Effect of brazing temperature on microstructure and tensile strength ofγ-TiAl joint vacuum brazed with micro-nano Ti−Cu−Ni−Nb−Al−Hf filler

A novel micro-nano Ti−10Cu−10Ni−8Al−8Nb−4Zr−1.5Hf filler was used to vacuum braze Ti−47Al−2Nb−2Cr−0.15B alloy at 1160−1220℃ for 30 min.The interfacial microstructure and formation mechanism of TiAl joints and the relationships among brazing temperature,interfacial microstructure and joint strength were emphatically investigated.Results show that the TiAl joints brazed at 1160 and 1180℃ possess three interfacial layers and mainly consist of α_(2)-Ti_(3)Al,τ_(3)-Al_(3)NiTi_(2) and Ti_(2)Ni,but the brazing seams are no longer layered and Ti_(2)Ni is completely replaced by the uniformly distributed τ_(3)-Al_(3)NiTi_(2) at 1200 and 1220℃ due to the destruction of α_(2)-Ti_(3)Al barrier layer.This transformation at 1200℃ obviously improves the tensile strength of the joint and obtains a maximum of 343 MPa.Notably,the outward diffusion of Al atoms from the dissolution of TiAl substrate dominates the microstructure evolution and tensile strength of the TiAl joint at different brazing temperatures.

Simulation and Optimization of the Fluid Solidification Process in Brazed Plate Heat Exchangers

When a brazed plate heat exchanger is used as an evaporator,the working mass in the channel may undergo soli-dification,thereby hindering the refrigeration cycle.In this study the liquid solidification process and its optimi-zation in a brazed plate heat exchanger are investigated numerically for different inlet velocities;moreover,different levels of corrugation are considered.The results indicate that solidificationfirst occurs around the con-tacts,followed by the area behind the contacts.It is also shown that deadflow zones exist in the sharp areas and such areas are prone to liquid solidification.After optimization,the solidification area attains its smallest value when a corrugation spacingλ=4.2 mm is considered.

MONOBRAZE单层翅片箔与三层复合翅片箔耐腐蚀性能对比研究

采用金相显微镜、电位计、EPMA和SWAAT腐蚀试验等手段,研究了分别采用三层复合翅片箔和MONOBRAZE单层翅片箔钎焊后的两种冷凝器接头断面形貌、微观组织、元素扩散、电极电位和耐腐蚀性能。结果表明:与热轧三层复合翅片箔相比,MONOBRAZE单层翅片具有同样的钎焊连接效果,而且钎焊后强度更高、无明显熔蚀、翅片厚度无明显减薄,为MONOBRAZE翅片进一步减薄、大面积替代复合翅片、降低热交换器制造成本创造了有利条件。同时,采用MONOBRAZE单层翅片钎焊后的冷凝器有着更优良的耐腐蚀性能,MONOBRAZE翅片优先被腐蚀,可以对MPE管起到更好的牺牲阳极保护作用,大幅提高热交换器整体寿命。

Research on the heat conduction mechanism of induction brazecoating

Induction brazecoating technology is an important means to improve the surface properties of materials.In this paper,copper plate and corundum are selected as substrates for induction brazecoating respectively.The temperature variation of powder and paste coating is systematically studied,and the heat conduction mode and path in the brazecoating process are analyzed.The results show that rise of the coating temperature mainly depends on the heat absorption from the substrate.The liquid-solid interface conducts heat violently and advances step by step,which promotes the melting spread of metal filler metal.The powdery brazecoating material is in a free state,and there is a gas insulation film between the powder particles and the diamond,making it difficult for substrate to conduct heat to the coating.The binder not only assists forming,shell making and oxygen isolation,but also plays an important role during melting.

