Intermetallics最新文献

Complex concentrated multi-element metallic systems, commonly referred to as high-entropy alloys (HEAs), exhibit a combination of unique physical properties when compared to conventional metallic materials. That makes this class of alloys promising for a variety of functional applications. However, HEAs are too expensive to be used for material-intensive products like structural materials, so their functionality can only be implemented in micro-scale applications. The electrical resistance sensors for detecting and measuring tension stress, pressure, micro-displacements, weight, and other physical parameters seem to be appropriate areas where HEAs could find their own place. This study addresses strain gauge characteristics in several HEAs, such as TiZrHfNb, TiZrHfNbTa, and FeCoCrMnNi (Cantor alloy). We discuss the pressure and strain gauge sensitivities in the systems employing experimentally measured electrical, magnetic, and thermal properties as well as ab initio calculations. We conclude that HEAs can be considered as promising materials for strain-sensitive resistance transducers that outperform commercial alloys in terms of a combination of performance characteristics.

The asymmetric growth of Cu₆Sn₅ intermetallic compound (IMC) in a Cu/Sn/Cu interconnection system was studied during the transient liquid phase (TLP) soldering process with the assistance of the vertical ultrasonic vibration. Being different from the symmetrical growth during isothermal aging without ultrasonic waves (USW), highly asymmetrical growth of Cu₆Sn₅ at the upper and down Sn/Cu interfaces was observed with the vertical USW, i.e., Cu₆Sn₅ grains exhibited scallop-type morphology, and were discrete at the upper Sn/Cu interface (the side of ultrasonic action); while that at the lower Sn/Cu interface (the opposite side of ultrasonic action) exhibited column-type morphology, and were conterminous. Under the assistance of USW, the Cu₆Sn₅ grains were remarkably refined, the shear strength of joint was increased, and the fracture mode was changed from transgranular fracture to transgranular and intergranular fracture. This anomalous behavior can be completely ascribed to the asymmetrical ultrasonic effects across the entire Sn the intermediate layer of Sn.

In this work, the effects of rapid annealing on the nanocrystallization behavior and magnetic properties of Fe_83-xNi₂B₁₅Cu_x (x = 0, 0.6, 0.9, 1.1, 1.3) alloy were systematically investigated. Additionally, the influences of Cu addition on structure, thermal stability, crystallization behavior and soft magnetic properties of Fe_83-xNi₂B₁₅Cu_x alloys were also studied in detail. It was found that a fully amorphous structure was formed in the as-spun ribbons. Analysis of thermal properties showed that with the increase of Cu content, the onset temperature of the first crystallization peak (T_x1) decreased sharply for the as-spun Fe_83-xNi₂B₁₅Cu_x alloy ribbon and a large ΔT (ΔT = T_x2 -T_x1) of 105 K was obtained in Cu1.3 alloy which facilitated the precipitation of α-Fe phase. The H_c results from annealed samples indicated that soft magnetic properties can be optimized using rapid annealing treatment primarily due to the grain refinement caused by the large overheating and short duration time during annealing process. With appropriate addition of Cu element and rapid annealing treatment, uniform and dense microstructure consisting α-Fe grains with an average size distribution around 15 nm within amorphous matrix was achieved in rapid annealed Cu1.1 alloy, leading to optimized soft magnetic properties with B_s of 1.85 T and H_c of 4.3 A/m.

Experiments were conducted to reveal the refinement of the microstructure and the evolution of the hardness of an additively manufactured (AM) CoCrFeNi multi-principal element alloy (MPEA) processed by severe plastic deformation (SPD) using high pressure torsion (HPT) technique. AM was carried out by laser powder bed fusion (L-PBF) technique at two different laser scan speeds. The as-built alloys for both laser scan speeds have a single-phase face-centered cubic (fcc) structure with <110> fiber texture parallel to the building direction. X-ray line profile analysis (XLPA) revealed that the dislocation density was considerably high even in the AM-processed state before HPT (3 × 10¹⁴ m⁻²) which increased by two orders of magnitude during HPT. The saturation of the lattice defects (dislocation density and twin fault probability) as well as the crystallite size occurred at a shear strain of about 10 during HPT. In both AM-processed alloys, <111> fiber texture developed parallel to the normal of the HPT-processed disks. For both laser scan speeds, the initial grain size in the AM-processed samples was refined from 70 to 90 μm to the nanocrystalline regime after 10 turns of HPT. Additionally, nanotwins formed with a probability of about 3 %. The initial hardness of the AM-processed MPEA samples for both laser scan speeds was 2700–2800 MPa, which is superior to that of CoCrFeNi produced by casting (about 1380 MPa). This can be explained by the high dislocation density in the AM-processed specimens. The formation of nanostructure with high lattice defect density during HPT resulted in a very high hardness value of about 5500 MPa in the AM-processed CoCrFeNi MPEA samples for both laser scan speeds.

