improving 72FNS microstructure
06-30-2009, 04:30 AM,
#1
Rolleyes  improving 72FNS microstructure
My first attempt at 72FNS came back with the following microstructure results:
Delamination - fail, integrity - fail, porosity - V4 as apposed to </=V3. All remaining results in limits including hardness.

Sprayed with 4" distance, Arg/Hydrogen, 15 sec cooling time between passes, GE nozzle, 73V 500Amps, 75nlpm primary gas, 3.8nlpm 2ndry gas, 7 nlpm carrier gas, 8.2 lbs/hr feed rate.

The machine is a metallisation system using a metco 9mb gun.

Any suggestions as to how I can improve on the above results and also, what are your thoughts on gas choice; is argon/ helium a better option??

Thanks
B[/font]
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06-30-2009, 08:37 AM,
#2
RE: improving 72FNS microstructure
G'Day Bigals,

No technical support and solutions from the local agents? LOL.
I bet you wish that there were other options......
Hey, you're not the local agent looking for info for clients are you? Wink

You don't need to go to the expense of a Helium secondary to fix the coating, that is unless the substrate is Titanium and then you must use Helium. Yes, I know this is a highly debated subject with Ti and Hydrogen embrittlement but the facts substantiaties the use.

PM me with more detail about what you're doing; type of components (industry), etc and I'll sort it for you.

Cheers

GlenB
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06-30-2009, 09:29 PM, (This post was last modified: 06-30-2009, 09:31 PM by bigals.)
#3
RE: improving 72FNS microstructure
Good morning Glen,

In answer to your first question, No, I'm not an agent; interesting thought though! Just a newby on the job down under.
The substraight is titanium and also inconel 718 in the aviation industry. There is interesting comments on hyd imbrittlement however the tables we use suggest arg/hyd on one component and on another may suggest arg/helium even though both materials are titanium. As the fixture that we mount the coupon on is like a rotary clothes line, there is limited heat retained in the coupon (no heat sink) and as such we don't use any external air jets. However, to preheat we do 3 passes prior to spraying.
Look forward to your input
B
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07-07-2009, 02:45 PM,
#4
RE: improving 72FNS microstructure
Hi Bigals

Sign0016 to the Surface Engineering Forum.

I would be inclined to use argon/helium in preference to argon/hydrogen if you want the best quality, easier/more consistent process control, avoidance of hydrogen embrittlement issue (whether or not this actually a problem Happy0193). Only downside is cost of helium and possible limitations on your Metallisation power supply if you want to try the more extreme higher energy parameters (some argon/helium parameters sets require 60-80 KW, ~1100A).

Take care with your preheating of titanium, all to easy to oxidise surface.

May be the addition of some external cooling air jets may help and avoid the "15 sec cooling time between passes".
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07-08-2009, 12:34 AM,
#5
RE: improving 72FNS microstructure
Thanks for the info. We'll give the external cooling and a reduced 'between pass time' cooling a go. We have noticed when using helium, the required hardness is more difficult to achieve. But, it is achieved everytime with hydrogen. Any thoughts appreciated.
B
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07-08-2009, 11:29 AM, (This post was last modified: 07-08-2009, 01:15 PM by LEN WOOD.)
#6
RE: improving 72FNS microstructure
You don't need to use a Secondary gas or a larger than standard 40-50kW System to spray high energy parameters. Generally Helium Secondary parameters are lesser coatings than H2 in terms of bonding, deposition rates, hardness, etc - despite the extra cost. What EM specifications are you working to - are they Military? If so some caution and discipline should be exercised expecially as the results so far have been 'below par'. I also wonder how you came to have such a Frankenstein system. Is the feeder SM or Metallisation? Without saying too much in the open there may be parameter setting abnormalities/inaccurancies that are basicly not allowing you to deliver the appropriate gas flows and goods to the 9MB torch.

I understood that the only Metallisation Plasma system in Australia had been decommissioned?

Tell me more about the OEM Engine Manual/Repair, etc and also why you are using a 'clothes line' type fixture for test piece manipulation. Is this for convenience or does it simulate the actual component to be coated. Remember that test pieces should be indicative of the actual substrate.

