Effect of Cold Working on the Properties and Microstructure of Cu-3.5 wt% Ti Alloy.

Cu-Ti alloys were strengthened by ß'-Cu4Ti metastable precipitation during aging. With the extension of the aging time, the ß'-Cu4Ti metastable phase transformed into the equilibrium ß-Cu4Ti phase. The Cu-3.5 wt% Ti(Cu-4.6 at% Ti) alloys with different processing were aged at different temperatures for various times after solution treatment at 880 °C for 1 h. The electrical conductivity of samples under different heat treatments had shown an upward trend as time increased during aging, but the hardness reached the peak value and then decreased. The hardness and electrical conductivity of the samples with 70% deformation after aging are higher tha n the samples without deformation. Deformation after aging would cause the metastable phase to dissolve into a matrix. The best combination value of conductivity and hardness is 13.88% IACS and 340.78 Hv, and the optimal heat treatment is 500 °C for 2 h + 70% deformation + 450 °C for 2 h.

Antibacterial property, corrosion and discoloration resistance of pure copper containing Zn or Ni.

This study focused on the effects of Zn and Ni addition on the antibacterial properties and corrosion resistance of copper alloys. The antimicrobial properties of copper and copper alloys were evaluated using Escherichia coli ATCC 8739 bacterial strain by employing the overlay and plate counting methods. X-ray photoelectron spectroscopy (XPS) was used to analyze the surface composition of the alloy after contact with bacteria. A salt spray method was used to simulate an artificial sweat contact environment to test the discoloration and corrosion resistance of the alloy, and scanning electron microscopy (SEM) was used to analyze the film layer and surface material composition of the corroded samples. The addition of Ni reduced the antibacterial performance of pure copper; however, the antibacterial performance of the alloy remained fast and efficient after the addition of Zn. Moreover, the addition of Zn and Ni significantly improved the corrosion resistance and surface discoloration of copper alloys in artificial sweat environments. This study provided support for the future application of copper alloys as antimicrobial surface-contact materials with safer public and medical environments in the face of diseases spread by large populations. Supplementary Information: The online version contains supplementary material available at 10.1007/s12598-022-02098-8.

Comparison of the Mechanical Properties and Microstructures of QB2.0 and C17200 Alloys.

As it is known, beryllium bronze, an important copper alloy, is widely used in the field of aerospace. Since the performance of domestic and imported beryllium bronze alloys have obvious differences, domestic beryllium bronze QBe2.0 and imported C17200 alloy were adopted, and the hardness and tensile properties of imported and domestic beryllium bronze alloys in the peak aging state were compared and analyzed. In addition, the microstructure morphologies of the C17200 alloy and QBe2.0 alloy were analyzed by SEM, EBSD, and TEM. This study adopted a data-driven exploration approach to elaborate the differences between C17200 and QBe2.0 alloy. After aging at 300 °C for 2 h (peak aging), the tensile strengths of the C17200 alloy and QBe2.0 alloy were 1357 MPa and 1309 MPa, the yield strengths were 1195 MPa and 1188 MPa, and the elongations were 5.5% and 4.0%, respectively. In the peak-aged state, the grain size, uniformity, small angle grain boundary, and twin density of the C17200 alloy were much better than those of the QBe2.0 alloy, which led to more significant grain refinement and twin strengthening effects. A large amount of γ' phase, γ phase, and ß phase were precipitated in both alloys, but the precipitation density of the γ' strengthening phase in the C17200 alloy was much greater than that of the QBe2.0 alloy. The C17200 alloy exhibited better mechanical properties under the combined effects of the various strengthening mechanisms, which provided a guideline for the subsequent improvement of domestic alloys and laid a solid foundation for the development of new copper alloys.

Effects of Co Addition on the Microstructure and Properties of Elastic Cu-Ni-Si-Based Alloys for Electrical Connectors.

The properties and microstructure evolution of quaternary Cu-Ni-Co-Si alloys with different Ni/Co mass ratios were investigated. The microstructure and morphological characteristics of the precipitates were analyzed by using electron backscatter diffraction (EBSD), transmission electron microscopy (TEM) and high-resolution transmission electron microscopy (HRTEM). The mechanical properties and conductivity of the alloys were significantly improved after the addition of Co. The grains presented an obvious growth trend with an increase in Ni/Co mass ratios, and the appropriate Co accelerated the recrystallization process. The δ-(Ni, Co)2Si phases of the Cu-Ni-Co-Si alloys and δ-Ni2Si phases of the Cu-Ni-Si alloys shared the same crystal structure and orientation relationships with the matrix, which had two variant forms: δ1 and δ2 phases. The precipitates preferential grew along with the direction of the lowest energy and eventually exhibited two different morphologies. Compared with that of the Cu-Ni-Si alloy, the volume fraction of precipitates in the alloys with Co was significantly improved, accompanied by an increase in the precipitated phase size. The addition of Co promoted the precipitation of the precipitated phase and further purified the matrix. A theoretical calculation was conducted for different strengthening mechanisms, and precipitation strengthening was the key reinforcement mechanism. Moreover, the kinetic equations of both alloys were obtained and coincided well with the experimental results.

