Mechanical Properties Of Alloys Research Articles

Effect of heat treatment on microstructure and mechanical anisotropy of direct energy deposited Ti-6.0Al-2.5Nb-2.2Zr-1.2Mo alloy

Ti-6.0Al-2.5Nb-2.2Zr-1.2Mo alloy (Ti-6321) exhibits excellent corrosion resistance and impact toughness, which can be used as a deep-sea pressure-resistant hull. However, the alloy tends to have high strength but low plasticity, poor impact toughness, and anisotropic mechanical properties by fabricating by direct energy deposition (DED) technology. In order to improve the impact toughness of DEDed Ti-6321 alloy while reducing its anisotropy of mechanical properties, this study manipulates the microstructure and mechanical properties of the alloy through heat treatment. The research finds that with the increase of the single-stage annealing temperature within the (α+β) two-phase region, the width of the α phase increases, the Ultimate Tensile Strength (UTS) remains essentially unchanged, the Yield Strength (YS) decreases, and the impact absorption energy significantly improves. For double annealing heat treatment at two-phase region, temperature increase at the first-stage annealing enlarges the width and decreases the aspect ratio of the primary α phase. Leading to the decrease of the UTS & YS and increase of the impact absorption energy, with a conversely tendency at 1000 °C. The increase in the second-stage annealing temperature raises the size and volume fraction of the secondary α phase, causing the alloy's UTS and YS to initially rise then fall, with a slight increase in impact absorption energy. The anisotropy in the mechanical properties of DEDed Ti-6321 alloy mainly addressed from the different distribution of α phase orientations at different loading directions, and can be eliminated through sufficient β single-phase zone annealing.

Co-evolution of M23C6 precipitates and cavities in a boron-free Ni-based alloy GH3617 under high-temperature He ion irradiation: Effects on cavity swelling and mechanical properties

Ni-based alloys are promising materials for advanced nuclear reactors operating at high temperatures due to their exceptional resistance to high temperatures and corrosion. Understanding the synergy of phase stability and helium effects is crucial for assessing the long-term performance and reliability of these alloys in advanced nuclear reactors. This study has investigated the co-evolution behavior of M23C6 precipitates and cavities in a boron-free solid solution strengthened Ni-based alloy GH3617 under high-temperature He ion irradiation, and its impact on alloy swelling and mechanical properties, by He ion irradiation experiments with the highest fluence of 1 × 1017 He/cm2 up to 800 °C. Transmission Electron Microscopy (TEM) and Nanoindentation are employed to investigate microstructural evolution and mechanical properties, respectively. The findings show that at room temperature and 500 °C, cavities and dislocation loops were the dominant irradiation defects, whereas at 800 °C, the density of cavities and dislocations reduced while the formation of M23C6 precipitates increased. These precipitates act as effective trapping sites for He and point defect, leading to cavity formation at the interfaces or within the precipitates. Moreover, increased irradiation fluence accelerates the co-evolution process, resulting in an increase in the density and size of both precipitates and cavities, ultimately leading to enhanced swelling. The {111} planes are favored interfaces between intragranular M23C6 precipitates and the matrix due to their minimal misfit, while the preferred interface planes between cavities with octahedral or cubo-octahedral shapes and the precipitate/matrix are also {111}, owing to their lower surface energy as well. The co-evolution of cavities and precipitates was found to influence mechanical properties, resulting in an irradiation hardening effect at lower fluences, while softening at higher fluences. This study provides novel insights into the degradation mechanisms of Ni-based alloys under coupling effect of He and high-temperature irradiation.

