Quasi-cleavage Fracture Research Articles

Effects of rapid infrared radiation heating on the warping deformation and mechanical properties of selective laser melted Co-Cr dental alloy.

Infrared radiation heating (IRH) technology has been innovatively applied to the annealing of selective laser melted (SLM) cobalt chromium (Co-Cr) frameworks. However, previous studies have not reported the effects of IRH on the warping deformation and mechanical properties of these frameworks. The purpose of this in vitro study was to investigate the effects of IRH on the warping deformation and mechanical properties of dental SLM Co-Cr alloy and to evaluate its potential applications in dental restorations. Two types of specimens, bone-shaped tensile specimens and warping deformation specimens (cantilever beam structures), were fabricated by SLM, followed by annealing using IRH and general furnace heating (GFH). The specimens were divided into 4 groups (n=6) based on the applied heat treatment method and build direction (IRH-XY; IRH-Z; GFH-XY; GFH-Z). The cantilever beam support structure of the warping deformation specimen was cut using wire cutting, and the warping deformation was measured using a digital image correlation optical extensometer. Tensile tests were used to evaluate mechanical properties, with the fracture characteristics being observed using a scanning electron microscope (SEM). A micro-Vickers hardness tester was used to measure the microhardness. The microstructures were analyzed using a metallographic microscope. All data were analyzed using a 1-way ANOVA and the Tukey Honestly Significant Difference test (α=.05). The surfaces of the SLM Co-Cr warping deformation specimens treated with IRH showed slight oxidation, while those treated with GFH exhibited a dark black appearance. No significant difference was found in deformation between the IRH group (0.412 ±0.039 mm) and the GFH group (0.379 ±0.070 mm) (P>.05). The elongation of the longitudinally built specimens was significantly higher than that of their transversely built counterparts (P<.05), while the yield strength showed an opposite trend. The longitudinally built specimens demonstrated ductile fracture characteristics, while the transversely built specimens displayed quasi-cleavage fractures. The specimens treated with IRH exhibited comparable tensile strength and microhardness with the GFH-treated specimens, with no statistically significant differences (P>.05). IRH treatment resulted in finer grains in the SLM Co-Cr alloy. Many fine second-phase particles precipitated from the matrix in the longitudinally built specimens, while few were observed in the transversely built specimens. The SLM Co-Cr specimens treated with IRH achieved comparable warping deformation and mechanical properties with those of the GFH-treated specimens. The IRH technology holds great potential for application to dental restorations.

Effect of Hydrogen on Tensile Properties and Fracture Behavior of Two High-Strength American Petroleum Institute Linepipe Steels

This study explored the influence of hydrogen on the tensile properties and fracture behavior of high-strength API X70 and X80 linepipe steels with bainitic microstructures under varying hydrogen charging conditions. The X70 steel exhibited a ferritic microstructure with some pearlite, while the X80 steel showed a bainitic microstructure and fine pearlite due to the addition of molybdenum. Slow strain rate tests (SSRTs) were conducted using both electrochemical ex situ and in situ hydrogen charging methods subjected to different current densities. The SSRT results showed that in situ hydrogen-charged SSRT, performed at current densities above 1 A/m2, led to more pronounced hydrogen embrittlement compared to ex situ hydrogen-charged SSRT. This occurred because hydrogen was continuously supplied during deformation, exceeding the critical concentration even in the center regions, leading to quasi-cleavage fractures marked by localized cleavage and tearing ridges. Thermal desorption analysis (TDA) confirmed that a greater amount of hydrogen was trapped at dislocations during in situ hydrogen-charged SSRT, intensifying hydrogen embrittlement, even with a shorter hydrogen charging duration. These findings highlight the importance of selecting appropriate hydrogen charging methods and understanding the hydrogen embrittlement behavior of linepipe steels.

