Brittle Fracture Mode Research Articles

Fatigue life of friction stir spot welds between Z91 magnesium alloy and ENAW7075-T651 aluminum alloy

Abstract Magnesium (Mg) and aluminum (Al) alloys are considered to be among the lightest structural metals. Using these materials in a design can considerably decrease weight, which brings many benefits like reducing fuel consumption and increasing the performance of an aircraft or a ground vehicle. However, these alloys are too difficult to be joined via fusion welding techniques. In this context, welding AZ91 Mg alloy to ENAW7075-T651 Al alloy by the solid-state welding method of friction stir spot welding was investigated comprehensively. These alloys were welded by utilizing a tool with a triangle pin and various tool rotational speeds (1,000, 1,400, and 1,800 rpm) and welding times (3 and 6 s). Macro and microstructure of the welds and their hardness, tensile strength, and tension-compression fatigue life were determined. Generally, an improvement in the mechanical properties of the weld was observed by increasing the welding time due to the expansion of the joining area. The welding with the best mechanical properties was obtained at 1,400 rpm, and the worst at 1,800 rpm. All the welds failed from the weld area during the tensile and fatigue tests and exhibited a brittle fracture mode due to the formation of intermetallic compounds in the welds.

Mechanical performance and flow heat transfer characteristics of topologically optimised Ti-6Al-4 V lattice structures

ABSTRACT Novel lattice structures were designed as unit cells through topological optimisation methods. Then the mechanical properties, heat transfer performance, and fluid flow characteristics of functional Ti-6Al-4 V porous components fabricated by laser powder bed melting (LPBF) were investigated, and the comprehensive performance evaluation model was established. Mechanical performance evaluations demonstrated that TopLC-L16 exhibits superior mechanical properties with a compressive strength of 486.87 MPa, a 70.76% improvement over TopFC-L16, and the fracture mechanism reveals a composite mode of ductile and brittle fracture. The temperature distributions indicate that the TopLC-L component exhibits the most efficient heat transfer performance, particularly the TopLC-L16, with a temperature gradient of 242.5 °C and a temperature gradient ratio of 64.7%. A comprehensive evaluation model shows that TopLC-L16 shows the best comprehensive performance. The study highlights the importance of optimising lattice structure design in enhancing mechanical performance and heat transfer efficiency, providing critical insights for advanced engineering applications.

Preparation and performance of C/Ta4HfC5-SiC composite fabricated by PIP combined with RMI process

Based on self-made Ta4HfC5 precursor, C/Ta4HfC5-SiC composite material were prepared by precursor impregnation and pyrolysis (PIP) combined with reactive melting infiltration (RMI) process. The density and open porosity of C/Ta4HfC5-SiC composite material are 2.71 ± 0.73 g/cm3 and 7.07 ± 1.29 %, respectively. Pores are distributed at multiple levels, including primarily nanopores below 40 nm, micropores between 0.04 and 8.5 μm, and a small number of macropores between 10 and 285 μm. The Ta4HfC5 phase exists in two forms: dispersed particles in the matrix and a "layered interface" on the surface of fibers within the bundle. The average bending strength, elastic modulus and fracture toughness of C/Ta4HfC5-SiC composite are 84.24 ± 8.71 MPa, 16.13 ± 5.42 GPa and 3.62 ± 0.63 MPa m1/2, respectively, showing a clear brittle fracture mode during the test. The line ablation rate and mass ablation rate of 60 s assessed by the oxyacetylene flame were 7.20 ± 0.35 μm/s and 10.84 ± 0.84 mg/s, respectively. The oxidation products such as Ta2O5, HfO2, Ta(Hf)CxOy formed by Ta4HfC5 phase during ablation present as thicker oxide layers, forming the main anti-ablation components.