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

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

Effects of post-heat treatments on the microstructure and mechanical properties of Ti–6Al–4V alloy fabricated by selective laser melting

In this study, post-heat treatments were applied to Ti–6Al–4V (TC4) alloy fabricated by selective laser melting (SLM) to investigate the effects of annealing temperature (750–950 °C in 50 °C intervals) on the alloy's microstructure, residual stress and mechanical properties. The initial microstructure of as-SLMed TC4 alloy was dominated by needle-like α′ martensite with a high density of dislocations and minor β phase, resulting in high strength (1190 MPa) but limited ductility (2.2% elongation). Annealing led to the transformation of α′ martensite into α phase, with the β phase content remaining relatively stable. Increasing the annealing temperature caused the acicular martensite to evolve into bundles of coarse α laths, forming a basket-weave microstructure. Annealing at 750 °C for 2 h reduced the yield strength to 1040 MPa and improved elongation to 8.3%. Interestingly, both the strength and ductility decreased with further increases in annealing temperature. This unusual phenomenon was rarely mentioned in current literature and was considered to be associated with the abnormal variations in the Schmid factor of (0001) [11-20] slip system and the reduction of mobile dislocations within the coarsened α martensite. Additionally, annealing combined with air cooling effectively alleviated residual tensile stresses in the SLM-formed TC4 alloy.

Hierarchical ferrous medium entropy with heterogeneous precipitates embedded in core-shell grain structure for superior mechanical properties

Superalloys designed for high-temperature applications, featuring a face-centered cubic matrix and L12 precipitates, have shown excellent tensile properties at both room and elevated temperatures. However, the substantial Ni and Co, necessary for generating a high fraction of the ordered L12 phase within the matrix, results in high mass density and cost, subsequently limiting their widespread industrial application. It is important to increase Fe content over Ni and Co while preserving outstanding mechanical properties at ambient and high temperatures. In this study, we propose a novel approach to introduce a hierarchical structure in a 60-at%-Fe-based medium entropy alloy. The heterogeneous nano-precipitates embedded in harmonic (core-shell) grain structure reinforce mechanical contrast between soft and hard domains, achieving an excellent heterostructure. The present alloy incorporates hierarchical heterogeneity at multi-scales, combining heterogeneous grain at micrometers, precipitates at tens of nanometers, and elemental fluctuation at nanometers. This hierarchical structure shows superior mechanical properties at room and high temperatures comparable to those of conventional superalloys. Further, the high content of Fe in this alloy system shows excellent performance in alloy cost and mass density. This work suggests the unique hierarchical heterostructure to overcome the trade-off dilemma in alloy cost, mass density, and mechanical properties in room/elevated temperatures.

Effect of Pouring Temperature Variation on Cooling Rate, Hardness and Microstructure of Al-Zn in Aircraft Structures

Al-Zn alloys are widely utilized in industries such as automotive, aircraft manufacturing, and advanced military equipment due to their exceptional strength-to-weight ratio. Among various fabrication methods, metal casting is a commonly used technique for producing structural components from these alloys. However, a significant challenge with metal casting is the reduction in mechanical properties compared to the base material before melting. This reduction highlights the need for research to identify the optimal casting conditions, particularly the casting temperature, which plays a crucial role in maintaining and potentially enhancing the material's mechanical properties. Aluminum alloy 7075, known for its high strength, was selected for investigation. According to the Al-Zn phase diagram, the melting point of aluminum alloy 7075, based on the weight percentage specified by the Standard Aluminum Association, is approximately 660°C. Experiments were conducted by varying the pouring temperature during casting in 30°C increments above this melting point. Specifically, the alloy was melted and cast at three different temperatures: 690°C, 720°C, and 750°C. The mold temperature was consistently maintained at 220°C to isolate the effects of the pouring temperature. Results indicate that increasing the casting temperature significantly affects the alloy's microstructure and mechanical properties. As the casting temperature increases, the cooling rate decreases, leading to a finer grain structure. This finer grain size directly contributes to an increase in hardness, suggesting that higher casting temperatures can enhance the mechanical properties of Al-Zn alloys. These findings emphasize the importance of precise control over casting temperatures to optimize the performance characteristics of aluminum alloy 7075 in high-strength applications.

