Welding in the World最新文献

 This paper treats different fatigue (FAT)-scenarios for determining damage-equivalent stress ranges according to two methods for transforming a stress or load spectrum into a damage-equivalent constant amplitude loading, i.e., the Modified Equivalent Stress (MES) and the Required Fatigue Strength (RFS) concepts. The MES method is suggested by the IIW-recommendations for fatigue design and the RFS method is applied especially in the design of vehicle safety components. The resulting MES- and RFS-ranges are similar, but not equal. The MES-method delivers a damage-equivalent stress range that depends on the selected FAT-value, i.e., the position of the Woehler-curve is decisive. In contrast, the RFS-method results in a damage-equivalent fictitious Woehler-line that indicates the lowest necessary strength quality for a given stress spectrum. The allocation of the modified equivalent stress range to the appertaining bi-linear Woehler-curve does not result in the fatigue life caused by the spectrum. Only in the case of a linear Woehler-curve, the fatigue life is directly obtained. In the case of the RFS-application, the fatigue life is by definition equal to the spectrum length. For durability tests, the modified equivalent stress range (at ({L}_{S}) cycles) and the associated FAT-Woehler-curve should not be used. However, the Woehler-curve derived by the RFS-method allows experimental durability proofs for any amplitude-cycle combination along it. Furthermore, the required lowest necessary strength also enables the selection of the most cost-effective manufacturing technique and quality. The RFS-Woehler-curve also results in a FAT-value with a defined probability of failure depending on the required safety factor.

In this paper, the brazing of high-reliability C/C composite-metal joints for high-temperature application was studied. The surface of C/C composites was modified by the Cr metallization process and then brazed to Ni-based superalloy by AgPd braze. Alumina block was used as interlayer, and a zig-zag interfacial structure was constructed at the composites/braze interface. The results show that, after the metallization process, a strong adhesion reaction layer consisting of Cr carbides was coated on the C/C surface which in turn obviously improved the wettability of braze. The molted braze filled completely into the laser-machined holes in the C/C substrate and well-bonded interfaces and a homogeneous Ag(Pd) solution microstructure were obtained in the joint. The strength of the joint with C/C metalized at 1100 ℃ is higher than that of the joint with 1300 ℃. The joints exhibit very high bending strength of up to 82 MPa and shear strength of up to 54 MPa, respectively. The braze spikes increase the connection area and provide a strong pinning effect.

K417G superalloy is widely applied in gas turbine components such as blades, vanes, and nozzles. In this study, wide-gap brazing of K417G superalloy is investigated using BNi-5 filler alloy. The brazing experiment is conducted at 1150 °C for different holding times with the fixed gap of 0.2 mm. For the joints brazed for 15 min, the brazing seam mainly consists of γ/γ’ phase, Ni₂Si and TiC phase. The average tensile strength tested at 950 °C is 401 MPa. As the holding time increased, the excessive element diffusion phenomenon is observed. Hence, Ni₂Si intermetallic phases gradually become embedded in the additive alloy particles. The interfacial evolution and fracture behavior are discussed.

MIG welding still had a lot of potential in the titanium alloy industry with many advantages. How to achieve stable process and forming was still a hard nut to crack for titanium alloy MIG welding. The conventional MIG welding torch had a small coverage of shielding gas which causes an obvious insufficient capability of isolating air. Therefore, this study introduced the fluid field composite MIG process, proposed a novel strategy of titanium alloy MIG welding process under the synergistic effect of coaxial dual channel gas path, and had explored the impact of the synergistic effect of internal gas flow(Q) and external gas flow(q) on the welding process from three aspects: droplet transfer characteristics and weld surface morphology, weld cross-section. The results showed that the form of “one large droplet + several small droplets” was always maintained during transition process. Q mainly impacted on the variation law of the droplet transition; however, the length of transition period was mainly affected by q. In addition, the arc length was reduced meanwhile the geometric parameters of welds’ cross-section had more regular changes after adding q. The surface morphology was the worst when Q acted solely; however, it was straight and uniform after adding q. When q = 40L/min and Q = 15L/min, the coverage and protective effect of shielding gas was excellent, no turbulence was generated, and no pores generated in the cross-section of the weld. It was easier to obtain a more stable forming of titanium alloy MIG welding when Q and q worked together.

Due to electronics miniaturization, the size of voids is becoming comparable to that of solder joints, thereby increasing the risk of reduced reliability. This work presents a novel method of achieving void reduction through preliminary characterization of the flux and, consequently, the proper flux selection and adjustment of the temperature profile during soldering. To validate this approach, five SAC305 solder pastes differing in flux composition were subjected to testing. The flux components were characterized by a gas chromatograph combined with a mass spectrometer (GC–MS) and thermogravimetric analysis (TGA). Subsequently, four temperature profiles differing in the heating rate were employed for reflow soldering of the test boards with components while maintaining the same peak temperature for all profiles. The results of the X-ray computed tomography (XCT) analysis indicated that as the temperature gradient decreased, the number of voids decreased by up to 36%. The decrease in the number of flux residues detected by TGA present at the peak process temperature was also accompanied by a decrease in the void area within the solder joint. Moreover, a comparison between the GC–MS and XCT results revealed that certain flux compounds, such as butylated hydroxytoluene, were found to have a greater impact on void formation than others. The proposed method combining flux characterization by GC–MS and TGA and adjustment of temperature gradient during the soldering process can be an efficient way to reduce voids in solder joints. Additionally, it appears that a lower temperature gradient is generally associated with a lower incidence of voids.