Interfacial structure and mechanical properties of contact-reaction TC4/TC4 joint brazed with copper filler

TC4 alloy was brazed by contact reaction brazing without flux in vacuum brazing furnace with copper foil as intermediate layer. The variation of microstructure and strength of the sandwich TC4/Cu/TC4 brazed joints with different brazing temperature were discussed. The results showed that the joint consisted of diffusion zone (β-Ti), interface zone (Ti2Cu) and center zone (a large amount of complex Ti-Cu compounds) with low brazing temperature (920 ℃). With the increase of temperature, the center zone firstly disappeared, then the interface zone, finally leaving the diffusion zone and little of interface zone (1010 ℃). After the compression shear testing, it showed that with the increasing brazing temperature, the shear strength of the joints raised, the maximum shear strength can reach 735MPa at 980 ℃. Although further increasing the brazing temperature increases the joint strength, the high processing temperature (above the α→β phase transus temperature of about 985 ℃) deteriorates the properties of the TC4 base metal. The fracture mode with low brazing temperature presented cleavage fracture while the fracture mode with high brazing temperature appeared quasi-cleavage fracture.

Hydrogen Embrittlement Sensitivity of X70 Welded Pipe Under a High-Pressure Pure Hydrogen Environment.

With the rapid development of hydrogen pipelines, their safety issues have become increasingly prominent. In order to evaluate the properties of pipeline materials under a high-pressure hydrogen environment, this study investigates the hydrogen embrittlement sensitivity of X70 welded pipe in a 10 MPa high-pressure hydrogen environment, using slow strain rate testing (SSRT) and low-cycle fatigue (LCF) analysis. The microstructure, slow tensile and fatigue fracture morphology of base metal (BM) and weld metal (WM) were characterized and analyzed by means of ultra-depth microscope, scanning electron microscope (SEM), electron backscattering diffraction (EBSD), and transmission electron microscope (TEM). Results indicate that while the high-pressure hydrogen environment has minimal impact on ultimate tensile strength (UTS) for both BM and WM, it significantly decreases reduction of area (RA) and elongation (EL), with RA reduction in WM exceeding that in BM. Under the nitrogen environment, the slow tensile fracture of X70 pipeline steel BM and WM is a typical ductile fracture, while under the high-pressure hydrogen environment, the unevenness of the slow tensile fracture increased, and a large number of microcracks appeared on the fracture surface and edges, with the fracture mode changing to ductile fracture + quasi-cleavage fracture. In addition, the high-pressure hydrogen environment reduces the fatigue life of the BM and WM of X70 pipeline steel, and the fatigue life of the WM decreases more than that of the BM as well. Compared to the nitrogen environment, the fatigue fracture specimens of BM and WM in the hydrogen environment showed quasi-cleavage fracture patterns, and the fracture area in the instantaneous fracture zone (IFZ) was significantly reduced. Compared with the BM of X70 pipeline steel, although the effective grain size of the WM is smaller, WM's microstructure, with larger Martensite/austenite (M/A) constituents and MnS and Al-rich oxides, contributes to a heightened embrittlement sensitivity. In contrast, the second-phase precipitation of nanosized Nb, V, and Ti composite carbon-nitride in the BM acts as an effective irreversible hydrogen trap, which can significantly reduce the hydrogen embrittlement sensitivity.

Achieving high strength in AA2024 alloy by natural aging and asymmetric cold rolling

