Nickel Alloy BNi-5a DIFF
Heat-treated state
UNS N99651 · ISO B-Ni5a
DIFF = diffusion heat treated after brazing
Select where joint ductility, higher remelt temperature and creep life matter; boron diffuses into the parent metal and the brittle centreline is largely eliminated.
Values for the DIFF condition
Other BNi-5a tempers and conditions
BNi-5a is listed in 2 conditions; see the grade overview at BNi-5a.
- AS-BRAZED
- DIFF
Compare all 2 conditionsHide
| Condition · open for datasheet | Best for | Yield MPa | Tensile MPa | Elong. % | Hardness | Conductivity |
|---|---|---|---|---|---|---|
no post-braze diffusion cycle | Baseline condition straight out of the vacuum furnace; hardest and most brittle because of retained centreline borides. | 420 | 480 | 1 | 55 HRC | 1.3 % IACS |
DIFFThis page Diffusion heat treated after brazing | Select where joint ductility, higher remelt temperature and creep life matter; boron diffuses into the parent metal and the brittle centreline is largely eliminated. | 430 | 650 | 5 | 36 HRC | 1.6 % IACS |
What is BNi-5a DIFF?
BNi-5a DIFF is BNi-5a heat treated to DIFF — select where joint ductility, higher remelt temperature and creep life matter; boron diffuses into the parent metal and the brittle centreline is largely eliminated. The elastic modulus is 198 GPa (28.7 Msi). BNi-5a DIFF has a density of 7.85 g/cm³ (0.284 lb/in³), lighter than 95% of nickel alloy grades. It melts at 1,030°C (1,886 °F).
Advantages
- Conducts heat well — 15 W/m·K (8.67 BTU/hr·ft·°F), better than 81% of nickel alloy grades
- High service temperature — 1,000°C (1,832 °F), better than 79% of nickel alloy grades
Limitations
- Difficult to machine — 8/100, worse than 96% of nickel alloy grades
- Difficult to weld — 15/100, worse than 87% of nickel alloy grades
- Hard to polish — 60/100, worse than 84% of nickel alloy grades
BNi-5a DIFF properties
Typical room-temperature values for BNi-5a DIFF; 22 are specific to this condition. Other listed values are BNi-5a reference data and may not represent this condition. Bars are the position among nickel alloy grades.
Physical3
BNi-5a DIFF has a density of 7.85 g/cm³ (0.284 lb/in³), lighter than 95% of nickel alloy grades. It melts at 1,030°C (1,886 °F).
Mechanical6
The elastic modulus is 198 GPa (28.7 Msi).
Thermal6
BNi-5a DIFF is rated for continuous service to 1,000°C (1,832 °F). It conducts heat at 15 W/m·K (8.67 BTU/hr·ft·°F), better than 81% of nickel alloy grades. Thermal expansion is 13 µm/m·K (7.22 µin/in·°F).
Electrical3
BNi-5a DIFF conducts electricity at 1.6 % IACS, better than 70% of nickel alloy grades.
Chemical & Environmental2
Corrosion resistance is very good (75/100), worse than 63% of nickel alloy grades.
Sustainability3
Producing a kilogram of BNi-5a DIFF takes about 200 MJ of energy and emits 14 kg of CO₂ — more than 78% of nickel alloy grades. Typical recycled content is 10%.
Manufacturability5
BNi-5a DIFF's machinability is not recommended (8/100, worse than 96% of nickel alloy grades); weldability poor (15/100).
Values are nominal handbook figures for design screening. Confirm any required mill or lot documentation when quoting.
Working with BNi-5a DIFF
Is BNi-5a easy to machine?
The solidified braze deposit is a hard boride/silicide-bearing alloy — remove only by grinding or EDM, never expect conventional turning or milling.
Can BNi-5a be welded?
Not a welding consumable; fusion welding over a BNi-5a joint causes hot cracking and boride liquation, so re-braze rather than weld repair.
Can BNi-5a be formed, bent or molded?
Supplied as atomized powder, binder paste, tape or sintered preform — no wrought forming; control joint gap to 0.025–0.075 mm for capillary flow.
What surface finishes work on BNi-5a?
Braze in vacuum (10⁻⁴ mbar) or dry hydrogen at about 1120–1205 °C, hold briefly, then apply a diffusion cycle; fillets can be blended and passivated with the parent stainless steel.
BNi-5a chemical composition (wt %)
Limits by weight percent from the governing specification, written the way the spec states them — a single maximum for impurities, a range for alloying elements, and the base element as balance. Nominal is the typical mid-range value.
| Element | Spec limit (wt %) | Nominal |
|---|---|---|
| Cr | 18.5 – 19.5 | 19 |
| Si | 7 – 7.5 | 7.25 |
| Bmelting-point depressant, diffuses into parent metal | 1 – 1.3 | 1.15 |
| C | ≤ 0.06 | — |
| Fe | ≤ 0.5 | — |
| P | ≤ 0.02 | — |
| S | ≤ 0.02 | — |
| Al | ≤ 0.05 | — |
| Ti | ≤ 0.05 | — |
| Zr | ≤ 0.05 | — |
| Other (total) | ≤ 0.5 | — |
| Ni | balance | — |
BNi-5a DIFF — frequently asked
What is BNi-5a DIFF used for?
BNi-5a DIFF is typically used for turbine hardware brazing, high-temperature nickel alloy assemblies, tight-clearance capillary joints, stainless steel vacuum-brazed assemblies, hot-section static components and heat exchanger and manifold joints. In short: improved flow versus BNi-5; high-chromium oxidation resistance; 950 C service limit.
Is BNi-5a DIFF easy to machine?
Not especially — machinability is rated not recommended (8/100, worse than 96% of nickel alloy grades). The solidified braze deposit is a hard boride/silicide-bearing alloy — remove only by grinding or EDM, never expect conventional turning or milling.
Can BNi-5a DIFF be welded?
Not readily — weldability is rated poor (15/100). Not a welding consumable; fusion welding over a BNi-5a joint causes hot cracking and boride liquation, so re-braze rather than weld repair.
What surface finishes work on BNi-5a DIFF?
Braze in vacuum (10⁻⁴ mbar) or dry hydrogen at about 1120–1205 °C, hold briefly, then apply a diffusion cycle; fillets can be blended and passivated with the parent stainless steel.
Can BNi-5a DIFF be formed, bent or molded?
Supplied as atomized powder, binder paste, tape or sintered preform — no wrought forming; control joint gap to 0.025–0.075 mm for capillary flow.
What is the maximum service temperature of BNi-5a DIFF?
BNi-5a DIFF is rated for continuous use to about 1,000°C (1,832 °F). Strength falls off well before that limit — check the elevated-temperature data for load-bearing parts.
Sources
- AWS A5.8M/A5.8 Specification for Filler Metals for Brazing and Braze Welding — American Welding Society (2019)
- ASM Handbook Vol. 6 — Welding, Brazing and Soldering — ASM International (1993)
- Brazing Handbook, 5th ed. — American Welding Society (2007)
- Nickel-base brazing filler metal powder datasheets — Wall Colmonoy / Höganäs / Lucas-Milhaupt (2023)
Property data is compiled from published supplier and standards handbooks and normalised for comparison. Nothing on this page is a certification — request mill certs, CoC or material test reports with your order.