Plasma arc fusion-pressure welding of Al-ZrO2 system composite synthesized by XD method

In this paper, an Al-ZrO2 system composite synthesized by XD method is welded by a new plasma arc fusion-pressure welding method. Their joint forms and microstructures are investigated. The results show that the optimum process parameters for the Al-ZrO2 System composite (Ф7mm) are as follows: welding current is 150A and welding time is 2s, no adding filling materials, spring upset force is 2.45N. There are no defects such as large gas pore, micro-hole, or incomplete fusion in the joint. During the solidification of the molten pool, the melted Zr3Al grows fully along the minimum growing energy direction , thus the slender stick precipitates of Zr3Al appear in the weld. The joint form and the microstructure are affected by the processing parameters such as welding current. For example, a larger current will cause the defect of micro-hole in the joint

Non-Standard Errors

In statistics, samples are drawn from a population in a data-generating process (DGP). Standard errors measure the uncertainty in estimates of population parameters. In science, evidence is generated to test hypotheses in an evidence-generating process (EGP). We claim that EGP variation across researchers adds uncertainty: Non-standard errors (NSEs). We study NSEs by letting 164 teams test the same hypotheses on the same data. NSEs turn out to be sizable, but smaller for better reproducible or higher rated research. Adding peer-review stages reduces NSEs. We further find that this type of uncertainty is underestimated by participants

Non-standard errors

In statistics, samples are drawn from a population in a data-generating process (DGP). Standard errors measure the uncertainty in estimates of population parameters. In science, evidence is generated to test hypotheses in an evidence generating process (EGP). We claim that EGP variation across researchers adds uncertainty: Non-standard errors (NSEs). We study NSEs by letting 164 teams test the same hypotheses on the same data. NSEs turn out to be sizable, but smaller for better reproducible or higher rated research. Adding peer-review stages reduces NSEs. We further find that this type of uncertainty is underestimated by participants

Ti/Cu/Kovar Multilayer Interlayer PTLP Diffusion Bonding Si3N4/Ht250

In this paper, partial transient liquid phase (PTLP) diffusion bonding between Si3N4 ceramics and Ht250 cast iron was carried out by using an Ti/Cu/Kovar/Cu/Ti interlayer. The effects of the heating temperature and holding time on the microstructure, formation mechanism, and mechanical properties of Si3N4/Ht250 cast iron joints were studied. The results show that the maximum shear strength of the joint is 112 MPa when the welding temperature is 1000 °C and the holding time is 1 h. In addition, the problems of Ti/Cu/Ti intermetallic compound formation and Cu/Si3N4 ceramic residual thermal stress in the joint can be effectively alleviated

Ti/Cu/Kovar Multilayer Interlayer PTLP Diffusion Bonding Si₃N₄/Ht250

In this paper, partial transient liquid phase (PTLP) diffusion bonding between Si3N4 ceramics and Ht250 cast iron was carried out by using an Ti/Cu/Kovar/Cu/Ti interlayer. The effects of the heating temperature and holding time on the microstructure, formation mechanism, and mechanical properties of Si3N4/Ht250 cast iron joints were studied. The results show that the maximum shear strength of the joint is 112 MPa when the welding temperature is 1000 °C and the holding time is 1 h. In addition, the problems of Ti/Cu/Ti intermetallic compound formation and Cu/Si3N4 ceramic residual thermal stress in the joint can be effectively alleviated

Microstructure and properties of MgAlCd filler metal scraped brazing AZ31 magnesium alloy joint

In order to simplify the brazing process of magnesium alloy and make the liquid filler metal rapidly wet the base metal, the phase diagram method was used to design the series of Cd22.8Mg9.2Al and Cd26.3Mg15.3Al series filler metal. The brazing of AZ31 magnesium alloy was realized by scraping brazing under the condition of flame heating. The microstructure and phase of the filler metal and brazing seam were analyzed by XRD, SEM, and EDS. The results show that the microstructure of filler metal is composed of CdMg matrix, granular Al12Mg17, and massive (Al) solid solution. The amount of Al12Mg17 and (Al) solid solutions in filler metal increases with the increase of Al content, and the hardness of filler metal also increases. The Al content increases from 9.2 to 15.3%, and Vickers hardness increases from 183.6HV to 252HV. DSC results show that the melting point of filler metal is between 396.1 °C and 401.5 °C. The analysis results of the brazing seam show that the microstructure of the brazing seam is composed of CdMg3 and Al12Mg17. With the increase of Al content in filler metal, the fracture morphology changes from a river like pattern to rock sugar shape, the fracture mode changes from trans-granular fracture to intergranular fracture and the shear strength of joint decreases from 71 MPa to 53 MPa. The main reason for this phenomenon is the increase in the amount and size of the Al12Mg17 phase

Influence of Sintering Process Conditions on Microstructural and Mechanical Properties of Boron Carbide Ceramics Synthesized by Spark Plasma Sintering

Boron carbide (B4C) ceramics were synthesized by spark plasma sintering at a temperature between 1600 and 2050 °C without employing any sintering additives. The effect of sintering process parameters, such as temperature, holding time, pressure, hearting rate, and pulsed electric current, and the particle size of the raw powder on the densification behavior and mechanical properties of B4C ceramics, were comprehensively and systematically investigated. Hardness and fracture toughness of B4C that has a density close to the theoretical value were found to be 33.5 ± 0.2 GPa and 3.21 ± 0.13 MPa·m1/2, respectively. Electron backscatter diffraction (EBSD) analysis revealed no abnormal growth of grains due to an increase in holding time and pressure. Twin structures present in ceramics are beneficial for their mechanical performance

Effect of longitudinal magnetic fields on the grain growth of hollow stud welded joints

In this study, a drawing arc stud welding method combined with a longitudinal magnetic field was used for welding a 30CrNi3MoV low-alloy super strong steel substrate and Q235 hollow steel, and the effects of a longitudinal magnetic field on the microstructure growth process and mechanical properties of stud welds were studied. The results show that an arc controlled by a longitudinal magnetic field stirred the molten pool continuously, reducing the number of coarse proeutectoid ferrite, increasing the proportion of acicular ferrite, and smoothing the transition of alloyed elements near the weld joint fusion line within a certain range of excitation current. Under the action of the magnetic field, the weld grain size was refined from 4.30 μm to 3.14 μm, and the proportion of large-angle grain boundaries in the weld area increased from 24.27% to 34.2%. After the magnetic field application, the toughness of the welded joint was significantly improved. With an increase in the excitation current, the shear strength of the joint first increased and then decreased to 312 Mpa. Similarly, the impact toughness of the joint first increased and then decreased to 31.88 J·cm−