Optimization of the Microstructure and Mechanical Properties of a TC4 Alloy Joint Brazed with a Zr-Based Filler Containing a Co Element.

Herein, we fabricated a low-melting-point Zr-16Ti-6Cu-8Ni-6Co eutectic filler based on a Zr-Ti-Cu-Ni filler to achieve effective joining of a Ti6Al4V (TC4) titanium alloy. The temperature at which the brittle intermetallic compound (IMC) layer in the seam completely disappeared was reduced from 920 °C to 900 °C, which broadened the temperature range of the Zr-based filler, brazing the TC4 without a brittle IMC layer. The shear strength of the Zr-16Ti-6Cu-8Ni-6Co brazed joint increased by 113% more than that of the Zr-16Ti-9Cu-11Ni brazed joint at 900 °C. The proportion of ß-Ti in the seam of the Zr-16Ti-6Cu-8Ni-6Co brazed joint increased by 21.31% compared with that of the Zr-16Ti-9Cu-11Ni brazed joint. The nano-indentation results show that the elastic modulus of the ß-Ti (143 GPa) in the interface is lower than that of the α-Ti (169 GPa) and (Ti,Zr)2(Ni,Cu,Co) (203 GPa). As a result, the ß-Ti is subjected to a greater strain under the same stress state compared with the α-Ti and (Ti,Zr)2(Ni,Cu,Co), and the Zr-16Ti-6Cu-8Ni-6Co brazed joint can maintain a higher strength than the Zr-16Ti-9Cu-11Ni brazed joint under a middle-low erosion area of the TC4 base metal. This provides valuable insights into the use of high-strength, fatigue-resistant TC4 brazed joints in engineering applications.

The inhibition mechanism of ultrasonic vibration on stick-slip phenomenon of sliding friction pair.

Frictional vibration often occurs during sliding, commonly referred to as the stick-slip phenomenon. It is more likely to occur in the range of the Stribeck curve, where friction and velocity have negative gradient characteristics. In this study, ultrasonic vibration is applied to the metal/metal sliding friction pair which reduce both static and kinetic friction forces. The inhibition mechanism of ultrasonic vibration on the stick-slip phenomenon is investigated for a sliding pair moving at low velocities (0.05-1.0 mm/s) under the condition of dry friction and oil lubrication. Under the condition of dry friction, ultrasonic vibration reduces the slider's friction force by up to 89%, and the displacement fluctuation by up to 61%, effectively inhibiting the stick-slip phenomenon. Under the condition of oil lubrication, the friction force fluctuates when driving at a constant velocity, and the displacement fluctuation also fluctuates with the change of driving velocities. After ultrasonic vibration is applied, the friction reduction of the slider changes greatly with the driving velocity, so that the inhibition effect of ultrasonic vibration on stick-slip phenomenon under oil lubrication condition is unstable.

Brazing of TC4 Alloy Using Ti-Zr-Ni-Cu-Sn Amorphous Braze Fillers.

In order to address the issues of excessive brittle intermetallic compounds (IMC) formation in the TC4 brazed joints, two types of novel Ti-Zr-Cu-Ni-Sn amorphous braze fillers were designed. The microstructure and shear strength of the TC4/Ti-Zr-Ni-Cu-Sn/TC4 brazed joints were studied by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffractometer (XRD) and electronic universal materials testing machine. The results show that the optimized Ti35Zr25Ni15Cu20Sn5 braze filler whose chemical composition is closer to the eutectic point possesses a lower melting point compared with the equiatomic Ti23.75Zr23.75Ni23.75Cu23.75Sn5. This was beneficial to the sufficient diffusion of Cu and Ni elements with the base metal during brazing and reduces the residual (Ti,Zr)2(Ni,Cu) content in the joint, which helps to improve the joint performance. The room-temperature and high-temperature shear strength of the TC4 brazed joints using the near eutectic component Ti35Zr25Ni15Cu20Sn5 filler reached a maximum of 472 MPa and 389 MPa at 970 °C/10 min, which was 66% and 48% higher than that of the TC4 joints brazed with the equiatomic Ti23.75Zr23.75Ni23.75Cu23.75Sn5 braze filler. Microstructural evolution and the corresponding mechanical response were in-depth discussed.

Novel trifunctional electrocatalyst of nickel foam supported Co2P/NiMoO4 heterostructures for overall water splitting and urea oxidation.

The process of electrocatalytic water splitting for hydrogen generation is significantly limited by sluggish kinetics of the anodic oxygen evolution reaction (OER). The efficiency of H2 electrocatalytic generation can be improved by reducing the anode potential or substituting urea oxidation reaction (UOR) for oxygen evolution process. Here, we report a robust catalyst based on Co2P/NiMoO4 heterojunction arrays supported on nickel foam (NF) for water splitting and urea oxidation. In the hydrogen evolution reaction in alkaline media, the optimized catalyst Co2P/NiMoO4/NF displayed a lower overpotential (169 mV) at a large current density (150 mA cm-2) compared to 20 wt% Pt/C/NF (295 mV@150 mA cm-2). In the OER and UOR, the potentials were as low as 1.45 and 1.34 V. These values surpass (for OER), or compare favorably to (for UOR), the most advanced commercial catalyst RuO2/NF (at 10 mA cm-2). This outstanding performance was attributed to the addition of Co2P, which has a significant effect on the chemical environment and electron structure of NiMoO4, while increasing the number of active sites and promoting charge transfer across the Co2P/NiMoO4 interface. This work proposes a high-performance and cost-effective electrocatalyst for water splitting and urea oxidation.