To decrease the sensitivity of high-B_s Fe-based nanocrystalline soft magnetic alloys to heat-treatment process parameters and promote their engineering applications, the effect of Nb addition on the glass-formation ability (GFA), crystallization behavior, soft magnetic properties, and Fe₃(B, P) compound phase stability in Fe_83−xC₄B_6.5P_5.5Cu₁Nb_x (x = 0, 0.15, 0.5, 1.0, and 2.0 at. %) alloys were systematically investigated. It was found that Nb addition did not decrease the GFA of this alloy system. Thermophysical analysis indicates that Nb addition has little effect on the first crystallization peak, but it can effectively increase the second crystallization peak, which increases from 785.2 K for the Nb-0 alloy to 803.4 K for the Nb-2.0 alloy. Analyzing the relationship among soft magnetic properties, structure, and heat-treatment process parameters, including annealing temperature (T_a), holding time, and heating rate, confirmed that Nb addition to this alloy system effectively delays the precipitation of the Fe₃(B, P) compound phase and decreases the influence of heat-treatment process parameters on soft magnetic properties. The optimal T_a range increases from 50 K for the Nb-0 alloy to 100 K for the Nb-2.0 alloy, and the optimal holding time increases from 6 min for the Nb-0 alloy to 45 min for the Nb-2.0 alloy when annealing at 753 K. The heating rate decreases from the rapid heating for the Nb-0 alloy to 40 K/min for the Nb-2.0 alloy when the T_a = 753 K.

An AlCoCuFeTi high-entropy alloy with excellent wear resistance and high hardness was successfully produced by arc melting. The effects of annealing on the microstructure, nanomechanical behaviors, tribological properties, and corrosion resistance were systematically investigated. The results showed that the AlCoCuFeTi consisted of a Co-enriched L2₁ phase, a Cu-enriched FCC phase, and a (Fe, Ti)-enriched Laves phase. Annealing promoted the formation of FCC and Laves phases but decreased the volume fraction of the L2₁ phase. The high hardness of AlCoCuFeTi is attributed to the formation of L2₁ and Laves phases. The highest hardness (14.1 ± 1.3 GPa) and reduced Young's modulus (256 ± 11 GPa) were achieved in the 1100 °C annealed and 900 °C annealed specimens, respectively. All specimens exhibited excellent wear resistance compared to typical HEAs due to the mild-oxidational wear mechanism. The 1100 °C annealed specimen possessed the highest elastic strain to failure (H/E_r) and yield pressure (H³/E_r²), corresponding to its best-measured wear resistance. The segregation of Cu led to galvanic corrosion during the polarization tests, and the area ratio of cathode to anode (A_c/A_a) determined the corrosion rate. The 1100 °C annealed specimen exhibited good corrosion resistance due to its low A_c/A_a value.

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 $\bar{1}$ 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 $\bar{1}$ 1}_α deformation twins.

The utilization of ultrafine, near-spherical Kovar alloy powders is promising for applications such as injection molding and additive manufacturing. This study successfully produced these powders using the newly developed water–gas combined atomization technique. Subsequently, the morphology and surface structure of the as-prepared powders were investigated by using scanning electron microscopy, transmission electron microscopy and electron probe microanalysis. Our findings revealed that the water–gas combined atomization yields a high powder output. In addition, an inhomogeneous layer of Fe₂O₃ oxide film was observed on the powder surfaces. Kovar alloys sintered with the as-produced powders exhibit higher relative density than those produced with gas atomization powders. This increased density results from the nonuniformity of the oxide film, promoting sintering neck formation and accelerating densification. The insights from this research contribute to the design of Kovar alloy and offer valuable guidance for refining production processes to enhance powder quality and performance.

This study investigates the Fe50Mn30Co10Cr10 high entropy alloy (HEA), featuring a dual-phase structure with face-centered cubic (FCC) and hexagonal close-packed (HCP) phases, in both cast and forged states. The cast samples exhibited an average tensile strength of 675.9 MPa and an elongation at break of 34 %, while the forged samples showed superior properties with a strength of 821.0 MPa and 50 % elongation. Impact tests at room temperature, 200 K, and 77 K revealed that forged samples consistently had higher impact energy (144 J, 119 J, and 109 J, respectively) compared to cast samples (99 J, 80 J, and 66 J). This research underscores the significant influence of the dual-phase structure and fabrication process on the mechanical and impact properties of the Fe50Mn30Co10Cr10 system HEAs.

The microstructure and tensile mechanical properties of novel FeNiCrAl_xTi_y medium-entropy alloys (MEAs) were investigated. The results showed that the microstructure of the MEAs undergoes a transformation from FCC single-phase to FCC + BCC dual-phase with increasing Ti and Al content. The addition of Ti and Al significantly increases the strength while maintaining appropriate ductility. Specifically, the (FeNiCr)₉₄Ti₂Al₄ exhibits excellent combinations of yield strength (∼1.2 GPa and ∼1.5 GPa) and tensile ductility (13 % and 19 %) at both 298 K and 77 K. Microstructural analysis reveals that the excellent cryogenic mechanical properties are attributed to the co-existing multiple strengthening mechanisms. This work provides a simple route for designing low-cost MEAs with excellent cryogenic tensile properties.