TiC Reaction Research Articles

C/C composite surface modified by electrophoretic depositing SiC nanowires and its brazing to Nb

A novel surface treatment method by electrophoretic depositing SiC nanowires on the C/C composite was introduced to reinforce the C/C–Nb brazed joints. Results showed that the electrophoretic deposition (EPD) process of SiC nanowires could improve the wettability of the liquid AgCuTi alloy on the C/C substrate because of the reaction between SiC nanowires and active element Ti in the AgCuTi alloy. With the introduction of SiC nanowires, the formation of continuous brittle Ti3Cu4 layer was inhibited and the Ti3Cu4 changed into lumps. The thickness of the TiC reaction layer was 500 nm when the EPD time was 5s which was larger than that of the original brazed joint. As the EPD time continued to increase, the thickness of the TiC reaction layer decreased gradually and the size of brittle Ti3Cu4 phase in the joint became smaller and smaller. With the combined effects of the change in the Ti3Cu4 morphology and the TiC reaction layer thickness, the average shear strength of joints achieved a peak of 48 MPa when the EPD time was 30s, which was 60% higher than that of the original brazed joints.

The in-situ synthesis of TiC in Cu melts based on Ti–C–Si system and its mechanism

Introduction of carbon into metal melts, especially those with limited carbon solubility, for composites preparation by casting method is very difficult due to the poor wettability between carbon and melts. In this work, carbon in various forms has been effectively introduced into Cu melts and TiC has been in-situ synthesized based on Ti–C–Si system, and its mechanism has been investigated. It is found that, after the addition of TiC mixture into Cu melts, carbon can be wetted by Cu through TiC reaction. However, because of the TiC interconnected network formation, the mixture tends to become the block which cannot be dispersed into the melts. Using Ti–C–Si instead of TiC system is an effective way to wet carbon and in-situ synthesize TiC while prevent the formation of TiC network. It is considered that Si changes the reaction pathway of the system. The Ti5Si3 which is prior to be formed in Ti–C–Si system can prevent the following formed TiC from interconnecting and its subsequently dissolution due to TiC formation can further help the products to distribute more uniformly in Cu melts.

In-situ synthesis of TiC-Al2O3 coating on copper surface

In-situ TiC-Al2O3 strengthening coating was applied on copper, using the vacuum-expendable pattern casting (VEPC) in combination with the self-propagating high-temperature synthesis (SHS) technology. Due to the high heat consumption, highly exothermic CuO-Al (CA) reaction was employed to guarantee 100% completion of the TiC reaction. Consequently, TiC- Al2O3 coating was obtained after the ignition of Ti-C-CuO-Al SHS system by molten copper. Here, the optimal CA content was 10 wt%. During the casting process, molten copper infiltrated into the SHS coating, resulting in the achievement of dense coating microstructure. The hardness and wear resistance were also significantly improved. The hardness value of copper matrix was only 40 HB, while that of the composite coating was up to 195 HB. The mass loss reduced from 7.98 g to 0.44 g at 40 N load. Besides, metallurgical bonding was obtained with an ideal bond strength of 293 MPa.

The preparation and mechanical properties of carbon/carbon (C/C) composite and carbon fiber reinforced silicon carbide (Cf/SiC) composite joint by partial transient liquid phase (PTLP) diffusion bonding process

Using Ti/Ni/Ti multiple foils as interlayer, carbon/carbon (C/C) composite was bonded to carbon fiber reinforced silicon carbide (Cf/SiC) composite by partial transient liquid phase (PTLP) diffusion bonding process. The multiple gradient structures, i.e. C/C composite | Ti-C reaction layer | Ni-Ti intermetallic compound | residual Ni foil | Ni-Ti intermetallic compound | Ti-C reaction layer | Cf/SiC composite, were formed during joining process. All the interfaces are bonded well, except for some micro-pores appeared in the interface between the residual Ni layer and Ni-Ti layer. The shear strength of the joint was 44.7 ± 12.8 MPa at room temperature. The X-ray result indicates that only diffraction peaks of C, TiCx and Ni-Ti Intermetallic compound were observed, while no diffraction peaks of Si were found on the fracture surface. Thus, it could be deduced that fracture occurred in the interfacial area adjacent to C/C composite side.

