Lab #2 - Microstructural Examination of Alloys By Group 2...

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Microstructural Examination of Alloys By: Group 2 Brian Donovan Claire Schiff Alan Masand Evan Sprenger Joshua Gomberg October 23, 2006 Lab section 1
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Introduction Microstructure, the structural features of an alloy that are subject under a microscope, is integral to its mechanical properties. Some examples of this include strain and phase structure. This lab examined the microstructures of two families of alloys: steel and an aluminum-copper alloy. While steel is one of the most principle structural materials, aluminum/copper alloys are also important primarily because of their low density and specific strength. They are especially useful in the aeronautical field where these properties are crucial. The goal of this lab was to discover the effects of composition and processing techniques in terms of the microstructure. Procedure In this lab the samples that were used were of two types of metal alloys. There were three samples of each and they were all small sections of the metals that were set in discs so that they could be handled without damaging them. The small rectangle sections of the cut-out metals were polished and etched so that the grain boundaries and other microstructures would be visible under an optical microscope. The samples were then placed, one by one, underneath the microscope and were examined at different magnifications. The magnifications that were assumed to be most characteristic of the given sample were saved for further analysis. Results The chart attached has been filled in with the phases present and the fraction of each material. The chart below provides a brief, verbal description of each sample: Sample Code Verbal Description A The lighter areas, pearlite, are spread out across the region. B The lines leading to the dark regions are cementite, surrounded by the lighter, smoother ferrite. M Small alternating layers of cementite and ferrite. 1 Layers that indicate a phase transition from liquid to solid 3 Primary regions of θ with borders of α 4 Black markings indicating damaged sample with a layer indicating a phase transition
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Discussion 1. Sample A: This specimen was predicted to have one equilibrium phase at the higher temperature and two equilibrium phases at the lower temperature. At 900˚C, the region is mostly brown; indicating the austenite predominantly present while at 400˚C, the image taken is filled with alternating layers of light and dark brown. This indicates the ferrite and cementite present in the sample. This is apparent because this specimen was slow- cooled to room temperature, passing through these various phases. Basically, this means that the specimen was slow cooled enough for these two phases to form. There are distinct lines of the grain boundaries arranged in a random fashion. 2. Sample B: In this particular sample of steel it was predicted that there would be two
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Lab #2 - Microstructural Examination of Alloys By Group 2...

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