Desirable Combination Of Strength Research Articles

Low cycle fatigue properties of CoCrFeNiMn high-entropy alloy with heterogeneous microstructure

Heterogeneous microstructure is a hot topic in materials science which facilitates tackling the dilemma of strength-ductility trade-off in engineering materials including high-entropy alloys. The present investigation was conducted on the impact of different microstructures including heterogeneous microstructure, constructed by thermomechanical treatment including cold rolling followed by annealing, on the monotonic and cyclic behavior of a CoCrFeNiMn high-entropy alloy. The tailored microstructure contained three features: non-recrystallized as a hard domain, ultrafine-recrystallized, and fine-recrystallized regions. A desirable combination of strength and ductility including UTS of ∼1.1 GPa together with an elongation of ∼15 % was achieved due to benefiting from hetero-deformation-induced hardening and activation of deformation twins in the fine recrystallized grains. Regarding low-cycle fatigue behavior, at the strain amplitude of 0.4 %, heterogeneous microstructure exhibits remarkable fatigue properties, including high maximum stress and extraordinary lifetime (more than 2 × 105). The compelling reasons for these desirable properties are triggering deformation twins in fine recrystallized grain, the absence of brittle sigma phase as a good location of crack initiation, and the non-recrystallized area as a hard domain for suppressing crack propagation. The results suggested that the heterogeneous microstructure has significant benefits during applying low strain amplitude, however, at high strain amplitude, grain refinement is not recommended, and coarse-grained microstructure provides better properties. The present investigation is a step forward to understand the significance of heterogeneous microstructures to improve fatigue properties of high- or medium-entropy alloys.

Design and manufacture of near-net-shape metal-ceramic composites with gradient-layered structure and optimized damage tolerance

Optimizing the composition and structure of materials in localized regions of the materials is an effective approach to enhance the material utilization efficiency and achieve a performance-on-demand design. However, it is challenging to achieve such design owing to limitations in manufacturing technology. In this study, we devised a method involving vat photopolymerization 3D printing and magnet-assisted pressure infiltration techniques for fabricating near-net-shape customized gradient composites with Al/Al2O3 as the model system. The mechanical properties of the fabricated Al/Al2O3 composites at specific locations could be optimized by appropriately setting the thickness ratio of the metal layer to the ceramic layer, and a desirable combination of strength, toughness, and wear resistance could thereby be achieved. The fracture behavior of the composites was analyzed through in situ observation and finite element simulations. The proposed design concept and fabrication method are flexible and adaptable, and they can be easily extended to other material systems and structural models. They are expected to pave the way for the development of lightweight, strong, tough, and near-net-shape structural and functional materials.

Effect of Heat Treatment on the Microstructure and Mechanical Properties of Additive Manufactured Ti-6.5Al-2Zr-1Mo-1V Alloy.

Ti-6.5Al-2Zr-1Mo-1V (TA15), widely used in the aerospace industry, is a medium- to high-strength, near-α titanium alloy with high aluminium equivalent value. The TA15 fabricated via laser powder bed fusion (L-PBF) normally presents a typical brittle appearance in as-built status, with high strength and low ductility. In this study, the microstructure and properties of L-PBF TA15 were engineered by various heat treatments below the β-transus temperature (1022 °C). After heat treatment, the original acicular martensite gradually transforms into a typical lamellar α + β dual-phase structure. Withannealing temperature increases, the lamellar α phase thickened with a decreased aspect ratio. Globularisation of the α grain can be noticed when annealing above 800 °C, which leads to a balance between strength and ductility. After heat treatment between 800-900 °C, the desired combination of strength and ductility can be achieved, with elongation of about 12.5% and ultimate tensile strength of about 1100 Mpa.

Microstructure refinement, strengthening and ductilization mechanisms in Al–Mg–Mn–Er–Zr alloy with high Mn content by friction stir processing

In the present work, the friction stir processing (FSP) has been conducted on the extruded Al–6.0Mg–1.1Mn–0.19Er–0.1Zr alloy and subsequently the microstructure evolution and mechanical property were systematically investigated after FSP. The results showed that FSP is an effective approach to achieve remarkable refinement and homogeneity of microstructure. The coarse band shape grains are gradually replaced by the fine equiaxial grains with a mean diameter of 2.54 μm after fully dynamic recrystallization, which can be ascribed to severe plastic deformation and considerable heat input from the stir effect. Additionally, both the primary intermetallic compounds and the short rod-like secondary dispersoids are refined and evenly distributed in the matrix during FSP. The tensile tests demonstrated that the elongation of the FSPed alloy can be improved by 105% without sacrificing any strength compared with that of the base material (BM), proving that FSP is a good method for improving alloy with a desirable combination of strength and ductility after FSP. Compared with the BM, the grain boundary strengthening and the dispersion strengthening mainly contribute to the compensation for the decrease of dislocation strengthening in the FSPed alloy. Based on the observation of the fracture surfaces and the side view near the fracture, the ductilization can be attributed to the refinement of the primary intermetallic compounds and the rod-like secondary dispersoids by suppressing the initiation and propagation of microcracks during the tensile deformation.

