Brazing Q & A
 BRAZINGQ& A
Thefollowing Brazing Q & A articles were published in the Welding Journal andare available online: Brazing Q & A
  • June2006By R. L. Peaslee
    Q: We have purchased a vacuum furnaceto braze aircraft assemblies in a 10–3 to10–5 vacuum atmosphere. The questionhas come up as to how fast can assembliesbe heated within the furnace.

    A: Since you indicate thatyou are goingto have different assemblies of differentsizes and masses, it is not possible to givea definitive answer. Basically, each assemblyis a beast unto itself...Go

  • April2006By R. L. Peaslee
    Q: We designed and brazed a beam, per brazing specification AWS C3.6,Class C, using BNi-2 brazing filler metal, and the beam appears to havesagged at the brazing temperature of 1950°F (1066°C). The beamis constructed of AISI 1018 CRS, 0.024 in. thick, and is 35 in. long x4.5 in. wide x 4.0 in. high, with eight bulkheads throughout the lengthof the beam. There is a plate 17 in. long x 2.0 in. wide x 0.188 in.thick brazed in the top-center of the beam. Brazing was done in avacuum furnace with the following cyle: Ramp up at 30°F (17°C)per min from ambient to 1800°F (971°C)guaranteed soak for 10min, ramp approximately 75°F (42°C) permin to 1950°F (1066°C), hold for 45 minat the brazing temperature, furnace coolto 1600°F (871°C), 2 min guaranteed soak,nitrogen quench cool to ~120°F (49°C).Would a lower-temperature brazingfiller metal eliminate the sagging, or isthere a coefficient of thermal expansiondifference between the base metal and thebrazing filler metal that could be causinga problem?

    A: Your design is anexcellent project for brazing, and the final box-beam brazement will bea very rigid structure -- Fig. 1. The sagging of the beam structure iscaused by...Go

  • February 2006By R. L. Peaslee
    Q: Why is electrolytic nickel plating ofbase metals required prior to brazing Alloys738, 617, X750, and similar base metalsthat contain alloying elements of aluminumand titanium? Titanium and its alloysdo not require electroplating withnickel prior to brazing.

    A: Titanium and its alloysare critical base metals that readily absorb most metal and gaselements during foundry melting and fabrication. Gases such as oxygenor nitrogen, when absorbed into titanium base metals, severely lowerthe ductility and...Go

  • October2005 By R. L. Peaslee
    Q. There is a requirement on the heat exchangers we are making out of347 base metal brazed with BNi-2 brazing filler metal that allows amaximum of five cracks in the brazing filler metal, when checking themicrograph taken from the brazement. We are within the acceptable cracklimit, with five or fewer cracks that are only in the brazed fillets.The customer is finding many more cracks and they are in the filletarea. What is the source of these cracks and why would the customer befinding so many more and even some in the joint area. The customerbelieves that we are closing the cracks by smearing the base metal overthe crack. Is this possible?

    A. Over years ofinvestigation, carefully prepared metallurgical specimens confirmedthat brazements coming out of the brazing furnace...Go

  • August2005 By R. L. Peaslee
    Q: We are looking for brazing filler metals with excellent creeprupture strength at 1250°F. The design requires a long life, 15years (~150,000 hours), with continuous service at 1250°F. Amongthe potential base metals being considered for this design are Alloy625, UNS No. 6625; Alloy 230, UNS No. 6230; or Alloy 214, UNS No. 7214.Do you have creep rupture data for these alloys? Do you have data outto 10,000 or 100,000 hours?

    A:Unfortunately, I onlyhave limited information on the stress rupture properties of brazedjoints. In the middle 1940s, when...Go

  • June2005 By R. L. Peaslee
    Q: Do you have any information on the electrochemical potential ofBNi-2, BNi-5, and BNi-5 phosphorus modified relative to 304L stainless?

    A: Unfortunately, we do nothave any electrochemical potential readings on the BNi-2, BNi-5, orBNi-5 phosphorus modified relative to 304L stainless. This informationwould be highly...Go

  • April2005 By R. L. Peaslee
    Q: There was one big crash when the crane hook failed when carrying a37-ton roll of paper that dropped 15 feet to the paper mill floor. Thefailed hook had been braze weld coated with a copper alloy. Failureanalysis indicated that the copper alloy had penetrated the hook of A36steel. We understand that this is called liquid metal embrittlement. Aswe can find little information on this problem, could you enlighten uson this phenomenon?

    A: Liquid metalembrittlement, also called stress corrosion cracking, has been knownto...Go

  • February2005 By R. L. Peaslee
    Q: We have a customer who wants to braze Ti-6-4 to sapphire. We triedBNi-1 with a binder in high vacuum. This seemed to work; however, itlooks like it formed a lower-melting-point eutectic and melted part ofthe Ti-6-4 base metal. It brazed, but could you explain what happened?

    A. You were fortunate tohave it braze at all. If some of the titanium and BNi-1 had not ...Go

  • June2004 By R. L. Peaslee
    Q: When brazing 304L stainless steel, we see the brazing filler metaleating holes into the stainless in some of the assemblies. We do notunderstand what is causing this. We would like to know what ishappening and why.

    A. You are encounteringwhat is termed erosion. In testing conducted years ago, we divided theerosion mechanism into three ...Go

  • April2004 By R. L. Peaslee
    Q: There are two items I have been wondering about, and I am hoping youcan shed some light on them:First, we have a continuous furnace with a 314 stainless belt with0.25-max carbon that we are using to copper braze 300 series stainlesssteel assemblies. We are running with pure dry hydrogen and arewondering if the pure dry hydrogen will decarburize the belt. Also,would the pure dry hydrogen cause hydrogen embrittlement of the belt?

    A. Pure dry hydrogen willnot decarburize the 314 stainless belt. What could causedecarburization is...Go

  • February2004 By R. L. Peaslee
    Q: We vacuum furnace braze dental equipment with BNi-5 and are unableto obtain the smooth fillets that the customer requires. Our filletsare rough and porous. How can we obtain smooth fillets?

    A. The question aboutsurface quality of fillets is one that comes up frequently. Thesolution requires...Go

  • October2004 By R. L. Peaslee
    Q: We have been brazing 304L with BNi-2 at our facility for more thanten years. To the best of my knowledge, we have not had problemsregarding corrosion resistance until we subjected an assembly to amixture of salt fog, sulfur, nitrogen oxide, and aircraft exhaust. Thismixture forms a highly acidic (pH 2.4­4.0) moisture film. Do youhave any knowledge as to whether there are any electrolytic issuesbetween 304L and BNI-2 braze material?

    A: Yes, I know about thisproblem; it is a result of...Go


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