Information on high nickel alloys.

[tom206]

I am working on a possible design for a component. I have to be very vague given the nature of the assembly but I have a few questions, I was really hoping to get some insight from those out there that may have experience with the material specifically.

The part I am working on designing must endure a high heat application. At this point I have three materials that I think may be suitable, Inconel 718, Waspaloy, and Hastelloy X. All three seem to exhibit the mechanical and chemical properties that I need. The design will place the component in an assembly in where it will be fixed in the XYZ axis but only rotate along the central axis, but due to interference and other conditions it will need to be predictable in growth across the cross section of the piece.


I have just a few questions related to the materials that I am hoping some on here may have experience with.
-Will Inconel 718, Hastelloy, or Waspaloy finish to an adequate finish for a bearing surface finish?
-Do these materials have very predictable behavior related to thermal expansion?


These are the main driving questions right now, I am hoping that as I get real world feedback I will be able to narrow things down and will eventually have even more questions.

 

[EdStainless]

You need to visit the web sites of Special Metals and Haynes and look at alloy data sheets.
The three alloys that you are looking at were developed in the 1940-50's. There are newer alloys that may offer some advantages to you.
Are you looking for a cast alloy (investment cast)? or a Wrought alloy? These are two different groups.

Surface finish - Bearing against what? They will not work as roller element bearings at elevated temp. But they are commonly used as plain bearing surfaces even at high temps. Some special care is needed.
CTE - These alloys tend to have high CTE, but after they are heat treated (aged), then if you thermal cycle them a few time they will be very predictable.


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P.E. Metallurgy, consulting work welcomed

 

[tom206]

I did look at the Haynes info but I was hoping for more in-depth feedback about the thermal expansion predictability. The Haynes information about the Inconel 718 stops at 200C, but it does give me a starting point of 12.8 µm/m°C. I am expecting this application to see temperatures close to 200C but the concern I have is complicated by the variations in cross section over the length of the part. I am considering using internal cooling through the shaft to hold a very specific percentage of growth, but the repeatability over time of the growth was one of my prime concerns. I would need the growth at given temperature to repeatedly retain concentricity of about 0.0127-0.0254mm that would be considering cycling of temperature. I think that the wrought state would be the best bet as considering discontinuity would be a severe impact as there will be complicated machining to the part.

The bearing is most likely going to have to be a coated babbitt style bearing, similar to a shell bearing, but considering the absolute importance of concentricity I would have to add flaking to maximize the hydraulic effect across the surface area of the journal. That is good info about the needle bearing that you mentioned, I really wasn’t sure if the surface would be able to support a needle bearing as a race. I had my obvious doubts but I wanted to ask. I am vaguely familiar with the mentioned alloys which is why I began with those three and went down that route. I also considered Monel S/K but I am not sure how the copper content will affect the torsional stress through the part at about 750mm long. I hadn’t really considered the aged consideration, that does make sense. Would you have any other alloys that would be worth considering.

 

[EdStainless]

Ok, Why Ni alloys?
Magnetic properties?
Modulus?
200C max? What is the real max temp of exposure? What about max operating temp?
I presume air, but any other exposure issues?
What strength do you really need?
What CTE do you really want?
There are a bunch of really great journal bearing materials (filled with various stuff) that will be a lot better than babbitt.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, consulting work welcomed