Joining and consumables · Workhorse
Vacuum braze alloys
AgCuvalues describe: BAg-8
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Why it wins
The joint chemistry of the sealed vacuum world: eutectic AgCu on metallized ceramic, gold alloys for the first joints of multi-step assemblies, active alloys that wet ceramic directly. The step-braze ladder is the architecture of every tube.
Why not the alternative
Welding cannot join ceramic to metal; adhesives cannot hold bake, voltage, or decades.
Watch out
Every alloy in the ladder must clear the vapor pressure bar: no Zn, no Cd bearing brazes, ever, whatever the plumbing catalog says.
Properties
The values below are candidate: compiled from the sources named, not yet individually validated. Provisional provenance: AWS Brazing Handbook; Morgan Wesgo alloy data; Electron tube and ceramic-to-metal sealing practice.
Wet cleaning
| Recipe | both faying surfaces degreased and oxide-free immediately before the cycle; fluxless vacuum brazing needs a chemically clean surface, not a flux |
|---|---|
| Forbidden | flux in a vacuum braze; fingerprints on the faying surface |
| Limit | oxide regrowth between cleaning and furnace loading |
Vacuum and outgassing
| Outgassing, unbaked (10 h) | 1e-9 mbar·L/s/cm² |
|---|---|
| Outgassing, baked | 1e-12 mbar·L/s/cm² |
| Vapour pressure | silver evaporates in hot service; never use Cd-bearing braze in vacuum |
Temperature
| Bake, assembled | 450 °C |
|---|---|
| Vacuum degas | 600 °C |
| Braze / H2 firing | 577-1219 by filler °C |
| Metallurgical limit | BAlSi-2 solidus 577 °C to Palco 1219 °C |
Thermal
| Thermal conductivity | 355 W/m·K |
|---|---|
| Specific heat | 380 J/kg·K |
| Emissivity | 0.05 |
| Melting / softening | 577-1219 °C |
| CTE | 19.6 ppm/K2018 |
Mechanical
| Strength | joint property |
|---|---|
| Density | 9.9 g/cm3 |
Electrical and magnetic
| Relative permeability | ~1.0 |
|---|---|
| Resistivity | 2 µΩ·cm |
Engineering
| Corrosion | silver tarnishes |
|---|---|
| Joining | the workhorse after Mo-Mn metallisation; ABA alloys braze ceramics directly |
| Process notes | gold-nickel where silver would evaporate |
| Availability and cost | commodity filler; gold alloys expensive |
By grade
These grades differ by an order of magnitude, so their values are carried per grade and override the card.
| Parameter | Cusil / BAg-8 (Ag72Cu28), 780 C | Nioro / BAu-4 / AMS 4787 (Au82Ni18), 955 C | Ticusil (Ag68.8Cu26.7Ti4.5), 780-900 C | Cusil-ABA (Ag63Cu35.25Ti1.75), 779-816 C | Incusil-ABA / APA-7 (Ag59Cu27.25In12.5Ti1.25), 715-740 C | Cusin-1 ABA (Ag63Cu34.25Ti1.75Sn1), 775-806 C | Palcusil 15 (Ag65Cu20Pd15), 850-900 C | Palcusil 10 (Ag58Cu32Pd10), 824-852 C | Palco / BPd-1 (Pd65Co35), 1219 C | Incusil 15 / BAg-29 (Ag61.5Cu24In14.5), 605-725 C | Incusil 10 (Ag63Cu27In10), 685-730 C | Nicoro-80 (Au81.5Cu16.5Ni2), 910-925 C | Indalloy 182 / 80Au/20Sn (Au80Sn20), 280 C | BCu-1 (Cu100), 1093-1149 C | BNi-1, 1066-1204 C | BAlSi-2 / AL 4343 / AA 4343 / EN AW-4343 / UNS A94343 (Si7.5Al bal), 617-672 C | BAu-1 / 37.5Au-62.5Cu (Au37.5Cu62.5), 1016-1093 C | TiCuNi / EP 0238433, 925-945 C | 35Au/65Cu (Au35Cu65), 990-1010 C | BNi-2 / Nicrobraz LM / AMS 4777 (Cr7B3.1Si4.5Fe3Ni bal), 1010-1175 C | 4047 / BAlSi-4 / AL 104 (Al88Si12), 577-582 C | 35Au-62Cu-2Ti-1Ni / 62Cu-35Au-2Ti-1Ni (Au35Cu62Ti2Ni1), 1015-1026 C |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Braze / H2 firing | 780 °C2018 | 955 °C2019 | 780-900 °C2018 | 779-816 °C | 715-740 °C | 775-806 °C | 850-900 °C2018 | 824-852 °C | 1219 °C2018 | 605-725 °C2018 | 685-730 °C2018 | 910-925 °C | 280 °C | 1093-1149 °C2010 | 1066-1204 °C2010 | 617-672 °C2022 | 1016-1093 °C2010 | 925-945 °C | 990-1010 °C | 1010-1175 °C2019 | 577-582 °C | 1015-1026 °C2012 |
| CTE | 19.6 ppm/K2018 | 17.5 ppm/K2019 | 18.5 ppm/K2018 | — | — | — | — | — | 17 ppm/K2018 | 18.5 ppm/K2018 | 19.58 ppm/K2018 | — | — | — | — | 21.6 ppm/K2022 | 18.8 ppm/K2018 | — | — | — | — | — |
