Grain Boundary Embrittlement and De-Embrittlement in Age Hardenable Iron Alloys

2012 ◽  
Vol 710 ◽  
pp. 11-18
Author(s):  
Yoon Uk Heo ◽  
Hu Chul Lee
Keyword(s):  
Grain Boundary ◽  
Critical Role ◽  
Aging Treatment ◽  
Iron Alloys ◽  
Age Hardening ◽  
Dislocation Glide ◽  
Ti Alloys ◽  
Grain Boundary Embrittlement ◽  
Boundary Embrittlement ◽  
Boundary Strength

Grain boundary embrittlement and de-embrittlement observed in age hardening iron alloys were reviewed. Fe-Mn-Ni and Fe-Ni-Ti alloys show excellent hardening response during aging treatment. However these alloys all suffer grain boundary embrittlemnt and show no tensile ductility even after very short aging treatment. Precipitation of intermetallic phases, θ-MnNi in Fe-Mn-Ni alloys and η-Ni3Ti in Fe-Ni-Ti alloys, at grain or lath boundaries was suggested as the reason for the weakening of grain boundary strength. Grain boundary strength recovered when these precipitates transform to austenite after extended aging. Dislocation glide or dislocation climb did critical role in conversion of these grain boundary precipitates to austenite.

Grain Boundary Precipitation and Tensile Ductility of Fe-Mn-Ni Alloys

2007 ◽  
Vol 539-543 ◽  
pp. 1595-1600 ◽  
Author(s):  
Yoon Uk Heo ◽  
Seung Ho Mun ◽  
Hu Chul Lee
Keyword(s):  
Grain Boundary ◽  
Tensile Ductility ◽  
Aging Treatment ◽  
Boundary Precipitate ◽  
Intermetallic Particles ◽  
Ni Alloy ◽  
Alloy Addition ◽  
Stable Austenite ◽  
Grain Boundary Embrittlement ◽  
Boundary Embrittlement

The mechanism of grain boundary embrittlement and the improvement of the tensile ductility afforded by alloy addition or heat treatment was investigated in an Fe-Mn-Ni alloy. The precipitation of θ-MnNi intermetallic particles was observed at the prior austenite or interlath boundaries during the aging treatment and this was believed to be responsible for the grain boundary embrittlement of these alloys. After prolonged aging or aging at higher temperatures above 520°C, these metastable intermetallic particles were transformed into the thermodynamically stable austenite phase, thereby leading to the recovery of the grain boundary strength. The addition of Mo caused the grain boundary precipitate to be changed to austenite and resulted in a significant improvement in the tensile ductility after aging.

The Grain Boundary Embrittlement and De-Embrittlement Mechanism in Age Hardenable Fe-Ni-Ti Steels

2006 ◽  
Vol 118 ◽  
pp. 469-474 ◽  
Author(s):  
Min Saeng Kim ◽  
Yoon Uk Heo ◽  
Hu Chul Lee
Keyword(s):  
Electron Microscopy ◽  
Fracture Surface ◽  
Grain Boundary ◽  
Vickers Hardness ◽  
Prior Austenite ◽  
Aging Treatment ◽  
Austenite Grain ◽  
Grain Boundary Embrittlement ◽  
Prior Austenite Grain ◽  
Boundary Embrittlement

The strengthening and grain boundary embrittlement in an age hardenable Fe-20.4Ni-2.8Ti ternary alloy were investigated. The Vickers hardness and tensile properties were evaluated using a Vickers hardness and tensile tester and the precipitation behavior during aging treatment was observed by transmission electron microscopy (TEM). The fracture surface was observed using low voltage field emission scanning electron microscopy (FE-SEM). The alloy showed typical aging hardening curves with a single aging peak near 640 HV, but was found to undergo severe grain boundary embrittlement from the initial stages of aging treatment. Many fine particles were observed at the grain boundary fracture surface. These particles were identified as η-Ni3Ti precipitates nucleated at the prior austenite grain boundaries. When the aging time was extended, austenite nucleated at the interface of the matrix and η-Ni3Ti precipitate. With the formation of the austenite, the tensile ductility was recovered. It was concluded that the precipitation of the η-Ni3Ti intermetallic particles at the prior austenite grain boundaries and formation of the austenite are the main causes of embrittlement and subsequent de-embrittlement in aging of this alloy.

