Multi-principal element alloys (MPEAs), renowned for their exceptional properties, have garnered significant attention in materials science. However, their limited ductility has restricted their widespread applications. In our investigation, the toughness of a Co-free dual-phase (B2 + L12) FeNi2Al medium-entropy alloy was improved by manipulating the microstructure through rapid solidification. A significant improvement in the total tensile elongation (TE) and ultimate tensile strength (UTS) of the as-cast FeNi2Al alloy at 253 K compared to the as-melted counterpart can be observed. Specifically, the as-cast alloy exhibited enhanced values of 13.1% for TE and 1111.0 MPa for UTS, whereas the as-melted FeNi2Al alloy displayed 6.1% for TE and 1176.2 MPa for UTS. This represents a remarkable 114.1% increase in TE, with only a marginal 6.3% decrease in UTS. Microstructure analysis indicates that augmenting the L12 phase content, refining the grain size, and fostering interfacial transition zones between the B2 and L12 phases, all achieved through rapid solidification, collectively contributed to the improved ductility of the FeNi2Al alloy. This work presents an effective and promising strategy for enhancing the ductility of multi-phase MPEAs, offering new opportunities for their broader application in various industries.

Multi-scale microstructure manipulation of an additively manufactured CoCrNi medium entropy alloy for superior mechanical properties and tunable mechanical anisotropy

Laser beam powder bed fusion (PBF-LB) additive manufacturing (AM) technology has become a versatile tool for producing new microstructures in metal components, offering novel mechanical properties for different applications. In this work, enhanced ductility (∼55% elongation) and tunable mechanical anisotropy (ratio of ductility along vertical to horizontal orientation from ∼0.2 to ∼1) were achieved for a CoCrNi medium entropy alloy (MEA) by multi-scale synergistic microstructure manipulation (i.e., melt pool boundary, grain morphology and crystallographic texture) through adjusting key PBF-LB processing parameters (e.g., laser power and scan speed). By increasing the volumetric energy density (VED) from 68.3 to 144 J/mm3, the melt pool size enlarges, and the crystallographic texture transitions from <100>//BD to <110>//BD due to the maximum thermal flux direction changing for different melt pool dimensions, which affects the proportion of grains that have different growth directions. Moreover, excellent mechanical properties of 890 MPa ultimate tensile strength and ∼55% elongation to failure can be achieved for loading perpendicular to the build direction with only a ∼15% reduction in properties for loading along the build direction. The superior combination of mechanical properties is achieved by processing parameter-controlled strengthening of melt pool boundary interfaces, heterogeneous deformation induced strengthening through bimodal grain structures, and favorable grain orientation for dislocation slip and twinning formation, which was significantly more activated in the <110>//BD texture than in the <100>//BD. This study offers new insights into achieving multi-scale synergistic microstructure manipulation via PBF-LB for desired strength, ductility, and mechanical anisotropy in a CoCrNi MEA.

Metastable microstructure evolution and grain refinement in a Low-Ta containing γ-TiAl alloy through heat treatment

The paper comprehensively describes the evolution of metastable microstructures in a cast low-Ta-containing γ-TiAl alloy during cooling-tempering-lamellarization heat treatments. The behavior and mechanism of microstructure refinement are discussed. The rapid cooling generates metastable microstructures, including Widmanstätten, feathery, and massive structures, with many γ variants in small sizes and different orientations. It significantly refines the coarsened colonies and randomizes the texture. The tempering can effectively stabilize the metastable microstructures. During tempering, the γ→α phase transformation is more active at higher temperatures while coarsening and recrystallization dominate at lower temperatures. After tempering, a refined microstructure with spherical grains and convoluted structures forms. Subsequent lamellarization treatment optimizes the microstructure and obtains a fine-grained nearly-lamellar microstructure with small colonies (∼70 μm) and dispersed fine γ grains (∼10 vol%), which yielded a 1.0 % elongation with a 487 MPa yield strength (0.2%) and a 589 MPa ultimate tensile strength at room temperature. Finally, the unique promotion effects and mechanism of a small amount of Ta addition on the nucleation, growth, evolution, and stabilization of metastable microstructures are concluded and discussed, which is crucial for the refinement of cast γ-TiAl alloy by heat treatment alone.

Enhanced Yield Strength and Total Elongation of an Ultrahigh Strength Hot‐Stamped Steel via Tempering Treatment

A 2460 MPa ultimate tensile strength (UTS) has been achieved in this experimental steel, which was processed by a conventional hot stamping process with water quenching to room temperature. Additionally, comparing the microstructure evolution and strengthening mechanism before and after tempering, the microstructure has changed from fresh martensite transformed into tempered martensite with acicular carbides, and the fracture mode has also changed from brittle fracture transformed into ductile fracture mainly. Meanwhile, the main strengthening mechanism has changed from dislocation strengthening to precipitation and dislocation strengthening. Overall, the tempering process reduces dislocation density and produces acicular carbides, which decrease UTS. However, the tempering process reduces the quenching residual stress and changes the morphology of twin martensite, resulting in an increase in ductility. Meanwhile, it enhances the effect of carbide pinning dislocations, significantly enhances precipitation strengthening, and improves yield strength.

Temperature dependence of mechanical strength in HPDC Mg–6Y–3Zn–1Al alloy with LPSO phase

The temperature dependence of mechanical strength including yield strength (YS) and ultimate tensile strength (UTS) in HPDC WZA631 alloy is investigated in a wide temperature range from room temperature (RT) to 350 °C. It is found that at 25–300 °C, YS and UTS do not drop markedly, from 173 MPa and 274 MPa at RT to 113 MPa and 170 MPa at 300 °C, respectively. While above 300 °C the flow stress falls rather rapidly, to 74 MPa for YS and to 108 MPa UTS at 350 °C. The (Al,Zn)2Y phase exhibits similar behavior between 150 °C and 350 °C, breaking up under stress and becoming the relatively stable crack source without catastrophic cracking. The LPSO phase, keeping steady and excellent critical resolved shear stress (CRSS) below 250 °C, remains unchanged with complete network structure at 150 °C and 250 °C. Therefore, the LPSO phase reinforces the alloy with slow flow stress reduction at RT-300 °C for WZA631 alloy. The tensile property deteriorates above 300 °C due to the destruction of the network structure as well as the reduction of CRSS for the prismatic slip of LPSO under tensile loading. Thus, the LPSO phase determines the mechanical strength evolution of WZA631 alloy, which is similar to the behavior of γ’ phase in the Ni-based superalloys. Besides, the relationship between strength and temperature is described by the Arrhenius equation, which may be reduced to an exponential model in the form of σ=a+bT for HPDC WZA631 alloy.