| Strength | 272 MPa2018 | 686 MPa2019 | 292 MPa2018 | — | — | — | 379 MPa2018 | — | 344 MPa2018 | 386 MPa2018 | 345 MPa2018 | — | — | — | — | — | — | — | — | — | — | — |
Grades
| Cusil / BAg-8 (Ag72Cu28), 780 C | the eutectic workhorse on Mo-Mn plus Ni metallization |
|---|---|
| Nioro / BAu-4 / AMS 4787 (Au82Ni18), 955 C | first joints of step-brazed stacks, corrosion duty |
| Ticusil (Ag68.8Cu26.7Ti4.5), 780-900 C | direct ceramic wetting, no metallization step |
| Cusil-ABA (Ag63Cu35.25Ti1.75), 779-816 C | direct ceramic wetting, no metallization step |
| Incusil-ABA / APA-7 (Ag59Cu27.25In12.5Ti1.25), 715-740 C | the low step: joins after everything else is closed |
| Cusin-1 ABA (Ag63Cu34.25Ti1.75Sn1), 775-806 C | Ag-Cu-Sn-Ti titanium-active braze filler, solidus to liquidus 775-806 C |
| Palcusil 15 (Ag65Cu20Pd15), 850-900 C | Ag-Cu-Pd braze filler, solidus to liquidus 850-900 C |
| Palcusil 10 (Ag58Cu32Pd10), 824-852 C | Ag-Cu-Pd braze filler, solidus to liquidus 824-852 C |
| Palco / BPd-1 (Pd65Co35), 1219 C | Pd-Co braze filler, solidus, congruent melting 1219 C |
| Incusil 15 / BAg-29 (Ag61.5Cu24In14.5), 605-725 C | Ag-Cu-In braze filler, solidus to liquidus 605-725 C |
| Incusil 10 (Ag63Cu27In10), 685-730 C | Ag-Cu-In braze filler, solidus to liquidus 685-730 C |
| Nicoro-80 (Au81.5Cu16.5Ni2), 910-925 C | Au-Cu-Ni braze filler, solidus to liquidus 910-925 C |
| Indalloy 182 / 80Au/20Sn (Au80Sn20), 280 C | Au-Sn solder, solidus, congruent melting 280 C |
| BCu-1 (Cu100), 1093-1149 C | Cu braze filler, recommended brazing window 1093-1149 C |
| BNi-1, 1066-1204 C | Ni-Cr-B-Si braze filler, recommended brazing window 1066-1204 C |
| BAlSi-2 / AL 4343 / AA 4343 / EN AW-4343 / UNS A94343 (Si7.5Al bal), 617-672 C | Al-Si braze filler, recommended brazing window 617-672 C |
| BAu-1 / 37.5Au-62.5Cu (Au37.5Cu62.5), 1016-1093 C | Au-Cu braze filler, recommended brazing window 1016-1093 C |
| TiCuNi / EP 0238433, 925-945 C | Ti-Cu-Ni titanium-active braze filler, solidus to liquidus 925-945 C |
| 35Au/65Cu (Au35Cu65), 990-1010 C | Au-Cu braze filler, solidus to liquidus 990-1010 C |
| BNi-2 / Nicrobraz LM / AMS 4777 (Cr7B3.1Si4.5Fe3Ni bal), 1010-1175 C | Ni-Cr-B-Si braze filler, recommended brazing window 1010-1175 C |
| 4047 / BAlSi-4 / AL 104 (Al88Si12), 577-582 C | Al-Si braze filler, solidus to liquidus 577-582 C |
| Cu-TiH2-Ni | Cu-TiH2-Ni titanium-active braze filler, no melting data read |
| Nicusil 3 (Ag71Cu28Ni1) | Ag-Cu-Ni braze filler, no melting data read |
| 97Ag-1Cu-2Zr / Ag-1Cu-2Zr (Ag97Cu1Zr2) | Ag-Cu-Zr titanium-active braze filler, no melting data read |
| Ag-31.5Cu-10Pd (Cu31.5Pd10Ag bal) | Ag-Cu-Pd braze filler, no melting data read |
| 35Au-62Cu-2Ti-1Ni / 62Cu-35Au-2Ti-1Ni (Au35Cu62Ti2Ni1), 1015-1026 C | Au-Cu-Ti-Ni titanium-active braze filler, solidus to liquidus 1015-1026 C |
| 60Zr-25V-15Cb (Zr60V25Nb15) | Zr-V-Nb titanium-active braze filler, no melting data read |
| 50Zr-30V-20Cb (Zr50V30Nb20) | Zr-V-Nb titanium-active braze filler, no melting data read |
| 56Zr-28V-16Ti (Zr56V28Ti16) | Zr-V-Ti titanium-active braze filler, no melting data read |
| 35Nb-65V (Nb35V65) | Nb-V braze filler, no melting data read |
| pure vanadium (V100) | V braze filler, no melting data read |
| 50Cu-40Pd-10Ni (Cu50Pd40Ni10) | Cu-Pd-Ni braze filler, no melting data read |
| palladium (Pd100) | Pd braze filler, no melting data read |
| 48Ti-48Zr-4Be (Ti48Zr48Be4) | Ti-Zr-Be titanium-active braze filler, no melting data read |
| 49Ti-49Cu-2Be (Ti49Cu49Be2) | Ti-Cu-Be titanium-active braze filler, no melting data read |
| 13In-27Cu-60Ag (In13Cu27Ag60) | In-Cu-Ag braze filler, no melting data read |
| 10Sn-30Cu-60Ag (Sn10Cu30Ag60) | Sn-Cu-Ag braze filler, no melting data read |
| 71.5Ti-28.5Ni / Ni/Ti eutectic 28.5:71.5 (Ti71.5Ni28.5) | Ti-Ni titanium-active braze filler, no melting data read |
Sources · 2
- AWS Brazing Handbook
- Morgan Advanced Materials, Wesgo alloys data