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    Effect of heat treatments on the microhardness and tensile strength of Al-0.25 wt.% Zr alloy
    (ELSEVIER SCIENCE SA, 2015) Cadirli, Emin; Tecer, Hicran; Sahin, Mevlut; Yilmaz, Elif; Kirindi, Talip; Gunduz, Mehmet
    In the present work, the effect of heat treatments on the microhardness and tensile properties of the Al-0.25 Zr (wt.%) alloy have been investigated. The Al-0.25 Zr (wt.%) alloy was melted in a vacuum furnace, and the molten alloy was poured into crucibles held in a hot filing furnace. Then, the samples were directionally solidified from bottom to top and aged isothermally and isochronally in a muffle furnace. Aging was performed in two ways: using a wide range of temperatures (350-600 degrees C) with a constant aging time (100 h) and a wide range of aging times (3-240 h) with a constant temperature (400 degrees C). The dependence of the microhardness (HV) and ultimate tensile strength (sigma(UTS)) on the aging temperatures and aging times was determined. According to the experimental results, the HV and sigma(UTS) values of the aged samples increase at a certain aging temperature and aging time values, reaching peak values at specific temperatures and aging times. The microhardness and ultimate tensile strength decreased with further increase of aging temperatures and aging times. The microscopic fracture surfaces of the aged samples under different aging conditions were observed using scanning electron microscopy. Fractographic analysis of the tensile fracture surfaces shows that the type of fracture changed significantly from ductile to brittle depending on the aging times. Transmission electron microscopy was also used to characterize the precipitation processes in an Al-0.25 Zr (wt.%) alloy aged at 400 degrees C for 120 h. (C) 2015 Elsevier B. V. All rights reserved.
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    Microstructural Evolution and Mechanical Properties in Directionally Solidified Sn-10.2 Sb Peritectic Alloy at a Constant Temperature Gradient
    (UNIV FED SAO CARLOS, DEPT ENGENHARIA MATERIALS, 2016) Yilmaz, Elif; Cadirli, Emin; Acer, Emine; Gunduz, Mehmet
    The Sn-10.2 Sb (mass fraction) peritectic alloy was prepared using a vacuum melting furnace and a hot filling furnace. The samples were directionally solidified upwards at steady state conditions with a constant temperature gradient (G = 4.5 +/- 0.2 K. mm(-1)) under different growth velocities (V = 13.3-266.7 mu m. s(-1)) in a Bridgman-type directional solidification apparatus. The effects of the growth velocity (V) on the dendritic spacings were investigated. Primary dendrite arm spacing (PDAS) of a phase in directionally solidified Sn-10.2 Sb peritectic alloy was measured on the longitudinal and transverse sections of 4 mm diameter cylindrical samples. Secondary dendrite arm spacing (SDAS) was measured on the longitudinal section. The experimental results show that the measured PDAS (lambda(IL),lambda(IT)) and SDAS (lambda(2)) decrease with increasing growth velocity. The dependence of PDAS, SDAS, microhardness (HV) and compressive strength (sigma(c)) on the growth velocity were determined by using a linear regression analysis. The experimental results were compared with the previous experimental results and the results of the experimental models.