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BRAZING & SOLDERING TODAY

SEPTEMBER 201040

To ensure durable, leak-free joints,proper soldering and brazing proceduresmust be in place when joining metal tubesand fittings on appliances, plumbing, andheating, ventilation, air-conditioning, andrefrigeration (HVACR) systems — seelead photos.

Yet, too often, many of the critical careprocedures are overlooked, leaving jointsineffective. A weak joint in a HVACR sys-tem, or hot and cold water pipes, can dam-age the entire structural backbone of abuilding. One pipe burst, or even a contin-ual minor leak, can put an entire facilityout of commission and be costly to repair.

Following a few simple tips and tricksof the trade can help any craftsman makea dependable connection for a stronger,more reliable joint.

Recognizing Both Soldering and Brazing

As defined by The American WeldingSociety, the difference between solderingand brazing is the temperature required tomelt the filler metal. Soldering is a joiningprocess that takes place at below842°F/450°C, and brazing is a similarprocess that occurs above 842°F/450°C but below the melting point of the base metal.

Both soldering and brazing involve thesame basic steps — measuring and cutting,reaming, cleaning, fluxing, assembly andsupport, heating, applying the filler metal,and cooling and cleaning.

The joining process is also the same forboth connections in measuring and cut-ting, reaming, cleaning, fluxing, and as-sembly and support. Similarly, these pro-cedures are basically the same for all

diameters of tube. In contrast, the vari-ables between the two applications are inthe composition of the filler metal, type offlux used, and amount of time and heatnecessary to melt the filler metal within anindividual joint.

From start to finish, attention to detailin each technique contributes to thestrength and overall success of each joint.

Five Guidelines to Follow

1. Make AccurateMeasurements

When measuring the length of eachtube, accuracy is the key. If the tube is tooshort, it will not reach all the way into thefitting, creating a weak link. If the tube istoo long, it could cock in the fitting and putstrain on the system. Both of these condi-tions could affect the life of the system. Ineither case, if the tube is not seated in thefitting cup to its full depth, then the in-tegrity of the joint may be compromised.

2. Cut Properly

Once the tube is measured, it can becut. The cut must be square with the runof the tube to ensure the best fitting. Re-gardless of the type of equipment used inthe cutting procedure, respect for the ma-terial must be taken to avoid deformitiesin the structure of the tube. The tube must then be reamed to remove any burrs.

3. Clean with Care

Although one of the quickest and easi-est steps, cleaning is often the most over-looked. Unremoved oxides, surface soils,

and oils can inhibit proper flow of the fillermetal into the joint causing failure. Clean-ing the tube and fitting is critical for thefiller metal to flow into the joint and forma strong connection.

When applying the flux, or chemicalcleaning agent, it’s important to chooseone that is not too corrosive and use onlythe minimum amount of flux needed tomake a joint. Careless craftsmanship inapplying a flux can be dangerous to thesystem long after installation.

Fluxes used for soldering are differentfrom those used for brazing; plus, the twotypes cannot be used interchangeably.Also, the type of flux used can be a goodindication of the required temperature ofthe application.

4. Employ Skilled AssemblyPractices

After both the tube and fitting surfacesare fluxed, they should be assembled. Aquick way to be sure of even flux applica-tion is to slightly twist the pipe within thefitting, making sure the tube is set againstthe base of the fitting. Furthermore, uni-form space around the entire circumfer-ence of the joint will ensure a successfuljoint, while excessive space can cause thefiller metal to crack under stress or vibration.

Good practice suggests that after aproduct has been cleaned, fluxed, and as-sembled, it should be soldered or brazedwithin the same period. If left to sitovernight, the joint will need to be disas-sembled, recleaned, and refluxed beforecontinuing. Protecting the surface that hasbeen cleaned and fluxed and completingthe soldering or brazing operation intimely manner ensures clean uncontami-

Tips for Producing StrongSoldered and Brazed Joints

By using five easy-to-understand steps, dependable connections for more reliable joints ca be made

BY GREG MITCHELL

GREG MITCHELL ([email protected]) is the central regional manager for TurboTorch®, a Thermadyne brand. For moreinformation, visit www.thermadyne.com/turbotorch.

Mitchell Brazing and Soldering Feature September 2010:Layout 1 8/9/10 9:10 AM Page 40


41WELDING JOURNAL

nated surface material that provides anoptimum working surface.

