Microstructure and mechanical properties of Cu joints soldered with a Sn-based composite solder, reinforced by metal foam

In this study, Ni foam, Cu coated Ni foam and Cu-Ni alloy foams were used as strengthening phases for pure Sn solder. Cu-Cu joints were fabricated by soldering with these Sn-based composite solders at 260 °C for different times. The tensile strength of pure Sn solder was improved significantly by the addition of metal foams, and the Cu-Ni alloy/Sn composite solder exhibited the highest tensile strength of 50.32 MPa. The skeleton networks of the foams were gradually dissolved into the soldering seam with increasing soldering time, accompanied by the massive formation of (Cu,Ni)6Sn5 phase in the joint. The dissolution rates of Ni foam, Cu coated Ni foam and Cu-Ni alloy foams into the Sn matrix increased successively during soldering. An increased dissolution rate of the metal foam leads to an increase in the Ni content in the soldering seam, which was found to be beneficial in refining the (Cu,Ni)6Sn5 phase and inhibiting the formation of the Cu3Sn IMC layer on the Cu substrate surface. The average shear strength of the Cu joints was improved with increasing soldering time, and a shear strength of 61.2 MPa was obtained for Cu joints soldered with Cu-Ni alloy/Sn composite solder for 60 min

An E-Tailer’s Operational Strategy under Different Supply Chain Structures

Motivated by the enormous business success of E-tailers and their distinct business strategies, this paper analyzes the characteristics of dual online channel competition and the fundamental willingness of an E-tailer to open its marketplace to other retailers while at the same time competing with them. We build game theory models to study the dual-channel competition between an incumbent E-tailer and other online retailers under different supply chain structures. Either the manufacturer or authorized third-party retailers can start an online store in the E-tailer’s marketplace. The results show that the transaction fee charged by the platform and the service level provided to customers play significant roles in deciding the marketplace business strategy—the E-tailer faces complicated issues when these two factors fluctuate. A pure strategy of raising the transaction fee may not always be beneficial and a competitor’s superior service level may help to enhance a rival’s sales price. In the expanded research, dual online channel competition with an unauthorized third-party retailer, which is common in the online marketplace, is also examined

Femtosecond Laser-Induced Evolution of Surface Micro-Structure in Depth Direction of Nickel-Based Alloy

The surface coating properties of turbine blades are highly dependent on the material’s surface roughness, and the femtosecond laser-induced micro-structure can provide a wide range of roughness with periodicity. However, precise control of femtosecond laser-induced micro-structure is difficult. In this paper, we extend the application of the two-temperature model and combine it with experiments to accurately reveal the evolution law of micro-structure depth at different single pulse energies, as well as the influence of two processing parameters on micro-structure, namely, defocusing amount and scanning speed. The findings of this study provide reliable theoretical guidance for fast and accurate control of material surface roughness and open new possibilities for coating properties

Mechanical Behavior and Optimization of Tubing String with Expansion Joint during Fracturing in HTUHP Wells

During the formation testing in high-temperature (HT) and ultra-high-pressure (UHP) wells, one of the major challenges is packer failure in the downhole caused by high-rate fracturing. In such a case, the axial shrinkage trend of the tubing string could be caused by the sudden drop in temperature, but the actual axial length of the tubing string would not change because of the constraints at wellhead and packer. Therefore, this could lead to the upward pull-out of the packer that is due to excessive load from the tubing string. This out-of-control downhole pressure often leads to irreversible consequences, even well abandonment. An expansion joint, as a movable splicer, has the characteristic of mitigating packer load, which can theoretically enhance packer safety. To study the protective effect of an expansion joint on the packer quantitatively, the microscopic characteristics and macroscopic properties of the tubing material (13Cr110) are obtained through experimental tests. Moreover, the mechanical properties of the material at different temperatures are also tested. Then, the testing results are extended to modeling the finite element model (FEM) of the whole section of tubing string with the expansion joint—casing and simulating its internal force changes under fracturing conditions with different injection rates. Our simulation results indicated that an expansion joint can significantly change the distribution of the internal forces in the tubing string, and this change can effectively reduce the load on the packer. Eventually, a tubing string buckling identification plate that considers the injection rate and expansion joint–packer length is obtained to optimize the placement of an expansion joint in the tubing string. Our work can provide a detailed theoretical reference and basis for an expansion joint in field application