First-principles calculations on wetting interface between Ag-Cu-Ti filler metal and SiC ceramic: Ag (1 1 1)/SiC (1 1 1) interface and Ag (1 1 1)/TiC (1 1 1) interface

Interfacial properties of Ag (1 1 1)/SiC (1 1 1) interface and Ag (1 1 1)/TiC (1 1 1) interface were researched by first-principles calculations to investigate the reason that Ag-Cu-Ti filler metal shows the superior reactive wettability on SiC ceramic. The calculated results show that, 7 atom-layers Ag (1 1 1) surface, 11 atom-layer SiC (1 1 1) surface and 9 atom-layer TiC (1 1 1) surface can represent the Ag bulk, SiC bulk and TiC bulk, effectively. Ag (1 1 1)/SiC (1 1 1) interface and Ag (1 1 1)/TiC (1 1 1) interface with C-terminated structure and TL stacking sequence show the highest interfacial stability. Chemical bonds at Ag (1 1 1)/SiC (1 1 1) interface and Ag (1 1 1)/TiC (1 1 1) interface are mainly formed by the interaction between 1st layer C atoms in SiC (or TiC) slab and 1st layer Ag atoms in Ag slab. Interfacial energy of Ag (1 1 1)/SiC (1 1 1) interface is much larger than that of Ag (1 1 1)/TiC (1 1 1) interface, which indicates that the formed TiC reaction layer between Ag-Cu-Ti filler metal and SiC ceramic indeed plays the positive role on improving the wettability of Ag-Cu-Ti filler metal on SiC ceramic.

Effects of carbon content and size on Ti-C reaction behavior and resultant properties of Cu-Ti-C alloy system

TiC-strengthened Cu alloys with various nominal compositions were prepared by a high-energy ball-milling process, followed by consolidation using spark plasma sintering (SPS), and a subsequent heat treatment. The results indicated that the lower atomic ratio of C/Ti, the more residual Ti in copper matrix, resulting in a lower electrical conductivity but higher microhardness of alloy. The optimal atomic ratio was found to be close to1.0. The reaction behavior of Ti-C in the Cu-Ti-C system during this process was investigated. Microstructural results suggested that TiC formation is through a diffusion-controlled mechanism. A thin TiC layer was formed at the surface of C particles, and the growth of TiC layer was controlled by interdiffusion of C and Ti atoms across the TiC layer. An incomplete chemical reaction between Ti and C, characterized by a core-shell structure, was observed when the initial C particles were large, and the TiC particle size was found to strongly depending on the C particle size.

Microstructure and mechanical strength of SiC joints brazed with Cr3C2 particulate reinforced Ag-Cu-Ti brazing alloy

Joining of SiC ceramic with Ag-Cu-Ti active alloy reinforced with Cr3C2 particulates to control the microstructure and increase joint strength was investigated. The results indicated that the reaction of titanium in the brazing alloys and Cr3C2 particulates was detected, but it would not affect the reaction of Ti and SiC. TiC reaction layer with a thickness about 100 nm was formed at the interface between SiC ceramic substrate and brazing alloy. Ti5Si3 silicide phases were also observed near the reaction layer. The Cr3C2 particulates randomly distributed in the braze matrix (< 10 vol% Cr3C2) and refined the Ag-rich and Cu-rich solid solution phase. Cu2Ti intermetallic phase was also found in the joint. The clustering and particle-to-particle contact behavior of Cr3C2 particulates was observed in the joint with high amount of Cr3C2. The joint strength increased with increasing the volume fraction of added Cr3C2 particulates first and then decreased. The shear strength of the joint brazed with 10 vol% Cr3C2 addition reach up to 212.8 MPa, which was 134.2 MPa higher than that brazed with Ag-Cu-Ti brazing alloy.

Wetting behavior of graphite and CFC composites by Cu-Ti compacts

The wetting behavior of Cu-Ti powder compacts with 22 wt % Ti and 50 wt % Ti on carbon materials, including graphite and carbon fiber reinforced carbon composites (CFC), has been investigated in a vacuum using the sessile drop method. The equilibrium contact angles of Cu-22Ti (containing 22 wt% Ti) on the graphite and the CFC substrates at 1 253 K are 32° and 26°, respectively, whereas the equilibrium contact angle of 9° is obtained for Cu-50Ti (containing 50 wt% Ti) on both the graphite and the CFC substrates at 1 303 K. Microstructural analysis of the wetting samples shows that a thin TiC reaction layer is developed at the interfacial area and Ti-Cu intermetallic compounds are formed over the reaction layer. The investigation on the spreading kinetics of Cu-Ti compacts on carbon materials substrates at fixed temperatures reveals that the spreading is controlled by the interfacial reactions in the first stage and then by the diffusion of the active Ti from the drop bulk to the triple line in the later stage. The spreading is promoted by the intense reaction at higher Ti concentrations.

