In Al-5%CNT by powder metallurgy route.After ball milling(1hr,toulene) and compaction(200Mpa),the strength of green composite is too low. After ball milling and drying observed small lumps of powder.Pls suggest methods to improve green strength.
May be your CNT dispersion in Al matrix is not good.. These may provide you some help...
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Cold compaction of Al-CNT powder does not give the sufficient strength...you should coat these CNT with Nickel ..it will increase the wettability of it..Another way is to do hot compaction of these powders..it will definitely work..I have faced the same problem for Al-Carbon fiber composite.
Of course many different parameters are related with this problem. If you want to find a solution without changing your target composition I will suggest you following solutions:
1) Addition of a suitable binder in proper amount (but it is really difficult task to find suitable one which will leave from your system without leaving any impurities).
2) To apply annealing to milled powder prior to compaction. (Note: it should be definetely under protective atmosphere)
3) Apply warm compaction or direct consolidation to full density via advanced technics.
Good Luck for your studies.
I think that toluene itself and its amount could be a problem. We were successful up to 3 wt% of CNTs after milling with Al powder in argon without liquid ( only few droplets of ethyl alcohol). Initial length of CNTs could matter also, however, we found them significantly broken into small pieces. You did not provide several details of the milling itself, a lot of parameters, including the jar lining could influence the final effect of milling.
Its a zirconia jar with ball to powder ratio of 5: 1.Milling time was 1 hour at 380 rpm.
Your milling parameters were not very hard. I do not have experience in milling in toluene. It looks as if you lost metalic Al )oxidation or reaction with dispersing agent. You could change dispersing agent to wax or similar or you could add some nano SiC as additional dispersing agent. Also addition of glassy carbon helps in prevention of Al oxidation. Your task is not easy, we also had several problems with repeteability of milling results. Wish you success.
Hi Dear researcher
I think that is a common result but by severe plastic deformation process after pre-compaction, you can achieve a good green density, or by using different compaction methods like the floating die or double action compaction methods.
Best Regards
Although you might have gotten a solution, but just to clarify, I'm putting this response. You didn't mention the unit of %. However, I'd consider it as volume percentage (not weight). In this case, even if all the parameters (at milling and compaction stages) are well controlled and oxidation is prevented, 200 MPa isn't the pressure that gives you a green compact with enough strength. Actually, successful compaction of composite powder mixtures up to 5% of brittle contents is reachable, but beyond that, it's hard to achieve. To do so, uniform dispersion of reinforcements, controlling the atmosphere, coating the fibres and hot compaction of powders would help. However, the interface may tend to form brittle compounds due to the presence of high temperatures. It should also be well controlled.
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