Effect of holding time on microstructure and mechanical properties of SiC/SiC joints brazed by Ag-Cu-Ti + B4C composite filler

The composite fillers have a number of advantages comparing with the traditional filler metals, and have been widely used for brazing ceramics. However, previous researches mainly focus on the strengthening mechanism of either whiskers or particles. It is still of great interest to investigate the reinforcement effect with the presence of both whiskers and particles. In this study, Ag-Cu-Ti + B4C composite filler was developed to braze SiC ceramics, and effects of holding time on the microstructure evolution and mechanical properties of the joints were investigated in detail. With the prolongation of holding time, the overall thickness of Ti3SiC2 + Ti5Si3 layers adjacent to SiC ceramic was increased correspondingly and the reaction between active Ti and B4C particles was promoted more extensively. The bending strength of the joints increased with holding time until the maximum bending strength of 140 MPa was reached and then decreased dramatically. The hardness and Young's modulus of the joints were characterized by nano-indentation to reveal the strengthening of the brazing seam. In addition, the strengthening mechanism of the joints brazed by the Ag-Cu-Ti + B4C composite filler was proposed on the basis of experimental observation and theoretical analysis

Igg, Igm and Iga Antibodies against the Novel Polyprotein in Active Tuberculosis

Background The present study was aimed to evaluate whether IgG, IgM and IgA antibodies levels detected against a novel Mycobacterium tuberculosis polyprotein 38 F-64 F (with 38 F being the abbreviation for 38kD-ESAT6-CFP10 and 64 F for Mtb8.4-MPT64-TB16.3-Mtb8) are suitable for diagnosing active tuberculosis, and for monitoring the efficacy of chemotherapy on TB patients. Methods In this study, a total of 371 active TB patients without treatment were selected and categorized into S+/C+ group (n = 143), S-/C+ group (n = 106) or S-/C- group (n = 122). A series of serum samples were collected from 82 active TB patients who had undergone anti-TB chemotherapy for 0–6 months at one month interval. Humoral responses (IgG, IgM and IgA) were determined for the novel Mycobacterium tuberculosis polyprotein using indirect ELISA methods in all of serum samples. Results For S+/C+, S-/C+ and S-/C- active tuberculosis patients before anti-TB chemotherapy, the sensitivities of tests based on IgG were 65.7%, 46.2% and 52.5% respectively; the sensitivities based on IgM were 21.7%, 24.5% and 18.9%; and the sensitivities based on IgA were 25.2%, 17.9% and 23.8%. By combination of three isotypes, for all active tuberculosis patients, the test sensitivity increased to 70.4% with the specificity being 91.5%. After anti-TB chemotherapy, there were no significant differences between groups with different courses of anti-TB chemotherapy. Conclusions The novel Mycobacterium tuberculosis polyprotein 38 F-64 F represents potential antigen suitable for measuring IgG, IgM and IgA antibodies. However, the serodiagnostic test based on the 38 F-64 F polyprotein appears unsuitable for monitoring the efficacy of chemotherapy

Joining C/C–SiC composite and Ti60 alloy using a semi-solid TiNiCuNb filler

This paper developed an innovative pressure-free contact reaction brazing technique that facilitated joining ceramics at low temperatures. Using this method, a semi-solid TiNiCuNb filler was employed to join C/C–SiC composite and Ti60 alloy. By facilitating elements’ diffusion through the partial liquid of semi-solid TiNiCuNb alloy, Ti could be introduced into this alloy without pressure, and the complete melting was achieved above 950 °C. Based on this, Ti60 alloy was joined to C/C–SiC composite below its β-transus temperature. Significant reaction differences between C/C and SiC with filler were found, mainly due to the different solubility and diffusion characteristics of C and Si in liquid filler. SiC exhibited higher sensitivity to temperature changes and was more prone to overreaction to induce defects. At 1010 °C, the maximum shear strength of 22.5 MPa was obtained due to the moderate reaction of both C/C and SiC with filler. This work contributed to manufacturing lightweight brake systems