Wire-Arc Directed Energy Deposited Super Martensitic Stainless Steel with a Desirable Combination of Strength and Plasticity

Wire-Arc Directed Energy Deposited Super Martensitic Stainless Steel with a Desirable Combination of Strength and Plasticity

Low-temperature annealing behavior and tensile properties of the rapidly solidified Cu3Ag0.5Zr0.4Cr0.35Nb alloy reinforced by cold rolling

To obtain a uniform microstructure with fine second-phase particles, the Cu3Ag0.5Zr0.4Cr0.35Nb alloy is fabricated through gas atomization and hot isostatic pressing, followed by cold rolling. The microstructural evolution and tensile properties of the alloy after isothermal annealing at low temperature are investigated. The results show that the low-temperature annealing leads to an obvious increase in elongation but a mild decrease in strength, and the desirable combinations of strength and elongation after annealing for different times are achieved. When annealed at 350 °C for 1 h, the alloy exhibits a high strength of 665 MPa and an acceptable elongation of 10%. Prolonging the duration to 8 h, a decreased strength (610 MPa) and high elongation (15%) are obtained. The stable nano-sized Cr2Nb and micro-sized Cu4AgZr particles provide a strong pinning effect on boundary migration and significantly slow the subgrain growth during recovery, which contributes to the retention of good strength. The improved ductility results from the recovered ability to accumulate dislocations after annealing.

{10−12} twinning assisted microstructure and mechanical properties modification of high-force fiction stir processed AZ31B Mg alloy

High-force friction stir processing technology was conducted on AZ31B Mg alloy plate. The activity of {10−12} twinning behavior made great contributions to grain refinement and texture randomization in the stir zone. This work offers a choice for producing bulk Mg alloys with desirable combination of strength and ductility.

Design, Manufacture and Test of an In-Situ Consolidated Thermoplastic Variable-Stiffness Wingbox

Thermoplastic composites offer the potential for reducing the overall manufacturing costs of aircraft structures by allowing continuous production methods to be applied without the ancillary need for ovens or autoclaves by using in situ consolidation techniques. In the last 10 years, carbon-fiber/polyether-ether-ketone-based composites have become available with desirable combinations of strength, stiffness, and toughness properties. By combining the latest manufacturing techniques with these new materials and with new design methods, cheaper, lighter, and better-performing aircraft structures become a viable prospect. As such, a variable-stiffness unitized integrated-stiffener thermoplastic composite wingbox was developed, which was manufactured by laser-assisted automated tape placement with winding and in situ consolidation. The wingbox loads were determined by assuming its location to be at 85% of the wing semispan of a B737/A320-size aircraft. At this load, the wingbox was designed to buckle elastically. A full-scale structural test using a bespoke testing frame with representative bending moment and shear load was undertaken. Indeed, the wingbox buckled elastically at a load close to that predicted numerically. The current results highlight the potential advances that become possible in primary aerospace structures by combining fiber steering and in situ consolidation of carbon-fiber thermoplastic composites together with new blended, unitized structural concepts.

Quenching and partitioning steel produced through hot rolling, direct quenching and annealing

A novel type of quenching and partitioning steel was developed using direct quenching after hot finishing rolling, followed by intercritical annealing, quenching and partitioning (DQ–Q&P) process. The desirable combination of strength and ductility was obtained. The effect of various intercritical annealing temperatures on the microstructures and mechanical proprieties was studied. With the decreasing intercritical annealing temperature, the amount of acicular retained austenite increased, which exhibited a good work-hardening behaviour resulting in enhanced tensile strength and total elongation. After annealing at 740°C, superior mechanical properties, which were the ultimate tensile strength of 1015 MPa and total elongation of 32.22%, were achieved.

Effect of heat treatment on microstructure, mechanical properties and fracture behaviors of sand-cast Mg-4Y-3Nd-1Gd-0.2Zn-0.5Zr alloy

Microstructure, mechanical properties and fracture behaviors of sand-cast Mg-4Y-3Nd-1Gd-0.2Zn-0.5Zr (wt%) alloy in different thermal conditions were investigated. The as-cast alloy was comprised of α-Mg matrix, Mg24Y5, Mg41Nd5 and β1 phases. After solution treatment at 525°C for 6h, the eutectics dissolved into α-Mg matrix, leading to a huge improvement of plasticity. Alloys peak-aged at 200°C and 225°C exhibit high strength due to fine dense β″ and β′ precipitates. Aged at 250°C for 10h, the precipitates in the alloy are coarse sparse coupled β1/β′ phases. A desirable combination of strength and ductility was obtained with 198MPa in yield strength, 276MPa in ultimate tensile strength and 7.6% in elongation when over-aged at 250°C for 10h. Alloys under different thermal conditions show different fracture behaviors, which are closely linked to the structures of both inner grains and grain boundaries.