A General Model for the Ductility of Intermetallics Applied to Fe-Co Alloys

The mechanical properties, specifically ductility, of high performing soft magnets such as Fe-Co alloys are a limiting factor to their broader use in a number of systems. The understanding of the mechanical robustness in these materials is currently insufficient to be able to support the growing interest in applications such as magnetic shielding or electric motors. Fe-Co alloys provide the highest commercially available magnetic saturation and high magnetic permeability but have very poor ductility. The addition of vanadium to these alloys has allowed for significant commercialization and some ductility improvements, but the fundamental reasons for the observed improvements are not well understood. In most published work on mechanical properties in these alloys, the precise chemistry of the alloys investigated, often a critical aspect of intermetallics, is not reported or controlled and thermal history is unclear. This work creates a ductility model that is sensitive to changes in chemistry and can predict relative strain to failure as well as brittle fracture mode for intermetallics and is applied to Fe-Co alloys. Through the application of density functional theory (DFT), this model identifies defect stabilities, anti-phase boundary (APB) energies, the energy necessary to cross-slip, and cleavage energies and combines them through energetic competition to determine a relative failure strain. The model correctly predicts ductility improvements with the addition of vanadium as well as the transition from intergranular to transgranular cleavage, though more precise experiments are necessary to appropriately validate the various improvements observed.

Microstructural characteristics and mechanical properties of laser-welded Ta10W/GH3030 joints with beam offset

Influences of the laser beam offset (LBO) on the microstructures as well as room-temperature and high-temperature mechanical properties of Ta10W/GH3030 dissimilar-material joints were investigated. In laser-welded Ta10W/GH3030 joints prepared under three conditions with LBOs of −0.2 mm (offset toward Ta10W), 0 mm, and + 0.2 mm (offset toward GH3030): the fusion zones (FZ) all contained expulsed substances Ni3Ta, NiTa, and Cr2Ta and their microhardness was certainly higher than the base metal (BM); a transition layer containing high contents of Ni3Ta, NiTa, and Cr2Ta phases was observed at the Ta10W/FZ interface. With the increase of the LBO, the contents of Ni3Ta, NiTa, and Cr2Ta in the FZ gradually declined, the average grain size in the FZ increased slightly, the microhardness of the FZ dropped rapidly, and the thickness of the transition layer at the Ta10W/FZ interface reduced obviously. Either in the room-temperature or high-temperature (750 °C) tensile tests, Ta10W/GH3030 joints were always fractured at the Ta10W/FZ interface, showing the typical brittle fracture mode, and the tensile strength of joints was enhanced with the increasing LBO. Under LBOs of −0.2, 0, and + 0.2 mm, the room-temperature tensile strengths of Ta10W/GH3030 dissimilar-material joints were 266.4, 308.6, and 341.2 MPa, while the high-temperature (750 °C) tensile strengths were 97.6, 191.5, and 202.7 MPa, respectively.

Effects of microstructures on the fracture properties of silicon nitride ceramics at elevated temperatures

AbstractCeramic components often fail by a brittle fracture mode during the service process. Various factors can affect the fracture properties of ceramics. Experimental methods are usually used to investigate fracture behaviors. However, they give a composite result and the contribution to fracture from each factor is not clear. In the present work, a micromechanical model is developed to quantitatively characterize the fracture properties of ceramics at elevated temperatures. The control method for the microstructures of ceramics is proposed based on the Voronoi diagram. The temperature‐dependent surface energy model of ceramics is revised by considering the effects of thermal decomposition and phase transformation. The interface energies at different temperatures are obtained by the inversion method. The criterion for crack propagation of ceramics at elevated temperatures is developed based on the G‐criterion. The effects of temperature, grain size, grain size distribution, and grain boundary phase thickness on the fracture behaviors of silicon nitride are studied numerically.

Deformation behavior and constitutive equation of Sn-37Pb solder alloy at cryogenic temperature