Microstructural characterization of graphite/CuCrZr joints brazed with CuTiH2Ni-based fillers

Brazing of graphite to CuCrZr alloys has been achieved using CuTiH2Ni-based fillers (CuTiH2Ni, CuTiH2Ni+TiC and CuTiH2Ni+B) at 1173 K. Microstructural observation of the joints reveals a favorable interfacial bonding. The joining area of joints with CuTiH2Ni filler is composed of a TiC reaction layer and a filler layer containing Cu-based solid solutions, τ1-Ti(CuxNi1-x)2, Ti2(Cu,Ni) and TiCu intermetallics. For the graphite/CuTiH2Ni+TiC/CuCrZr joints, both TiC particles distribution in the filler layer and liquid filler penetration into the graphite open pores are observed. In the case of joints with CuTiH2Ni+B filler, TiB whiskers synthesized by the in situ reaction of boron with Ti are dispersed uniformly in the filler layer. Compared to CuTiH2Ni filler, the introduced TiC particles and TiB whiskers can work as ceramic reinforcements to strengthen the graphite/CuCrZr joints. Meanwhile, these reinforcements can also provide heterogeneous nucleation sites for the molten filler layer and suppress the grain growth of the precipitated phases, resulting in strengthening the filler layer by grain refinement. The electrical resistivity of the joining area in the joints brazed with CuTiH2Ni-based fillers is relatively low, satisfying the requirement for the applications of carbon commutators.

Deposition characteristics of titanium coating deposited on SiC fiber by cold-wall chemical vapor deposition

The deposition characteristics of titanium coating on SiC fiber using TiCl4-H2-Ar gas mixture in a cold-wall chemical vapor deposition were studied by the combination of thermodynamic analysis and experimental studies. The thermodynamic analysis of the reactions in the TiCl4-H2-Ar system indicates that TiCl4 transforms to titanium as the following paths: TiCl4 → TiCl3 → Ti, or TiCl4 → TiCl3 → TiCl2 → Ti. The experimental results show that typical deposited coating contains two distinct layers: a TiC reaction layer close to SiC fiber and titanium coating which has an atomic percentage of titanium more than 70% and that of carbon lower than 30%. The results illustrate that a carbon diffusion barrier coating needs to be deposited if pure titanium is to be prepared. The deposition rate increases with the increase of temperature, but higher temperature has a negative effect on the surface uniformity of titanium coating. In addition, appropriate argon gas flow rate has a positive effect on smoothing the surface morphology of the coating.

Thermodynamic assessment of the Ti + C → TiC reaction in the presence of nickel and a moderator

We present thermodynamic calculations concerning the adiabatic temperatures of the SHS reaction producing TiC in the presence of nickel, either metallic or resulting from the aluminothermic reduction of nickel monoxide, and a reaction moderator, alumina or magnesia. In addition, some emphasis is put on the amounts of the various liquid phases which may have a key role in the densification of resulting products.

Microstructures, mechanical and oxidation behaviors of C/C composites modified by NiAl alloy

Carbon/carbon composites modified by NiAl alloy were prepared using vacuum reactive melt infiltration methods with NiAl and titanium mixed powders as raw materials. The microstructures were investigated by scanning electron microscopy. The fracture behavior, infiltration and oxidation mechanism were further discussed. The results indicated that NiAl alloy exhibited good wettability on the C/C preform because a TiC reaction layer formed at the interface. Multi-layer (PyC/TiC/NiAl+TiC) coating evenly and compactly distributed on the surface of the carbon fiber in tubular form. The penetration depth of molten NiAl alloys depended on the reaction between the PyC and titanium. The impact fracture was inclined to along the interface between the NiAl permeability layer and C/C matrix. Al2TiO5 and TiO2 formed on the surface, while the interior multi-layer tubular structure partially remained after oxidation at 1773 K for 30 min.

Brazing of graphite to Cu with Cu50TiH2 + C composite filler

Brazing of graphite to Cu has been successfully realized with Cu50TiH2 (containing 50 wt% Cu)-based fillers (including Cu50TiH2 filler and Cu50TiH2 + C composite filler) in vacuum at 1223 K. The average shear strength is 10.8 MPa for the joints brazed with Cu50TiH2 filler. Microstructure observation of the joints shows the crack-free interfaces both at the graphite and the Cu sides. The filler layer mainly consists of Cu base solid solution and Ti–Cu intermetallics. Furthermore, a thin TiC reaction layer is developed close to the graphite substrate. With regard to the joints brazed with Cu50TiH2 + C composite filler, the average shear strength of the joints increases to 18.0 MPa. Microstructural characterization reveals that TiC particles have been synthesized in situ in the filler layer. Cu base solid solution and Ti–Cu intermetallics together with TiC particles are detected in the filler layer. The TiC particles synthesized in situ distribute uniformly in the filler layer, which may act as reinforcements and consequently benefit the improvement of the graphite/Cu joints.