Comparative Study on Laser Welding Thick-Walled TC4 Titanium Alloy with Flux-Cored Wire and Cable Wire.

In the welding process of thick-walled titanium alloys, the selection of the wire type is one of the critical factors affecting the welding quality. In this paper, flux-cored and cable wires were used as filler materials in the welding of thick-walled titanium alloys. The macrostructure, microstructure, texture, and grain size of both welded joints were compared by employing an optical microscope (OM), scanning electron microscope (SEM), and transmission electron microscope (TEM), and the tensile and impact properties were also evaluated. The comparison result showed that the fusion zone microstructure of both welded joints was dominated by a basketweave structure composed of interwoven acicular α' martensite, whereas the microstructure of flux-cored wire welded joints was finer, and the degree of anisotropy was low. The strength of both welded joints was higher than that of the base metal, ensuring that fracture occurred in the base metal area during tension. The Charpy impact energy of the flux-cored wire welded joint was 16.7% higher than that of the cable wire welded joint, indicating that the welded joint obtained with the flux-cored wire performed better in the welding process of thick-walled titanium alloys.

Microstructure and properties analysis of the brazing alloy prepared from recycled E-waste.

In order to realize the efficient and comprehensive utilization of e-waste resources and short process preparation of alloy brazing materials, this study has analyzed the microstructure and properties of e-waste recycled brazing alloys by the analysis methods of inductively coupled plasma emission spectrometer, differential scanning calorimeter, scanning electron microscope, metalloscope, X-ray diffractometer, micro-hardness tester. Experimental results showed that phase compositions are significant differences between the alloys prepared by the recycled e-waste and the pure metals. The circuit board recycling alloy mainly consisted of α-Fe dendrites, (Cu, Sn) phases, Sn-rich phases and Cu matrix, while the alloy obtained by pure metals is composed of (Cu, Sn) phase, Sn-rich phase and Cu matrix. The melting temperature of alloy obtained by melting the circuit board is in the range of 985.3°C-1,053.0°C, which was wider and higher than that of alloy obtained by pure metal smelting. The shear strengths of the joints brazed by the brazing alloys prepared by the recycle e-waste and pure metals are 182.21 MPa and 277.02 MPa, respectively. There is little difference in hardness between the two types of brazed joints. In addition, there are a large number of precipitated phases in alloy obtained by the recycled circuit board, owing to the precipitation strengthening mechanism. The main strengthening mechanism of alloy obtained by pure metals is solid-solution strengthening. The paper focused primarily on alloy obtained by melting the circuit board and studying the specific composition, melting temperature, structure, and properties of alloys formed by melting the circuit board and pure metals. Meawhile, the size, morphology and other microstructure evolution of the second phase of brazing alloy were investigated to provide theoretical guidance for the brazing alloy in the subsequent actual production process.

Microstructures and Mechanical Properties of V-Modified Ti-Zr-Cu-Ni Filler Metals.

TA2 titanium alloy was brazed with Ti-Zr-Cu-Ni-V filler metals developed in a laboratory. The melting properties, the microstructures, phase compositions of filler metals and wettability, erosion properties, tensile properties of the brazed joint were studied in detail. The results show that with the increase of V content, the solidus-liquidus temperature of Ti-Zr-Cu-Ni-V filler metals increased, but the temperature difference basically remained unchanged, trace V element had a limited influence on the melting temperature range of Ti-Zr-Cu-Ni filler metals. The microstructure of Ti-Zr-Cu-Ni-1.5V filler metal was composed of Ti, Zr matrix, (Zr, Cu) solid solution and crystal phase. With the addition of V content, these phases containing V such as Ni3VZr2, NiV3, Ni2V in the molten filler metals increased. V was more inclined to combine with Ni to slow down the diffusion of Ni to titanium matrix. The wettability of filler metal with trace (≤0.5 wt.%) V to TA2 titanium alloy became worse, the wettability improved significantly with continuous increase of V content. The thickness of embrittlement layer and intergranular infiltration region decreased significantly by adding V. With the increase of V content, V could regulate the brazing interface reaction, more strengthened phases generated, which resulted the significant increase of the strength (302.72 MPa) and plasticity index (16.3%) of the brazed joint with Ti-Zr-Cu-Ni-1.5V filler metal.

Contact Reactive Brazing of TC4 Alloy to Al7075 Alloy with Deposited Cu Interlayer.

