Intermetallics最新文献

The effect of Cu and Si on the microstructure and properties of CoCrFeNiCu_1-xSi_x alloys (x = 0, 0.2, 0.5, 0.8 and 1) was studied in this work. The results indicate that as the x value increased from 0 to 1, the phase compositions of CoCrFeNiCu_1-xSi_x alloys evolved from FCC + Cu-rich phases to FCC + Cu-rich + NiSi-rich phases to FCC + BCC + NiSi-rich phases. Therefore, the decrease in Cu content led to the decreasing Cu-rich phase content, whereas Si addition not only favored the formation of intermetallic compounds, but also promoted the phase transition from FCC to BCC. Due to the competition between BCC phase suppressing corrosion and Cu-rich + NiSi-rich phases inducing galvanic corrosion, the corrosion resistance of CoCrFeNiCu_1-xSi_x alloys improved with the increasing x value. The microstructure change also resulted in an improvement in hardness and wear resistance, and a deterioration in fracture toughness of CoCrFeNiCu_1-xSi_x alloys. Moreover, the main wear mechanism evolved from adhesive wear and abrasive wear to slight abrasive wear. Comparison among five alloys indicates that Cu_0.2Si_0.8 alloy exhibited the excellent comprehensive properties, revealed by the corrosion current density of 4.81 × 10⁻⁸ A/cm², the hardness value of 510.5 HV, the fracture toughness of 8.57 MPa·m^1/2 and the wear rate of 0.88 mm³·N⁻¹ · m⁻¹.

Eutectic high - entropy alloys (EHEAs) effectively strike a delicate balance between strength and ductility in metallic materials by creating heterogeneous biphasic layered structures on the micron and nanometer scales. However, designing EHEAs remains a difficult challenging. In this work, a method is proposed to design EHEAs based on the redistribution of mixing enthalpy and binary eutectic compositions. Four new types of non-equal molar ratio EHEAs have been successfully designed. Namely Co_27.6Cr_7.89Fe_18.34Ni_32.5Nb_13.67, Co_29.44Cr_8.1Fe_18.5Ni_29.96Ta₁₄, Cr_11.62Fe₂₇Ni_47.38Nb₁₄, and Cr_11.93Fe_27.2Ni_47.37Ta_13.5. The microstructure of four EHEAs consists of FCC phase and Laves phase. The experimental results show that it is possible to design EHEAs with excellent performance using the new strategy.

Although relevant theories and models have been used in certain studies on the magnetic properties of amorphous alloys, the influence mechanism of metalloid elements on the magnetic properties of amorphous alloys is currently unclear. The effects of adding the same group of metalloid elements, C, Si, and Ge, on the magnetic properties of FeP amorphous alloys were systematically investigated by utilizing first-principle molecular dynamics. With the replacement of P atoms by C, Si, and Ge, the magnetic moments of the three types of amorphous alloys increase, and the results of the theoretical simulation are in line with the trend of the experimental results. The study revealed that when smaller-radius C atoms replace larger-radius P atoms, these C atoms tend to fill the gap positions of amorphous alloys so that the number of Fe atoms around the Fe atoms gradually increases, which induces an increase in the magnetic moment of the Fe atoms and ultimately leads to an increase in the magnetic moment of the C_x (x = 5, 10 and 15) amorphous alloys. Nevertheless, when the P atoms are substituted by Si or Ge atoms, their atomic radii are comparable to those of the other atoms. The original positions where the P atoms are located are replaced by Si or Ge atoms, which increases the volume of the amorphous alloy, thereby increasing the distance between the Fe atoms and resulting in a gradual increase in the magnetic moment of the Si_x and Ge_x (x = 5, 10, and 15) amorphous alloys. Additionally, compared with C atoms, when Si or Ge with an atomic radius not much different from that of P is used for replacement, more regular icosahedral distributions appear, which enhances the symmetry of the local atomic structure. This may be one of the reasons why the magnetic moment of Si_x or Ge_x amorphous alloys is greater than that of C_x amorphous alloys.