Microstructure and mechanical properties of Si3N4/42CrMo joints brazed with TiNp modified active filler

Si3N4 ceramic/42CrMo steel joints were obtained by employing TiNp modified Ag–Cu–Ti active filler and subsequently the effect of TiNp content on the microstructure and mechanical properties of the joints was investigated. Microstructural examination revealed that TiN+Ti5Si3 reaction layer was adjacent to the Si3N4 ceramic while a TiC reaction layer was close to the steel substrate. With the increase of TiNp content, more fine grains and less Ag–Cu eutectic appeared in the joint and the reaction layers near the two base materials became thinner. The flexural strength of the joint obtained by four-point bending test climbed about 100% with the optimum TiNp content of 5vol%, comparing with the case without TiNp. Thermal stress distributions in the joint were analyzed using finite element modeling computations, which accorded well with the bending test results.

SYNTHESIS AND BIOLOGICAL ACTIVITY OF IMIDAZOLE DERIVED CHALCONES AND IT’S PYRIMIDINES

Microbial contribution increasing rapidly due to i nvasion by the pathogenic organisms like bacteria, fungi and virus in the present disease burden of human health . To treat these diseases many potent and broad spectrum antibiotics were discovered e.g ., ampicillin, amoxicillin, carbenicillin, oflo xa cin and tetracycline etc., E ven th ough antibiotics are life saving drugs in therapeutics but t hey are potentially harmful. The se harmful effects include allergic and anaphylac tic reaction, development of resist ance, destruction of normal non - pathogenic bacterial flora and selective toxicity like aplastic anemia, kidney damage. As the microbial resistance make anti - microbial therapy very complex, there i s a definite need of novel anti microbials or drugs for combination therapy with standard antibiotics. Our aim wa s to synthesize and explore the anti - microbial activity of chalcones and its derived pyrimidines against various pathological micro organisms. Novel imidazole derived chalcones were synthesized and characterization was carried out by analyzing melting poin t, IR, 1 H NMR data. The synthes ized chalcones and pyrimidines are tested for their antimicrobial activity against various bacteria as well as fungi . Further synthesis of novel heterocyclic chalcones, s tructural elucidation, s pectral analysis, biological ac tivity of synthesized chalcones and its derived pyrimidines gives a hope for enhanced biological action using QSAR Studies.

Modeling and simulation of the TiC reaction layer growth during active brazing of diamond using DICTRA

The growth kinetics of the TiC reaction layer during active brazing of diamond with Cu–Sn–Ti and Ag–Cu–Ti based filler alloy has been investigated by kinetic simulations and comparing with available experimental data. First, to obtain a reliable mobility database, the atomic mobilities of C and Ti in fcc (face-centered cubic) TiC are assessed using software DICTRA based on available diffusion data from literatures. Then, to carry out simulations for GB (Grain Boundary) diffusion in TiC, the bulk activation energy multiplier is determined by evaluating the available GB diffusion data. With the obtained mobility data, the TiC growth for Cu–Sn–Ti–Zr filler as a function of brazing temperature and time is simulated using various possible GB diffusion parameters. Afterwards, the determined GB diffusion parameters are validated by simulating the TiC growth for various Cu–Sn–Ti or Ag–Cu–Ti brazing alloys and comparing the simulated results with experimental data. Based on the optimized GB diffusion parameters, the influence of brazing temperature, filler alloy composition, and braze layer thickness on growth kinetics of TiC are simulated and discussed. Finally, the experimentally observed segregation of Cu at the interface between diamond and TiC layer during brazing of diamond using Cu–Sn–Ti or Ag–Cu–Ti filler is analyzed by diffusion simulations.

Interfacial microstructure and mechanical properties of TiAl and C/SiC joint brazed with TiH2–Ni–B brazing powder

Abstract (TiH 2 –66Ni) 1 − x B x (x = 3 wt.%) brazing powder was fabricated by mechanical milling of a TiH 2 , Ni and B mixture with the milling time ranged from 30 to 180 min. TiAl alloy and C/SiC composite were successfully brazed using this filler metal at 1180 °C for 10 min. The microstructure and mechanical properties of the brazed joints were investigated. The typical microstructure of the joint was divided into three characteristic zones, including the TiC reaction layer formed adjacent to C/SiC composite, the TiB-whisker reinforced central zone, and the β layer transformed from TiAl alloy. The in situ synthesized TiB whiskers acted as an effective reinforcement phase aid to decrease the residual stress and improve the shear strength of the joints. The joint strength reached 105 MPa at room temperature, and cracks primarily propagated in the C/SiC substrate with the pull-out of carbon fibers and partially in the TiC layer and τ 3 phase. The joint strength decreased slightly with the testing temperature increased to 500 °C, and remained at 70 MPa when tested at 600 °C. The crack propagation path diverted from the TiC reaction layer to the τ 3 phase when the joint was tested at 600 °C.