Are you getting any other good 'across the board' results with this system? Sad
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07-08-2009, 06:41 PM,
#7
RE: improving 72FNS microstructure
Hi Bigals and Glen

On the whole I agree with what Glen is saying. but I would like to clarify a few things regarding WC/Co type coatings. I still stand by my previous post regarding preference for argon/helium parameters for producing the best coating properties (from a technical stand point of wear resistance and ductility).

Quote:You don't need to use a Secondary gas or a larger than standard 40-50kW System to spray high energy parameters.

Agree, but if using argon only and to slightly lesser extent argon/helium you need a power supply system capable of delivering high current well in excess of 500A, even if power level is only 30-40 kW. Argon and argon/helium plasma tends to be less restrictive and require lower voltage. High energy plasma spraying is a bit of a misleading term, as it is usually used to describe high velocity plasma (high kinetic energy) as a posed to plasma having high kW power ratings (high thermal energy).

Quote:Generally Helium Secondary parameters are lesser coatings than H2 in terms of bonding, deposition rates, hardness, etc - despite the extra cost.

Agree to large extent, but (a big but Happy0193) to get the best out of WC/Co coatings requires a very delicate balance in process parameters. Metco 72FNS is a sintered and crushed powder, where particles have a matrix of essentially pure cobalt containing a fine WC phase. Ideally, the coating itself should reflect this with a soft ductile relatively pure cobalt matrix containing a high concentration of unaffected hard WC phases. This is where the delicate balance in process parameters comes in, essentially, to get powder particles to form coating without any changes apart from deforming to produce dense coating. Too little heat/velocity results in poor density and bonding. Too much heat on the other hand results in WC phase reacting/dissolving with cobalt matrix and loss of carbon to oxidation - resultant coating now contains lower WC phase and a matrix contaminated with various hard brittle metastable phases of Co,W,C - while these coatings can very often show increased hardness, better deposit efficiency and some times less porosity, their wear and ductility can be seriously compromised. This can be problematic as to detect this condition requires careful metallographic analysis. Argon/helium plasma has advantages in that it can provide higher velocity. Also, helium secondary tends to produce a more stable plasma - tiny changes in conditions with say hydrogen flow can have a significant effect on coating, while helium tends to be more forgiving. High velocity spraying/lower heat input is the way to go for high quality carbide coatings, hence the move towards HVOF/HVAF. To approach the quality of a good HVOF/HVAF WC/Co coating now, you would really need HEP, helium and plasma jet breaking speed of sound.

Quote:We have noticed when using helium, the required hardness is more difficult to achieve. But, it is achieved everytime with hydrogen. Any thoughts appreciated.

First, I would like to stress the point that with WC/Co type coatings hardness is NOT necessarily a good indicator (certainly not by itself) of quality or potential wear resistance. In fact, I go as far to say that with equal density coatings of Metco 72FNS, I would favour the lower hardness coatings over the higher hardness coatings in a contest of abrasive wear resistance and impact/hammer wear.

Depending on the parameters you are using, I'm not really surprised you are getting lower hardness over using argon/hydrogen. The main factors effecting hardness of WC/Co coatings is coating density/particle bonding and hardening effect from cobalt matrix - high hardness as a result of high density/bonding is what you want in preference to hardening the matrix. I know that probably that does not help much if you are struggling to meet customer hardness specifications. I can only suggest a bit of process/coating development work to raise hardness just over minimum required. Avoid common mistake of thinking the harder it is, the better it is - its simply not always true and far more complex.

Quote:You don't need to go to the expense of a Helium secondary to fix the coating

Well, I can't really argue over the economics as long as coating meets customer requirements and everybody is happy Rolleyes I have recommended WC/Co coatings and parameters in the past where in a few cases people have ignored my advice and sprayed the coatings using some rough and ready argon/hydrogen parameters dreamt up from God knows where. Metallography of test pieces after the event showed a coating not of typical WC/Co structure, more a WCo alloy - a very poor coating and one I would not expect to perform well at all. Well it turn out customer and sprayer were happy. What do I know? Ashamed0002 suppose at the end of the day it down to fitness for purpose. All I know is if these were aircraft parts, I would not fly Happy0193
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07-09-2009, 02:12 AM,
#8
RE: improving 72FNS microstructure
Thanks for the indepth analisys. We are currently awaiting results from using argon/helium with the following parameters used: GP nozzle, 2.5" spray distance, with other settings as per Metco standards. We need to achieve a minimum Rockwell 15N hardness of 83; and have generally been seeing @ 70-75. Any ideas as to what adjustments/settings can be made to improve hardness.
Gordon: We have started to use the 'Gas flow conversion calculator' from this site and find primary gas OK however on ocassions the secondary gas (be it either helium or hydrogen) figures are excessive to achieve voltage! ie As an example - with 450NS, helium converted figures are @ 60NLPM but to operate within voltage range we had to drop flow down to 30NLPM.
Thanks
for your input

