Iridium

I've read that iridium is used in the impact shielding of radioisotope thermoelectric generators (RTG) on spacecraft because of its hardness, high melting point, and extreme corrosion resistance. With stats like that, why isn't it being used in more applications? I know it is expensive, but so are many other exotic alloys and composites. It seems that it would be perfect for numerous aggressive environment applications but is largely ignored. Any thoughts on other uses/reasons for non-use?
Thanks!
Jim Painter Materials Science and Engineering Georgia Institue of Technology

Jim Painter wrote:
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It is very hard and also it's brittle, which makes it very difficult to machine or work and, I guess, the latter limits the number of uses. Engineers don't like brittle materials.
HTH

Chris H wrote:
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According to my material database:
Platinum iridum alloy: Compressive strength 110-1285, elongation 1-40%, youngs modulus 180-285 GPa, vickers hardness is 90-410 HV, tensile strength is 245-1520 MPa.
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I think it's too expensive and that you can get better materials for cheaper price in most applications.
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Yep, I can see that it has good properties against everything. But why use a material that is better than necessary if the application doesn't require it and since the material is very expensive?
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I don't see that iridium alloys should be brittle. You can also get it annealed. I have a reference: ASM Handbook, 9th ed. vol.2, p.693 for Platinum-5%iridium alloy, annealed: elongation is 20-40%
Med venlig hilsen / Best regards Martin Jørgensen

Martin Jørgensen wrote:
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That would be a platinum alloy.

Chris H wrote:
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Oh yes, that's correct. I just searched for "iridium" in my database and the only thing that was found was 13 platinum iridium alloys (from 5-30% alloyed).
Perhaps platinum is always alloyed with iridium for practical purposes, anyone? I don't see any other materials together with iridium and I don't see the properties for pure iridium in my database...
Hard platinum-30%Iridium alloy, has 1-3% elongation, so this is brittle (and hard: Tensile strength is about 13-1400 MPa)... There is also an annealed version with properties for that in my database.
Med venlig hilsen / Best regards Martin Jørgensen