Preparation Process On The Aircraft Brake Material Microstructure And Properties Of Iron-based Powder Metallurgy

Systematical studies on the fabrication process of given branded P/M aeronautic friction materials based on iron were carried out. The influences of basic process parameters such as pressing pressure, sintering temperature, sintering pressure and cooling rate on the microstructures, densification and mechanical properties, as well as the friction and abrasion behaviors of the friction materials were analyzed respectively.(1) As the pressing pressure was increased, facilitated rearrangement of Fe powders and ambulation accelerate, the Fe powders of preferable-plasticity, which, generated plastic deformation in locality space, the Fe powders of low-plasticity and hard particles were fragmented gradually, the contact areas of the components increased, and the size and number of pores decreased accordingly. As a result, the hardness and density of friction materials increased effectively, and the wear-resistance was improved obviously.(2) When the sintering temperature was increased from 900 to 930℃, the plasticity of Fe powders and Cu powders were more increased, plastic deformation was much more facility, facilitated densification, heteromorphic transition occurred resulting in the slight increase of the self-diffusion coefficient of Fe atoms and the decrease of the diffusion coefficient of C atoms within Fe phase. Under these two competing actions, the density of friction materials increased slowly, and soft-ductile ferrite was dominant phase, as a result, the wear-resistance was poor; when the sintering temperature was further increased from 930 to 1020℃, the plasticity of Fe powders and Cu powders were much more increased, the diffusion coefficients of both Fe and C atoms increased markedly, the density of friction materials increased rapidly, the fraction and distribution of pearlite phase enhanced, consequently the wear-resistance was improved obviously.(3) When sintering pressure was increased from 1.6 to 2.8MPa, the deformation ratio of the greens increased, the pores within the material and in the grain boundary reduced correspondingly, so the density and hardness, as well as the wear-resistance of friction material was improved markedly; When sintering pressure was further increased from 2.8 to 3.2MPa, there was no obvious change of the hardness, density and wear-resistance, which means that it shows no longer effective improvement on the materials properties by continuing to increase the sintering pressure.(4) When the flowing rate of cooling water was increased from 0 to 0.04m~3/s, the cooling rate of sintering green first went up and then went down, which is related to the structure of the sintering furnace. The larger the flowing rate, the more dramatic the water flashed up on the interface between the inner cover and cooling water, as a result, the cooling rate fell down; when the flowing rate was 0.027m~3/s, the cooling rate of sintering green rose to the maximum, flaky and granular pearlite was dominant phase in the friction materials, and the space between the flaky pearlite was the smallest, so the hardness and wear-resistance was improved.