The brazing of Titanium alloy to Aluminum alloy is of great significance for lightweight application, but the stable surface oxide film limits it. In our work, the surface oxide film was removed by the ion bombardment, the deposited Cu layer by magnetron sputtering was selected as an interlayer, and then the contact reactive brazing of TC4 alloy to Al7075 alloy was realized. The microstructure and joining properties of TC4/Al7075 joints obtained under different parameters were observed and tested, respectively. The results revealed that the intermetallic compounds in the brazing seam reduced with the increased brazing parameters, while the reaction layer adjacent to TC4 alloy continuously thickened. The shear strength improved first and then decreased with the changing of brazing parameters, and the maximum shear strength of ~201.45 ± 4.40 MPa was obtained at 600 °C for 30 min. The fracture path of TC4/Al7075 joints changed from brittle fracture to transgranular fracture, and the intergranular fracture occurred when the brazing temperature was higher than 600 °C and the holding time exceeded 30 min. Our work provides theoretical and technological analyses for brazing TC4/Al7075 and shows potential applications for large-area brazing of titanium/aluminum.

Vacuum Brazing of C/C Composite and TiAl Intermetallic Alloy Using BNi-2 Brazing Filler Metal.

C/C composite was brazed to TiAl intermetallic compound using a commercial BNi-2 brazing filler metal under vacuum brazing condition. The brazing temperature was 1030~1150 °C and the holding time was 20 min. The joint interfacial microstructures and mechanical properties were studied, and the fracture behavior and joining mechanism were also investigated. The effect of brazing temperature on the joint shear strength was explored. The results showed that a perfect interface joint can be obtained by using BNi-2 to braze C/C and TiAl. During brazing, Ti, Cr, and other carbide forming elements diffused to C/C composite side, forming Cr3C2, Cr7C3, TiC, and other carbides, and realizing metallurgical joining between the brazing filler metal and C/C composite. The microstructure of the interface of C/C composite and TiAl intermetallic compound joint is as follows: TiAl alloy → TiAl + AlNi3 → AlNi2Ti → Ni(s, s) + Ti3Al + Ni3Si → Ni(s, s) + Ni3(Si, B) + CrB → Ni(s, s) + Ni3Si + TiCr2 → (Ti, Cr)C → C/C composite. When the holding time is fixed, with the increase of brazing temperature, the shear strength of the joint increases first and then decreases. The maximum average room temperature shear strength of the brazed joint was 11.62 MPa, while the brazing temperature was 1060 °C and the holding time was 20 min.

Highly Efficient MnO2/AlOOH Composite Catalyst for Indoor Low-Concentration Formaldehyde Removal at Room Temperature.

Indoor formaldehyde from substandard furniture and decorative materials seriously endangers human health. How to remove effectively indoor formaldehyde with low concentration at room temperature is a challenging problem. Using a MnO2/AlOOH composite by the MnO2 modification as a catalyst provides an effective approach to solve this challenge. Here, a new type of MnO2/AlOOH composite catalyst with high ability to remove indoor low-concentration formaldehyde was prepared by redox reaction at room temperature. A MnO2/AlOOH composite with a homogeneous dispersion of MnO2 has high specific surface area and a large amount of surface hydroxyl (-OH) which plays a major role in the adsorption of formaldehyde. A partially crystalline structure was observed in the composite, which contains multivalent Mn ions and a large number of vacancy defects. The surface -OH of composite shows strong oxidation activity through the charge exchange of multivalent Mn ions and vacancy defects. The composite has a higher ability to remove indoor low-concentration formaldehyde compared to the birnessite MnO2 at room temperature. This study proposes a new idea for the improvement of catalytic performance in the structure and composition of the catalyst.

Reliability issues of lead-free solder joints in electronic devices.

Electronic products are evolving towards miniaturization, high integration, and multi-function, which undoubtedly puts forward higher requirements for the reliability of solder joints in electronic packaging. Approximately 70% of failure in electronic devices originates during the packaging process, mostly due to the failure of solder joints. With the improvement of environmental protection awareness, lead-free solder joints have become a hot issue in recent years. This paper reviews the research progress on the reliability of lead-free solder joints and discusses the influence of temperature, vibration, tin whisker and electromigration on the reliability of solder joints. In addition, the measures to improve the reliability of solder joints are analyzed according to the problems of solder joints themselves, which provides a further theoretical basis for the study of the reliability of solder joints of electronic products in service.

Ultrasonic effect mechanism on transient liquid phase bonding joints of SiCp reinforced Mg metal matrix composites using Zn-Al-Zn multi-interlayer.

The effect of ultrasound on transient liquid phase bonding of SiCp reinforced Mg metal matrix composites was investigated based on microstructure evolution, phase composition, SiC particles redistribution, mechanical properties and fracture path of the bonded joint. The results indicate the joint of full solid solution without SiC particles aggregation was obtained by inducing the secondary ultrasonic-assisted holding process at 430 °C for 30 s and the joint shear strength reach to 175.5 MPa (87.5% base material strength). The time needed for the isothermal solidification process was significantly shortened to several second time, which is mainly ascribed to the ultrasonic vibration can squeeze out a large fraction of residual liquid phase and facilitate the atomic diffusion in grain boundary.