Specialty alloy

Citation

(1999), "Specialty alloy", Aircraft Engineering and Aerospace Technology, Vol. 71 No. 1. https://doi.org/10.1108/aeat.1999.12771aad.023

Specialty alloy

Specialty alloy

Keywords Alloys, Carpenters

A new specialty alloy reportedly combines an unprecedented high strength-to-weight ratio with fracture toughness and ductility that are exceptional at the material's high strength level.

AerMet 310 alloy, developed by Carpenter Technology Corp., Reading, Pennsylvania, is offered as a candidate for next generation aircraft landing gear and hardware, tooling and any parts or components that might benefit from higher strength, smaller size and/or lighter weight.

A companion to Carpenter's high-strength AerMet 100 alloy, the new steel, according to Carpenter, can achieve an ultimate tensile strength (UTS) of 315ksi. This is said to be higher than the maximum 302ksi reached by the original AerMet grade when aged at 875°F.

AerMet 310 alloy is said to have a 1.10 mega-inch strength-to-weight ratio (specific strength), which is thought to be about 10 per cent higher than three other alloys known for such high values. AerMet 100 alloy is also said to have a specific strength of 1.01 mega-inches, titanium 6AL-4V alloy a strength of 1.00 mega-inches and Carpenter's recently developed Custom 465 stainless a strength of 0.92 mega-inches.

Carpenter notes that AerMet 310 alloy provides a 10 per cent increase in strength over the strongest existing commercial alloy (AerMet 100 alloy) with very good ductility. Production heats of the new alloy averaged 14.5 per cent elongation and 63.1 per cent reduction in area.

Designers consider different measures of toughness depending on the service conditions expected for the part. Three common measures for toughness are:

1. 1.

   the area under the stress-strain curve in the tensile test, which can be considered as a figure of merit for toughness;

2. 2.

   the Charpy V-notch impact energy; and

3. 3.

   fracture toughness.

The company reports that its new alloy has the highest figure of merit for toughness, compared with other high strength alloys. This value of 4,340 measures the amount of energy that can be absorbed before the alloy fractures. Computations are based on a combination of ultimate tensile strength, yield strength and percentage elongation. Only one other alloy ­ AerMet 100 alloy ­ has a toughness figure of merit over 4,000.

Charpy V-notch impact tests conducted on production heats reportedly showed AerMet 310 alloy had an average impact energy in excess of 20ft.lbs. This value compares with 10ft.lbs average for conventional tool steels.

The new double-vacuum-melted alloy has 65ksi (check)in. fracture toughness in the longitudinal direction Extensive testing is said to have shown that AerMet 310 alloy has a very favorable K_ic/YS ratio (fracture toughness to yield strength). This characteristic should permit designers to make more damage-tolerant parts while utilizing the alloy's high strength.

AerMet 310 alloy has a stated stress corrosion cracking (scc) resistance in 3.5 per cent NaCl solutions equivalent to that of AerMet 100 alloy, which is thought to be distinctly superior to that of other high strength alloys as measured in the slow strain rate scc test.

Nominal chemical composition of AerMet 310 alloy is: carbon 0.25 per cent, chromium 2.40 per cent, nickel 11.0 per cent, molybdenum 1.40 per cent, cobalt 15.0 per cent, balance iron.

For more information about the alloy and its availability, contact Jim Dahl. Tel: +1 (610) 208 2235.

(Canadian readers can obtain additional information from Carpenter's Toronto Service Center by calling +1 800 268 4740.)