Morphology and atomic structure of segregated grain boundaries in Cu-Sb

1992 ◽  
Vol 50 (1) ◽  
pp. 254-255
Author(s):  
R. W. Fonda ◽  
D. E. Luzzi
Keyword(s):  
Grain Boundary ◽  
Grain Boundaries ◽  
Intergranular Fracture ◽  
Atomic Structure ◽  
Copper Alloys ◽  
Polycrystalline Materials ◽  
Grain Boundary Embrittlement ◽  
Boundary Embrittlement

The properties of polycrystalline materials are strongly dependant upon the strength of internal boundaries. Segregation of solute to the grain boundaries can adversely affect this strength. In copper alloys, segregation of either bismuth or antimony to the grain boundary will embrittle the alloy by facilitating intergranular fracture. Very small quantities of bismuth in copper have long been known to cause severe grain boundary embrittlement of the alloy. The effect of antimony is much less pronounced and is observed primarily at lower temperatures. Even though moderate amounts of antimony are fully soluble in copper, concentrations down to 0.14% can cause grain boundary embrittlement.

Grain Boundary Embrittlement of Fe Induced by P Segregation: First-Principles Tensile Tests

2011 ◽  
Vol 409 ◽  
pp. 455-460 ◽  
Author(s):  
Motohiro Yuasa ◽  
Mamoru Mabuchi
Keyword(s):  
Tensile Strength ◽  
Grain Boundary ◽  
First Principles ◽  
Tensile Tests ◽  
Bond Breaking ◽  
Charge Densities ◽  
Grain Boundary Embrittlement ◽  
Boundary Embrittlement

The GB embrittlement mechanism of Fe enhanced by P segregation has been investigated by first-principles tensile tests because a P atom is a famous GB embrittler in Fe. The first-principles tensile tests have been performed on Fe with two P-segregated GBs, where P atoms are located at the different sites, and with a nonsegregated GB. The tensile strength and the strain to failure in the P-segregated GBs were lower than those in the nonsegegated GB. The first bond breaking occurred at the Fe-P bond owing to the covalent-like characteristics, although the charge densities were high at the Fe-P bonds even just before the bond breaking. This premature bond breaking of Fe-P was independent of the location of the P atom.

Effect of solution aggressiveness on the crack - growth resistance and cracking mechanism of AA2024-T3

CORROSION ◽  
10.5006/3839 ◽  
2021 ◽  
Author(s):  
Christina Charalampidou ◽  
Christiaan Pretorius ◽  
Roelf Mostert ◽  
Nikolaos Alexopoulos
Keyword(s):  
Grain Boundary ◽  
Crack Growth ◽  
Compact Tension ◽  
Crack Growth Resistance ◽  
Corrosion Attack ◽  
Secondary Cracks ◽  
Cracking Mechanism ◽  
Grain Boundary Embrittlement ◽  
Corrosive Environments ◽  
Boundary Embrittlement

Aluminium alloy 2024-T3 was examined – using a range of microscopy techniques – at the early stages of corrosion attack to investigate the corrosion-induced cracking mechanism. Two different corrosive environments, exfoliation corrosion (EXCO) and 3.5 % wt. NaCl, were used for the exposure of tensile and pre-notched compact-tension C(T) specimens of AA2024-T3. Different embrittlement mechanisms are noticed for the two investigated corrosive environments. Significant intergranular corrosion (IGC) and grain boundary embrittlement is evident in the specimens exposed to EXCO solution, while this was not the case for the milder solution; comprising of 3.5 % wt. NaCl. With regards to the milder solution, corrosion attack is not restricted to the grain boundary, but evolves transgranularly to the neighbouring grains of the IGC attacked region and, consequently, the grain boundary strength in the direct vicinity is not notably affected. The extent of secondary cracks – after the exposure of C(T) specimens to EXCO solution and the subsequent crack-growth resistance evaluation – were found to correlate with the diameter of the plastically affected zone (≈ 3.78 ± 0.04 mm). Additionally, the depth of these cracks was found to correlate well with the thickness of the intergranular fracture surface, giving evidence that the secondary cracks form due to grain boundary embrittlement; probably attributed to hydrogen embrittlement phenomena.

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