B
Reply
07-09-2009, 01:53 PM,
#9
RE: improving 72FNS microstructure
Gordon, I agree entirely with what you are saying but not everyone has the luxury of an onsite metallurgist who can directly relate coating characteristics and flaws straight back to system set up or parameter? Or the budget for playing around.

Gator Gard (a High Velocity 'plasma arrangement') runs on high purity/high flow Primary & Secondary & Carrier Helium at upper Amperages. The Hard coatings are amongst the best you'll see in terms of integrity, hardness, bonding and also greater thickness limitation. Even today Gator Gard and the D-Gun still sit atop the bulk of the approvals. The fact that both proprietary processes were unobtainable saw the advent of widespread HVOF and HVAF use.

While the use of Helium (if finely tuned) does yield excellent coatings. I don't understand why you would use it unless the substrate was Titanium or an absolutely critical part: Space shuttle, N Reactor, Military or Raquel Welsh's hip replacement? Big Grin

What is also doubtful is if you would achieve the optimum with the system you have? I would also favour the F4. Also remember that Helium will find the leaks and will make its escape. The gas system needs to be really tight or you're PS-fiftying in the wind!

The thing is that the OEM vendors promote systems to do all. But with some coatings the reality is that consistency and good results are hard to achieve and a Dark Art to maintain. Why is 'Bigals' et al seeking help in your forum and why do Spraywatch type systems make so much sense?

Of course it can be done, but whose going to tell you how to leap ALL the hurdles?
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07-10-2009, 04:13 PM,
#10
RE: improving 72FNS microstructure
Hi Bigals

(07-09-2009, 02:12 AM)bigals Wrote: Thanks for the indepth analisys. We are currently awaiting results from using argon/helium with the following parameters used: GP nozzle, 2.5" spray distance, with other settings as per Metco standards. We need to achieve a minimum Rockwell 15N hardness of 83; and have generally been seeing @ 70-75. Any ideas as to what adjustments/settings can be made to improve hardness.
Gordon: We have started to use the 'Gas flow conversion calculator' from this site and find primary gas OK however on ocassions the secondary gas (be it either helium or hydrogen) figures are excessive to achieve voltage! ie As an example - with 450NS, helium converted figures are @ 60NLPM but to operate within voltage range we had to drop flow down to 30NLPM.
Thanks
for your input

B

Quote:We need to achieve a minimum Rockwell 15N hardness of 83; and have generally been seeing @ 70-75. Any ideas as to what adjustments/settings can be made to improve hardness.

What is the coating thickness on hardness test piece (after surface prep)?

Before advising on adjustments/settings to improve hardness, I think we need to be sure that the standard or baseline parameters are being achieved. The standard Metco coating should be good and will a good baseline to work from if needed. From the sounds of it, your coating does not sound representative of the typical standard coating - which suggests a problem somewhere. This really needs sorting before doing any further coating development work.

Quote:We have started to use the 'Gas flow conversion calculator' from this site and find primary gas OK however on ocassions the secondary gas (be it either helium or hydrogen) figures are excessive to achieve voltage! ie As an example - with 450NS, helium converted figures are @ 60NLPM but to operate within voltage range we had to drop flow down to 30NLPM.

This worries me somewhat. Helium conversion is based on theoretical calculations and I have not had chance to verify experimentally. Argon theoretical calculations agree very well with experimental results, so I would not expect a problem, but I will check to see if I have made any errors. Hydrogen is a bit different as the flow meter arrangement is not the same and is effected by system back pressure, so these conversions should be treated as approximations, though they seem to work well for typical conditions for GH and GP nozzles.