PERFORMANCE OF BRAZED DIAMOND CUP-TYPE WHEELS WITH DEFINED GRAIN PATTERN IN GRINDING CEMENTED CARBIDE

A new cup-type grinding wheel of the brazed monolayer diamond is developed with a defined grain pattern on the wheel surface. Grinding performance of the brazed wheel in the surface grinding of cemented carbide is studied. Experimental results show that when continuous dry grinding is employed, grits of the brazed diamond grinding wheel fail mainly in attritious wear and fracture modes and no pull-out ones are found in conventional electroplated and sintered diamond wheels. It indicates the strong retention of brazing alloy to diamond grits and the longer service life of the wheel. In addition, the ground surface has good roughness. The theoretical surface roughness agrees well with experimental results.

BONDING INTERFACE AND WEAR BEHAVIOR OF CBN GRAINS BRAZED USING NANO-TiC POWDER MODIFIED FILLER

A new kind of composite fillers,composed of Ag-Cu-Ti alloy and nano-TiC powders,is utilized to braze cubic boron nitride （CBN） grains and tool substrate. The bonding system,including the interfacial microstructure and reactive products between CBN grains and filler layer,is observed by optical microscope and scanning electron microscope （SEM）. Resistant-to-wear experiments of the brazed grains are performed. Results show that the nano-TiC powders evenly distribute in the filler layer so that the resultants grow compactly and uniformly on the surface of CBN grain. This indicates that the chemical bond is established between CBN grains and nano-TiC modified filler. Accordingly,the bonding strength of the grains is ensured. The CBN grains are worn smoothly without grain pull-out.

Microstructure and properties of Cu/Al joints brazed with Zn-Al filler metals

The mechanical properties and microstructural distribution of the Cu/A1 brazing joints formed by torch-brazing with different Zn-A1 filler metals were investigated. The microstructure of the Zn-A1 alloys was studied by optical microscopy and scanning electron microscopy, and the phase constitution of the Cu/A1 joints was analyzed by energy dispersion spectrometry. The results show that the spreading area of the Zn-A1 filler metals on the Cu and A1 substrates increases as the A1 content increases. The mechanical results indicate that the shear strength reaches a peak value of 88 MPa when A1 and Cu are brazed with Zn-15AI filler metal. Microhardness levels from HV122 to HV515 were produced in the three brazing seam regions corresponding to various microstructure features. The Zn- and Al-rich phases exist in the middle brazing seam regions. However, two interface layers, CuZn3 and A12Cu are formed on the Cu side when the A1 content in the filler metals is 2% and more than 15%, respectively. The relationship between intermetallic compounds on Cu side and Zn-xA1 filler metals was investigated.

Sawing Performance Comparison of Brazed and Sintered Diamond Wires

Great attention has been paid on fabricating diamond wire by using the brazing diamond because of its strong chemical bonding strength and controllability of grits distribution. Although several serving performances of brazed diamond wire have been reported, seldom do these studies refer to its process characteristics. Sawing performances of a brazed diamond wire are investigated and compared with those of a sintered diamond wire on a wire saw machine. The surface topographies of beads selected from the two wires are micro observed before sawing. The sawing tests are carried out in constant feed rate feeding（CFF） and constant normal force feeding（CNFF）. In CFF test, sawing force, power, and the cut depths of positions on contact curve are measured. Then, coupled with the observations of beads topographies, sawing force and its ratio, relations of power against material removal rate, and contact curve linearity are compared and discussed. In CNFF test, the sawing rates of the two wires are investigated. The results indicate that the brazed wire performs with lower sawing force（less 16% of tangential force and 28% of normal force）, more energy efficiency（nearly one-fifth of sawing power is saved）, at a higher sawing rate （the rate is doubled） and with better contact curve linearity as compared with the sintered wire. This proposed research experimentally evaluates the sawing performances of brazed diamond wire from the aspect of process parameters, which can provide a basis for popularizing the brazed diamond wire.

