i have carried out cold compaction of aluminum-graphene and pure aluminum milled powder at 500 MPa. sintering cycle is 15 degree/ minute rise in temperature till 500 degree centigrade and soaking samples for 4 hours followed by water circulation cooling. i observed that samples upper layer is not solidified so i have planned to put samples again in sintering furnace and again following a sintering cycle upto 600 degrees. Is this gonna help. any advice?
Dear Farhan,
You can try 550/600 °C (~88% of the melting temperature of the pure aluminium power), with a holding period of 2-4 h and in an argon atmosphere. Try with a heating and cooling rate of 5 C/min.
Reduce the sintering temperature and apply exact water circulation rate.
No need for re sintering
sir im working on aluminum-graphene composite. i have carried out ball milling in a planetary ball mill for different times and graphene reinforcement. 100 gram Aluminum powder and 0.50,0.75 and 1 wt % graphene were milled in argon environment and 8.5 ml methanol as process control agent. Milled powder were compacted at pressure of 500 Mpa in green compacts of 75mm length and 10x10 (Thickness & Width) . green compacts were then sintered at 600 degree centigrade in argon environment with 15 c/ min heating rate with 4 hours holding time. Furnace was then cooled by water circulation which is approx 3-8 degree / minute. I noticed my samples are still not sintered are are like green compacts. One of samples i dropped accidentally and it broke. Samples are still like powder from inside and i dnt see any sort of diffusion at all. Please see the pictures for reference.
in addition last one is of the sample which i compacted couple of days back but today morning i found it like this..No clue what happened to it. following sample contains 1 weight % graphene and had been milled for 5 hours.
In this circumstance your sintering process could be called as solid state sintering. so you have to raise your temperature for sufficient diffusion of aluminium atoms between grains and formation of necks. Otherwise you should use minor addition (%
Im using argon environment during sintering as reported in many papers, but If aluminum melts at 660 then how can i heat it above melting temperature....
According to me, you should change milling conditions. 5 hours is very long time for Al milling. After milling, your powders may be oxidation. All process should occur in glove box and you should make sintering in hydrogen atmosphere
Some useful comments has already been made. What was the size of the starting powder and how much oxidized it was before milling? Mixing rather than milling is more advantageous. Try to mix/mill it in a high purity argon environment and raise the temperature a little if required after seeing the result from sintering and even if proper mixing has been done earlier (depends). Liquid phase sintering may result in chemical reactions depending upon the addition. Good purging of high purity argon should be done before sealing for an inert environment. Eventhough the cooling rate employed is low but furnace cooling may be helpful.
Did you check the calibration of your furnace? It should be a good idea to check the temperature calibration of the furnace maybe there is a significant temperature difference between the furnace real temperature and set temperature from time to time this control has to be done. There may be a problem with the heating elements. Also as already mentioned by many people to increase the sintering temperature and to decrease the heating rate would be helpfull.
there may be a problem of oxide formation during milling or during storage. usually any powders milled for long time, immediate after expose to atmosphere powders will react with oxygen and forms there oxides. so go for XRD study immediate after milling and before compaction. from there you will know the phases formed during milling and during storage. if any trace of AL2O3 or Al-C phases noticed so change milling condition. if possible check the milled powders in FESEM from there you will be able to see the surface morphology of milled powders whether powders are free from any sort of possible contamination or coating on it. these oxides/ coating will hinder in sintering of aluminum. even though you sinter the samples above the MP of Al you will get the same result.
metal like Al, Cu compacted at 500 MPa will itself become like solid, to check this try with pure Al and see the effect of compaction load.
along with these you need to check the exact temperature near the sample zone, whether any leakage is there in furnace, rate of organ purging, purity of organ, etc.
if you sinter the sample under nitrogen atm there is possibility of formation of AlN phases.
its been a while since i updated my ongoing problem.sorry for tht
I got the Xrd results of pure aluminum powder and Al-0.5 % graphene sample milled for 03 hours. it is showing aluminum not aluminum oxide..So chances of the sample being oxidized are eliminated. And now question is if its aluminum then why it is not being sintered. meanwhile i intend checking fol:
1. Is furnace working properly
2. increasing holding time from 04 hours to 06 hours
im uploading Xrd result of alu-graphene sample. plz let me know if you see anything which might help me
hello...can i change the sintering condition from argon gas to vacuum..how it will effect my samples or reults
hello.. im uploading my samples from after sintering process. sintering cycle involved heating the samples upto 150 degree centigrade and holding for 02 hours, then heating upto 250 degrees and holding for 01 hour, heating upto 400 degrees and holding for 01 hour in the end heating upto 600 degree and holding for 02 hours followed by furnace cooling. these samples are partially sintered.
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