4J29 (Expansion alloy)
(Common Name: Kovar, Nilo K, KV-1, Dilver Po, Vacon 12)
Kovar is a nickel-cobalt ferrous alloy compositionally identical to Fernico, designed to be compatible with the thermal expansion characteristics of borosilicate glass (~5 × 10−6 /K between 30 and 200 °C, to ~10 × 10−6 /K at 800 °C) in order to allow direct mechanical connections over a range of temperatures. It finds application in electroplated conductors entering glass envelopes of electronic parts such as vacuum tubes (valves), X-ray and microwave tubes and some lightbulbs.
The name Kovar is often used as a general term for Fe-Ni alloys with these particular thermal expansion properties. Note the related particular Fe-Ni alloy Invar which exhibits minimum thermal expansion.
4J29 also known as Kovar alloy. it was invented to meet the need for a reliable glass-to-metal seal, which is required in electronic devices such as light bulbs, vacuum tubes, cathode ray tubes, and in vacuum systems in chemistry and other scientific research. Most metals cannot seal to glass because their coefficient of thermal expansion is not the same as glass, so as the joint cools after fabrication the stresses due to the differential expansion rates of the glass and metal cause the joint to crack.
4J29was invented to meet the need for a reliable glass-to-metal seal, which is required in electronic devices such as light bulbs, vacuum tubes, cathode ray tubes, and in vacuum systems in chemistry and other scientific research. Most metals cannot seal to glass because their coefficient of thermal expansion is not the same as glass, so as the joint cools after fabrication the stresses due to the differential expansion rates of the glass and metal cause the joint to crack.
Mainly used in electric vacuum components and emission control, shock tube, igniting tube, glass magnetron, transistors, seal plug, relay, integrated circuits lead, chassis, brackets and other housing sealing.
Style of supply
| Alloys Name | Type | Dimension | |
| OhmAlloy-4J29 | Wire | D= 0.1~8mm | |
| OhmAlloy-4J29 | Strip | W= 5~250mm | T= 0.1mm |
| OhmAlloy-4J29 | Foil | W= 10~100mm | T= 0.01~0.1mm |
| OhmAlloy-4J29 | Bar | Dia= 8~100mm | L= 50~1000mm |
Normal composition%
| Ni | 28.5~29.5 | Fe | Bal. | Co | 16.8~17.8 | Si | ≤0.3 |
| Mo | ≤0.2 | Cu | ≤0.2 | Cr | ≤0.2 | Mn | ≤0.5 |
| C | ≤0.03 | P | ≤0.02 | S | ≤0.02 | | |
Tensile Strength, MPa
| Code of condition | Condition | Wire | Strip |
| R | Soft | ≤585 | ≤570 |
| 1/4I | 1/4 Hard | 585~725 | 520~630 |
| 1/2I | 1/2 Hard | 655~795 | 590~700 |
| 3/4I | 3/4 Hard | 725~860 | 600~770 |
| I | Hard | ≥850 | ≥700 |
Typical Physical properties
| Density (g/cm3) | 8.2 |
| Electrical resistivity at 20ºC(OMmm2/m) | 0.48 |
| Temperature factor of resistivity(20ºC~100ºC)X10-5/ºC | 3.7~3.9 |
| Curie point Tc/ ºC | 430 |
| Elastic Modulus, E/ Gpa | 138 |
| The heat treatment process |
| Annealing for stress relief | Heated to 470~540ºC and hold 1~2 h. Cold down |
| annealing | In vacuum heated to 750~900ºC |
| Holding time | 14 min~1h. |
| Cooling rate | No more than 10 ºC/min cooled to 200 ºC |
Coefficient of expansion
| θ/ºC | α1/10-6ºC-1 | θ/ºC | α1/10-6ºC-1 |
| 20~60 | 7.8 | 20~500 | 6.2 |
| 20~100 | 6.4 | 20~550 | 7.1 |
| 20~200 | 5.9 | 20~600 | 7.8 |
| 20~300 | 5.3 | 20~700 | 9.2 |
| 20~400 | 5.1 | 20~800 | 10.2 |
| 20~450 | 5.3 | 20~900 | 11.4 |
Thermal conductivity
| θ/ºC | 100 | 200 | 300 | 400 | 500 |
| λ/ W/(m*ºC) | 20.6 | 21.5 | 22.7 | 23.7 | 25.4 |