The effect of natural aging followed by cold single-roll drive rolling (SRDR) on microstructural evolution, texture, hardness, tensile behavior, and fracture surface of an Al–Cu–Mg alloy was investigated. The average grain width of the cold-deformed samples was remarkably decreased from ∼ 13.2 to ∼ 6.5 µm. During the cold SRDR, the large Al7Cu2Fe particles in the as-received alloy were fragmented into smaller particles. The maximum content of deformation bands belonged to the samples after 24 h natural aging followed by 50 % SRDR. With an increase in the aging time from 0 to 24 h, shifting of the peak toward the right (higher 2θ angle) was observed due to the reduction in the coherency between precipitates and alpha-aluminum. The intensity of shear texture in all rolled samples had a high value owing to the use of the SRDR process, which causes strong shear deformation in the sample. After 24 h natural aging followed by 50 % cold SRDR, the sample indicated the peak hardness value of 217.4 HV due to the presence of semi-coherent interfaces of S’ precipitates. By increasing the natural aging duration up to 24 h, the yield strength and ultimate tensile strength were significantly increased to 642.7 and 706.1 MPa, respectively, whereas the ductility was decreased to 8.7 %. A remarkable increase in strain hardening of the 192-h sample promoted uniform elongation and retarded necking (localized deformation) and fracture. In all samples the fracture mode was ductile and in the 24- and 96-h samples there were several flat surfaces, which suggested local quasi-cleavage fracture. The fracturing of the Al7Cu2Fe particles was rarely seen in the fracture surface of the 96-h sample due to the low ductility of the aluminum matrix.

Performance of the GH4169 Joint Using a Novel Ni-Based Amorphous Brazing Filler Metal

A novel Ni-Cr-Si-B filler metal (JNi-5) was designed and further fabricated into the amorphous brazing filler metal for joining the GH4169 alloy. The effect of brazing temperature on the microstructure and mechanical properties of GH4169 joints was investigated. The typical microstructure of the joint at 1030 °C is composed of four specific zones: the base metal (BM), heat-affected zone (HAZ), isothermal solidification zone (ISZ), and athermal solidification zone (ASZ). The typical microstructure of the joint is GH4169/(Nb, Mo)-rich boride+(Cr, Nb, Mo)-rich boride/γ(Ni)/Ni-rich boride+γ(Ni)/γ(Ni)/(Cr, Nb, Mo)-rich boride+(Nb, Mo)-rich boride/GH4169. As the temperature increased, the HAZ continued to widen and the ASZ depleted at 1090 °C and 1120 °C. Additionally, the borides within the HAZ coarsened at temperatures of 1090 °C and 1120 °C. At 1030 °C, the fracture path is in the ASZ, and the existence of the brittle phase in the ASZ provides the potential origin for crack growth. The fracture mode is a quasi-cleavage fracture. At 1060 °C, 1090 °C, and 1120 °C, the fracture behavior mainly happened in the HAZ, and the existence of borides in the HAZ provides the potential origin for crack growth. Namely, the shear strength of joints was principally dominated by the brittle precipitations in the HAZ. The fracture mode of these joints is the hybrid ductile. At 1060 °C, the shear strength of the obtained joint is the highest value (693.78 MPa) due to the volume fraction increase in the Ni-based solid solution. Finally, the optimized brazing parameter of 1060 °C/10 min was determined, and the corresponding highest shear strength of 693.78 MPa was obtained owing to the increased content of the Ni-based solid solution in the joint.

Enhanced wear resistance and fracture resistance of spherical WC reinforced nickel-based alloy coating by adding non-spherical WC

Spherical WC particles are widely employed as hard phases to reinforce metal matrix coatings; however, their deposition during the surfacing process presents a significant challenge, resulting in limited improvements in coating hardness and wear resistance. In this work, these spherical WC as well as spherical/non-spherical WC particles have been used to prepare the WC reinforced nickel-based alloy coatings. The microstructure, mechanical, wear and fracture behavior of these coatings were investigated by detailed characterization. Results showed that spherical WC exhibited rapid sedimentation, and the primary decomposition products existed lump-like W2C. The ultimate decomposition process was based on the exfoliation of the diffusion layer. The spherical WC/Ni coatings exhibited a hardness of 13 GPa and an elastic modulus of 253 GPa, respectively. Notably, the wear rate of these coatings was relatively high, measuring 7.038 × 10−6 mm3/(N·m), while the stress and strain were comparatively low, standing at only 272.5 MPa and 0.72 %. In contrast, spherical/non-spherical WC/Ni coatings demonstrated distinct differential sedimentation behavior. Spherical WC particles settled at the bottom of the coating, whereas non-spherical WC particles were dispersed in the middle and upper regions. The decomposition of non-spherical WC particles was governed by the dissolution and diffusion of W2C, forming a skeleton-braided structure of M7C3, γ, and M23C6 phases on the coating surface. This unique structure increased the hardness of the coating to 21 GPa and the elastic modulus to 369 GPa, while reducing the wear rate to 2.853 × 10−6 mm3 (N · m) −1. In addition, the stress and strain reached 497.10 MPa and 1.97 % respectively, shifting the fracture mode to quasi-cleavage fracture with tear ridges. Overall, the spherical/non-spherical WC/Ni coating exhibited improved deformation resistance and superior wear resistance.

