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At what temperature F does EN become liquidous?

I have parts made of Kovar, then plated with Elect Nickel .00015 - .00025 per surf. Then a requirement of a vacuum sintered bake at 1550 to 1925 for 1 hour. the cross section of the material is .150. When the processor baked the parts they were touching each other, and 42 out of 50 were brazed together. My question is at what temperature does EN become liquidous. The purpose of the bake is to remove impurities from the EN for a Laser weld process that follows. all parts exhibited blistering. what help can anyone give.

Jack Nester
- Dallas, Texas
2003

Electroless nickel melts about 1800 °C. This varies depending on the phosphorous content. There are many factors that effect the adhesion of electroless nickel.

Todd Osmolski
- Charlotte, North Carolina, USA
2003

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First of two simultaneous responses

What Todd said is correct and to complement the idea, according to the ASM Metals Handbook a high phosphorous EN containing 10.5% P will melt at even less temp (1630 deg F). Also, there are many types of EN. For instance the ones containing 5% boron melt around 2000 deg F. About your blisters, if big and scattered are typical of cast substrates and indicate entrapped liquids in pores beneath the plate whereas numerous small ones indicate a poor adhesion and the corresponding lift produced by internal compression stress in the plate. If the later was the case there are steps to correct the problem, but if you have a porous substrate the chances are slim.

Guillermo Marrufo
Monterrey, NL, Mexico
2003

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Second of two simultaneous responses 2003

There is a eutectic L = Ni + Ni3P at 879 C (1698 F) in the Ni-P phase diagram, http://cyberbuzz.gatech.edu/asm_tms/phase_diagrams/pd/Ni-P.JPG and thus, there should be some liquid above this temperature for 0.17 to 15 wt% P. If you first bake below this temperature, the limited amount of P should diffuse into the Kovar, and subsequently remain in solid solution to a higher temperature. Kovar is 54Fe-29Ni-5Co, and Fe has a much higher solubility for P than does Ni. http://klara.met.kth.se/pd/element/Fe-P.html

Ken Vlach [deceased]
- Goleta, California
Finishing.com honored Ken for his countless carefully researched responses. He passed away May 14, 2015.
Rest in peace, Ken. Thank you for your hard work which the finishing world, and we at finishing.com, continue to benefit from.