Grade 2 titanium plating 3

[spiridij]

Has anyone had any luck with plating grade 2 titanium with pure silver (without nickel or any other materials)? I'm looking to improve my brazing process by pre-plating the surfaces with silver, but I'm not sure if it's possible or if the silver will actually be bound to the underlying material. Any thoughts?

 

[EdStainless]

What braze are you using?
I would not think of silver as helping at all with Ti.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, Plymouth Tube

 

[spiridij]

I'm sandwiching a thin sheet of pure silver between two grade 2 titanium flanges and performing a resistance brazing operation and a subsequent stress-relieving annealing cycle. I've had success in the past, but over time, the joints fail. I though maybe I'd silver plate the Ti flange before brazing in order to reduce the oxide layer's effects on the brazing as much as possible.

 

[EdStainless]

Do they fail because of the brittle secondary phases that are formed?
I thought that this was done with Ti-Zr-Cu-Ni, or Ti-Zr-Cu, or Ti-Cu-Ni fillers.
I have heard of using Ag-Cu with very aggressive fluxes.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, Plymouth Tube

 

[spiridij]

Quite honestly, it is unclear to me how they are failing. I pressure test them immediately at about 140 psig after the stress-relieving annealing process and they all pass easily. After a few months, I re-tested them and they all failed at between 5-20 psig. My theory is that I am heating the titanium, causing the oxide layer to dissolve and since the parts are squeezed together (at a relatively high pressure) with the silver layer in between, the silver melts onto a relatively oxide-free surface. I have seen the silver melted and a good bond created between the three parts, but it puzzles me as to why I'm getting late failures. I assumed I wasn't getting good adhesion of the silver to the Ti.

 

[EdStainless]

Sounds like you need to do more SEM work on both new and old parts.
This does not sound like a very robust process.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, Plymouth Tube

 

[WKTaylor]

spiridij...

The AWS Brazing Handbook has a lot of important information regarding process and alloys for brazing titanium/Ti-Alloys. It also points to several important AWS specs for various aspects of the processing.

You should become very familiar with the AWS BH CHAPTER 30—REACTIVE METALS: TITANIUM, ZIRCONIUM, AND BERYLLIUM. Titanium is 'reactive alloy' that is difficult to braze without strict controls for various factors.

Titanium can be successfully brazed with silver, copper, aluminum, Ti-Ni and Ti-Zr-Be alloys. What is worrisome is diffusion of hydrogen and oxygen into the titanium matrix during the processing, so very careful atmosphere/moisture controls and overall cleanliness are mandatory.

NOTE. Titanium and silver can be a bad combination, since silver can embrittle titanium if diffused into the alloy matrix.... such as by plating and subsequent heating to brazing temperatures.

Regards, Wil Taylor

o Trust - But Verify!
o We believe to be true what we prefer to be true. [Unknown]
o For those who believe, no proof is required; for those who cannot believe, no proof is possible. [variation,Stuart Chase]
o Unfortunately, in science what You 'believe' is irrelevant. ["Orion"]
o Learn the rules like a pro, so you can b

 

[spiridij]

Thanks WKTaylor! So you do not recommend plating the titanium with silver prior to resistance brazing, because of embrittlement of the titanium? Is this embrittlement going to affect the weld at the interface of the to materials or the bulk of the titanium?

 

[EdStainless]

There are Ti-Ag intermetallics that will form where ever the Ag diffuses.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, Plymouth Tube

 

[tbuelna]

From MIL-HDBK-1568:

 

[spiridij]

thanks tbuelna, it looks like the MIL-HDBK is describing corrosion resistance as a rationale for not plating Ti with Ag. Is that your understanding as well?

 

[tbuelna]

From NASA-STD-6016 sec. 4.2.2.3.2 - "Mercury, cadmium, silver, and gold have been shown to cause liquid-metal-induced embrittlement and/or solid-metal-induced embrittlement in titanium and its alloys."