Formation ability, phase decomposition and mechanical properties of Ti39Zr39Ni20Ag2 and Ti39Zr39Ni20Cu2 bulk icosahedral quasicrystalline alloys

An icosahedral quasicrystalline (IQ) phase forms in the as-spun ribbons as well as as-cast bulk rods with a diameter of 2 mm for the Ti39Zr39Ni20Ag2 and Ti39Zr39Ni20Cu2 alloys. The Ti39Zr39Ni20Ag2 alloy ribbon consists of a mostly amorphous phase containing a small amount of IQ phases and exhibits good bending plasticity. The decomposition of their metastable phases occurs accompanying exothermic peaks at 694 K and 890 K, followed by an endothermic peak at 991 K. The former two peaks are due to the transitions from amorphous to IQ + cF96-(Ti, Zr)2Ni phases, and to C14-TiZrNi Laves phase, respectively. The latter endothermic peak originates from the change of IQ to C14-TiZrNi Laves and β-(Ti, Zr) phases. Compared with the complex phase decomposition behavior of the quaternary alloys, the decomposition of the metastable phase of the Ti40Zr40Ni20 alloy ribbon occurs accompanying only an endothermic peak at a peak temperature of 952 K, followed by a melting peak. For the quaternary alloys, the as-cast rods consist of an IQ single phase, in contrast to three phases of IQ, C14-TiZrNi Laves and β-(Ti, Zr) phases for the Ti40Zr40Ni20 rod. The ternary alloy rod fractures in the quasi-cleavage fracture mode, while the fracture mode of the quaternary alloy rod is cleavage fracture. In the Ti39Zr39Ni20Ag2 rod, IQ phase displays a spherical morphology with an average diameter of approximately 0.27 μm. The formation of the bulk IQ rod as well as the enhancement of amorphous phase formability for the Ag/Cu-containing IQ alloys are presumably due to the stabilization of supercooled liquid caused by the development of more dense-packed atomic configurations resulting from the sequent atomic size change of Zr > Ti > Ag/Cu > Ni as well as by the necessity of the separation to Ti-Zr-Ni and Ti-Zr-Ag/Cu atomic pairs resulting from the positive heats of mixing for Ni-Ag and Ni-Cu pairs.

Optimization of bobbin tool friction stir welding parameters of AZ31 magnesium alloy based on FEM and its influence mechanism on mechanical properties

Based on the 3D transient heat transfer theory, the finite element model of bobbin tool friction stir welding (BT-FSW) of AZ31 magnesium alloy sheet is established. The effects of different process parameters on the quality of BT-FSW joint of magnesium alloy were discussed using temperature distribution, mechanical properties, fracture morphology analysis, and EDS element distribution analysis. The results show that in the process of BT-FSW, the cross-section temperature of the plate is symmetrically distributed in an hourglass shape, the AS is slightly lower than that of RS, and the transverse temperature is distributed in an ‘M’ shape. When the rotating speed is 700 rpm and the welding speed is 180 mm/min, the weld surface is smooth, and its ultimate tensile strength can reach 81.82% of the base metal strength. The tensile specimen is quasi-cleavage fracture. When the heat input is insufficient, there are a lot of Al8Mn5 Precipitated phases in the TMAZ fracture zone, which increases the fracture brittleness of the joint. When the heat input is enough, the precipitated phase dissolves evenly, the river-like fracture surface of the joint retains the dimple characteristics, and the mechanical properties are improved.