Brazing of C/C composite and Ti-6Al-4V with graphene strengthened AgCuTi filler: Effects of graphene on wettability, microstructure and mechanical properties

Graphene nanosheets (GNSs) strengthened AgCuTi composite filler (AgCuTiG) was used to braze C/C composite and Ti-6Al-4V. The effects of GNSs on the wettability of AgCuTiG filler on the C/C composite surface and the interfacial microstructure and mechanical properties of brazed joints were investigated. The results indicate that the addition of GNSs reduced the wettability of AgCuTiG. The interfacial microstructure of brazed joints evolved with the addition of GNSs, where Ti3Cu4 and TiCu4 were converted to TiCu and the thickness of the reaction layer adjacent to the base material decreased. The maximum shear strength of joints brazed at 0.3wt% GNSs was 23.3 MPa (880 °C/10 min). Further adding GNSs deteriorated the shear strength of the joints. Fracture of the joints occurred in the C/C composite substrate and the TiC layer adjacent to C/C composite. Keywords: Brazing, Graphene nanosheets, Mechanical properties, Microstructure, Wettin

APPLICATION OF THE WELDING PROCESS IN THE MANUFACTURE OF BOILER COMPONENTS

U diplomskom radu ukratko je opisano područje zavarivanja. U prvom poglavlju diplomskog rada navedena je podjela i opis postupaka zavarivanja pritiskom i taljenjem koji se primjenjuju u izradi komponenata kotlovskih postrojenja. U drugom poglavlju navedeni su praktični primjeri primjene pojedinih postupaka zavarivanja u pogonskim uvjetima u izradi komponenata kotlovskih postrojenja. Navedeni su detalji zavara, učinkovitost, parametri zavarivanja i ograničena u praktičnoj primjeni s obzirom na vrstu i debljinu materijala. U trećem poglavlju prikazana je automatizacija i robotizacija pojedinih postupaka zavarivanja koji se primjenjuju u kotlovskom postrojenju, opisani su primjeri iz prakse koji se obavljaju unutar proizvodnje tvrtke „Đuro Đaković Termoenergetska postrojenja d.o.o.“.This graduate thesis briefly describes welding domain. The first chapter of the thesis deals with the division and description of welding and melt welding procedures that are applied in the manufacturing of boiler plants components. The second chapter consists of practical examples of the application of certain welding procedures in operating conditions in the design of boiler plants components. Also, the details of welding, efficiency, welding parameters and limitations in practical application with respect to the type and thickness of the material are mentioned. The third chapter presents the automation and robotization of individual welding procedures applied in the boiler plant. Examples of practices that are carried out within the company „Đuro Đakoović Termoenergetska postrojenja d.o.o“ are described

Research progress of composite fillers

Using composite filler is a very potential way to braze dissimilar material, especially braze metals with ceramics. The composite filler which is added varieties of high temperature alloy, carbon fiber and ceramic particles has a suitable coefficient of thermal expansion. The application of composite filler can release the residual stress caused by mismatch of thermal expansion coefficient in the brazing joints and improve the overall performance significantly. According to the traditional classification method of composite materials, the composite filler is divided into micron-reinforced composite filler and nano-reinforced composite filler, of which the feature and research status are discussed in this text. According to the influence of different size reinforced phases on microstructure and mechanical property of the brazing joints, nano-reinforced composite filler has more uniform and better structure compared with micron-reinforced composite filler, and higher joint strengh can be obtained by using it. However, the reinforced mechanism is still an open question, and will become the key area of the future research work

A novel method for improving interfacial joining strength of vacuum brazed TiAl/GH3536 thin-walled structure by Au coating