In this work, the tensile property, ductile-to-brittle transition (DBT) mechanism and constitutive relations of 63Sn-37Pb (Sn-37Pb) solder alloy at cryogenic temperature were studied by uniaxial tensile experiments for different temperatures. The tensile strength of Sn-37Pb solder alloy increases from 38.2MPa (293K) to 178.9MPa (123K) and then declines to 145.2MPa (77K) with decreases of temperature, and its fracture elongation changes from 42.8% (293K) to 10.2% (77K). Mechanical behavior of Pb second phase in Sn-37Pb alloy at low temperatures is illustrated: when the temperature drops to 123K and below, the fracture failure of β-Sn matrix occurs in an open mode. As a result, Sn-37Pb solder alloy fails by brittle fracture mode. Anand model is adopted as a unified viscoplastic intrinsic law to describe the intrinsic relationship of Sn-37Pb solder alloys. Above 123K, Anand model can effectively fit the stress-strain curves of Sn-37Pb solder alloys. When the temperature lower than 123K, the deformation characters of Sn-37Pb solder alloys change from elasto-viscoplastic to elasto-plastic, and Anand model is unable to continue to fit the intrinsic relationship of Sn-37Pb solder alloys. Sn-37Pb solder alloy exhibits more obvious strain hardening at low temperature, and its low-temperature intrinsic response is successfully described by Hollomon’s equation. The research method of the solder alloy is of great significance to solve the reliability problem of low temperature electronic devices.

Induction of ductile modes of ice fracture and drastic enhancement of its fracture energy by means of introduction of nanoscale additives

Ice brittleness and low strength limits its usage as a construction material in cold climate regions on Earth (Arctics, Antarctic, high mountain regions on other continents) as well as in construction of habitable colonies at Moon and Mars planned by several countries despite attractiveness of its other properties. The paper presents experimental study of enhancement of ice carrying capacity and fracture energy by introduction of SiO2 nanoparticles and polyvinyl alcohol into it. Concentration dependences of these properties enhancement are found. Quantitative characteristics of transition from brittle fracture mode in pure ice to ductile one in ice composite caused by growing content of additives are revealed. This transition results in 2–3 orders of magnitude increase in ice fracture energy.

High-temperature tensile rupture property of (Nb,W) co-alloying TiAl-based alloys

In order to explore whether (Nb,W) co-alloying TiAl-based alloys with relatively higher W addition have better high-temperature tensile rupture property, Ti-44Al-4Nb-1 W-0.1B alloy is designed and prepared. Ti-44Al-8Nb-0.1B alloy and Ti-44Al-7.2Nb-0.2 W-0.1B alloy are also prepared for comparative study. The rupture property testing is carried out at 800 °C and different tensile stresses. The property data, macro/microstructure evolution, fracture surface, W content, crack failure behaviors are studied. The results show that the (Nb,W) co-alloying alloys have better rupture property than the pure Nb alloying alloy. For the (Nb,W) co-alloying alloys, the higher W contained Ti-44Al-4Nb-1 W-0.1B alloy has the better property under lower tensile stress, and the lower W contained Ti-44Al-7.2Nb-0.2 W-0.1B alloy has the better property under higher tensile stress. The relationships of rupture life t and stress σ for the three alloys are given. All the three alloys have a coupling fracture mode of ductile fracture and brittle fracture. The ductile fracture exhibits the typical dimple characteristics. The brittle fracture exhibits the typical trans-granular cleavage, river-like pattern and trans-lamella fracture characteristics. The higher the stress, the more brittle fracture characteristics there are. After rupture property testing, the (α2 + γ) lamella colony sizes of the three alloys all decrease, indicating that DRX and grain boundary slip occur not only along (α2 + γ) lamella colony boundary, but also inside it. The colony boundary regions have the stress concentration, where the B2 phase produces the better buffering and coordination, and as well as the dislocation tangles, DRX and grain boundary slip can be found by EBSD and TEM. EPMA results show that the more W added in the alloy, the more W content is in the (α2 + γ) lamella matrix, which is beneficial for the rupture property. However, more W addition will also lead to the formation of more B2 phase in the initial as-cast microstructure. So that, under higher tensile stress, when the stress intensity factor K is higher, the crack failure is more likely to occur.