The interpretable descriptors for fatigue performance of wrought aluminum alloys

Aluminum alloys are extensively utilized in the transportation and aerospace industries due to their excellent processability and corrosion resistance. A key aspect affecting the application of aluminum alloys is fatigue failure, with fatigue strength constituting an essential indicator for assessing the failure mode. In this study, 859 data sets were collected to evaluate the effects of aluminum alloy composition and mechanical properties on fatigue strength. To comprehensively evaluate the features that exert a great influence on the fatigue strength of wrought aluminum alloys, atomic physical quantities of aluminum alloys were added to the original data set. To improve the computational efficiency and physical interpretability of the model, Spearman correlation analysis, optimal subset method, and other methods were used to perform feature selection on the atomic feature quantities and mechanical properties in the data set. Finally, a mathematical relationship between material descriptors and fatigue strength was established based on the alloy composition and the three most relevant features in the feature screening, which helps to better understand and predict the fatigue behavior of wrought aluminum alloys.

Metastable phase transformations and mechanical properties of an as-extruded TiAl-based alloy during two-step heat treatment

Metastable phase transformations of TiAl-based alloys provide a pathway for grain refinement and performance improvement. In this paper, the microstructure evolution of an as-extruded Ti-47Al-2Cr-0.2Mo alloy during quenching and tempering was investigated by scanning electron microscope (SEM), electron backscatter diffraction (EBSD) and transmission electron microscope (TEM), and the mechanical properties of the alloy were further evaluated by tensile tests. The results indicated that the analogous Σ3 coincidence site lattice (CSL) and γ/γ true twin interface appeared in both the Widmanstätten structure (γw) and feathery structure (γf), implying that sympathetic nucleation mechanism was responsible for the nucleation of the metastable phases. A 6 H intermediate phase with the long period stacking ordered structure (LPSO) was discovered after short-term water quenching, which provided an evidence supplement of the sympathetic nucleation mechanism. The transformation path of the metastable γw phase was proposed to follow the sequence of α/α2→6 H→γ. Apparent refinements of both grains and α2/γ lamellar colonies ((α2+γ)L) were exhibited after metastable phase transformation. The ultimate tensile strengths of the heat-treated alloy at whether room temperature (RT) or 800 °C were obviously improved, and the elongation at RT also kept at a considerable level.

Effect of drawing deformation on microstructure and mechanical properties of Fe-Cr-Co-W alloy

The mechanical properties of strain gauge wire are intricately linked to the process of drawing deformation, playing a pivotal role in the performance of associated sensors. This study delves into the impact of varying degrees of drawing deformation on both the mechanical properties and microstructure of FeCrCoW strain gauge alloy wires. Through a comprehensive analysis of tensile testing, XRD, SEM, and TEM, a detailed and systematic exploration was conducted on the influence of different tensile deformation variables on the mechanical properties of alloys, while also exploring fracture mechanisms. The research results showed that the yield strength and fracture strength of FeCrCoW alloy gradually increase with the tensile deformation raising, while the fracture strain and work hardening rate gradually decrease. Advanced TEM investigations have elucidated that the phenomenon of grain refinement and the concomitant rise in dislocation density within the alloy escalates markedly with escalating levels of drawing deformation. This enhanced microstructural evolution is posited as the principal driver linking the alloy's mechanical properties to the magnitude of deformation experienced. Concurrently, the dynamic interplay between tungsten (W)-rich nanoparticles and the alloy's dislocations during the drawing process is identified as a significant contributor to the observed alterations in mechanical behavior. The synergistic effects of these microstructural changes are likely responsible for the nuanced shifts in the alloy's mechanical attributes.

Effect of welding current on the mechanical properties of Al 5083 alloy processed using high-current gas metal arc welding

This study investigated the effect of welding current during gas metal arc welding (GMAW) on the microstructure and composition of an Al 5083 alloy. As the welding current increased from 650 to 950 A, several changes were observed in the heat-affected zone (HAZ): grain coarsening and the formation of liquation cracks, and in the weld zone (WZ): increasing average secondary arm spacing and Mg loss. Therefore, the welding currents above 800 A are likely to cause liquation cracks in the HAZ and deterioration of the alloy's mechanical properties. Thus, welding condition with low heat input must be applied to improve the mechanical properties of the welds. This study provides a correlation between the weldability of Al 5083 alloy and welding current, offering a competitive advantage of liquid hydrogen storage containers.

