Type Analysis | Description | Applications | Physical Properties
Magnetic Properties | Thermal Expansion Properties | Preparation For Sealing | Workability | Typical Mechanical Properties

Type Analysis

Description

Kovar alloy is a vacuum melted, iron-nickel-cobalt, low expansion alloy whose chemical composition is controlled within narrow limits to assure precise uniform thermal expansion properties. Extensive quality controls are employed in the manufacture of this alloy to ensure uniform physical and mechanical properties for ease in deep drawing, stamping and machining.

Applications

Kovar alloy has been used for making hermetic seals with the harder Pyrex glasses and ceramic materials.
This alloy has found wide application in power tubes, microwave tubes, transistors and diodes. In intergrated circuits, it has been used for the flat pack and the dual-in-line package.

Physical Properties

Specific gravity.......................................8.36                           Curie temperature
Density                                                                                           °F.................................................... 815
   lb/cu in............................................... 0.302                               °C.................................................... 435
   kg/cu m............................................... 8359                          Melting Point
Thermal conductivity                                                                     °F.................................................. 2640
   Btu-in/ft²/hr/°F...................................... 120                                °C................................................. 1450
   W/m-K.................................................. 17.3                          Modulus of elasticity
Electrical resistivity                                                                         psi x 10(6) ..................................... 20
   ohm-cir mil/ft......................................... 294                               MPa x 10(3) .................................. 138
   microhm-mm......................................... 490

Magnetic Properties

Kovar alloy is magnetic at all temperatures below the Curie point. Magnetic properties will depend upon heat treatment; the lower the hardness, the higher the permeability values and lower hysteresis loss. Examples of permeability properties are shown in the following chart:

Thermal Expansion Properties

The following are the average coefficient of expansion properties after annealing in hydrogen for 1 hr at 1650°F (900°C) and 15 minutes at 2010°F (1099°C) and cooled to room temperature within 1 hr. Material heat treated using this procedure should not exhibit any transformation when cooled to -112°F (-80°C) for 4 hrs. This was determined by means of metallographic examination.
Mean coefficient of thermal expansion as annealed.

Preparation for Sealing

All degreased, fabricated Kovar alloy parts should be degassed and annealed in a wet hydrogen atmosphere. Atmosphere is to be made moist by bubbling the hydrogen through water at room temperature. Care must be taken to prevent surface carbon pickup. Furnace should have a cooling chamber provided with the same atmosphere.
Heating should be conducted within the 1540/2010°F temperature range. Time at temperature should be approximately two hours for lowest temperature to 20 minutes for the highest temperature. Parts should then be transferred to the cooling zone and held until below 570°F, then removed.
An oxide film on the metallic part is preferred for metal-to-hard glass sealing. The best oxide film is thin and tightly adhering. The film can be produced by heating the parts to 1200/1290°F in regular ambient atmosphere for a time sufficient to form a dark gray to slight brown oxide.

Workability

Forging
The principal precaution to observe in forging is to heat quickly and avoid soaking in the furnace. Long soaking may result in a checked surface due to absorption of sulfur from the furnace atmosphere and/or oxide penetration. A forging temperature of 2000/2150°F is preferred.

Coolant
It is important to control heat build up, the major cause of warpage. A suggested coolant would be Cool Tool. Cool Tool contains fatty esters to reduce friction in the cutting zone and a refrigerant to remove the heat generated by friction between the cutting tool and work place.

Tooling
T-15 Alloy, such as Vasco Supreme-manufactured by Vanadium Alloys Company. M-3 Type 2, such as Van Cut Type 2-manufactured by Vanadium Alloys Company. Congo manufactured by Braeburn.
For machining with carbide tools, a K-6 manufactured by Kennemetal, Firthie HA manufactured by Firth Sterling, or #370 Carboloy could be used, or a K2S manufactured by Kennemetal, or Firthie T-04 manufactured by Firth Sterling would be satisfactory. One thing of prime importance is that all feathered or wire edges should be removed from the tools. They should be kept in excellent condition by repeated inspection.

Turning
If steel cutting tools are used, try a feed of approximately .010" to .012" per revolution and a speed as high as 35/FPM could probably be attained. Some of the angles on the cutting tools would be as follows:

• End cutting edge angle -Approximately 7°

• Nose radius -Approximately .005"

• Side cutting edge angle -Approximately 15°

• Back rake -Approximately 8°

• Side rake -Approximately 8°

When cutting off high speed tools are better than carbide tools, and a feed of approximately .001" per revolution should be used. The cutting tools should have a front clearance of about 7° and a fairly big tip--larger than 25° would be helpful.

Drilling
When drilling a 3/16" diameter hole, a speed of about 40/FPM could possibly be used, and the feed should be about .002" to .0025" per revolution, for a 1/2" hole, approximately the same speed could be used with a feed of about .004" to .005" per revolution. The drills should be as short as possible, and it is desirable to make a thin web at the point by conventional methods. By conventional methods, we mean do not notch or make a crank shaft grinding. It is suggested that heavy web type drills with nitrided or electrolyzed surfaces be used. The hole, of course, should be cleaned frequently in order to remove the chips, which will gall, and also for cooling. The drill should be ground to an included point angle of 118° to 120°

Reaming
Reaming speeds should be half the drill speed, but the feed should be about three times the drill speed. It is suggested that the margin on the land should be about .005" to .010", and that the chamfer should be .005" to .010" and the chamfer angle about 30°. The tools should be as short as possible, and have a slight face rake of about 5° to 8°.

Tapping
In tapping, a tap drill slightly larger than the standard drill recommended for conventional threads should be used, because the metal will probably flow into the cut. It is suggested that on automatic machines, a two or three fluted tapping tool should be used. For taps below 3/16", the two fluted would be best. Grind the face hook angle to 8° to 10°, and the tap should have a .003" to .005" chamfered edge. If possible, if binding occurs in the hole in tapping, the width of the land may be too great, and it is suggested that the width of the heel be ground down. Again, it is suggested that nitrided or electrolyzed tools be used. Speed should be about 20/FPM.

• *When using carbide tools, surface speed feet/minute (SFM) can be increased between 2 and 3 times over the high speed suggestions. Feeds can be increased between 50 and 100%.

• Note: Figures used for all metal removal operations covered are average. On certain work, the nature of the part may require adjustment of speeds and feeds. Each job has to be developed for best production results with optimum tool life. Speeds or feeds should be increased or decreased in small steps.

• The information and data presented herein are typical or average values and are not a guarantee of maximum or minimum values. Applications specifically suggested for material described herein are made solely for the purpose of illustration to enable the reader to make his own evaluation and are not intended as warranties, either express or implied, of fitness for these or other purposes.

Typical Mechanical Properties

Typical Mechanical Properties of Strip
Tested parallel to the direction of rolling. Material annealed 1830°F for 30 minutes, then furnaced cooled.

Kovar - Current Inventory Stock