Lightweight components and materials based on the joining of dissimilar materials have attracted wide attention in aerospace field. To obtain the optimized micromorphology and interfacial microstructure of the brazed joints, a new method of Au layer deposition on TiAl base metal was proposed to assist the brazing of TiAl plate to GH3536 thin-walled structure. Significantly, the design of Au layer affected the brazing fillet, dissolution of GH3536 core and the evolution of interface, and then the maximum force under tensile loading of the hetero-thin-walled structure. The effect of Au layer thickness on the interfacial microstructure and mechanical properties was discussed in detail. Upon the deposition of an Au layer with a concentration of 0.2 wt% onto the TiAl plate, the load-bearing capacity of the brazed thin-walled structure was observed to undergo a significant enhancement. Specifically, the maximum force sustained under tensile loading was measured to be 391 N, thereby exhibiting a remarkable increase of 117 % relative to that of the Au-free system.The authors gratefully acknowledge the financial support from the National Natural Science Foundation of China (Grant Nos. 52175307 and 51905125) and the Taishan Scholars Foundation of Shandong Province, China (No. tsqn201812128)

Diffusion Bonding of Ti₂AlNb Alloy and High-Nb-Containing TiAl Alloy: Interfacial Microstructure and Mechanical Properties

In this study, reliable Ti2AlNb/high-Nb-containing TiAl alloy (TAN) joints were achieved by diffusion bonding. The effects of bonding temperature and holding time on the interfacial microstructure and mechanical properties were fully investigated. The interfacial structure of joints bonded at various temperatures and holding times was characterized by scanning electron microscopy (SEM), energy dispersive spectrometer (EDS) and X-ray diffraction (XRD). The results show that the typical microstructure of the Ti2AlNb substrate/O phase/Al(Nb,Ti)2 + Ti3Al/Ti3Al/TAN substrate was obtained at 970 °C for 60 min under a pressure of 5 MPa. The formation of the O phase was earlier than the Al(Nb,Ti)2 phase when bonding temperature was relatively low. When bonding temperature was high enough, the Al(Nb,Ti)2 phase appeared earlier than the O phase. With the increase of bonding temperature and holding time, the Al(Nb,Ti)2 phase decomposed gradually. As the same time, continuous O phase layers became discontinuous and the Ti3Al phase coarsened. The maximum bonding strength of 66.1 MPa was achieved at 970 °C for 120 min

Microstructural Evolution and Mechanical Properties of Ti₂AlNb/GH99 Superalloy Brazed Joints Using TiZrCuNi Amorphous Filler Alloy

Dissimilar materials brazing of Ti2AlNb alloy to GH99 superalloy is of great pragmatic importance in the aerospace field, especially the lightweight space aircraft components manufacturing. In this work, TiZrCuNi amorphous filler alloy was used as brazing filler, and experiments were carried out at different brazing temperatures and times to investigate the changes in interfacial structures and properties of the joints. The typical interfacial microstructure was Ti2AlNb alloy/B2/β/Ti2Ni (Al, Nb) + B2/β + (Ti, Zr)2(Ni, Cu) + (Ti, Zr)(Ni, Cu)/(Cr, Ni, Ti) solid solution + (Ni, Cr) solid solution/GH99 superalloy when being brazed at 1000 °C for 8 min. The interfacial microstructure of the joints was influenced by diffusion and reaction between the filler alloy and the parent metal. The prolongation of brazing process parameters accelerated the diffusion and reaction of the liquid brazing alloy into both parent metals, which eventually led to the aggregation of (Ti, Zr)2(Ni, Cu) brittle phase and increased thickness of Ti2Ni (Al, Nb) layer. According to fracture analyses, cracks began in the Ti2Ni (Al, Nb) phase and spread with it as well as the (Ti, Zr)2(Ni, Cu) phase. The joints that were brazed at 1000 °C for 8 min had a maximum shear strength of ~216.2 MPa. Furthermore, increasing the brazing temperature or extending the holding time decreased the shear strength due to the coarse Ti2Ni (Al, Nb) phase and the continuous (Ti, Zr)2(Ni, Cu) phase