Theoretical study and numerical simulation of the stress fields of the Al_2O_3 joints brazed with composite filler materials

Non-linear finite element code MSC. Marc was utilized to analysis the field of stress of the Al2O3 joints brazed with composite filler materials. The properties of the filler materials were defined by using the mixing law, method of Mori-Tanaka and theory of Eshelby to ensure the accuracy and reliability of results of finite element method （FEM）. The results show stress in brazed beam is higher than that in base material. The maximal stress can be found in the interface of joint. And the experimental results show that the shear strength of joints increases from 93.75 MPa （ Al2O3p Ovol. % ） to 135.32 MPa （ Al2O3p 15vol. % ） when composition of titanium is 3wt% in the filler metal.

Al2_3/Al2O3 Joint Brazed with Al2O3-particulate-contained Composite Ag-Cu-Ti Filler Material

Microstructure and interracial reactions of Al2O3 joints brazed with Al2O3-particulate-contained composite Ag-Cu-Ti filler material were researched by scanning electron microscopy （SEM）, electron probe microscopy analysis （EPMA）, energy dispersive spectroscopy （EDS） and X-ray diffraction （XRD）. The interracial reaction layer thickness of joints brazed with conventional active filler metal and active composite filler materials with different volume fraction of Al2O3 particulate was also studied. The experimental results indicated although there were Al2O3 particulates added into active filler metals, the time dependence of interracial layer growth of joints brazed with active composite filler material is t^1/2 as described by Fickian law as the joints brazed with conventional active filler metal.

Brazeability evaluation of Ti-Zr-Cu-Ni-Co-Mo filler for vacuum brazing TiAl-based alloy

Ti-47Al-2Nb-2Cr-0.15B(mole fraction,%)alloy was vacuum brazed with amorphous and crystalline Ti.25Zr-12.5Cu-12.5Ni-3.0Co-2.0Mo(mass fraction,%)filler alloys,and the melting,spreading and gap filling behaviors of the amorphous and crystalline filler alloys as well as the joints brazed with them were investigated in details.Results showed that the amorphous filler alloy possessed narrower melting temperature interval,lower liquidus temperature and melting active energy compared with the crystalline filler alloy,and it also exhibited better brazeability on the surface of the Ti.47Al.2Nb.2Cr.0.15B alloy.The TiAl joints brazed with crystalline and amorphous filler alloys were composed of two interfacial reaction layers and a central brazed layer.Under the same conditions,the tensile strength of the joint brazed with the amorphous filler alloy was always higher than that with the crystalline filler alloy.The maxmium tensile strength of the joint brazed at 1273 K with the amorphous filler alloy reached 254 MPa.

Fabrication of in-situ synthesized ceramic reinforced Ni-based alloy composite coatings by reactive braze coating processing

In-situ synthesized ceramic such as TiC,Cr7C3 and Cr5B3 reinforced Ni-based alloy composite coating was fabricated on the surface of mild steel substrate by reactive braze coating processing with colloidal graphite,Cr,Ni,ferro-boron,Si and titanium powders as the raw materials at low temperature of 1000℃,and a new kind of coating materials was developed.By means of SEM,EDS,XRD and surface hardness tester,the microstructures,phases,hardness and wear-resistance of the coating were analyzed,respectively.The results revealed that the coating was mainly composed of the ceramic in-situ synthesized reinforcement phases of TiC,Cr7C3 and Cr5B3 and the binder phases in-situ synthesized of Ni31Si12 and(Ni,Fe)solid solution;The ceramic reinforcement phases of TiC,Cr7C3 and Cr5B3 were randomly distributed in the binder phases of Ni31Si12 and(Ni,Fe)solid solution;The coating had about 15vol%pores and can possibly be applied as a self-lubrication coating;The coating and the substrate were integrated together by metallurgical bonding;The coating had a hardness up to 91-94HR15N.