It’s recommended to preheat the tube,then preheat the fitting. Preheating with theflame ensures a uniform distribution of heatinside and out. When preheating, careshould be taken not to overheat the joint.

While similar to soldering, brazing gen-erally involves air settling swirl or oxyfueltorches due to the higher temperatures re-quired to melt the filler metals. First, pre-heat the tube, then the fitting. When thefiller metal starts to flow, it will be drawninto the joint by capillary attraction ensur-ing a strong, dependable connection.

Similar to preheating, care must betaken not to overheat the joint. Also, cool-ing should be allowed naturally. Shockcooling with water may cause unnecessarystress on the joint.

Because purging with nitrogen reducesthe chance of oxidation at the joints, manyHVACR professionals always carry apurging kit with materials such as a nitro-gen regulator, charging hoses, blow pipe,and purging and cleaning tips.

Lastly, clean off any flux residue withhot water and/or a wire brush to avoid fu-ture corrosion.

5. Work Smart and Safe

Because soldering and brazing requirean open oxyfuel or air-fuel flame at hightemperatures, care must be taken for thesafety of the operator as well as the mate-rials being used. Proper safety training isessential to avoid dangers such as burns,eye damage, fumes, and overexposure toultraviolet light.

With the use of new technologies andproper protection, the risk of injury asso-ciated with metalworking can be greatlyreduced. It’s important that the user al-ways practice safe operating proceduresand wear protective equipment. As an ad-ditional word of caution, make certain toread and follow all operation instructionsbefore using any oxyfuel or air-fuel apparatus.

Close attention to detail and strict ad-herence to all steps will ensure any pro-fessional a strong, long-lasting connectionfor years to come.

New Advances inSoldering and Brazing

As the soldering and brazing industries

continue to grow, improved equipmentcapabilities and efficiency are essential ifthe plumbing, heating, ventilation, air-conditioning, and refrigeration industrieswant to keep up with user demands.

Additionally, manufacturers are re-sponding to these needs. TurboTorch®,for example, a manufacturer of air-fueland oxyfuel torches and accessories, re-cently expanded offerings with the Viper™line of brazing alloys, solders, and fluxes.The new alloys, featuring compositions fora range of flow and fill characteristics, areuseful for joining copper to copper and areself-fluxing in this application.

Other industry advancements includecadmium-free and lead-free solders thatare approved for plumbing and buildingindustries. As more products are engi-neered for field repair, once difficult tasksnow produce quick and consistentlydurable results.

With manufacturers dedicated to de-signing and producing better, safer metal-lurgy equipment, and soldering and braz-ing professionals crossing new thresholds,today’s joints are stronger than ever before.�

Soldering, pictured in use here, is a joining process that takes placeat below 842°F/450°C.

Brazing, shown above, generally involves air settling swirl or oxyfueltorches due to higher temperatures used to melt filler metals.

Mitchell Brazing and Soldering Feature September 2010:Layout 1 8/9/10 9:11 AM Page 41

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TECHNOLOGY NEWSLead-Free Solder with LowSusceptibility to Copper Leaching

A lead-free solder, which is signifi-cantly less susceptible to copper leachingin a molten state, was developed andtested at Senju Metal Industry Co., Ltd.,Tokyo, Japan (Ref. 1). Testing was car-ried out by dipping coil ends of the cop-per wire into the liquid solder at 400°C(752°F).

Exemplary compositions of the soldercontain the following: 1) copper 8 wt-%,cobalt 1 wt-%, nickel 1 wt-%, and tin inthe balance (melting range 228°–409°C,copper leaching rate is 1 μm/s); 2) cop-per 6 wt-%, cobalt 0.3 wt-%, nickel 0.3wt-%, gallium 0.07 wt-%, phosphorus0.02 wt-%, germanium 0.01 wt-%, andtin in the balance (melting range227°–380°C, copper leaching rate is 1.5μm/s); 3) copper 2 wt-%, silver 2 wt-%,cobalt 0.2 wt-%, nickel 0.2 wt-%, gallium0.07 wt-%, phosphorus 0.01 wt-%, andtin in the balance (melting range218°–281°C, copper leaching rate is 2.2μm/s). For comparison, the standard Sn-

3Ag-0.5 Cu solder exhibits a copperleaching rate of 5.3 μm/s.

