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Microstructure and Properties of Biomaterials Mg-Zn-Ca Alloy by High Pressure Torsion

Author: RenZhenWei
Tutor: GuanShaoKang
School: Zhengzhou University
Course: Materials Processing Engineering
Keywords: High pressure torsion (HPT) Mg-Zn-Ca alloy Microstructure Corrosion Microhardness
CLC: TG146.22
Type: Master's thesis
Year: 2010
Downloads: 171
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Abstract


Magnesium and magnesium alloys used in biodegradable material, there are two problems: rapid degradation rate and mechanical properties can not meet the medical requirements. High pressure torsion (High pressure torsion, HPT) grain refinement effect is significant, so as to improve the mechanical properties and corrosion resistance, to become the most one of the ways to solve the biological applications of magnesium alloy. By OM, SEM, XRD, TEM and SAED analysis of high pressure torsion deformation of Mg-Zn-Ca alloy microstructure. By immersion test and electrochemical test analysis before and after deformation magnesium alloy corrosion degradation behavior in simulated body fluid. The results show that: the cast magnesium alloy consists of α-Mg and MgZn phase composition, grain size of ~ 130μm, and the second phase is mainly dispersed at the grain boundaries. The HPT state magnesium alloy by α-Mg and Mg4Zn7. Strain induced phase transition. The second phase particles are mainly distributed in the interior of the grains, the size in the range of 10 ~ 75nm. The central area of ??the sample grain size ~ 1.2μm, the grain boundary is more pure; grain size of the edge region ~~ 1μm ultrafine grain structure, grain boundary non-equilibrium grain boundary. With increased from the center of the sample from the position, the the sample aiming strain value increased, up to 6.5. Unlike the strain distribution, high pressure torsion the deformation hardness value is more evenly distributed along the diameter direction the average (115Hv0.1) than cast alloy (39Hv0.1) increased nearly three times. Explore the deformation mechanisms that occur in the process of high pressure torsion dynamic recrystallization led magnesium alloy ultrafine grain structure. The soaking experiments show that, with the immersion time, the pH of the solution was increased, but slower the HPT-state growth of magnesium alloy. Cast magnesium alloy surface there are a large number of corrosion pits, corrosion pits there are a large number of Ca-P salt deposition, forming the OCP phase and (Ca, Mg) CO3 phase. Mg (OH) 2 film is formed while in HPT-state specimen, with the immersion time, the Mg (OH) 2 membrane rupture becomes (Ca, Mg) CO3 deposition, and there is a small amount of calcium and phosphorus salt deposition, but did not appear corrosion pits. The polarization curves show that the the the HPT state magnesium alloy current density than small cast alloy as-cast alloy nearly 100 times, nearly two orders of magnitude, polarization resistance and corrosion in simulated body fluid slowed, corrosion resistance increases . AC impedance spectroscopy cast magnesium alloy composed by two capacitive loop and an inductive loop. HPT state has only one capacitive arc. Establishment of an equivalent circuit, the HPT-state transfer resistance of magnesium alloy the cast alloy majority middleweight. High pressure torsion deformation of the material before and after corrosion mechanism: more cast magnesium alloy Jinzhong Jing boundary defects, and the second phase is mainly distributed in the grain boundary, and to promote the emergence of corrosion pits galvanic corrosion. HPT state magnesium alloy, the grain boundary is more pure, nano-particles of the second phase is distributed in the interior of the grains, the corrosion products are relatively dense matrix phase formed by etching, to prevent corrosion in the second phase expansion of the grain interior.

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CLC: > Industrial Technology > Metallurgy and Metal Craft > Metallurgy and Heat Treatment > Metallic materials > Non - ferrous metals and their alloys > Light non-ferrous metals and their alloys > Magnesium
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