Defect detection in brazed weldment with lattice structure using ultrasonic Lamb wave technique

In this paper, defects detection in brazed weldment with lattice structure is studied using ultrasonic Lamb wave. Based on the ultrasonic guided wave theory, the frequency dispersion curves for phase and group velocity of I Cr18Ni9Ti are obtained by solving the Rayleigh-Lamb equation. The incident angles of different modes are determined through theoretical calculation and experimental analyses. Artificial defects of through-wall slots with different dimensions are made and tested. Experimental scattering effects of the fundamental symmetric mode S2 and asymmetric modes A1 and A0 are analysed and compared. The results show that mode Ao is suitable for detecting artificial defect, and the amplitude of the received signals are in good agreement with the defect size. Brazed weldment specimen containing lack of brazing with certain dimensions is made. Using the same methodology, scattering effects produced by weld defects are measured. The results show that the clutter wave brought about by the filler metal will certainly disturbs the identification of defect signal. But, when the defect is 3.0 mm in width, the presented mode Ao could be used potentially.

Electron beam braze-welding of vanadium alloy to stainless steel with electroplated Cu/Ag coatings

Cracks may easily occur in the fusion weld between vanadium alloys and stainless steel due to the brittle intermetallics and welding stress. The high vacuum electron beam braze-welding has been successfully used to join vanadium alloy（V-5Cr-STi） to stainless steel （HR-2） with electroplated Cu and Ag coating. To investigate the effects of electroplated coating on the weldability, the joint appearaace, the microstrueture and the mechanical properties of the joints have been thoroughly analyzed. The results show that the joint surface configuration was good and root reinforcement was full and smooth. A reaction zone （RZ） was gained on the interface between the V-5 Cr-5 Ti alloy and HR-2 stainless steel base metals. The width of reaction zone at the top of the joint was up to O. 65 mm, wider than that in the bottom of the joint （ 0.46 mm）. The reaction zone consisted of considerably smaller dendritic structures with an average grain size of less than 10μm. Element Ag and Cu almost enriched the interface between V-SCr-5Ti alloy substrate and RZ, serving as a physical barrier which decreases or avoids the formation of intermetallics. The maximum tensile strength of vanadium alloy^stainless steel dissimilar alloy joint was more than 300 MPa. The joint was defects free.

Thermal cycling behavior of alumina-graphite brazed joints in electron tube applications

Alumina was joined with graphite by active metal brazing technique at 895,900,905,and 910 ℃ for 10 min in vacuum of0.67 mPa using Ti-Cu-Ag（68.8Ag-26.7Cu-4.5Ti;mass fraction,%） as filler material.The brazed samples were thermal cycled between 30 and 600 ℃ and characterized.X-ray diffraction results show strong reaction between titanium and carbon as well as titanium and alumina.Scanning electron microscopy and helium leak tests show that the initial and thermal cycled brazed samples are devoid of cracks or anv other defects and hermeticity in nature.Brazing strength of the joints is found to be satisfactory.

Microstructure and Strength of Brazed Joints of Ti_(3)Al Base Alloy with Cu-P Filler Metal

Brazing of Ti3Al alloys with the filler metal Cu-P was carried out at 1173-1273 K for 60-1800 s. When products are brazed, the optimum brazing parameters are as follows： brazing temperature is 1215-1225 K; brazing time is 250-300 s. Four kinds of reaction products were observed during the brazing of Ti3Al alloys with the filler metal Cu-P, i.e., Ti3Al phase with a small quantity of Cu （Ti3Al（Cu）） formed close to the Ti3Al alloy; the TiCu intermetallic compounds layer and the Cu3P intermetallic compounds layer formed between Ti3Al（Cu） and the filler metal, and a Cu-base solid solution formed with the dispersed Cu3P in the middle of the joint. The interracial structure of brazed Ti3Al alloys joints with the filler metal Cu-P is Ti3Al/Ti3Al（Cu）/TiCu/Cu3P/Cu solid solution （Cu3P）/Cu3P/TiCu/Ti3Al（Cu）/Ti3Al, and this structure will not change with brazing time once it forms. The thickness of TiCu＋Cu3P intermetallic compounds increases with brazing time according to a parabolic law. The activation energy Q and the growth velocity/to of reaction layer TiCu＋Cu3P in the brazed joints of Ti3Al alloys with the filler metal Cu-P are 286 kJ/mol and 0.0821 m2/s, respectively, and growth formula was y2=O.O821exp（-34421.59/T）t.Careful control of the growth for the reaction layer TiCu＋Cu3P can influence the final joint strength. The formation of the intermetallic compounds TiCu＋Cu3P results in embrittlement of the joint and poor joint properties. The Cu-P filler metal is not fit for obtaining a high-quality joint of Ti3Al brazed.