Alloying solder with cobalt and nickeldecreases the dissolution of copper intothe solder melt. Adding P, Ge, and Ga insmall amounts inhibit oxidation of thesolder at high soldering temperatures.

Wetting of copper coupons with thenew solder occurred for 1.5 s of the com-position (a), 2.1 s of the composition (b),and 0.5 s of the composition (c), whilewetting with the standard Sn-3Ag-0.5 Cusolder occurred in 0.5 s at 400°C.

The low leaching rate prevents a sig-nificant reduction of diameter of insulat-ed copper wire or complete disappear-ance of the wire when the wire diameteris <100 μm.

Thermodynamic Properties of Lead-FreeSolders with Ag-Cu-Sn, Ag-Ni-Sn, andAg-Cu-Ni-Sn Systems

Detailed reference data were calculat-ed and presented in the form of tables inpapers (Refs. 2, 3) upon experimentalstudy of solder alloys, as well as the study

of phase diagrams made in the Instituteof Inorganic Chemistry/MaterialChemistry, University of Vienna, Austria.

Enthalpy of mixing of liquid alloysfrom Sn90Ag5Cu5 (at.-%) toSn40Ag10Cu50 (at.-%) were measuredexperimentally as for starting alloys andwith Ni additions of 0.05 to 0.3 at.-%with the increment of 0.05%. Also, com-positions of liquidus surface of the qua-ternary Ag-Cu-Ni-Sn system were determined.

Partial and integral enthalpies of mix-ing of liquid Ag-Cu-Ni-Sn alloys weredetermined at 1000°C by a drop calori-metric technique using a Calvet typemicrocalorimeter. They were obtainedby adding Ni to the ternary Ag-Cu-Snalloys with different compositions. Thedata were evaluated by an extendedRedlich-Kister-Muggianu polynomial fitfor substitutional solutions. The mini-mum and maximum in the quaternarysystem were also calculated. The maxi-mal integral enthalpy of mixing (13310J/mol at 41 at.-% Ag) occurs in the bina-ry Ag-Ni system while the minimum

TECHNOLOGY NEWS

SEPTEMBER 2010

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43WELDING JOURNAL

TECHNOLOGY NEWSintegral enthalpy of mixing (–21390J/mol at 61 at.-% Ni) occurs in the bina-ry Ni-Sn system. Moreover, the experi-mental data were compared to valuescalculated by different extrapolationmodels based on binary data.

Lead-Free Solder Resistant to TinWhisker Formation and Thermal Shock

The whisker-resistant solder alloy isproposed and tested by Iljin Copper FoilCo., Ltd., Iksan-city, Republic of Korea.The solder contains tin, 0.1–5 wt-% ofcopper, and 0.001–0.4 wt-% of beryllium(Ref. 4). Also, silver in amount of 1–3wt-% and boron in amounts of 0.003–0.5wt-% can be added. For example, thesolder compositions are 1) Cu 0.496 wt-%, Be 0.02 wt-%, and Sn in the balance;2) Cu 0.679 wt-%, Ag 1 wt-%, Be 0.021wt-%, and Sn in the balance; 3) Cu 2.88wt-%, Ag 3 wt-%, Be 0.12 wt-%, and Snin the balance; and 4) Cu 1 wt-%, Be 0.5wt-%, and Sn in the balance.

The average length of whisker gener-ated on the surface of soldered speci-

mens after thermal shock test was 3–3.4microns and number of whiskers per unitarea was from 3/mm2 to 5/mm2, whilethe standard lead-free solder Sn-3Ag-0.5Cu exhibited whiskers of 11.8–14.4microns in length at 11/mm2 to 14/mm2

whiskers per unit area.The Be-Cu master alloy is first manu-

factured when making this solder. Then,tin is melted in a melting pot, and silverwith Be-Cu master alloy are added to theSn melt. The melt is kept in the solderpot for a certain time at 600°–650°C(1112°–1202°F), and the ready solder Sn-Cu-Ag-Be is cast into bar-shaped ingots.

