The materials processing research base of the Materials Processing Center

An annual report of the research activities of the Materials Processing Center of the Massachusetts Institute of Technology is given. Research on dielectrophoresis in the microgravity environment, phase separation kinetics in immiscible liquids, transport properties of droplet clusters in gravity-free fields, probes and monitors for the study of solidification of molten semiconductors, fluid mechanics and mass transfer in melt crystal growth, and heat flow control and segregation in directional solidification are discussed

Fatigue threshold Kmax,th affected by static threshold K1scc

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Fracture toughnes K1c affecting static threshold K1scc

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Molecular Physics

Contains reports on two research projects.F.L. Freidman ChairNational Institutes of Health (Grant AM 25535)Whitaker FoundationInternational Business Machines, Inc

Molecule Microscopy

Contains research objectives and reports on four research projects.National Institutes of Health (Grant AM-25535)Whitaker FoundationFrancis L. Friedman Chai

Evolution of Microstructure and Texture during Warm Rolling Of a Duplex Steel

The effect of warm rolling on the evolution of microstructure and texture in a duplex stainless steel (DSS) was investigated. For this purpose, a DSS steel was warm rolled up to 90 pct reduction in thickness at 498 K, 698 K, and 898 K (225 °C, 425 °C, and 625 °C). The microstructure with an alternate arrangement of deformed ferrite and austenite bands was observed after warm rolling; however, the microstructure after 90 pct warm rolling at 498 K and 898 K (225 °C and 625 °C) was more lamellar and uniform as compared to the rather fragmented and inhomogeneous structure observed after 90 pct warm rolling at 698 K (425 °C). The texture of ferrite in warm-rolled DSS was characterized by the presence of the RD (〈011〉//RD) and ND (〈111〉//ND) fibers. However, the texture of ferrite in DSS warm rolled at 698 K (425 °C) was distinctly different having much higher fraction of the RD-fiber components than that of the ND-fiber components. The texture and microstructural differences in ferrite in DSS warm rolled at different temperatures could be explained by the interaction of carbon atoms with dislocations. In contrast, the austenite in DSS warm rolled at different temperatures consistently showed pure metal- or copper-type deformation texture which was attributed to the increase in stacking fault energy at the warm-rolling temperatures. It was concluded that the evolution of microstructure and texture of the two constituent phases in DSS was greatly affected by the temperature of warm rolling, but not significantly by the presence of the other phas

Stress corrosion cracking: Characteristics, Mechanisms and Experimental study

Stress corrosion cracking (SCC) is a phenomenon in which the cracking of a metal alloy usually results from the combined action of a corrodent and tensile stress. Stresses that cause cracking can be residual or may be applied during service. A degree of mechanistic understanding of SCC will enable most metallic engineering materials to operate safely though stress corrosion cracking failures still continue to occur unexpectedly in industry. In this paper, the characteristics, mechanisms and methods of SCC prevention are reviewed. The results of experimental studies on alpha brass are also reported of which the failure mode conformed with the film-rupture and anodic dissolution mechanism

The effect of post-cure annealing on the protective properties of polyimides on chromium substrates

The effect of post-cure annealing on the protective properties of thin (2.6-2.8 μm) polyimide films on chromium metallic substrates was investigated in aerated neutral 0.05, 0.5, and 5 M aqueous NaCl solutions at ambient temperature (≈20°C). The study was carried out using the technique of electrochemical impedance spectroscopy to monitor film degradation as a function of immersion time in the test solutions. Results obtained indicate that when exposed to aqueous NaCl solutions for extended periods, a majority of the nonannealed coated substrates failed; however, the performance of the annealed samples was significantly better. At face value, these results suggested improved protective properties of the polyimide due to annealing. However, a more in-depth analysis of the data revealed that post-cure annealing leads to the development of a thicker oxide on the chromium substrate. The change in the oxide occurring during the post-cure annealing treatment contributes to the improved corrosion resistance of the polyimide/Cr system