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Ultra High Temperature Nb-Ti-Si Base Alloy Organization and Compression Performance of Research

Author: ZhengPeng
Tutor: ShuiLi
School: Shenyang University of Technology
Course: Materials Science
Keywords: Nb-Ti-Si alloy Microstructure Compression performance Fracture mechanism
CLC: TG146
Type: Master's thesis
Year: 2011
Downloads: 82
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Abstract


The microstructure and fracture toughness properties of the Nb-Ti-Si based superalloy were investigated by means of heat-treatment, energy spectrum and XRD analysis. The conclusions can be drawn as following:The examination results of X-ray diffraction and energy spectrum showed that the main phase for as-cast alloy consist of（Nb、Ti）ss and Nb5Si3, and（Nb、Ti）ss crystallology phase as alloy matrix has excellent toughness. Silicide phase Nb5Si3 is mostly with mesh from enriched in eutectic tissues. The evaluation of Nb5Si3 after heat- treatment showed that it changed morphology from initial reticular to lamellar, massive. There are TiC phase precipitate during heat-treatment. The morphologies of TiC varied with variously heat-treatment time under same temperature（1150℃）, such as the changing from small granular to bigger block. This indicated that small particles of TiC linked and coarsens under the condition of extending holding time. It is advantageous to improving alloy strength and ability of plastic deformation.The compression test result show that the plastic deformation ability is not sensitive for the varying of compressed strain rate. Comparing room temperature compression stress-strain curves for the samples after different heat-treatment, it can be seen for 1050℃/24h+1150℃/24h heat-treatment process is optimal. Compression test stress-strain curves showed that at high temperature primary shapes was similar. After compression stress reached a peak, curves showed different degrees of wobble. The phenomenon suggested that the crack begun to initiate in alloy inner defect and occurred stress flow stress softening phenomenon. It can be caused by unstable microstructure under high temperature.After room temperature compression ruptured macroscopic fracture observation showed that there are plenty of secondary crack in inner alloy resulting in compressing stress influence. At the primary stage inner secondary crack linked each other and formed master crack pathway, and master crack propagated along the angle 45°or parallel with stress axis direction and extended until fracture at final stage after plastic deformation. Microfracture observation showed room temperature compression fracture mechanism exhibited the combination characteristics of cleavage and ductile fracture manners. Under the high temperature compression deformation grain shape change and became longer length along with compression stress direction. Because niobium base as matrix tenacity phase presented, observed a large number of half circle shape crack.high temperature compression fracture of the alloy was more sensitive for internal stomatal defects and the porosity presence become the main reasons for high temperature compression fracture.

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