Extruded Rods Comprise a PowderMixture of Filler Metal and Flux forBrazing Aluminum

A method for manufacturing brazingrods containing both the braze alloy andflux was developed by F.P. Soudage Co.,Aubagne, France, for joining aluminumalloy parts in air (Ref. 5). This productcomprises a solid, rigid, and compactedmaterial consisting of a powder mixture

of the flux 20–30 wt-% and Al-12Si(AWS BAl-4) in the balance. The flux isNOCOLOK® Cs supplied by Solvay,Belgium, that has a melting point of566°C and contains potassium 29 wt-%,cesium 1.8 wt-%, aluminum 17 wt-%,and fluorine 51 wt-%. Particle size of theflux powder is 10–20 microns. Meltingtemperature of the brazing rod is 580°C.Also, the composition may comprise theZn-2Al solder melting at 440°C and theflux containing cesium 51 wt-%, alu-minum 10 wt-%, and fluorine 32 wt-%.This flux is melted at 450°–460°C(842°–860°F).

The powder metal-flux mixture isgranulated to 3-mm-diameter particlesthat are dried at 120°–150°C(248°–302°F), and then subjected to hotextrusion at 7000 bars and 450°C for Al-12Si braze rods or 330°C (626°F) for Zn-2Al solder rods. The resulting product issuitable for manual torch brazing or sol-dering. The patent also describesschematically the devices for granulationand hot extrusion of the composite brazing rods.


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SEPTEMBER 201044

TECHNOLOGY NEWSNew Method for Brazing Steel andAluminum Sheets Using Spot WeldingEquipment

A novel method designed for produc-ing joints between a sheet steel compo-nent, in particular, a press-hardenedhigh-strength steel and a sheet aluminumcomponent, is disclosed by VolkswagenAG, Wolfsburg, Germany (Ref. 6).Firstly, a brazing filler metal or a solderdeposit is fixed on the steel component byusing arc or laser radiation in such a wayto keep it secured during transportation.Then, the process applys an electric cur-rent and a compressive force using spotwelding, pressing the sheet-metal compo-nents together, and local heating theregion to form the weld or brazed jointbetween steel and aluminum. Depositionof the brazing filler metal also can bedone by induction heating.

The brazing filler metal is selectedfrom Al-, Ni-, or Cu-based alloys or Zn-Al solder. Applications of the solder orcopper- or nickel-based braze alloys arepreferable because the Al-Si brazing filler

metal forms a brittle intermetallic layer atthe steel interface. Parameters of theprocess were not disclosed.

Joining Alumina and Steel by a Laser-Supported Brazing Process

A laser-supported method of joiningalumina ceramic with metals was studiedby the team of ForschungszentrumKarlsruhe GmbH and Institute ofMetalforschung, Eggenstein, Germany(Ref. 7). Pure alumina ceramic and zir-conia-toughened alumina (ZTA) (SN80,Ceramtec) were brazed to steels 100Cr6and Ck45 using a CO2 laser and theactive brazing filler metal CB4(BrazeTec) in the form of 50 microns foilthat contains Ag 70.5 wt-%, Cu 26.5 wt-%, and Ti 3 wt-%. The argon purgedwith a flow about 300 L/h to prevent oxi-dation of steel and the braze foil. Thelaser power was ramped up to 300–360W. The joining procedure is highly flexi-ble and can be easily adapted to complexcomponent geometries.

Processing time was several minutes,

which is significantly less than that ofvacuum furnace brazing. The wettingbehavior of the brazing alloy was alsoevaluated, and the contact angle onceramic was about 30 deg, which exhibitsgood adhesion to the ceramic. Titanium-rich zones were observed close to ceram-ic and steel interfaces on scanning elec-tron microscope images, as well as a (Ti,C, Fe) reaction layer at the steel Ck45interface and a (Ti, Cu, Al, O) reactionlayer at the ZTA ceramic interface.Mechanical tests of brazed joints showedthat the failure occurred within theceramic close to the interface betweenthe braze alloy and ceramic part.Thermally induced stresses may lead tocracks in the ceramic, which result in thefailure under mechanical loading. Thetypical bending strength varies between40 MPa (5.8 ksi) and 80 MPa (11.6 ksi)with a Weibull modulus ranging from 4.3to 6.1 that is lower than that of the orig-inal ceramic. Therefore, the laserprocess has to be optimized with thefocus on reduction of residual thermalstresses in the ceramic.

