''Heat treatment uniforms the grain structure thereby reduces the porosities'' was written in an article. But I couldn't find any supportive information anywhere else in the literature.
This statement is true, as a rule of thumb, for most materials, but critically depends on temperature and time, which should be high enough. Otherwise there is indeed no effect to expect. For metals, you can expect an effect at a temperature of typically 2/3 of the melting temperature.
Alain
the porosity may be reduced through high temperature HT. this due to the particles raised to an elevated temperature where through diffusion driven by the reduction of surface energy, the spaces between pores reduce in size leading to an overall decrease in porosity.
however in my research it not work
This rule of thumb is applicable at the early stages of sintering where the geometricaly present pores are more than few, usually even more than 10, percent because of reasons that you can find in the first few 10 pages of any sintering book. See wikipedia. At smaller pore fractions the process becomes too, too slow. Such enormous slowing down is observe also in grain growth.
Since these are simple constant composition diffusional process, its (pore fraction) time and temperature dependence must be something like:
squareroot(time) * exp(-1/T) and its rate mıst be proportional to:
squareroot (1/time) * exp(-1/T)
The temperature need not to be as high as 2/3Tm(K), only 1/3 Tm(K) may be sufficient with correct pore fraction.
Regards
The above answers are true, but are they applicable to the question asked? It seems to me that the questioner should elucidate his question, e.g. the term 'Aluminium composites' denotes a Metal Matrix Composite with which reinforcing particles or fibres?
Dear Professors,
Thank you for all your responses. I produced 5% B4C(p) / 5% SiC(p) Al 2014 hybrid composites by vacuum infiltration at 700 oC and I have studied on T6 treatment of these composites.
I observed that altough there is not a significant effect on the porosity as a result of the solution heat treatment at 510 oC, the porosity has been dramatically reduced during the artificial aging at 170 oC and 190 oC . Meanwhile, that the avarage porosity decreased 8-9 % to 2-3 % is very remarkable to me.
I would like to find out whether it is possible as well as the composites that consist components which have very different coefficients of thermal expansion from each other.
Kind Regards.
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