Reliability assessment of ultra-deep oil and gas wellbore casing using data statistics and numerical simulations

Ultra-deep oil and gas wells have become a new development trend in onshore oil and gas exploitation. However, Ultra-deep oil and gas wellbore casing is with high failure risk due to the harsh environment. It is essential to evaluate the reliability of wellbore casing. This paper assesses the operational reliability of wellbore casing using data statistics and numerical simulation. Firstly, the theoretical model for reliability analysis of wellbore casing is established, and the variables in the model are determined, including rock mechanics, cement ring, and casing string strength factors. Subsequently, considering the random distribution of model variables, many statistics and analyses are performed to determine the distribution parameters of the model variables. Eventually, Monte Carlo based numerical simulations are carried out to obtain the residual strength distribution and the reliability of wellbore casing. The production casing in the ultra-deep well with a depth of 6.5 km in China as an industrial case is used to illustrate the present study. It is observed that this study can be useful to guide a more accurate assessment of the reliability of ultra-deep wellbore casing.</p

Fabrication of MgO-Y₂O₃ Composite Nanopowders by Combining Hydrothermal and Seeding Methods

In this study, the combination of hydrothermal technique and seed-doping method was conducted to coordinately control the formation of fine MgO-Y2O3 powders, which are promising mid-infrared materials applied to hypersonic aircraft windows due to their excellent infrared transmissions over wide regions. Y(NO3)3·6H2O, Mg(NO3)2·6H2O, Y2O3 seeds and MgO seeds were used as raw materials to prepare the MgO-Y2O3 composite powders (50:50 vol.%), and the influences of the seed contents and hydrothermal treatment temperatures on the final powders and hot-pressed ceramics were investigated by XRD, SEM and TEM techniques. The results show that powders with a seed content of 5% that are hydrothermally synthesized at 190 °C can present a better uniformity and dispersion with a particle size of ~125 nm. Furthermore, the ceramics prepared with the above powders displayed a homogenous two-phase microstructure, fewer pores and a fine grain size with Y2O3 of ~1 µm and MgO of ~620 nm. The present study may open an avenue for developing transparent ceramics based on MgO-Y2O3 nanopowders prepared by hydrothermal technique

Development of a Design Method for Casing and Tubing Strings under Complex Alternating Loads

With the escalating intricacy of downhole operational scenarios, encompassing frequent well cycling, acidification, multi-stage fracturing, steam injection, and intensive extraction, the efficacy of traditional casing-string-design methods rooted in strength considerations is progressively unveiling its limitations. Henceforth, it becomes imperative to establish string-design method standards that embrace the entirety of a well’s lifecycle, encompassing the phases of drilling, completion, fracturing, and production operations. Beginning with an analysis of the advantages and limitations of traditional casing-string-design methods, this paper introduces the features of strain and sealing design methods developed for the full lifecycle of the string. The strain design method, a departure from conventional design philosophies, enables the design concept of the controllable deformation of the pipe string. The sealing design method currently stands as the sole standard method for the design of tubing strings. Simultaneously, this paper proposes the establishment of a time dimension-based lifecycle pipe string-design method standard. This approach considers the trend of pipe strength degradation, effectively addressing the safety concerns related to pipe string design in production and operation

Effects of process parameters on the mechanical properties and microstructure of Al-steel joint by magnetic pulse welding

In this paper, the effects of process parameters of Magnetic pulse welding (MPW) on the mechanical properties and microstructure of dissimilar metal joints of 6063-O and 20 steel tubes were investigated according to experiments. The experimental results show that the tensile strength of MPW joint is higher than that of the aluminium tube when the discharging energy of MPW attaches a certain value as well as the process parameters are reasonable, in which the mechanical joining was happened. Through the FEM analysis and experiments verification, the metallurgical joints were obtained with the moderate discharging energy, reasonable impact angle and radial gap. The results of micro hardness test show that the transition zone has a big change because the grain structure of joints in the interface was refined