Combined with the potential energy landscape of metallic glasses, this paper discusses the structural origins of rejuvenation at the atomic, nanoscale, and microscale scales in sequence. At the atomic scale, researchers discovered that the mechanism of rejuvenation undergoes a transformation from 2-atom cluster connections to 3-atom cluster connections, which is beneficial to enhancing ductility. At the nanoscale, it is observed that rejuvenation influences the shear-band nucleation behavior of metallic glasses through statistical analysis of nanoindentation. This process generates a high free volume and a large STZ volume, which make it easier to enhance shear-band density and improve ductility. At the microscale, rejuvenation significantly reduces the nano-hardness and elastic modulus of metallic glasses. The increased ductility of rejuvenated metallic glasses can be attributed to the changes in physical quantities at three scales. This study clearly demonstrates the structural origins of rejuvenation in metallic glasses through high-energy synchrotron X-ray diffraction and nanoindentation.

The Strength and toughness trade-off is a long-term dilemma in structural materials. Here, we report a new strategy for synergistically improving the strength and toughness of Nb/Nb₅Si₃ composites by incorporating high-performance graphene to tailor the interfacial coherency and strengthen the matrix. The fabricated graphene reinforced Nb/Nb₅Si₃ composite stands out from available reports on Nb/Nb₅Si₃ composites. The medium mismatch Nb–Nb₅Si₃ interface is transformed into the low mismatch Nb–Nb₄C₃–Nb₅Si₃ multi-interfaces because of the incorporation of graphene and the formation of nano-sized interfacial Nb₄C₃ phases. These low mismatch interfaces facilitate the multiplication of dislocations and the formation of long-range dislocations to annihilate, thereby leading to a superior combination of strength and toughness. Importantly, the low mismatch of Nb₄C₃–Nb and -Nb₅Si₃ interfaces are beneficial for forming a strong interfacial bonding and effectively promoting the anchoring effect to inhibit the pull-out of graphene, resulting in increasing the load transfer from matrix to graphene. The deflecting and bridging of cracks, as well as microcracks, are recognized as the toughening mechanisms in this composite. The present study reveals a strategy to evade the strength and toughness trade-off in Nb/Nb₅Si₃ composites by incorporating high-performance graphene to tailor the interfacial coherency and strengthen the matrix.

This research focuses on the effect of bonding temperature and holding time on the interfacial microstructure, mechanical performance and fracture behavior of diffusion bonded TiAl and Ti₂AlNb intermetallic alloys. Under the pressure of 20 MPa, various bonding temperatures and holding times were explored and the optimized bonding parameter was determined to be 975 °C/60 min. Along with the changing of bonding parameters, the bonding defect, elemental distribution, microstructural evolution, micro-nano mechanics and corresponding mechanical properties of bonded joints were investigated. The findings indicated that the reaction zone was composed of three distinct interfacial layers, that is, a dark gray α₂ layer next to TiAl alloy, a light gray α₂ layer with Al(Nb, Ti)₂ particles distributing between layer II and layer III, and a B2 + O mixed layer adjacent Ti₂AlNb alloy. The maximum elastic modulus of 205 GPa was measured in the α₂ phase on the Ti₂AlNb side, whereas the Al(Nb, Ti)₂ particles exhibited the highest nano-hardness of 14.5 GPa. By optimizing the bonding parameters, a subtle suture structure between layers I and II and well-distributed Al(Nb, Ti)₂ particles were regulated at the bonding interface, which endowed the resultant joint at 975 °C for 60 min with shear strength of 319 MPa. The subtle suture structure between layer I and layer II effectively prevented the propagation of fracture, while the fine Al(Nb, Ti)₂ particles alleviated the stress concentration at the bonding interface. Furthermore, crack bridging and crack blunting also enhanced the mechanical performance of the joint. The results in this paper provide a promising approach for addressing the challenge of joining dissimilar intermetallic alloys.

The ferromagnetic materials with large anomalous Hall effect have attracted numerous interests due to their excellent physical properties and wide application in spintronic devices. Here, we report the magnetic and electrical transport properties of MnGaGe single crystal grown by Ga flux method. Easy-axis ferromagnetic ordering and large magnetocrystalline anisotropy are observed below Curie temperature T_C = 459 K in MnGaGe single crystal. The positive magnetoresistance is observed at low temperature and becomes negative above 60 K. The magnetoresistance presents nearly linear behavior without any sign of saturation with the applied magnetic field up to 5 T. The anomalous Hall effect of MnGaGe is mainly contributed from the extrinsic mechanism. Moreover, we find that the phonon-induced skew scattering plays an important role in this system and increases with increasing temperature. The high transition temperature, large anisotropic out-of-plane magnetism, and remarkable anomalous Hall effect render MnGaGe potential material for spintronic devices.