Study on interface bonding and mechanical properties of arc-shaped bamboo-poplar wood composites

The bamboo-wood composite is a high-performance product that utilizing the strengths of both materials, which also can effectively reduce the weight of the composite material. An equal arc-shaped bamboo split has been studied by our research group, which retains the natural arcuate structure and achieves a utilization rate of approximately 85%. Based on this, a new composite made of arc-shaped bamboo split and poplar wood is prepared in this paper. And another material made of flattened bamboo and poplar wood also prepared as a control. The mean flexural modulus and strengths for arc-shaped bamboo split were 12179.33MPa and 195.77MPa respectively, the shear strength of the adhesive layer in the composite of arc-shaped bamboo and poplar wood was a robust 8.02MPa. The flexural maximum load of arc-shaped bamboo-poplar composite was 9896.29N, nearly twice as much as that of flattened bamboo-poplar composite, whose excellent performance was expected to exceed the requirements of industrial products. The phenol-formaldehyde (PF) adhesive penetrated into the bamboo and wood quite deeply, allowing it to secure the two pieces of board together like many small glue nails. Besides the physical connections, lots of effective chemical bonding were formed between PF and the two boards. In addition, it was also found that the fracture mode of arc-shaped bamboo and poplar wood composites was ductile fracture, which was different from the brittle fracture mode of traditional bamboo and wood composites. Overall, this new arc structural composite material has high performance and will expand the application of bamboo engineering materials in industry products.

Laser lap joining of R60702 zirconium alloy and 304 stainless steel utilizing CoNiTiV high entropy alloy

In this study, the laser lap welding of R60702 zirconium alloy and 304 stainless steel was successfully achieved by incorporating CoNiTiV high entropy alloy (HEA) interlayer. The addition of HEA interlayer altered elemental diffusion and prevented the formation of Zr-Fe intermetallic compounds. The maximum tensile and shear strength of the joint (998.4 N) is 2.5 times that of the sandwich joint without the HEA layer (392.1 N), with the displacement also increasing by 85 %. The inclusion of the intermediate HEA layer transforms the original brittle fracture mode into a tough-brittle mixed fracture mode. The elimination of Zr-Fe intermetallic compounds is the primary factor contributing to the enhancement of mechanical properties. The main phase composition includes α-Zr, Cr2Zr, CoTi2, Ni7Zr2 and Zr3Co phase.

Recrystallization behavior and strengthening mechanism of friction stir welded T-joint of Ti80 titanium alloy

In this study, Ti80 titanium alloy T-joints were produced by friction stir welding (FSW), and the joint temperature and residual stress distribution of the joints were analyzed by numerical simulation based on the ABAQUS platform, and the correlation between microstructure and performance of FSWed T-joint was investigated. The results show that the SZ is lamellar α grains due to the fact that the peak temperature of all joints exceeds β phase transus. The deformation and dynamic recrystallization behavior take place in the β phase region. During the subsequent cooling stage, the acicular α/α' phase is precipitated from refined prior β phase. The non-uniform heating and cooling results in the significant microstructure differences in the weld thickness direction. The top and middle of the SZ are composed of basketweave structure, while the bottom of the SZ shows a bimodal structure. The microhardness distribution along the skin shows a higher value in the weld area, and the weakest area is located in the HAZ due to recovery, resulting in a significant reduction in dislocation density of the weld. The tensile specimen breaks in the HAZ when it is stretched along the skin direction, while it breaks in a direction parallel to the skin when it is stretched along the stringer. The fracture mechanism of the joint changes from a hybrid mode of ductile and brittle fracture to ductile fracture as the rotation speed increases from 600 rpm to 750 rpm.

Effect of Sn content on microstructure and mechanical properties of Mg-2Zn-1Ca-xSn /Al composite plate