Microstructural design in quenched and partitioned (Q&P) steels to improve their fracture properties

Quenching and partitioning (Q&P) is receiving increased attention as a novel heat treatment to produce advanced high strength steels (AHSSs) containing martensite/retained austenite mixtures, with desirable combination of strength, ductility and toughness. Despite the significant body of research on microstructure and mechanical properties of Q&P steels, there is still a significant lack of knowledge on the effect of complex microstructure on their mechanical performance. This work addresses the effect of microstructural architecture in multiphase Q&P steels on their fracture behavior at macro- and micro-scales. It is demonstrated that the RA volume fraction does not affect significantly the local fracture initiation toughness, whereas it can greatly improve the total crack growth resistance in Q&P steels. In addition, matrix conditions can play an important role in the fracture behavior of Q&P steels. Based on the analysis of the experimental results, a general recipe to tailor fracture properties of Q&P steels is proposed.

Ultrahigh strength nano/ultrafine-grained 304 stainless steel through three-stage cold rolling and annealing treatment

An approach involving grain refinement through three-stages of cold rolling and annealing was explored with 304 austenitic stainless steel to obtain ultrahigh strength. Equiaxed nano/ultrafine austenite grains of average grain size of ~150nm (the smallest grain size was ~80nm) was obtained with desirable combination of strength and moderate ductility (yield strength −1120MPa, tensile strength −1440MPa, and elongation −12%). The mechanism of transformation of martensite to austenite was diffusional reversion, when the specimens were annealed in the temperature range of 550–650°C.

Influence of 10 % Cold Rolling Reduction on Ageing Behaviour of Hot Rolled Al-Cu-Si–Mn-Mg Alloy

In the current study, the effect of 10 % cold rolling on the different ageing phenomena of Al-Cu-Si–Mn-Mg alloy was investigated. Both hot rolled and cold rolled alloys were subjected to both natural and artificial ageing processes. Hardness was measured to understand the change in the mechanical property of the alloy before and after rolling and also during ageing processes. From microscopy, it was evident that the cold rolling and subsequent ageing provided the alloy with a structure in which CuAl2 precipitates were uniformly distributed. The alloy exhibited the peak hardness value of 92 VHN after 2 days of natural ageing, whereas the cold deformed (10 %) alloy exhibited the higher peak hardness value of 139 VHN after 3 days of natural ageing. Peak hardness of the alloy reached 94 VHN, when hot rolled alloy was subjected to ageing at 250 °C for 1 h, whereas 10 % cold rolling followed by ageing (100 °C, 15 min) demonstrated accelerated and elevated hardening. The ageing behaviours thus obtained permit the alloy to provide a range of desirable combinations of strength and ductility for high strength weight saving applications.

Influence of vanadium on the strengthening of 0.4% C-4% Cr-18% Mn austenitic steel during aging

1. The optimum content of vanadium in austenitic 0.4 C-4 Cr-18 Mn-V steel, guaranteeing the most desirable combination of strength and ductility characteristics upon aging, is 1.2–1.5%. 2. The primary mechanism of strengthening during the aging of this alloy is the precipitation of vanadium carbide, VC. The optimum aging temperature is 650°C. 3. The maximum level of strength attained upon aging rises with increasing quenching temperature from 1050 to 1175°C. 4. After quenching from 1100°C and after the optimum aging treatment at 650°C, the following properties are typically obtained: ultimate tensile strength, 100–110 kg/mm2; yield strength (0.2% offset), 75–80 kg/mm2; elongation, 35–45%; reduction in area, 40–50%.

PYROMET 538

Abstract PYROMET 538 is a solid-solution strengthened, austenitic alloy with a desirable combination of strength, corrosion resistance, oxidation resistance, and economy. This datasheet provides information on composition, physical properties, hardness, elasticity, and tensile properties as well as creep. It also includes information on high temperature performance and corrosion resistance as well as forming, heat treating, machining, and joining. Filing Code: SS-247. Producer or source: Carpenter Technology Corporation.

CUFENLOY-30

Abstract CUFENLOY 30 is a 70/30 copper-nickel alloy specially cold worked and heat treated develop a desirable combination of strength, ductility, and resistance to stress corrosion. This datasheet provides information on composition, physical properties, elasticity, and tensile properties as well as creep. It also includes information on corrosion resistance as well as forming, heat treating, machining, joining, and surface treatment. Filing Code: Cu-153. Producer or source: Phelps Dodge Copper Products Corporation.