NickE:
I appreciate your apology, and perhaps I came down a bit hard. It is very frustrating to those of us who are serious about this process to be lumped in with the "get rich quick" people. People who make wild, un-informed claims about "making metal denser", or "enhancing the molecular(!) structure of metals", or whatever have perhaps done irreparable harm to the field of cryogenic processing. Some companies are so paranoid about being scammed that they just will not use anything that has even the hint of taint to it. It is frustrating, because I see companies going broke because they are not competitive, and I have at least an answer to help them, AND THE ONLY WAY TO GET MORE RESEARCH DONE IS TO GET THE PROCESS MORE WIDELY USED SO IT ATTRACTS MORE RESEARCH.
I am not familiar with the theory of micro crack closure. Could you give me reference to go to on this? I would like to read it and also add it to my data base of cryo research.
Putting RA aside, especially since it does not explain why cryo works on copper, aluminum, some plastics, etc. cryogenic processing has been shown by NASA to reduce residual stresses in aluminum welds (Effects of Cryogenic Treatment on the Residual Stress and Mechanical Properies of an Aerospace Aluminum Alloy, Po Chen, Tina Malone, et al, Marshall Space Flight Center). There have been similar findings on steel, but I do not have their reference at hand. This in itself is interesting, though, because we treat a lot of valve springs that have been shot peened to induce compressive residual stresses to enhance fatigue life. We get about triple the life, so if I am reducing the compressive residual stresses, why does it last longer?
But I digress. Collins found the creation of very fine carbide particles. This may have some pinning affect to the crystal structure, but it is not valid for non-ferrous materials, of ferrous materials that lack carbide forming elements.
A common thread that is emerging from the studies that I have read is that something must be happening in the sub-micro structure. Any real theory would have to abandon the RA and eta carbide angle to work on other metals. I have put a theory forward to almost all the cryo researchers that I talk to. It comes out of looking at the metallic bond as if it were a chemical bond. I got this idea from reading some work by Dr. Mark Eberhard (Colorado School of Mines). His work states (as I understand it, as I'm a mechanical engineer, not a trained metallurgist) that for each atom in a crystal structure there is a preferred distance it wants to be from the other atoms in the structure. If it is not at that preferred distance, the structure contains more energy than the preferred state. My THEORY is that as we reduce the temperature of the crystal structure, we reduce the energy available to the atoms to be "out of place". By warming the part back up slowly, we do not put that energy back in, so the crystal structure is more perfect.
Please realize that this is stated in pretty simple, lay-man's terms. I have put this THEORY in front of a lot of metallurgists, and either they were being pretty polite and not laughing out loud, or they really did think that it should be investigated. I invite people to comment on this or other theories. This is the only way that we will be able to direct what few research dollars that are spent on cryo to the best possible experiments.