Effect of Ag on Properties, Microstructure, and Thermostability of Cu-Cr Alloy.

Cu-Cr-based alloys exhibit excellent electrical conductivity and strength, but their poor thermal stability limits their application in industry. In this paper, Cu-0.2Cr (at. %) and Cu-0.2Cr-0.12Ag (at. %) alloys were prepared to study the effect of Ag on the properties, microstructure, and thermal stability of the Cu-Cr alloy. Microstructure and precipitation were observed by an optical microscope (OM) and a transmission-electron microscope (TEM). After cold-drawing by 99.9% and aging at 450 °C for 2 h, the peak hardness and electric conductivity of the Cu-Cr alloy were 120.3 HV and 99.5% IACS, respectively, and those of the Cu-Cr-Ag alloy were 135.8 HV and 98.3% IACS, respectively. The softening temperature of the Cu-Cr alloy was 500~525 °C, and that of the Cu-Cr-Ag alloy was about 550 °C. The creep strains of the Cu-Cr and Cu-Cr-Ag alloys at 40 MPa and 400 ℃ for 50 h were 0.18% and 0.05%, respectively. Ag elements improved the thermal stability of the Cu-Cr alloy. Recovery and recrystallization occurred before the coarsening of precipitates during the softening process. Ag atoms mainly improved the softening resistance of the alloy by delaying recrystallization, and mainly increased creep resistance by preventing the increase in mobile-dislocation density.

Size Effect on Mechanical Properties and Deformation Behavior of Pure Copper Wires Considering Free Surface Grains.

The size (grain size and specimen size) effect makes traditional macroscopic forming technology unsuitable for a microscopic forming process. In order to investigate the size effect on mechanical properties and deformation behavior, pure copper wires (diameters range from 50 µm to 500 µm) were annealed at different temperatures to obtain different grain sizes. The results show that a decrease in wire diameter leads to a reduction in tensile strength, and this change is pronounced for large grains. The elongation of the material is in linear correlation to size factor D/d (diameter/grain size), i.e., at the same wire diameter, more grains in the section bring better plasticity. This phenomenon is in relationship with the ratio of free surface grains. A surface model combined with the theory of single crystal and polycrystal is established, based on the relationship between specimen/grain size and tensile property. The simulated results show that the flow stress in micro-scale is in the middle of the single crystal model (lower critical value) and the polycrystalline model (upper critical value). Moreover, the simulation results of the hybrid model calculations presented in this paper are in good agreement with the experimental results.

Hot Deformation Behavior and Microstructure Evolution of Cu-Ni-Co-Si Alloys.

The Cu-1.7Ni-1.4Co-0.65Si (wt%) alloy is hot compressed by a Gleeble-1500D machine under a temperature range of 760 to 970 °C and a strain rate range of 0.01 to 10 s-1. The flow stress increases with the extension of strain rate and decreases with the rising of deformation temperature. The dynamic recrystallization behavior happens during the hot compression deformation process. The hot deformation activation energy of the alloy can be calculated as 468.5 kJ/mol, and the high temperature deformation constitutive equation is confirmed. The hot processing map of the alloy is established on the basis of hot deformation behavior and hot working characteristics. With the optimal thermal deformation conditions of 940 to 970 °C and 0.01 to 10 s-1, the fine equiaxed grain and no holes are found in the matrix, which can provide significant guidance for hot deformation processing technology of Cu-Ni-Co-Si alloy.

In-Situ SEM Observation on Fracture Behavior of Titanium Alloys with Different Slow-Diffusing ß Stabilizing Elements.

The fracture-behaviors of two Ti-Al-Sn-Zr-Mo-Nb-W-Si alloys with different slow-diffusing ß stabilizing elements (Mo, W) were investigated through in-situ tensile testing at 650 °C via scanning electron microscopy. These alloys have two phases: the α phase with hcp-structure (a = 0.295 nm, c = 0.468 nm) and the ß phase with bcc-structure (a = 0.332 nm). Three-dimensional atom probe (3DAP) results show that Mo and W mainly dissolve in the ß phase, and they tend to cluster near the α/ß phase boundary. Adding more slow-diffusing ß stabilizing elements can improve the ultimate tensile strength and elongation of the alloy at 650 °C. During tensile deformation at 650 °C, microvoids mainly initiate at α/ß interfaces. With increases in the contents of Mo and W, the ß phase content increases and the average phase size decreases, which together have excellent accommodative deformation capability and will inhibit the microvoids' nucleation along the interface. In addition, the segregation of Mo and W near the α/ß interface can reduce the diffusion coefficient of the interface and inhibit the growth of microvoids along the interface, which are both helpful to improve the ultimate tensile strength and plasticity.