Fracture behaviors and microstructure evolution of an Al–Mg–Mn-Sc-Zr alloy at elevated and cryogenic temperature

The mechanical properties and fracture behavior of Al-5.8Mg-0.4Mn-0.25Sc-0.1Zr alloy were investigated across cryogenic temperatures (−196.15 °C ∼ −56.15 °C) and elevated temperature (room temperature ∼ 250 °C), with results indicating sensitivity of the alloy's mechanical properties to temperature. Firstly, the tensile test at elevated temperatures shows a decrease in strength and strain hardening exponent (n) due to thermal softening effects, while elongation increases and then decreases, peaking at 100 °C. Within the temperature range of −196.15 °C ∼ −56.15 °C, the yield stress (YS), ultimate tensile strength (UTS), and ductility tend to increase with the decreasing temperature gradually, which can be attributed to the decrease in lattice thermal vibration energy at low temperatures, resulting in an elevated external force requirement for dislocation motion. Meanwhile, throughout the entire high-temperature range, the alloy exhibits ductile fracture, with the number of dimples peaking at 100 °C. Differently, when the alloy is deformed at low temperatures, dislocations tend to accumulate within the grains, and with the grain boundaries acting as weak bonding areas between grains and experiencing significant stress concentration, the fracture mechanism gradually transitions from transgranular to intergranular fracture. Microstructural analysis at low temperatures shows minimal texture content changes, while at elevated temperatures, regular changes in texture components occur due to grain orientation rearrangement. Furthermore, high-resolution transmission electron microscopy was employed to investigate the evolution of precipitates at various temperatures, and the results shows that uniform and fine Al3(Sc1−x, Zrx) precipitates are distributed within the crystal, acting as effective dislocation pinning sites and leading to a uniform intragranular dislocation arrangement after tensile test at cryogenic temperature. Notably, after tensile test at higher temperatures, a few precipitates lose coherency with the matrix and started growing, which diminishing grain boundary pinning effect and promoting recrystallization.

A strategy for high-entropy copper alloys composition design assisted by deep learning based on data reconstruction and network structure optimization

Complex mapping relationships between high-entropy alloy compositions and performances struggle to precisely elucidate by traditional machine learning models, hindering the accurate and efficient design of high-performance alloys. In this work, a novel alloy design strategy combined self-decision deep neural network, data reconstruction with network structure optimization was proposed, which effectively enhanced the model's ability to predict the mapping relationships between high-dimensional composition spaces and mechanical properties of alloy. Compared to other machine learning methods, significantly improves model prediction accuracy (hardness model: 97.98%; strength model: 94.40%). Through above model, the mechanical properties of 308 new (CuNiMn)-X high-entropy copper alloys was studied added other elements such as Al, Ti, Cr, and Fe, which designed and produced a novel (CuNiMn)60Al20Cr20 alloy with high hardness of 474 HV, high compressive strength of 2322 MPa, and high fracture strain of 25.20%. The primary factors influencing alloy performance and their respective thresholds were also quantitatively revealed (hardness: electronegativity deviation (0.02, 0.1) and nuclear charge deviation (0, 0.25); compressive strength: mean nuclear charge (25, 30) and mean atomic radius (134 p.m.)). These findings provide a new perspective and approach for the design and mechanism understanding of high-performance alloys with complex compositions.

Effect of elastic strain energy on precipitation process of Co81Al5V14 alloy based on microscopic phase field method

The L12 phase volume fraction, size, microstructure significantly influences alloy's important physical and mechanical properties in Co-Al-V superalloy. Based on microscopic phase field method and microelasticity theory, precipitation of ordered L12 phase in Co81Al5V14 alloy were studied. The results indicate that precipitation sequence of Co81Al5V14 alloy is minimally influenced by elastic strain energy and precipitation sequence can be divided into four stages. Elastic strain energy does not significantly affect incubation period of alloy, but it does promote the formation of transitional ordered phase L10 with a single orientation and facilitates precipitation of ordered phase L12. Elastic strain energy causes precipitates to grow and coarsen along specific elastic "soft" direction ([100] and [001]). Elastic strain energy promotes process of ordering and atomic occupancy of the alloy. The effects of elastic strain energy on precipitation mechanism, microstructure and atomic occupancy are discussed in this work, which provides theoretical guidance for the design of Co-Al-V alloys with better properties.