The size, aspect ratio, and distribution of reinforcement, referred to as the scale characteristic parameters (SCP), are critical factors that influence the mechanical properties of discontinuous reinforced titanium matrix composites (DRTMCs). To investigate the impact of SCP evolution on the microstructure and mechanical properties of TiBw, this study employed spherical Ti6Al4V-TiBw composite powder prepared by electrode induction melting gas atomization (EIGA) as feedstock for fabricating Ti6Al4V-TiBw composites through electron beam powder bed fusion (EB-PBF) process. By implementing a two-step rapid cooling approach in EIGA and EB-PBF processes to “freeze” the TiBw at nanoscale within Ti6Al4V-TiBw composites, a significantly wider regulation window for microstructure and mechanical properties was achieved. Subsequently, heat treatment was conducted at temperatures ranging from 850 to 1200 °C to systematically elucidate the mutual influence regulation among SCPs, microstructure, and mechanical properties of TiBw. Based on our findings, it can be concluded that when subjected to heat treatment temperatures higher than 950 °C, an orientation relationship between TiBw and α-Ti is observed: {0001} _α-Ti//{001} _TiBw, {11 $\bar{2}$ 0} _α-Ti//{010} _TiBw, {10 $\bar{1}$ 0} _α-Ti//{100} _TiBw. Additionally, the cross-section of columnar-shaped TiBw exhibits semi-coherent interfaces with coherent interfaces bonded to Ti along its (100) crystal plane while displaying incoherent interfaces with Ti matrix along its (101) and (10 $\bar{1}$) crystal planes. The strength of Ti6Al4V-TiBw composites exhibited a trend of initial increase followed by decrease with the evolution of TiBw scale characteristic parameters, while the elongation demonstrated an overall decreasing pattern. This research aims to establish a foundation for microstructure and properties control of DRTMCs and provide experimental references and theoretical basis for high-performance DRTMCs research.

In this study, a zinc (Zn) interlayer was applied in the diffusion bonding of pure copper (Cu) and titanium (Ti). The interfacial microstructure evolution and metallurgical reaction mechanisms of Cu/Ti joints with Zn interlayer were investigated by SEM, EDS and TEM. The addition of the Zn interlayer facilitated metallurgical bonding between Cu–Zn and Ti–Zn at low temperatures. The shear strength of joints exhibited a gradual increase followed by a sharp decline as the bonding temperature increased. An intimate bonding between Cu and Ti was achieved at 450 °C, and the highest average shear strength of 106.82 MPa was obtained at 490 °C. The weld seam is primarily composed of a β′-CuZn layer, which exhibited excellent plasticity and hindered the formation of brittle Cu–Ti intermetallic compounds. The τ₁-Cu₂TiZn layer, adjacent to β′-CuZn, demonstrated stronger resistance to crack propagation compared to the brittle TiZn₃ and TiZn₂ layers. Furthermore, the predominant β′-CuZn layer and τ₁-Cu₂TiZn layer formed a coherent interface, ensuring a reliable bonding. These results demonstrate that the addition of Zn interlayer is an effective strategy for preparing highly reliable Cu/Ti joints at low temperatures.

With the current advancements in materials science, the development of high entropy alloys (HEAs) is progressively increasing. Hence, research on their processability is essential to make them competitive alternatives to common engineering alloys that are widely used in structural applications. One manufacturing technique commonly employed in this sector is gas tungsten arc welding (GTAW). This technique allows to obtain single monolithic parts from separate components, often at the cost of local microstructural and mechanical properties variation across the joint. As such, GTAW processing is capable of supplying relevant knowledge regarding the feasibility of joining new materials and their potential industry uptake. In this study, we present a comparative analysis on the use of GTAW on two distinct multiphase high entropy alloys: CoCu₂₀FeMnNi and the CoCu₃₀FeMnNi. Firstly, microstructural observations coupled with CalPhaD-based calculations and synchrotron X-ray diffraction analysis, allowed to delve, and compare, the microstructural evolution across both welds. It was possible to observe the dual phase nature of the microstructure throughout the welded joint alongside the nucleation of a B2 BCC phase in the heat affected zone (HAZ) of both HEAs. Considering the mechanical properties of the welded materials, results evidenced a poorer, yet still acceptable mechanical performance. The observed decrease in mechanical strength is attributed to the residual stress conditions and large grain size that developed owing to the process thermal cycle, which contrasted deeply with the microstructure of each base material.