Relationship between Microstructure and Properties of Cu-Cr-Ag Alloy.

The microstructure evolution and properties of a Cu-Cr-Ag alloy during continuous extrusion and an aging process were studied by Scanning Electron Microscope (SEM) and Transmission Electron Microscope (TEM). Owing to strong shear deformation that happened during continuous extrusion with working temperatures of 450 to 480 °C, a larger number of fine grains were obtained. Both face-centered cubic (FCC) and body-centered cubic (BCC) precipitates simultaneously existed in the matrix when aged for 450 °C for 2 h, and the Cr phases with BCC structure had an N-W relationship with the matrix. After continuous extrusion, 60% cold deformation, 875 °C × 1 h solid solution treatment, 60% cold deformation, 450 °C × 2 h aging treatment, and 70% cold deformation, the Cu-Cr-Ag alloy acquired excellent comprehensive properties: tensile strength of 494.4 MPa, yield strength of 487.6 MPa, and electrical conductivity of 91.4% IACS.

Synthesis of Sulfur-Selenium Doped Carbon Quantum Dots for Biological Imaging and Scavenging Reactive Oxygen Species.

The sulfur-selenium doped carbon quantum dots (S,Se-CQDs) were synthesized by one-step through hydrothermal method in this study, which have high fluorescence quantum yield (43%) and advanced ability to scavenge reactive oxygen species (ROS). They were characterized by transmission electron microscope (TEM), nuclear magnetic resonance (NMR), X-ray photoelectron spectroscopy (XPS), fourier transform infrared spectroscopy (FTIR). The results showed that the clearance rate of free radical reached to 40% with 200 µg/mL of S,Se-CQDs. The antioxidant activity of S,Se-CQDs is related to -SH and Se-SH on carbon quantum dots. S,Se-CQDs were able to access to cells which is beneficial to enhance the removal efficiency to ROS. In the biocompatibility experiment, the cell survival rate exceeded 95%, there was little effect on hatching rate, survival rate and heart rate of zebrafish which demonstrated that S,Se-CQDs have an excellent biocompatibility. It prompts that S,Se-CQDs will has proud application prospects in the field of biomedicine.

Influence of the Ni/Co Mass Ratio on the Microstructure and Properties of Quaternary Cu-Ni-Co-Si Alloys.

The properties and microstructural evolution of quaternary Cu-Ni-Co-Si alloys with different Ni/Co mass ratios are investigated systematically. These alloys exhibit higher mechanical properties when the Ni/Co mass ratio is 1.12-1.95 (NC-4-NC-5) and show excellent electrical conductivity when the Ni/Co mass ratio is 0.05-0.5 (NC-1-NC-3). With an increase in the Ni/Co ratio, the dimension of precipitated phase continues to increase and the grain size also visibly grows and coarsens. At the same time, the precipitation process of the NC-5 alloy is the most adequate, resulting in the highest mechanical properties. In addition, the precipitated phase in the alloys was confirmed to be the (Ni, Co)2Si composite phase. The number of Ni2Si phases in the precipitated phase gradually increased, and the Ni atoms exhibited the strongest co-segregation alongside the increasing Ni/Co ratio. Compared with the alloy without a Co element, the addition of Co helped refine the grain size and accelerate the precipitation of the particle phase and purify solute atoms in the matrix, thereby simultaneously improving mechanical properties and conductivity. The present work provides a new method for the development of multicomponent Cu-Ni-Si-Co-X alloys with outstanding comprehensive performance.

Effect of Ni/Si Mass Ratio and Thermomechanical Treatment on the Microstructure and Properties of Cu-Ni-Si Alloys.

The effect of the Ni/Si mass ratio and combined thermomechanical treatment on the microstructure and properties of ternary Cu-Ni-Si alloys is discussed systematically. The Cu-Ni-Si alloy with a Ni/Si mass ratio of 4-5 showed good comprehensive properties. Precipitates with disc-like shapes were confirmed as the Ni2Si phase with orthorhombic structure through transmission electron microscopy, high-resolution transmission electron microscopy, and 3D atom probe characterization. After the appropriate thermomechanical treatment, the studied alloy with a Ni/Si mass ratio of 4.2 exhibited excellent mechanical properties: a hardness of 290 HV, tensile strength of 855 MPa, yield strength of 782 MPa, and elongation of 4.5%. Compared with other approaches, the thermomechanical treatment increased the hardness and strength without sacrificing electrical conductivity. Theoretical calculations indicated that the high strength was primarily attributed to the Orowan precipitation strengthening and secondarily ascribed to the work hardening, which were highly consistent with the experimental results. The appropriate Ni/Si mass ratio with a low content of Ni and Si atoms shows high strength and excellent electrical conductivity through combined thermomechanical treatment. This work provides a guideline for the design and preparation of multicomponent Cu-Ni-Si-X alloys with ultrahigh strength and excellent electrical conductivity.