Microstructure and Interface of TiC &lt;i&gt;In Situ&lt;/i&gt; Synthesized Reinforced Steel-Based Surface Composite Prepared by V-EPC Infiltrating Method

In order to optimize the processing parameters of TiC/steel composite materials, in-situ TiC particle reinforced steel-based surface composites were prepared by vacuum evaporative pattern casting (V-EPC) infiltration process, and the structure and interface of the composites were investigated. The results show that, TiC particle size with Ti-C-20wt%Fe reaction system was much smaller than the composite with Ti-C reaction system in the same location of the composites. In the composites, the TiC particle size and volume fraction increased and spherical degree dropped from the tradition layers (interface between the substrate and the composite layer) to the outer surface. But the increase of TiC particle size (1-3μm) and volume fractions (25.8%-43.5%) in the composite with Ti-C-20wt%Fe reaction system was obviously lower than that of TiC particle size (1-10μm) and volume fractions (12.3%- 67.7%) in the composite with Ti-C reaction system. The bond zone between TiC particles and the matrices was totally metallurgical bonding without apparent interface. Comparing with the composite with Ti-C-xFe reaction system, the tradition layer with Ti-C reaction system has a poorer internal quality. The forming process of TiC in situ synthesized reinforced steel substrate surface composites prepared by V-EPC infiltrating process was infiltrating of the melting and carbothermal reactions of C and Ti powder the result of joint action.

Effect of joining temperature and holding time on microstructure and shear strength of Ti2AlC/Cu joints brazed using Ag-Cu filler alloy

The present study investigated the effect of brazing temperature and holding time on the microstructure and mechanical properties of Ti2AlC-copper joints brazed with Ag-Cu filler alloy at 800–900°C for 10min and held for different times at 850°C. The representative structure of the joints was Ti2AlC/interaction area in the Ti2AlC substrate/brazing layer/diffusion area of the copper substrates/Cu. The brazing layer was composed of Cu-rich phases, AlCu2Ti intermetallic compounds and Ag[Cu] solid solutions. With increasing brazing temperature, more filler alloy was infiltrated into the ceramic substrate and reacted with Ti2AlC, accelerating the decomposition of Ti2AlC and the formation of Ti3AlC2, TiC and AlCu2Ti reaction phases. Moreover, more copper substrate was dissolved into the filler alloy; thus, more Cu-rich phase and AlCu2Ti were produced in the brazing layer. Moreover, the width of the brazing layer was reduced, while the widths of both the interaction area and diffusion area increased. As the brazing temperature was increased, the shear joint strength increased and then decreased. By prolonging the holding time, the widths of both the interaction area and the diffusion area were increased, while the width of the brazing layer was held constant at approximately 50μm. Neither the structure nor the shear strength of the joints was influenced by the holding time. The optimum brazing parameters for joining Ti2AlC ceramic to copper with Ag-Cu filler alloy were 850°C for 40min. The joints obtained exhibit a maximum shear strength of 203.3MPa.

Reaction-composite brazing of carbon fiber reinforced SiC composite and TC4 alloy using Ag–Cu–Ti–(Ti+C) mixed powder

Carbon fiber reinforced SiC (Cf/SiC) was successfully joined to TC4 alloy with Ag–Cu–Ti–(Ti+C) mixed powder by proper parameters. The interfacial microstructure was investigated by scanning electron microscopy (SEM), energy dispersive spectrometry (EDS) and X-ray diffraction (XRD). The mechanical properties of the brazed joints were measured by a mechanical testing machine. The results show that the Ti element in the interlayer can react with the brazed composite, the brazed joints mainly consist of TiC, Ti3SiC2, Ti5Si3, Ag, residual graphite, TiCu, Ti3Cu4 and Ti2Cu reaction products, and the performed joints have dense bonding layers reinforced by residual graphite and in situ synthesized TiC from reaction between C and Ti in the filler materials. The TiC particulates obviously relax the thermal stress in the heterogeneous joint resulting in an increase in shear strengths of the brazed joint. The maximum shear strengths of the brazed joints at room temperature, 500°C and 800°C are 145MPa, 70MPa and 39MPa, respectively. The shear strengths of the joints are remarkably higher than the optimal of the joints brazed with Ag–Cu–Ti.