Papers by Keyword: Diffusion Welding

Abstract: The purpose of this research was to study the diffuse element and mechanical property of Semi-solid casting (SSC) 7075 and 6061 Al alloy from diffusion welding (DW). The results found that Zn elements were successfully diffused. Mg₂Si and MgZn₂ intermetallics were precipitated from plate-like shape to flake shape. The high bonding temperature and bonding time caused diffuse elements distributed throughout the material. The mechanical property showed that the maximium average tensile strength was 76.80 MPa from bonding temperature at 723 K and 120 min bonding time. The hardness in bonded line was around 63 HV to74 HV.

Abstract: The article deals with the problem of obtaining the dependence of the product strength parameter on the welding time, welding temperature and pressure during mechanical tests, leak tests. The relevance of this work is due to the complexity of carrying out field experiments to identify dependencies. In particular, the complexity arises from the duration of diffusion welding and the high cost. Application of the method of regression analysis based on a non-compositional plan of the second order for three factors will allow to restore the dependence of the product strength parameter on the time during which welding was carried out, the temperature at which diffusion welding was carried out or could be carried out and on the applied pressure at which mechanical tests were carried out. In the current study, a non-compositional design of the second order for three factors was used - allowing to restore the dependence of the missing values of the strength of the product. The aim of the research is to improve the quality of mathematical modeling. Application of the proposed approach will make it possible to obtain the strength distribution function depending on time, temperature and pressure using the example of a product made of VT14 titanium alloy and 12X18H10T stainless steel. This will make it possible to obtain optimal parameters for the diffusion welding mode and to improve the quality of the resulting products.

Abstract: In this work, a study of the cases of destruction of the CuCrZr / 316L (N) bimetallic joint (BMJ) obtained by diffusion welding under conditions of hot isostatic pressing (HIP) was carried out. The identified defects are cracks propagating in the BMJ zone in the corner zone of the mock-ups of the heat-sink elements (HE). The analysis of the causes of destruction of the BMJ was carried out and the factors leading to the weakening of the BMJ zone are analyzed. The analysis of the thermal and stress-strain state of the HE mock-up during the manufacturing process was carried out. The study of the elements of the HE mock-up were carried out by methods of non-destructive testing (ultrasonic testing (UT)) and destructive testing (metallography; fractography; energy-dispersive X-ray spectroscopy; tensile tests). The inclusion of brittle phases in the zone of the BMJ was revealed and an assumption was made about the chemical composition of these phases. It was revealed that this line of brittle phases is a crack propagation zone in all cases of destruction of the BMJ in the HE mock-ups. The temperature range is revealed at which the effect of "ductility failure" of the CuCrZr is observed during the tensile testing of the samples.

Abstract: The diffusion welding (DW), known as direct bonding technique could be more used as an alternative approach to develop silicon carbide (SiC) Schottky rectifiers to existing mainstream metallization contact technologies. Measured results for p-type 4H-SiC Schottky barrier diodes (SBD) arepresented. And comprehensive numerical study to characterize the device has been performed. The simulations are carried out with ATLAS software (Silvaco). The measured and numerically simulated forward current-voltage (I–V) and capacitance-voltage (C–V) characteristics in a large temperaturerange are analyzed. Some of the measured p-type 4H-SiC Schottky diodes show deviation in specific ranges of their electrical characteristics. This deviation, especially due to excess current, dominates at low voltages (less than 1 V) and temperatures (less than room temperature). To verify the existence of electrically active defects under the Schottky contact, which influences the Schottky barrier height (SBH) and its inhomogeneity, the deep level transient spectroscopy (DLTS) technology was applied. DLTS measurements show the presence of a deep-level defect with activation energy corresponding typically for multilevel trap clusters.

Abstract: The dynamic measurement model for the interface cavities of the diffusion welded joint, which based on the effective resistivity, is established by using the damage factor and the Derby Model of the Bridgman Law. Then the quantitative relationship, which between the direct current potential and the effective area of the joint at high temperature and high pressure, can be obtained. In addition, on the basis of the dynamic four-probe DC potential method and the fieldbus technology, the computer measuring system is established, so that the creep propagation behaviour for the interface cavities of the 316L stainless steel can be monitored in real-time.

Abstract: In the last decades, silicon carbide (SiC) based heterostructures have gained a remarkable place in research field due to their exceptional properties. These properties make SiC highly suitable for high temperature, high frequency, and high power electronics applications. The most prominent polytypes (among 200 types) of SiC like 3C-SiC, 4H-SiC and 6H-SiC, have distinctive electrical and physical attributes that make them promising candidates for high performance optoelectronic applications. Silicon (Si) also has been accepted as a promising material for wide range of electronic, optical and optoelectronic applications. Heterostructures fabricated by the direct bonding of SiC polytype and Si may have interesting physical and electrical attributes. In this paper, micro and nano-scale simulations of the nn-heterostructures of Si/4H-SiC and Si/3C-SiC have been done with Silvaco TCAD and QuantumWise Atomistix Toolkit (ATK) softwares respectively. Voltage-current density characteristics of the nanoscale and microscale simulated devices are computed and discussed. In nanoscale devices, the effects of defects due to lattice misplacements (axial displacement of bonded wafers) are also studied. These simulations are the preparation for our future experiments, which are targeted to produce either a high electron mobility diode or a light emitting diode, by direct bonding (diffusion welding) of SiC polytypes.

Abstract: Diffusion welding is being used in aircraft, optic and electrical industry, where special alloys or combinations of metal or non-metal materials are often used. The alloys and materials come from limited sources and therefore they are expensive as well. These reasons lead to the fact that the destructive testing of diffusion bonded joints is not sufficient for the industry and the used components in operation. The paper discusses about the testing methods suitable for the diffusion bonded joints, which are commonly used in our research of diffusion welding and which are planned to be used afterwards.

Abstract: The aim of this article is to present possibilities of diffusion bonding utilization at creation heterogeneous joints where strength properties are taken into account. The joint was implemented to low-alloy structural ferrite-pearlite S355J2 steel and high-alloy austenitic AISI 316L steel. The fundamental theory of diffusion and also design and realisation of experimental creation of diffusion joint in thermal-mechanical simulator Gleeble 3500 is described in the article. Furthermore, procedure of technological parameters selection, when optimisation of strength properties of heterogeneous joint including metallographic evaluation are taken into account, are presented.

Abstract: Aerospace vehicle requires structures to withstand intense aerodynamic heating and propulsion system to provide very high effective heat exchange. In order to satisfy both requirements of effective thermal exchange and mechanical properties, high temperature materials, or sometimes dissimilar metals with different properties must be joined together. In this study, it is demonstrated that diffusion welding process can be applied to manufacturing lightweight integral structures of aerospace structural parts with titanium and stainless steel. The results show that the technology to design and develop the diffusion welding process of high temperature metals can be applied for manufacturing of aerospace components for high temperature application.

Abstract: Since solid state welded joint is formed from an intimate contact between two metals at temperatures below the melting point of the base materials, the structural integrity of welding depends on time, temperature, and pressure. This paper provides some of examples of friction stir welding and diffusion welding process for aerospace components. Friction stir welding process of AA2195 was developed in order to study possible application for a large fuel tank. Massive diffusion welding of multiple titanium sheets was performed and successful results were obtained. Diffusion welding of dissimilar metals of copper and stainless steel was necessary to manufacture a scaled combustion chamber. Diffusion welding of copper and steel was performed and it is shown that the optimum condition of diffusion welding is 7MPa at 890°C, for one hour. It is shown that solid state welding processes can be successfully applied to fabricate lightweight aerospace parts.