Ratcheting-fatigue behavior and fracture mechanism of 316H ASS under cyclic random loading block

In this study, a set of programmed random factors with non-zero mean were designed. Then various stress levels (15, 18 and 22 KN) were multiple superimposed to factors to form one random loading block (RLB), the blocks were repeated to failure to investigate the synergistic damage of 316H ASS under low-cycle fatigue (LCF), high-cycle fatigue (HCF) and ratcheting effect. The lifetime of cyclic RLB tests decreased with the increase of block-mean stresses σmBlock (208、255 and 311.5 MPa). The normalized strain amplitudes indicate that when the σmBlock amplitude below the yield strength (208 and 255 MPa), a stable ratchet accumulation phase allows the specimens to exhibit cyclic hardening behavior. When σmBlock (311.5 MPa) exceeds the yield strength, the ratcheting strain increases significantly and the specimens exhibit cyclic softening behavior. Especially, the transgranular cleavage fracture, quasi-cleavage fracture and intergranular secondary cracks were identified when the failure of cyclic RLB tests were induced by LCF, HCF and ratcheting. With the increase of σmBlock amplitude, the decrease of LAGB proportion and the increase of dislocation density further reduce the fatigue resistance. In addition to dislocation motion, the α’-martensite phase transformation induced by ratcheting-fatigue has been further demonstrated as a mechanism for coordinated deformation. The percentage of stresses (within one block) that exceeds the diverge critical stress (375.6 MPa) of stacking faults (SFs) determines the α’-martensite nucleation mechanism.

Bonding behavior of Ti-6Al-3Nb-2Zr-1Mo/WC composite coating on titanium alloy by gas tungsten arc welding cladding

In this study, tungsten carbide (WC) ceramic particles were introduced into the molten pool of gas tungsten arc welding (GTAW) to successfully prepare a composite coating without solidification cracking and with lower dilution. The formation mechanism and properties of the bonding interface are deeply analyzed. Results demonstrate that metallurgical bonding was achieved. The dissolution behavior of WC particles and the diffusion of W element into the heat-affected zone promoted the formation of a special β(Ti, W) diffusion layer below the fusion line. (Nb, Ti)C was mainly found distributed close to the diffusion layer. Nanoindentation test results show remarkable inhomogeneity in the interface area. The fracture surface of the broken coating revealed that the titanium matrix exhibited quasi-cleavage fracture, while the particles displayed brittle fractures. The fracture surface of coatings that experienced decohesive rupture in the shear test underwent plastic deformation in the shear direction.

Effects of hydrogen blending ratios and CO2 on hydrogen embrittlement of X65 steel in high-pressure offshore hydrogen-blended natural gas pipelines

In this study, the effects of hydrogen blending ratios and high CO2 content on hydrogen embrittlement (HE) of offshore natural gas X65 pipeline steel were investigated. In high-pressure hydrogen gas, the impact of hydrogen content on yield strength and tensile strength was minimal. However, the effect on elongation was more significant, with the area decreasing and the HE index increasing until the hydrogen-blended ratio approached 30%, at which point the HE index reached 8.94%. Introducing CO2 into high-pressure hydrogen-rich gas further increased the HE index with high CO2 content. At 40% CO2, the HE index was 2.42 times higher than in high-pressure hydrogen-blended mixtures (30% H2). Additionally, the local fracture morphology transitions from ductile to quasi-cleavage fracture with the addition of CO2 and H2.