Effect of C content on microstructure evolution and mechanical properties of CoCrFeNiTa0.1 high entropy alloy

A series of CoCrFeNiTa0.1Cx (x = 0.1, 0.2, 0.3, 0.4, 0.5) high entropy alloys (HEAs) with different C content were prepared by vacuum melting technology. The influence of different C element contents on the alloy microstructure and mechanical properties have been systematically investigated using X-ray diffraction, scanning electron microscopy, transmission electron microscopy, and a universal testing machine system. It is found that the introduction of trace amounts of C element content facilitates the precipitation of Laves phase in C0.1 alloy. As the C element content further increases, the volume fractions of both FCC matrix and Laves phases gradually decrease, while the volume fraction of M7C3 carbide increases. Notably, the CoCrFeNiTa0.1C0.3 HEA shows a ternary eutectic structure. Compression tests reveal an increase in yield strength from 342 MPa to 1475 MPa and hardness from 182 HV to 458 HV as the C content increases. The precipitation of Laves phase and M7C3 carbide is principally involved in the enhancement of strength and hardness. Nanoindentation tests indicate that the M7C3 carbide has a higher nano-hardness compared to FCC matrix and Laves phase. The fracture microstructure exhibits a mode transition from ductile fracture to cleavage fracture.

Effect of Zr content on microstructure and mechanical properties of MoNbTaTiZrx refractory high-entropy alloy

Abstract The purpose of this paper is to explore how Zr content affects the crystal structure, micro-morphology, and mechanical properties of (MoNbTaTi) 100-xZrx alloys (x = 5,15,25). The results reveal that with the varying Zr contents, the alloy changes from a single-phase solid solution structure of Zr5 to a solid solution structure of Zr15 and Zr25 with a double BCC phase. Higher Zr levels lead to more pronounced elemental segregation, particularly, which makes Zr element enriched in the interdendritic region, and with the increase of segregation degree, the second phase separates between dendrites. In other words, Zr and Ti elements are densely distributed in the BCC2 phase. With the formation of the BCC2 phase, the mechanical properties of the alloy also changed obviously. Notably, as the Zr content rises, the alloy’s hardness and strength improve, while its ductility initially decreases before subsequently increasing. The Zr15 alloy was in a transition period of a two-phase structure, and the two-phase structure was not stable at this time, which led to a decrease in the plasticity of the alloy. The yield strength of Zr25 alloy is 1595 Mpa, the Vickers hardness is 542 HV, and the compressive fracture strain is 29%, showing the best comprehensive properties.

Applications of unified phase-field methods to designing microstructures and mechanical properties of alloys

Applications of unified phase-field methods to designing microstructures and mechanical properties of alloys

Effect of Homogenization Process on Microstructure and Mechanical Properties of 4047 Aluminum Alloy

In this study, the homogenization heat‐treatment process and microstructural evolution of 4047 aluminum alloy are investigated. In the results, it is revealed that the homogenization process induces partial dissolution of metastable phases and modification of the fine needle‐shaped eutectic Si. Within the 4047 aluminum alloy, the fine needle‐shaped eutectic Si undergoes granulation, involving two stages: crystal dissolution and granulation of broken crystals. After optimal homogenization heat treatment, the eutectic Si phase transformed from a fine needle‐shaped structure to small, regular spherical structures, reducing stress concentration and improving the interfacial bonding capability and internal structure of the alloy matrix. This significantly reduces the likelihood of microcrack formation within the alloy and effectively hinders crack propagation, enhancing the alloy's mechanical properties.

A Review on Traditional Processes and Laser Powder Bed Fusion of Aluminum Alloy Microstructures, Mechanical Properties, Costs, and Applications.