This article explores the effects of different amounts of Sn (1,2,5 wt%) added to magnesium matrix on the microstructure and formability of Mg-2Zn-1Ca-xSn/Al composite plates. The second phase analysis results indicate that Sn element has a significant inhibitory effect on Ca2Mg6Zn3 phase. As the Sn element increases, the Ca2Mg6Zn3 phase gradually disappears, but the number and size of CaMgSn phase increase significantly (5–8μm). The tensile results at room temperature indicate that the composite plate has the highest strength but lower elongation when the Sn content is 2 wt%. It is mainly attributed to the dispersed distribution of small-sized second phases (<1μm), which cause pinning effect on dislocations and lead to dislocation accumulation. Excessive Sn (5 wt%) can promote dynamic recrystallization, resulting in equiaaxial grain distribution. The average Schmidt factor (0.22) of the basal slip is concurrently increased, makes the base slip system easier to start at room temperature. The Mg-2Zn-1Ca-5Sn alloy exhibits obvious softening, leading to a significant reduction in hardness difference between the Mg-2Zn-1Ca-5Sn alloy and the Al alloy. The enhanced feature also facilitates improved coordinated deformation capability and serves to prolong the occurrence of interface delamination in deformation. The Mg/Al composite plate exhibits excellent plastic deformation ability when the Sn content is 5 wt%, the average performance values were 207.52 MPa (UTS), 145.48 MPa (YS) and 17.45 %(EL), respectively. The fracture behavior of the composite plate undergoes a shift from brittle fracture to a combination of ductile and brittle fracture modes, occurring simultaneously. In summary, the incorporation of an optimal amount of Sn content can enhance the plastic formability of Mg/Al composite plates.

Mechanical properties of Si(1−x)–C(x): strength and stiffness of materials using LAMMPS molecular dynamics simulation

This study investigated the mechanical properties (elastic modulus, tensile strength, yield strength, and toughness) of different percent C of silicon carbide (SiC) using molecular dynamics simulations via the large-scale atomic/molecular massively parallel simulator (LAMMPS) with the uniaxial tensile test at four strain rates: 0.1, 0.5, 1.0, and 5.0 m s−1, using the Tersoff potential. The simulation uses 20 × 20 × 20 atoms (108.6 Å × 108.6 Å × 108.6 Å) of the diamond cubic structure of Si, then carbon atoms were placed randomly at 5% intervals from 0–50 percent C. Results show improved mechanical properties when increasing percent C until peaking at 25%, before decreasing. This is caused by the shortest bond length at 25 percent C from the increase of Si=C using the radial distribution function analysis. Increasing the strain rate generally improves the mechanical properties of the material. The deformation mechanism shows that increasing (decreasing) strain rate generally results in multiple (lesser) failure points with a ductile (brittle) fracture mode.

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

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

Analytical model for material removal rate in rotary tool micro-ultrasonic machining of hard and brittle materials

The rotary tool micro-ultrasonic machining (RT-MUSM) process is a newly developed variant of conventional micro-USM. It is preferred over conventional micro-USM due to its ability to remove material at a faster rate and with better accuracy than the machined microfeatures. Some experimental investigations have been conducted on the RT-MUSM process for the machining of hard and brittle materials. However, the theoretical model of the material removal rate (MRR) for the RT-MUSM process has not been discussed in the literature. Thus, the present research work reports on developing a predictive model of the MRR for the RT-MUSM process during glass machining. Pure brittle fracture mode was considered to be the material removal mechanism during the model's development. The developed model was verified through experiments. The estimated results were compared with the experimental results and found to be in good agreement with each other. Additionally, statistical analysis was carried out for the prediction accuracy of the developed model. The results revealed that the model is adequate, with a correlation coefficient of 0.9976 and a mean absolute percentage error of 2.45%. Hence, the developed model can be used to estimate the MRR for the RT-MUSM process of hard and brittle materials such as ceramics.

Simultaneous improvement in strength and ductility of friction stir welded Mg/Al joints by reducing micro-intermixing

Thread of pin has been proved beneficial to increasing shear action of tool and material intermixing, which however induces abundant formation of intermetallic compounds (IMCs) in Mg/Al dissimilar friction stir welding (FSW) leading to deteriorating the performance of joints. In this work, Mg alloy and Al alloy were well joined by threaded pin and unthreaded pin under the same welding parameters. For threaded pin joints, cracks occured in the banded structure (BS) region and bottom interface, then the main crack propagated along the Mg/Al interface, resulting in low strength and elongation. For unthreaded pin joints, necking and fracture occurred at the softened Al alloy to the retreating side (SAA-RS), and the fracture mode changed from brittle fracture (Mode I) to ductile fracture (Mode III). The tensile strength and strain of unthreaded pin joints are 201 MPa and 7.14 % respectively, significantly higher than those of threaded pin joints (i.e. 140 MPa and 1.15 %), and is the highest combination of strength and strain reported up until now. An unthreaded pin could reduce the local micro-intermixing between Mg and Al to suppress the formation of IMCs, which reduced the hardness in the BS region, preventing the formation and propagation of cracks.

