Effect of the Cooling Rate on the Microstructure and Properties of C92900 Bronzeстатья
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Дата последнего поиска статьи во внешних источниках: 4 августа 2021 г.
Аннотация:In mechanical engineering, antifriction tin bronzes are used for manufacturing friction parts, forexample, C92900 bronze, which is used on aircraft braking systems. One way to improve the properties ofleaded tin bronzes is to increase the cooling rate during solidification. In this work, the effect of the coolingrate and the changes in the content of alloying elements within the limits established by industry standards onthe properties of C92900 bronze are investigated. In order to provide different cooling rates, the alloys arecasted into molds made of resin-bonded sand, steel, and graphite, for which the cooling rates were 0.4, 5, and14.6°C/s. The influence of the cooling rate and the composition of bronze on the freezing range, macrostructure,microstructure, thermal conductivity, hardness, tensile properties, and wear rate are investigated. Bymeans of differential thermal analysis, it is shown that upper limit alloying of C92900 bronze leads to adecrease in the solidus temperature by 40°C, which should be considered during deformation processing andheat treatment. An increase in the cooling rate during the solidification of C92900 bronze ingots provides asignificant grain refinement and change in the amount, size, and morphology of the phases. For example, inthe case of metallic and graphite mold casting, the size of the lead particles decreases and its circularityincreases. The change in the Sn content within the range established by industrial standard has a significanteffect on the intermetallic γ-(Cu, Ni)3Sn phase fraction. The increase in the cooling rate has no significanteffect on the thermal conductivity of C92900 bronze, but it leads to an increase in hardness by 30 HB. It alsoimproves the yield strength and ultimate tensile strength of the bronze. The wear test, carried out in accordancewith the shaft–partial insert scheme in a kerosene medium using a steel counterbody, shows that anincrease in the cooling rate during solidification leads to an increase in the wear rate of bronze from ~0.4 ×10–8 to ~1.2 × 10–8. The change in the bronze composition within the industrial standard range has practicallyno effect on the wear rate, but leads to a slight increase in the coefficient of friction.