Due to its lightweight, high strength, good machinability, and low cost, aluminum alloy has been widely used in fields such as aerospace, automotive, electronics, and construction. Traditional manufacturing processes for aluminum alloys often suffer from low material utilization, complex procedures, and long manufacturing cycles. Therefore, more and more scholars are turning their attention to the laser powder bed fusion (LPBF) process for aluminum alloys, which has the advantages of high material utilization, good formability for complex structures, and short manufacturing cycles. However, the widespread promotion and application of LPBF aluminum alloys still face challenges. The excellent printable ability, favorable mechanical performance, and low manufacturing cost are the main factors affecting the applicability of the LPBF process for aluminum alloys. This paper reviews the research status of traditional aluminum alloy processing and LPBF aluminum alloy and makes a comparison from various aspects such as microstructures, mechanical properties, application scenarios, and manufacturing costs. At present, the LPBF manufacturing cost for aluminum alloys is 2-120 times higher than that of traditional manufacturing methods, with the discrepancy depending on the complexity of the part. Therefore, it is necessary to promote the further development and application of aluminum alloy 3D printing technology from three aspects: the development of aluminum matrix composite materials reinforced with nanoceramic particles, the development of micro-alloyed aluminum alloy powders specially designed for LPBF, and the development of new technologies and equipment to reduce the manufacturing cost of LPBF aluminum alloy.

Microstructures and mechanical properties of Ti-55511 alloy subjected to rolling in the α+β dual-phase region

In this study, dual-phase region rolling was conducted on a Ti-55511 alloy with different initial rolling reductions in the single-phase region. The mechanical properties and microstructural characteristics of the alloy with different deformation conditions were investigated. Microstructure observations show the formation of a heterogeneous structure with a gradient size distribution of the α phase at the recrystallized grain boundaries, induced by the non-uniform stress distribution. The α phase and the β matrix exhibit the Burgers orientation relationship in the recrystallized region with the gradient structure. However, in the unrecrystallized region of the partially recrystallized specimens and in the grain interiors of the fully recrystallized specimens, the α phase and the β phase exhibit Pitsch-Schrader orientation relationship (P–S OR). A large number of the nano-sized α" martensite bands were observed after the dual-phase region rolling. These bands originated from the α/β interfaces and grew towards the interiors of the α phase. As the deformation increased, these nano-bands underwent a transformation into the {10 1‾ 1}α deformation twins, resulting in the fragmentation of the α phase. Mechanical testing results show that the mechanical properties of the alloy can be improved by the dislocation strengthening, the generation of profuse α phase and other microstructures including the heterogeneous distribution of the α phase, the nano-sized α" martensite and the {10 1‾ 1}α deformation twins.

Investigation of Two Laser Heat Treatment Strategies for Local Softening of a Sheet in Age-Hardening Aluminum Alloy by Means of Physical Simulation

AbstractCar manufacturers increasingly aid high-strength aluminum alloys for their advantageous weight-to-strength ratio, but their limited formability poses challenges in plastic deformation processes. Tailored heat-treated blanks (THTBs) are a propitious approach to improve formability. Surface laser treatment is the predominant technology for obtaining THTB. To design this process quickly and accurately, without material waste, the use of physical simulation is increasingly promising. It allows replicating the process on a lab-scale and studying posttreatment mechanical and metallurgical properties. By adopting Gleeble® physical simulator, this study investigates the softening effects of local surface laser heat treatment on a EN AW 6082 T6 aluminum alloy blank. Two laser movement strategies—single linear path and multiple rectangular paths—were investigated at two treatment speeds for each. A finite element (FE) model was developed for simulating the process under all explored conditions. FE-derived thermal cycles were reproduced by means of physical simulation. After physical tests, alloy mechanical properties were evaluated. Results show that these properties depend on both the peak temperature thermal cycle and the interaction time between the laser source and the material surface. The comparison between the two strategies revealed that the multiple rectangular paths strategy allows to achieve a wider softened area at comparable interaction times.