Influence of Heat Treatment on Microstructure and Mechanical Properties of Laser Cladding Coatings

This study investigates the influence of various heat treatment processes on the microstructure and properties of laser cladding Fe314 coatings. The microstructure, phases, and impact fracture morphology of the cladding layer were observed using X-ray diffraction and scanning electron microscopy, among other methods. The hardness and impact performance of the cladding layer were also tested. The results indicated that there was compositional segregation and non-equilibrium microstructure in the untreated cladding layer, with an average microhardness of 368.67 HV and an impact toughness of 27 J, exhibiting quasi-cleavage fracture. The stress-relief annealing treatment resulted in a uniform distribution of M23C6 carbides inside the cladding layer. The pinning effect generated by M23C6 reduced the microhardness by 16.26% and increased the impact toughness to 54 J. The impact fracture surface exhibited ductile fracture. After secondary normalizing and annealing, the microstructure of the cladding layer transformed into a fine single-phase austenite structure, and fine M7C3 carbides precipitated at the grain boundaries. Under the effects of fine grain strengthening and dispersion strengthening, the microhardness of the cladding layer decreased by 38.14%, and the average impact absorbed energy of the specimen was 64 J, showing complete ductile fracture.

Microstructure, deformation and fracture mechanism of Mg-Gd-Y-Zn-Zr alloy with different rolling routes during tension

The microstructure, deformation and fracture mechanism of unidirectional rolling (UR) and cross rolling (CR) Mg-4.7Gd-3.4Y-1.2Zn-0.5Zr alloy during tension were studied. Both rolled alloys exhibit typical bimodal microstructures, with the difference being that UR alloy has elongated grains containing rod LPSO phase, while CR alloy has relatively rounded deformed grains containing lamellar LPSO phase. After tension until fracture, the LPSO phase morphology of the two alloys remains unchanged. CR alloy exhibits a higher yield strength and lower elongation than UR alloy. Although the higher average basal <a> slip Schmid factor result in the lower yield strength of UR alloy, the activation of the high proportion of non-basal slip is responsible for its higher elongation. UR alloy and CR alloy exhibit ductile fracture and quasi cleavage fracture characteristics, respectively. For UR alloy, a variety of dislocations accumulated near grain boundary and the weak slip transfer effects between grains both contributes to the propagation of grain boundary cracks. However, the effects of weak interfacial bonding between metastable lamellar LPSO phase and matrix, along with the similar orientation and higher geometric compatibility of CR alloy, lead to the rapid spread of transgranular cracks.

Origin of Serrated Markings on the Hydrogen Related Quasi-cleavage Fracture in Low-carbon Steel with Ferrite Microstructure

Origin of Serrated Markings on the Hydrogen Related Quasi-cleavage Fracture in Low-carbon Steel with Ferrite Microstructure

Low cycle fatigue behavior and failure mechanism of 34CrNiMo6 steel used as connecting rod for diesel engine

Abstract In this paper, for the 34CrNiMo6 steel material used in diesel engine connecting rods, the low-cycle fatigue properties and failure mechanism were studied. The metallographic structure of 34CrNiMo6 has been investigated by using optical microscopes, scanning electron microscopes, and transmission electron microscopes. Tensile tests and low-cycle fatigue experiments were performed at different levels of strain amplitudes, and the microstructural changes were monitored. The examination indicates that the structure of 34CrNiMo6 steel consisted primarily of a ferrite base and small spherical and rod-shaped carbides, with a mean particle size measuring 2 μm. It had exceptional mechanical characteristics of high strength and moderate plasticity. The total strain amplitude (TSA) of 34CrNiMo6 steel affected the cycling behavior, which was stable at low TSA (0.2% ~ 0.3%). At high TSA (0.4% ~ 0.7%), a large number of dislocations were annihilated through the dynamic recovery process, showing a typical cyclic softening phenomenon. The low-cycle fatigue failure behavior was mainly a combined mode of quasi-cleavage fracture and cross-grain fracture.