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TECHNOLOGY NEWSNeutron Diffraction Measurement ofResidual Stresses in Carbon-FiberComposite with Copper Alloys forNuclear Fusion Applications

A high heat flux plasma facing compo-nent proposed for the divertor of ITERnuclear fusion reactor is formed by anarmor carbon-fiber composite (CFC)NB31 and a heat-sink material (CuCrZralloy). Residual stresses and strains wereexperimentally measured in bar specimensof CFC brazed to CuCrZr alloy, as it mustwithstand cyclic thermal, mechanical, andneutron loads to provide the design life-time and reliability. The main problemrelated to CFC-Cu alloy joints is the largethermal expansion mismatch between thetwo base materials, which generates bigresidual stresses at the interface during thejoining process. A very ductile pure copperlayer between the CFC and CuCrZr alloy isaimed to partially relax these residualstresses in the joint.

Residual stresses and strains weremeasured in the joints using neutron dif-fraction by the team of Universita

Politechnica delle Marche and Politecnicodi Torino, Italy (Ref. 8). Firstly, the CFCsurface was modified by depositing achromium carbide layer, which providedwetting of the CFC composite by brazingfiller metal. Neutron diffraction experi-ments were performed at the E3 diffrac-tometer of HMI-BENSC, Berlin, having afixed neutron wavelength 1.37 angstroms.Thermal fatigue cycling was carried out byheating to 450°C followed by fast cooling toroom temperature in air using waterquenching. The cycles were repeated 50times for each specimen.

The results for the as-brazed speci-mens showed expected stress states (ten-sile in the CFC and compressive in theCuCrZr alloy). The effect of thermalfatigue cycling was a general relaxation ofresidual stresses, probably due to the for-mation of microcracks at the CFC-Cujoint during the cycling.

Brazing SiC Ceramic to Graphite UsingNi-51Cr Powder Mixture as a Filler Metal

Recrystallized SiC ceramic was

brazed in vacuum to high-strengthgraphite at 1380°C (2516°F) for 5 minusing the brazing filler metal composedof Ni and 51 wt-% Cr powders. Themechanical properties of the brazedjoints were investigated in BeijingUniversity of Aeronautics andAstronautics, P. R. China (Ref. 9). Themaximum three-point bending strengthof the brazed joints was 32.3 MPa (4.7ksi), which is equal to 81% of thegraphite strength.

Microstructure and phase analysesreveal that interdiffusion and chemicalreactions took place at the interfacesbetween base materials and braze alloy,as well as in contacts with the nickel andchromium powders. The braze alloypowder mixture was melted completely.A reaction layer 60–100 microns thickwas formed at the SiC surface, and aninterlayer 200 microns thick was foundbetween the reaction layer and graphitesurface. The reaction layer is mainlycomposed of Ni2Si, while the interlayeris mainly composed of Cr23C6 and Ni2Siphases. At the same time, Si and C dif-

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SEPTEMBER 201046

fused from the ceramic base materialinto the joint metal.

Low-Cost Joining of Silicon Carbidewith a Molten Glass in Air

A method for brazing SiC at1300°–1600°C in air using calcium alumi-nosilicate glasses as filler materials wasdeveloped in CEA Grenoble, France(Ref. 10), for joining parts of the largestreflector in the world (3.5 m diameter)for the Herschel telescope. This technol-ogy has a low cost due to no shieldingatmosphere and facilitates repairing dam-aged ceramic components. Many glass-ceramics were studied earlier to join SiCand SiCf/SiC composites in vacuum, butonly a few of them exhibited wetting andinterfacial reactions with ceramic. TheSiC substrate used in these tests com-prised 2 wt-% of B4C as a sintering aid.Wetting of calcium aluminosilicate glasson SiC was studied using the sessile droptechnique in air in the temperature range1100°–1590°C. Good wetting wasobserved at the temperature above





47WELDING JOURNAL

1300°C, as well as good filling of the jointgap by the glass containing 23CaO-15Al2O3-62SiO2 (wt-%).

Lowest contact angle of the glass onthe SiC substrate was found as little as~20 deg at 1400°–1500°C and holdingtime more than 3 min. Average shearstrength of SiC joints at RT was 42 MPa.These results clearly showed thatSiC/(23CaO-15Al2O3-62SiO2) is a reac-tive system, despite no reaction layer wasobserved at the interface. Reactivity isenhanced by oxygen from air that formsbubbles in the liquid glass. The wetting ofSiC ceramic occurs by dissolution of thesilica layer in the molten glass at the liquid-solid-vapor phase equilibrium.Further work is planned to study the for-mation of crystals at the edge of the joint.