Ultrasonic C-scan inspection of brazed joint in thin panel honeycomb structure

The non-destructive testing of brazed joint in honeycomb structure with thin panel （ thickness ： 0. 2 mm） was studied by ultrasonic C-scan method. Samples with different types of artificial defect were designed; the characteristic signal and the main parameters of the test were determined by the pre-experiment, and then parameters were optimized by orthogonal design, finally the optimum process was verified by a single panel sample. The multiple reflection echoes were chosen as the characteristic signal. The optimal C-scan results were achieved when the 20 MHz focus probe was used, and the pass band range for received signal were selected as 8 - 17. 5 MHz. The defects such as incomplete penetration and core damage can be detected with ultrasonic C-scan, and the detection accuracy can reach to 1 ram.

Fabrication of Ti-Ni-Mo-Si composite coating by reactive braze coating process

Ti-Ni-Mo-Si composite coating was fabricated on mild steel by reactive braze coating process with Ti61. 9Ni24. 6Si4. 411409.1 （ wt. % ） powders as the raw materials. Microstr^cture of the coating was characterized by optical microscopy, scanning electron microscopy, X-ray diffraction and energy dispersive spectroscopy and micro-hardness tester. Results indicate that the Ti-Ni-Mo-Si composite coating is metallurgically bonded to the mild steel substrate and has high hardness. The microstructure of the coating consists of the reinforcement of Ti5 Si3 and Mo9 Ti4 particles and the matrix of eutectic NiTi2. Due to the poor wettability of NiTi2 liquid at low temperature, TisSi3 and Mo9 Ti4 do not uniformly distribute in the NiTi2 matrix.

Defect detection in brazed weldment with lattice structure using acoustic shadow technique

Brazed weldment with lattice structure has been widely used in aerospace industry. The non-destructive testing is often difficult because of the poor inspection accessibility. The present paper illustrates how the plane-like defect lack of brazing can be detected rapidly in this kind of structure by using ultrasonic Lamb wave. Experimental weldments are prepared and weld defect are tested using S2 mode Lamb wave. Acoustic shadow technique is employed based on Lamb wave testing method. The character of the tested D-scan image and A-scan signal is studied. The experimental results show that acoustic shadow based Lamb wave testing method is effective in detecting through-wall lack of brazing. Meanwhile, the D-scan tested data can be rapidly collected and easily interpreted compared with pulse echo bused Lamb wave testing method.

A study on reactive braze coating of (TiC+Cr_3C_2)/Fe composite coatings

A new hardfacing process, reactive braze coating process (RBCC) was studied, and (TiC+Cr_3C_2)/Fe composite coatings were prepared by RBCC using carbon, Cr_3C_2, iron, ferrochromium and titanium powder as the raw materials in vacuum braze furnace. The results show that TiC is in-situ synthesized in the coatings. The methods of introducing Cr_3C_2 have great effects on the distribution of TiC. Adding Cr_3C_2 directly to the raw materials for coatings, fine TiC particles aggregate into discoids parallel to the coating surface, whereas, in-situ synthesizing Cr_3C_2 in coatings, the aggregations of TiC are lumpish. During braze coating, Cr_3C_2 particles directly added dissolve and precipitate to become needle-shaped. The coatings have an even and smooth surface and are combined with their mild steel substrates by a metallurgical bonding.