There are always a certain amount of metal oxides in the original metal powder. Due to the sintering in reducing atmosphere, metal oxides will be restored during the sintering process, resulting in gas reduction substances.
During the sintering process, there are gas precipitations. The greater the compaction pressure is, the greater the number of pores in the metal powder particles will be. The gaseous materials are also more difficult to discharge, resulting in the improvement of pores index in matrix as the compacting pressure increases.
Compacting pressure on the density of the material for the green density, sintered density with the compacting pressure change curve. By the pressure the green density curve can be seen that the compaction pressure increased from 200MPa to 400MPa, the green density increased considerably, and this is because the lower compaction pressure conditions, the gap between the particles and particles larger contact surface smaller the arch effect, a slight increase in pressure can make the arch was a certain degree of damage, the density of the compacts followed by a significant increase; compacting pressure is greater than 400MPa, the green density growth rate is relatively flat, which is when the suppression of Once the pressure is greater than the copper matrix yield limit (about 350400MPa), the metal particles occurs to a significant plastic deformation, a significant increase in contact area between the particles, while the role of work hardening, compression resistance increases, the degree of densification further increase the pressure required is greatly increased.
Compacting pressure on the compressive properties of the sintered body with the compacting pressure curve for the compressive strength of the sintered body. With increasing compaction pressure, the compressive strength of the materials first increased and then decreased and finally increased trend. Copper-based brake friction materials in the case of the same component, the defects in the matrix affect the compressive strength of the key. Relative to the low pressure system pressure (200MPa), moderate compaction pressure (400MPa) make the particles contact closely and more open pores in the matrix, both to shorten the diffusion distance between the particles, it also enabled the sintering process due to the reaction gas can be smoothly discharged, and then get fewer defects of the sintered body, and is conducive to the improvement of the compressive strength. Higher compacting pressure (600MPa), the green body particles in closer contact and more conducive to sintering, but the more the pores in the matrix, the compressive properties of the sintered body has declined. Further improve the compaction pressure (700MPa) metal particles to the overall incidence of significant plastic deformation, sintering, recrystallization nucleation greatly increase the number of help to the formation of finer grain organization, which largely make up the pores caused matrix strength is weakened, so the compressive strength of materials has been improved.
The compacting pressure on the friction and wear resistance of sintered materials wear. 0.220.23 changes between the friction coefficient of sintered samples compacting pressure has little effect on the friction performance. The wear of the sintered first drop up again and down trends. Friction in terms of performance, due to little change of the friction and wear adjust group composition and organization, so the friction coefficient of variation is not very obvious.
For copper powder (FCu) metallurgy aircraft break materials, compaction pressure affects the brake performance of sintered materials mainly through compacts performance. Its impact is as follows: compacting pressure increases from 200MPa to 400MPa. The matrix grain size becomes smaller. The grain size is trend to be uniform. When the compaction pressure reaches 700MPa, grain size is smallest and most uniform. At the same time, with the compaction pressure increases, the pores in the matrix also increased. With the compaction pressure increases, the compressive strength and wear resistance of the copper-based powder metallurgy brake materials are firstly increased and then decreased again. But changes in the friction coefficient are not very obvious.Source:http://www.mhcmp.com
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