I see little point in using Ar/He parameters for Metco 450, unless you are forced for some reason. For Metco 450 I certainly would prefer Ar/H2 or N2/H2. Looking at the only 450 Ar/He parameters I can find suggest a helium flow of 50 and argon of 35 all @ 55psi using GH/732 nozzle - so around 60 NLPM He sounds about right. You are using GH or 732 nozzle for Metco 450?

I'm not familiar with the metallisation control unit you are using, What plasma gas flow control system does it use? How long are the power cables to gun? Which powder feeder are you using?

I think we need to make sure we are all reading from the same sheet as far as parameters supplied to the gun. First lets ensure we can get a coating as intended from the standard Metco parameters ie generate same conditions using metallisation control unit as Metco 7MC etc.
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07-10-2009, 04:48 PM,
#11
RE: improving 72FNS microstructure
Hi Glen

(07-09-2009, 01:53 PM)GlenB Wrote: Gordon, I agree entirely with what you are saying but not everyone has the luxury of an onsite metallurgist who can directly relate coating characteristics and flaws straight back to system set up or parameter? Or the budget for playing around.

Gator Gard (a High Velocity 'plasma arrangement') runs on high purity/high flow Primary & Secondary & Carrier Helium at upper Amperages. The Hard coatings are amongst the best you'll see in terms of integrity, hardness, bonding and also greater thickness limitation. Even today Gator Gard and the D-Gun still sit atop the bulk of the approvals. The fact that both proprietary processes were unobtainable saw the advent of widespread HVOF and HVAF use.

While the use of Helium (if finely tuned) does yield excellent coatings. I don't understand why you would use it unless the substrate was Titanium or an absolutely critical part: Space shuttle, N Reactor, Military or Raquel Welsh's hip replacement? Big Grin

What is also doubtful is if you would achieve the optimum with the system you have? I would also favour the F4. Also remember that Helium will find the leaks and will make its escape. The gas system needs to be really tight or you're PS-fiftying in the wind!

The thing is that the OEM vendors promote systems to do all. But with some coatings the reality is that consistency and good results are hard to achieve and a Dark Art to maintain. Why is 'Bigals' et al seeking help in your forum and why do Spraywatch type systems make so much sense?

Of course it can be done, but whose going to tell you how to leap ALL the hurdles?

Certainly appreciate your views.

One point though regarding Ar/H2 v Ar/He. Ar/H2 is more difficult to ensure consistent results and is highly technique dependent. This in itself will require increased levels of metallographic process control over that of Ar/He.

Though, I tend to take everything I read from manuals and technical bulletins with a pinch of salt - consider why Metco recommended (not sure what Sulzer Metco now recommend Happy0193) Ar/He parameters for Metco 72F-NS and as far as I know never published any Ar/H2 parameters. If you have the old Metco 72F-NS technical bulletin you can see their explanation (one which I would partially agree with).
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08-04-2009, 05:33 PM,
#12
RE: improving 72FNS microstructure
Bigals- how's it going for your coating rpoblem, and i hope you could post some micrfilm to show your coating microstructure, then it will pretty much help in terms of the issue. Txs. nice posting and analysis from Gordon. Txs.
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04-02-2013, 07:15 PM,
#13
RE: improving 72FNS microstructure
(06-30-2009, 04:30 AM)bigals Wrote: My first attempt at 72FNS came back with the following microstructure results:
Delamination - fail, integrity - fail, porosity - V4 as apposed to </=V3. All remaining results in limits including hardness.

Sprayed with 4" distance, Arg/Hydrogen, 15 sec cooling time between passes, GE nozzle, 73V 500Amps, 75nlpm primary gas, 3.8nlpm 2ndry gas, 7 nlpm carrier gas, 8.2 lbs/hr feed rate.

The machine is a metallisation system using a metco 9mb gun.

Any suggestions as to how I can improve on the above results and also, what are your thoughts on gas choice; is argon/ helium a better option??

Thanks
B[/font]

some times it can be a bit misleading what is right and what is wrong difrent manufactures insist on difrent ways of doing the job, hydrogin embritalment for example some say use hydrogin others say must not but insted of messing about with gass paramitors try increasing the surface speed and decreasing the spray distance to about 2 1/2" double the surface speed that you would spray 450ns or simular powder this will reduce oxides forming as much with out compromizing desity or hardness set side coolers at cross jet 2 1/2" cross jet is very important and hopefully you will get the results you are looking for
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