Aug 6 2013
Topics Covered
Introduction
Chemical Composition
Physical Properties
Mechanical Properties
Other Designations
Fabrication and Heat Treatment
Machinability
Forming
Heat Treatment
Welding
Cold Working
Hardening
Applications
Introduction
Permalloy was primarily developed in the early 20th century for inductive compensation of telegraph cables. Permalloy is known for its very high magnetic permeability, which makes it useful as a magnetic core material in electrical and electronic equipment. The other key magnetic properties it possesses are near zero magnetostriction, low coercivity, and anisotropic magnetoresistance.
Super alloy Permalloy 80 is a high magnetic permeability alloy of nickel and iron.
The following sections will discuss in detail about super alloy Permalloy 80.
Chemical Composition
The chemical composition of Permalloy 80 is outlined in the following table.
|
Element |
Content (%) |
|
Nickel, Ni |
80.2 |
|
Iron, Fe |
14 |
|
Molybdenum, Mo |
4.85 |
|
Manganese, Mn |
0.5 |
|
Silicon, Si |
0.3 |
|
Chromium, Cr |
≤ 0.020 |
|
Cobalt, Co |
≤ 0.020 |
|
Carbon, C |
0.015 |
|
Aluminum, Al |
≤ 0.010 |
|
Phosphorus, P |
≤ 0.0050 |
|
Sulfur, S |
≤ 0.0010 |
Physical Properties
The physical properties of Permalloy 80 are tabulated below.
|
Properties |
Metric |
Imperial |
|
Density |
8.7 g/cm3 |
0.316 lb/in3 |
|
Melting point |
1454°C |
2650°F |
Mechanical Properties
The following table shows mechanical properties of annealed Permalloy 80.
|
Properties |
Metric |
Imperial |
|
Tensile strength |
682 MPa |
98900 psi |
|
Yield strength |
338 MPa |
49000 psi |
|
Elongation at break |
32% |
32% |
|
Hardness, Rockwell B |
80 |
80 |
Other Designations
Equivalent materials to Permalloy 80 are ASTM A753 ALLOY 4 and MIL N-14411 Comp 1.
Fabrication and Heat Treatment
Machinability
Super alloy Permalloy 80 can be machined using the common processes. The high nickel content in this alloy causes "gumminess" while machining. It displays the same characteristics as the 300 series austenitic stainless steels. It is recommended that high-speed steel or carbide tools be used along with lard oil lubricant. When using water-soluble cutting fluids care should be taken to immediately clean the parts thoroughly after machining so as to avoid corrosion contamination.
Forming
Super alloy Permalloy 80 can be formed using any of the conventional methods.
Heat Treatment
Permalloy 80 not hardenable by heat treatment. Annealing can be performed in a dry hydrogen atmosphere at 1176°C (2150° F) for 4 h, followed by furnace cooling to 593°C (1100°F), and then a cooling rate of 260°C (500°F)/ h from 593 to 372°C (1100 to 700°F). Air cooling should be done to 372°C (700°F). Strain relief annealing can be performed at 927°C (1700°F) for 1/2 h in a dry hydrogen or inert gas atmosphere.
Welding
Welding of super alloy Permalloy 80 can be performed using all the traditional welding methods.
Cold Working
Permalloy 80 has good ductility and is readily cold formed.
Hardening
Super alloy Permalloy 80 hardens only by cold work.
Applications
Permalloy 80 is chiefly used found in transformer core laminations and magnetic shielding.