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Structuresand Propertiesand Quality of Tialalloy Billets Directionally Solidified with Cold Crucible

Author: GuShiXin
Tutor: DingHongSheng
School: Harbin Institute of Technology
Course: Materials Processing Engineering
Keywords: directional solidification electromagnetism cold crucible TiAl-based alloys rare-earth lamellar structure
CLC: TG111.4
Type: Master's thesis
Year: 2010
Downloads: 64
Quote: 1
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Abstract


In this paper, Directional solidification experiments of selected alloys (Ti-46Al-0.5W-0.5Si-0.3Y, Ti-46Al-0.5W-0.5Si-0.2Gd, Ti-46Al-0.5W-0.5Si-0.5Y and Ti-46Al-0.5W-0.5Si-0.165Gd) are carried out with 3:1 near-rectangular cold crucible in different technical parameters. The surface quality, macro- and microstructures of these slab ingots are observed and analyzed, and the mechanical properties are tested.The observation showed that there are still pouring slab surface insufficient adhesion ripples and pits and other defects, the factors affecting the surface quality are analyzed. And a detailed description of the macro-organization of regional distribution.Observation and analysis are made to detect in which way the pull speed and the power aaffect the initial transition length, grain number and steady growth direction of columnar grain growth zone, and the number of grains. The influences of heating power and withdraw rate to the solidification interface are observed.The microstructures of the region near the solidification interface and steady directional solidification Ti-46Al-0.5W-0.5Si-0.3Y, Ti-46Al-0.5W-0.5Si-0.2Gd, Ti-46Al-0.5W-0.5Si-0.5Y and Ti-46Al-0.5W-0.5Si-0.165Gd slab ingots are observed and analyzed. The region near the solidification interface is partitioned off to three distinct areas , which are areas of solid phase region, last solidified liquid and triangle with bend side . the crystal morphology of last solidified liquid and triangle with bend side are Afterbirth-like crystal which progressively develops to dendrite and dendrite , respectively. The primary dendrite dendritic shows a four-axis symmetry pattern, the rest are six-axis symmetrical, indicating the primary phase are theβphase, and there is a small amount ofαphase. The dendrite growth is not completely perpendicular to the interface.There is a rich diversity of morphology in directional solidification TiAl, resulting in differences in performance of the local area.Finally, Using micro indentation to test directional solidification lamellar TiAl alloy fracture toughness, due to directional solidification of anisotropic materials has led to the fracture toughness anisotropy. . Fracture toughness value at a medium level. High-temperature tensile test at 800℃are pull speed 1.0mm/min of Ti-46Al-0.5W-0.5Si-0.3Y tensile strength of directionally solidified slab can be achieved 443MPa, extension rate reaches 1.66%. Lamellar solidification is mainly along the fracture cleavage layers, wear layers fracture and transgranular fracture, the blank with Y sample plastic is better, dimple rupture to become dominant, the fracture showed a strong plastic deformation.

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CLC: > Industrial Technology > Metallurgy and Metal Craft > Metallurgy and Heat Treatment > Metallurgy ( Physical Metallurgy ) > Physics of metals > The liquid structure of the metal and solidification theory
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