An Investigation of Fracture Origins in Heat-Treated Ti49Al47Cr2Nb2 Powder Compacts

Olivier Berteaux; Roger Valle; Monique Raffestin; Marc Thomas; G. Henaff

doi:10.4028/www.scientific.net/MSF.638-642.1422

Paper Titles

Second Phase Precipitation within a Laves Phase in the Ir-Y Binary System
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The Effects of Heat Treatments and Tungsten Additions on Microstructures and Tensile Properties of Powder Metallurgy Ti-48Al-2Nb-2Cr
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Crystal Growth and Characterization of FeAs-Based Superconductors
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Study of Refined Microstructures after Two-Step Heat Treatments by Means of EBSD Technique on γ-TiAl Alloys
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An Investigation of Fracture Origins in Heat-Treated Ti₄₉Al₄₇Cr₂Nb₂ Powder Compacts
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Fe-6.5wt.%Si High Silicon Steel Sheets Produced by Cold Rolling
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Growth of Crystals and Formation of C40/C11_b Lamellar Structure in (Mo_0.85Nb_0.15)Si₂
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Effect of Trace Boron Addition on the Microstructure and Tensile Elongation of Ti₂AlNb-Based Orthorhombic Titanium Alloys
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DSC and Microstructural Investigations of the Elektron 21 Magnesium Alloy
p.1447

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An Investigation of Fracture Origins in Heat-Treated Ti₄₉Al₄₇Cr₂Nb₂ Powder Compacts

Abstract:

The fatigue behaviour of a powder-metallurgy (PM) + heat-treated Ti49Al47Cr2Nb2 alloy is investigated using detailed SEM characterization. Based on the results of comparative static and cyclic loadings at RT, the fracture origins for the different test specimens is investigated. Conventional fractographic analyses revealed that internal structural defects inherent to powder metallurgy such as compaction defects, porosities and non-metallic inclusions can promote crack initiation. However, the fracture surface of test specimens is markedly affected by the microstructure, which is indicative of the microstructure dependence on crack initiation and propagation. In sub-transus heat treatment conditions, the detrimental effect of structural defects is illustrated by clear crack initiation sites onto the fracture surfaces. In super-transus conditions, crack propagation from defects can be blunted due to crack deflection, branching through lamellar interfaces, thus leading to lower defect sensitivity. Correlation of the results of these microfractographic examinations with the stress-strain curves corresponding to the various specimens allows identifying the role of such structural defects on the static and cyclic deformation behaviours. Finally, implications of such dependencies will be assessed relative to the requirements for aerospace gas turbine applications.