Machining Rene 80 and Rene 95: Grades for Turbine Disk Superalloys

Rene 80 and Rene 95: Superalloy Grades Built for Turbine Disks

Rene 80 and Rene 95 are among the most demanding nickel-based superalloys encountered in aerospace CNC machining. Developed by General Electric, both grades serve in turbine disk and shaft applications where temperatures exceed 650 deg C and centrifugal loads are extreme. For machine shops, these alloys represent a significant challenge in insert selection, cutting parameter optimization, and tool life management.

Material Overview and Machinability

Rene 80 is a cast polycrystalline superalloy with a nominal composition of 60% Ni, 14% Cr, 9.5% Co, 5% Mo, 4% W, and 3% Ti plus Al. Its hardness typically falls between 340-400 HB in the solution-annealed condition and can reach 45-48 HRC after full age hardening. Rene 95, designed for higher strength at intermediate temperatures, contains higher carbon (0.15%) and additional niobium (3.5%), giving it a finer gamma-prime distribution and slightly better machinability in the solutionized state.

Both alloys work-harden rapidly. The machinability index relative to free-cutting steel (B1112) is approximately 5-8% for Rene 80 and 8-12% for Rene 95, making them roughly 30-50% harder to machine than Inconel 718.

Recommended Insert Grades and Geometries

ISO S-Group (Heat-Resistant Super Alloys):

• Roughing: Seco CBN060K or Kennametal KD050 (PCBN, for aged condition above 42 HRC). For solution-annealed stock below 380 HB, use Sandvik Coromant S10T (PVD TiAlN coated carbide) or Kennametal KC5525.
• Semi-Finishing: Sandvik Coromant S05F (fine-grain PVD carbide) or Mitsubishi VP15TF with a 0.8mm nose radius.
• Finishing: Kyocera KBN250 (PCBN) for aged material or Sumitomo Secomax BN600 for interrupted finishing cuts.

Insert geometry should follow ISO CNMG 120408 or DNMG 150608 with a negative rake angle of -6 deg and a honed edge (T-land) of 20 x 0.02mm to resist chipping. For grooving, use a 3mm-wide N-style blade with 0.05mm edge hone.

Cutting Parameters for Turning

Rene 80 – Solution Annealed (340-380 HB):

• Cutting speed (Vc): 25-35 m/min for carbide, 80-120 m/min for PCBN
• Feed rate (fn): 0.10-0.18 mm/rev for roughing, 0.05-0.10 mm/rev for finishing
• Depth of cut (ap): 1.5-3.0 mm roughing, 0.3-0.8 mm finishing
• Coolant: High-pressure flood (70-100 bar) or minimum quantity lubrication (MQL) at 30-50 mL/hr

Rene 80 – Age Hardened (44-48 HRC):

• Cutting speed (Vc): 60-100 m/min for PCBN only; carbide not recommended
• Feed rate (fn): 0.08-0.15 mm/rev
• Depth of cut (ap): 0.5-1.5 mm
• Coolant: Through-tool high-pressure at 150 bar minimum

Rene 95 – Solution Treated (300-350 HB):

• Cutting speed (Vc): 30-45 m/min for PVD carbide
• Feed rate (fn): 0.12-0.20 mm/rev roughing
• Depth of cut (ap): 2.0-4.0 mm

Milling Considerations

For face and peripheral milling of Rene 80 and 95, use solid carbide end mills with AlTiN or nACo (nano-composite) coatings in 4-5 flute configurations. Recommended parameters:

• Diameter: 12-20mm end mills
• Cutting speed: 20-30 m/min (carbide)
• Feed per tooth: 0.03-0.06 mm/tooth
• Radial depth: 3-5% of cutter diameter (slotting), 50-70% (side milling)
• Axial depth: 0.5-1.0 x diameter

Trochoidal milling strategies reduce radial engagement and thermal loading, extending tool life by 40-60% compared to conventional side milling.

Drilling and Hole Making

Drilling Rene 80 and 95 requires peck cycles and through-tool coolant. Use solid carbide drills with 135-140 deg point angles and 0.8-1.2xD peck depth. For holes above 10mm diameter, consider pilot drilling with a 3mm carbide center drill followed by incremental stepping.

• Speed: 15-25 m/min surface speed
• Feed: 0.02-0.05 mm/rev
• Through-tool coolant pressure: 40-70 bar
• Peck retract: Full retract for chip evacuation

Tool Life Expectations

In continuous turning of age-hardened Rene 80 at 80 m/min with PCBN inserts, expect 15-25 minutes of effective cutting time per edge before reaching 0.3mm flank wear (VB). In solution-annealed condition with PVD carbide at 30 m/min, tool life typically ranges from 8-15 minutes per edge. These values assume stable clamping, minimal runout, and adequate coolant delivery.

Key Takeaways for Process Engineers

1. Machine Rene 80 and 95 in the solution-annealed condition whenever possible. Post-machining age hardening preserves tool life and achieves final mechanical properties.
2. PCBN inserts are mandatory for hardened stock above 42 HRC. Expect higher per-edge cost but dramatically better surface integrity.
3. Maintain rigid setups. Vibration and chatter accelerate notch wear at the depth-of-cut line, which is the dominant failure mode in superalloy turning.
4. Use constant surface speed (CSS) programming and avoid dwell at the workpiece surface. Thermal soaking softens the insert substrate.
5. Plan for 3-5x the tooling cost compared to standard alloy steel programs. Budget accordingly in quotations.