Coupling between phase transition and spallation in hierarchically structured high-strength martensitic steels under shock loading

This work presents a comprehensive and in-depth investigation of spall damage behaviors of bainitic and martensitic steels involving phase transitions. Plate-impact experiments, postmortem characterizations, molecular dynamics simulations considering realistic microstructures of bainitic and martensitic steels, and one-dimensional hydrodynamics simulations incorporating phase transition and spall damage are conducted and investigated. Origins of the multiple spall planes and their characteristics within steels are elucidated. Both steels exhibit a quasi-cleavage fracture mode involving phase transitions, with damage morphologies dependent on the microstructures and validated by molecular dynamics simulations. One-dimensional hydrodynamics simulations successfully replicate the dynamic spallation evolutions in steels considering phase transitions.

Study on low cycle fatigue properties of Cr-Mo steel in 50 MPa gaseous hydrogen

At present, a lack of fatigue design curves for Cr-Mo steel in high-pressure gaseous hydrogen worldwide impedes the use of the design fatigue curve (S-N curve) evaluation for vessel fatigue design, necessitating reliance on fracture mechanics methods related to the initial crack size. In this study, strain-controlled fatigue tests with a strain ratio of −1 were carried out in 50 MPa gaseous hydrogen to study the low cycle fatigue properties of Cr-Mo steel. Results indicate that hydrogen reduces the fatigue life of 4130X under high strain amplitudes. Under 0.5 % strain amplitude, different from characteristics of ductile fracture in air, the fracture in 50 MPa gaseous hydrogen showed quasi-cleavage and intergranular fracture characteristics. Based on the test results, the S-N curve in 50 MPa gaseous hydrogen was obtained with fatigue life safety factor 20 and stress amplitude safety factor 2. The S-N curve in 50 MPa gaseous hydrogen is under the curve in KD-320.2 M of the 2023 ASME Boiler & Pressure Vessel Code VIII-3, which does not consider the effect of hydrogen, when the number of cycles to failure is less than 1×106. This indicates that the fatigue life calculated by the S-N curve in KD-320.2 M cannot ensure that 50 MPa high-pressure hydrogen storage vessels avoid fatigue failure under high stress amplitudes.

Improving the Mechanical Properties of Al-Si Composites through the Synergistic Strengthening of TiB2 Particles and BN Nanosheets

The size and distribution of the silicon phase and intermetallic phase are important factors affecting the properties of Al11Si3Cu2NiMg alloy (M142). In this study, BNNS and micro-TiB2 were used to synergistically refine and reinforce M142 composites (M142-BNNS-TiB2). After T6 heat treatment, the comprehensive mechanical properties of M142-BN-TiB2 composites were excellent, with an ultimate tensile strength of 463 MPa and an elongation of 2.6%. In addition, the introduction of BNNS and micro-TiB2 changed the fracture mode of M142 from brittle fracture to quasi-cleavage fracture, and the introduction of BNNS and micro-TiB2 refined the Si phase and intermetallic phase, which could change the origin of the crack in the composite, thus improving the ductility of the composite.

Microstructure Regulation and Mechanical Properties of Mg–6xZn–xY Alloys Containing Icosahedral Quasicrystalline Phases

Mg–6xZn–xY (x = 0.8, 5, and 7 wt%) alloys containing an icosahedral quasicrystal phase (I‐phase) are synthesized, and the effects of Y doping on the microstructure and mechanical properties of the Mg matrix and I‐phase are investigated. The results show that as the Y content increases, the I‐phase content gradually increases, with the distribution of the I‐phase changing from a discontinuous to a continuous network and lamellar structures. Additionally, the eutectic structure (α‐Mg + I‐phase) in the alloys gradually increases, while the Mg matrix area decreases. The tensile strength of the as‐cast alloy initially increases and then decreases, reaching a maximum value at Y = 5. Heat treatment of the Mg–30Zn–5Y alloy reveals an optimal solid solution temperature of 320 °C, resulting in a tensile strength of 175.09 MPa and quasicleavage fracture characteristics. The maximum tensile strength of the alloy is achieved when the I‐phase distribution is continuous and the porosity of the Mg matrix is ≈66%. These results provide guidance for the microstructural design of I‐phase‐reinforced Mg alloys with rare earth elements to enhance their mechanical properties.