Abstract— At the end of the 60’s with the beginning of the space missions it was observed, that once the airships were sent into space and when they entered at the atmosphere, they presented an increase at the wear resistance on the structure of the space shuttles. It was concluded that the low temperature would have influenced in such changes. Over the year’s liquid nitrogen, gaseous nitrogen, helium and dry ice were used on metals and tool that were submitted to high wear and fatigue periods in order to increase the useful life of the material, this procedure was called cryogenic treatment. Once it was identified that low temperatures generated improvements to certain materials as steels, aluminum and some a ceramic materials and the problem emerged to establish the effect of this phenomena in materials as brass and bronze, so it was take the decision to determine the influence of the low temperatures in this materials. What microstructural changes and mechanical behavior could the cooper alloys suffer as the brass 60-40 and bronze SAE 64? Taking into account the time spent in the steel a pilot test was done to evaluate the effect in the variation of grain size and micro hardness to the state of delivering of material through ANNOVA method determined the amount of tubes to study per each material and time. In this case, the effect in the microstructure is evaluated by metallographic and the effect in the mechanic behavior will be evaluated with micro hardness and hardness testing. Were spent four brass tubes were used per each time of exposition where 24, 48, 72 and 120 hours respectively and bronze’s tubes used were there per each time of exposition likewise to brass. Finally it was observed a microstructural change and variations of mechanical properties where it is possible to conclude that to longer exposure of cryogenic treatment the resistance of the material increases. With an improvement in it is microstructure showing a grain with major dimensional stability.
Keywords— space missions, microstructural changes, ANNOVA, SAE 64.
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