Numerical and experimental studies on dissimilar joining of Hastelloy C-276 and SS-316L using microwave hybrid heating at 2.45 GHz

Dissimilar joints of SS-316L and C-276 (Hastelloy) were developed using C-276 powder with microwave exposure 600 s in microwave applicator (2.45 GHz, 900 W). A multi-physics model was validated with experimental studies and simulation were carried out to analyse the microwave-joint interaction characteristics. The simulation results showed that a concentrated electric field (5.86 × 104 V/m) and higher resistive losses (3.07 × 107 W/m3) at the joint region facilitated rapid heat generation locally. Microstructural characterization of the joint revealed the formation of cellular grains such as Fe-Ni intermetallic phases with Mo, Cr and W-carbides along the grain boundaries. Joints exhibited average microhardness of 290 HV, and tensile strength of 425 ± 10 MPa and 14% elongation with failure due to both ductile and brittle fracture modes.

Revealing the failure mechanism of industrial Fe-25Cr-20Ni stainless steel plate: Fine-grained segregation band and brittle phase induced delamination cracking

The use of heat-resistant stainless steel thick plates in industrial production often presents challenges due to the presence of uneven microstructure and segregation, which can pose a persistent challenge for the prolonged safe operation of critical components made from such materials. This study aimed to investigate the fracture mechanism of an industrial Fe-25Cr-20Ni stainless steel plate at room temperature through uniaxial tensile experiments and fully reversed strain-controlled tension-compression fatigue experiments. Delamination cracks were observed on the fracture surfaces of both experiments. The specimens with fracture delamination were systematically studied by detailed microstructural evolution, and the failure mechanism and main reasons of fracture delamination were analyzed. The results show that the fracture delamination is related to the fine-grained segregation band (FGSB) consisted of fine grains and sigma phase located at the center of the thickness of the stainless-steel plate. The FGSB demonstrates low transgranular and intergranular fracture modes and exhibits bamboo knobs crack during plastic deformation, leading to a mixed fracture mode of ductile and brittle fracture. Furthermore, FGSB, as an anisotropic microstructure, which has a high stress concentration with nearby grains during plastic deformation. The sigma phase fracture and the weakening of the interface strength of the microstructure in FGSB provide a potential initiation site for fatigue crack initiation, thereby contributing to the possibility of aggravating fatigue damage and deteriorating fatigue performance. It is concluded that FGSB, as a metallurgical defect in stainless steel plates, is responsible for delamination failure.

Effects of heat treatments on the microstructure and mechanical properties of Inconel 718 alloy fabricated by electron beam freeform fabrication

The present study investigated the effects of different heat treatments on the microstructure and mechanical properties of Inconel 718 alloy fabricated by electron beam freeform fabrication. The Laves phases, γʹ phases, and (Nb,Ti)C particles were precipitated in the as-deposited specimen. Solution at 960 °C promoted the partial dissolution of Laves phases and the precipitation of δ phases. Further increasing the solution temperature to 1060 °C dissolved the Laves phases effectively, facilitating the adequate precipitation and uniform distribution of γʹ and γʹʹ phases during the subsequent double aging heat treatment. The ultimate tensile strength (UTS) and elongation of the as-deposited specimen were 770 MPa and 12.2 % respectively. The solution heat treatment at 1060 °C increased the elongation to 38.1 % but decreased the UTS to 734 MPa. The microhardness and UTS of specimens that underwent double aging heat treatment were significantly increased, with the maximum average microhardness and UTS reaching 491 HV0.5 and 1285 MPa, respectively. The undissolved Laves phases and the precipitated δ phases at grain boundaries impaired the ductility. The transformation from single solution or double aging heat treatment to solution plus double aging heat treatment led to a shift from a ductile fracture mode to a mixed ductile and brittle fracture mode.