Testing of New Filler Metals for ReactiveAir Brazing Ceramic-to-Ceramic forFuel Cell Applications

Reactive air brazing (RAB) is a prom-ising method to join metals to ceramics inair using brazing filler metal modifiedwith copper or silver oxides. A number ofnew compositions of oxide-modified fillermetals were studied and characterized inAachen University (Ref. 11) andFraunhofer Institute fuer KeramischeTechnologien und Systems, Dresden,Germany (Ref. 12).

The following brazing filler metalswere tested for joining alumina in air at970°, 1050°, 1150°, and 1350°C for 20min: Ag8Cu, Ag8Cu0.5Ti, Ag8Ni,Ag0.5Al, Ag4Cu4Mn, and Ag4Cu4Ni.The contact angle of all these brazealloys on alumina was in the range of30–40 deg at all the above mentionedbrazing temperatures except the Ag8Nialloy at 1350°C that is about 90 deg. Thetensile strength of brazed joints dependson the brazing temperature — the braz-ing filler metal Ag8Cu showed strengthmore than 100 MPa after brazing at1050°C, while only about 60 MPa afterbrazing at 1150°C, and 40 MPa afterbrazing at 970°C. The filler metalAg8Cu0.5Ti provided tensile strength ofbrazed joints more than 80 MPa afterbrazing at 1150˚C, while only about 60MPa after brazing at 1050°C, and only 30MPa after brazing at 970°C. The brazingfiller metal Ag4Cu4Ni showed the bestresult more than 60 MPa after brazing at1350°C. All other filler metals had lowerstrength of brazed joints of alumina.

Thermal analysis clearly provided evi-dences of metal-oxide reactions duringbrazing resulted in the formation CuOand NiO oxides and their interaction with

alumina.Formation of interfacial layers —

controlled by thermal treatment —between RAB braze metal and the basemetal Crofer 22AP (Fe-22.7Cr-0.4Mn)was investigated at different amounts ofCuO (from 0 to 10.5 mol-%) added tosilver (Ref. 12). Thermal treatment waschanged by using induction or furnaceheating for brazing at 1000°C followedby annealing at 850°C for 200, 500, and800 h. The induction brazing process ledto the formation of thin interfacial layersboth at the interface with the ceramic3YSZ and the base metal. Ceramic sam-ples brazed with Mn-containing basemetal had thicker oxide layers at themetal interface than at the ceramicinterface, independently on the CuOcontent in silver paste. The growth of thelayers is controlled by diffusion of minorelements originating from the steelCrofer 22AP. Tailoring of the braze com-position by varying the content of CuOdoes not have a significant effect on themicrostructure of the interfacial layers.

Joining of Vanadium-Modified Diamondto (Kovar) Fe-42Ni Alloy Using the Zn-5Al Solder

A low-temperature process for joiningornamental diamonds to metal polishingjigs was developed and investigated inTokai University, Tokyo, Japan (Ref. 13).The process includes brief metallizationat 1080 K without compromising the dia-mond clarity. Reactive vanadium hydridepowder was used for low-temperaturevacuum metallization of the diamond sur-face that was covered by dot-like islandsof vanadium. The metallization processwas performed using Ag-Cu eutecticpowder and vanadium hydride powder atthe weight ratio of 1:4.5. After the forma-tion V4C3 at 1080 K for 240 s, silver dotswere deposited also by maintaining tem-perature to melt the Ag-Cu eutectic.Soldering with the Zn-5Al filler metalwas carried out in air using ultrasonicvibration.

Thermogravimetric and differentialthermal analysis of the vanadium hydride-

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diamond system were performed in argon to find out what vanadi-um carbide phases are formed in the contact. The formation ofvanadium carbides on the diamond surface is a continuous exother-mic reaction. The DTA test showed three reactions at 608, 710, and780 K. The diamond weight began decreasing with the formation ofV2C phase and continued decreasing during the formation of V4Cx.As the result V4C2.67, V4C3, and V8C7 carbides were found.

The average strength of the joints was 20 MPa. Joint strengthdoes not depend on the number of the surface modification cycles,whereas the wetting behavior of the solder was improved. It wasalso found that the Al4C3 reaction product was formed during theultrasound soldering process at 770 K.

