Metallurgical and Materials Engineering- Conference Papers

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    Open Access
    Heat Input Dependence of Weld HAZ Cracking in Aerospace Superalloy Haynes 282
    (The Canadian Society for Mechanical Engineering International Congress, 2012) Osoba, L.O.; Gao, Z.; Ojo, O.A.
    A study of weld heat affected zone (HAZ) cracking and its dependence on heat input during laser beam welding of a newly developed γ’ precipitation strengthened nickel-base superalloy Haynes 282 (HY 282) was carried out. Careful and detailed microstructural study of the nature of HAZ cracking in the alloy showed that the cracking is attributable to degradation of hot ductility of the alloy due to formation of liquid film along grain boundaries. An increase in the magnitude of laser heat input resulted in a considerable reduction in the HAZ cracking. The cracking variation with heat input is discussed in relation to the time that the subsolidus HAZ region spent at peak temperatures. The behavior is also discussed with the results of numerical simulation, which show that reduction in the magnitude of thermally induced strain rate gradient may contribute to reduced HAZ cracking that occurred with an increase in heat input.
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    Open Access
    Effect of Process Optimization Parameters and Hot Isostatic Pressing on Microstructure and Hardness of Additively Manufacture Co-Cr Aerospace Alloy
    (Canadian Welding Conference, 2018) Osoba, L.O.; Kozub, J.; Klassen, I.; Petrak, M.; Ojo, O.A.
    In the current study, the effect of carefully designed Powder Bed Fusion (PBF) laser parameters on the microstructure and hardness of Co-Cr alloy straight, thin-wall additively manufactured test coupons that are as-built or have undergone Hot Isostatic Pressing (HIP) was investigated. Commercially, it was important to evaluate the relationship between energy density (ED) input (laser power, scan speed) and the microstructure developed in the Co-Cr alloy coupons for an aerospace application. Both the high ED and low ED input processing laser parameters induce a higher percent (%) volume of defects in the as-built coupons when compared to the recommended OEM’s benchmark parameters. However, after HIP, the % volume fraction of defects reduces significantly, and the microstructure is homogenized. Furthermore, the hardness value (strength) of the test coupons manufactured using the recommended OEM’s laser parameters is comparable to those obtained in the low ED input test coupons after HIP; which could be utilized to enhance productivity. In addition, the surface roughness of the low ED input parameter coupons after HIP is similar to the coupons produced using the OEM’s laser parameters assessed with light optical magnification image evaluation. HIP can be an excellent post-processing method to reduce internal Co-Cr defects for a given range of laser energy densities in metal additive manufacturing at increased build speeds.
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    Open Access
    Thermo-mechanical properties of unsaturated polyester reinforced with coconut and snail shells
    (International Journal of Composite Materials, 2015) Adeosun, S.O.; Akpan, E.I.; Akanegbu, H. A.
    This study investigates the effects of coconut shell (CS) and snail shell (SS) volume fractions on the thermal and mechanical properties of Unsaturated Polyester Resin (UPR) composite. Varying percentages of the fillers were used as reinforcement in the unsaturated polyester resin to form composites and mechanical, thermal, flexural and morphological characteristics were examined. Results show that tensile strength, elongation at break, flexural strength, and hardness of the composite increase as filler concentration increases. Maximum tensile elongation of composites is found to possess 375 % improvement over virgin UPR while the micro-hardness a 125% improvement over virgin UPR. The maximum tensile strength of the composite is also a 140 % improvement over that of virgin UPR. However, impact strength of the composite decreases with increase in filler concentration. FTIR spectra of UPR composites show that, at 30 vol. % filler content there is good and effective interfacial interaction between UPR matrix and the fillers. The thermal properties from DTA measurement show that the glass transition temperature, Tg and Tm of the composites, at 5, 20 and 50 vol. % reinforcement contents, are lower and higher respectively to the cured-virgin UPR matrix. The morphology of fillers dispersion into the polymer matrix observed using the scanning electron microscopy (SEM) indicates homogeneous dispersion in the UPR matrix with strong interfacial adhesion between the fillers and UPR matrix. These results in enhance mechanical properties.