Low-Oxygen, Controlled Atmosphere Oxynon® Furnace forBrazing Stainless Steel Heat Exchangers and Metal-CeramicJoints

The drawback of continuous furnaces for controlled atmos-phere brazing (CAB) is the application of explosive gases such ashydrogen. A nonoxidizing continuous furnace using only inert gasatmosphere was newly developed by Kanto Yakin Kogyo Co.,Kanagawa, Japan, for brazing stainless steel heat exchangers at1443 K with BNi-5 filler metal (Ref. 14). The furnace has a car-bon/carbon composite conveyor belt that can be used up to 2873 K.The Oxynon® furnace employs a principle that is completely dif-ferent from hydrogen and carbon monoxide reduction. The partialoxygen pressure is low in the furnace atmosphere (less than 10–15

Pa) due to the formation of CO by reacting of carbon-based con-

veyor with residual oxygen contained in the inert gas atmosphere.The thermodynamics and chemistry of this principle are describedin the paper with details. The furnace was used for brazing SUS316small heat exchangers, as well as large heat exchangers with thedimensions 600 × 1000 × 110 mm, weighing ~230 kg.

Also, the same atmosphere can be used for brazing stainlesssteel SUS304 or Kovar to alumina ceramic. Both Ag-Cu filler metaland active Ag-Cu-Ti filler metal showed good wetting of ceramic inthe oxynon furnace, and ultrasonic tests confirmed the formation ofdense brazed joints.

References

1. Ohnishi, T. May 7, 2008. Lead-free solder. European PatentEP 1918064 A1, Int. class. B23K 35/26.

2. Saeed, U., Flandorfer, H., and Ipser, H. 2007. Lead-freesolders: enthalpies of mixing of liquid Ag-Cu-Ni-Sn alloys.Journal of Materials Research 22(11): 3218–3225.

3. Saeed, U., Flandorfer, H., and Ipser, H. 2006. Lead-free sol-ders: enthalpies of mixing of liquid alloys of Ag-Ni and Ag-Ni-Snsystems. Journal of Materials Research 21(5): 1294–1304.

4. Lee, D.-N., Kim, S.-B., and Kang, K.-S. July 10, 2008. Pb-free solder alloy. International Patent WO 2008/082191, Int. class.B23K 35/28.

5. Schmitt, P., and Bosi, B. May 21, 2010. Brazing product com-prising a mixture of brazing flux and filler metal, and procedure forits fabrication. French Patent 2938460.

6. Juetner, S., Graul, M., Staubach, M., and Noack, T., 2010.Method for producing joint between a sheet-metal component ofsteel and a sheet-metal component of aluminum. World PatentWO 2010/022709.

7. Rohde, M., Suedmeyer, I., Urbanek, A., and Torge, M.2009. Joining of alumina and steel by a laser supported brazingprocess. Ceramic International 35: 333–337.

8. Fiori, F., Calbucci, V., Casalegno, V., Ferraris, M., Salvo, M.,Guiliani, A., Manescu, A., and Rustichelli, F. 2008. Neutron dif-fraction measurement of residual stresses in CFC/Cu/CuCrZrjoints for nuclear technology. Journal of Physics: CondensedMatter v. 20, 104260: 1–6.

9. Yangwu, M., Shujie, L., and Liansheng, Y. 2008. Joining ofSiC ceramic to graphite using Ni-51Cr powders as filler. KeyEngineering Materials 368–372: 1600–1602.

Refs. 10–14 are abstracted from the 9th International Brazing& Soldering Conference held in Aachen, Germany, June 2010,DVS-Berichte.

10. Mailliart, O., Chaumat, V., and Hodaj, F. Wetting and join-ing of silicon carbide with a molten glass in air, v. 263, 76–80.

11. Bobzin, K., Schläfer, T., and Kopp, N. New filler metalswith improved contouring accuracy for brazing ceramics, v. 263,64–69.

12. Pönicke, A., Schilm, J., Kusnezoff, M., and Michaelis, A.Reactive air brazing as joining technology for SOFC, v. 263,70–75.

13. Yamazaki, T., Suzumura, A., and Ikeshoji, T.-T. Joining ofsurface-modified diamond to Fe-42Ni alloy using Zn-5Al solder,v. 263, 230–233.

14. Takahashi, S., Kojima, H., and Kanda, K. Development low-oxygen atmosphere controlled furnace and its application to braz-ing technology, v. 263, 289–295.

TECHNOLOGY NEWS

Information provided by ALEXANDER E. SHAPIRO([email protected]) and LEO A. SHAPIRO, Titanium Brazing, Inc., Columbus, Ohio.

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