Brittle intergranular fracture of a thread: The role of a carburizing treatment

2009 ◽  
Vol 16 (5) ◽  
pp. 1448-1453 ◽  
Author(s):  
G. Straffelini ◽  
L. Versari
Keyword(s):  
Intergranular Fracture ◽  
Brittle Intergranular Fracture

Slip, twinning, and fracture at a grain boundary in the L12 ordered structure—AΣ = 9 tilt boundary

1988 ◽  
Vol 3 (5) ◽  
pp. 848-855 ◽  
Author(s):  
M. H. Yoo ◽  
A. H. King
Keyword(s):  
Intergranular Fracture ◽  
Local Stress ◽  
Boundary Region ◽  
Anisotropic Elasticity ◽  
Tilt Boundary ◽  
Microplastic Deformation ◽  
Ordered Structure ◽  
Local Stress Concentration ◽  
Boron Segregation

The role of interaction between slip dislocations and a Σ = 9 tilt boundary in localized microplastic deformation, cleavage, or intergranular fracture in the Li2 ordered structure has been analyzed by using the anisotropic elasticity theory of dislocations and fracture. Screw superpartials cross slip easily at the boundary onto the (1$\overline 1$1) and the (001) planes at low and high temperatures, respectively. Transmission of primary slip dislocations onto the conjugate slip system occurs with a certain degree of difficulty, which is eased by localized disordering. When the transmission is impeded, cleavage fracture on the ($\overline 1$11) plane is predicted to occur, not intergranular fracture, unless a symmetric double pileup occurs simultaneously. Absorption (or emission) of superpartials occurs only when the boundary region is disordered. Slip initiation from pre-existing sources near the boundary can occur under the local stress concentration. Implications of the present result on the inherent brittleness of grain boundaries in Ni3 Al and its improvement by boron segregation are discussed.

scholarly journals Critical assessment of hydrogen effects on the slip transmission across grain boundaries in α -Fe

2016 ◽  
Vol 472 (2185) ◽  
pp. 20150617 ◽  
Author(s):  
I. Adlakha ◽  
K. N. Solanki
Keyword(s):  
Grain Boundaries ◽  
Intergranular Fracture ◽  
Energy Barrier ◽  
Strain Energy ◽  
Strengthening Mechanism ◽  
Dislocation Motion ◽  
Dislocation Network ◽  
Mode Transition ◽  
Slip Transmission

Grain boundaries (GBs) play a fundamental role in the strengthening mechanism of crystalline structures by acting as an impediment to dislocation motion. However, the presence of an aggressive environment such as hydrogen increases the susceptibility to intergranular fracture. Further, there is a lack of systematic investigations exploring the role of hydrogen on the dislocation–grain-boundary (DGB) interactions. Thus, in this work, the effect of hydrogen on the interactions between a screw dislocation and 〈111〉 tilt GBs in α -Fe were examined. Our simulations reveal that the outcome of the DGB interaction strongly depends on the underlying GB dislocation network. Further, there exists a strong correlation between the GB energy and the energy barrier for slip transmission. In other words, GBs with lower interfacial energy demonstrate a higher barrier for slip transmission. The introduction of hydrogen along the GB causes the energy barrier for slip transmission to increase consistently for all of the GBs examined. The energy balance for a crack initiation in the presence of hydrogen was examined with the help of our observations and previous findings. It was found that the presence of hydrogen increases the strain energy stored within the GB which could lead to a transgranular-to-intergranular fracture mode transition.

Grain boundary structure intergranular fracture and the role of segregants as embrittling agents

1980 ◽  
Vol 295 (1413) ◽  
pp. 165-165 ◽  
Keyword(s):  
Grain Boundary ◽  
Intergranular Fracture ◽  
Boundary Region ◽  
Boundary Structure ◽  
Orientation Relation ◽  
Substantial Evidence ◽  
Grain Boundary Structure ◽  
Different Types

There is substantial evidence, from studies of annealed and crept aluminium, which indicates that once a dislocation has entered the boundary region between two grains it dissociates to form several grain boundary dislocations of Burgers vectors determined by the orientation relation between the grains. Subsequent behaviour depends on boundary structure, the dissociation products remaining bunched together in certain boundaries and moving apart in others, indicative of a friction type stress active in the boundary. A simple classification of the different types of boundary, where friction stresses were either high or low, into coincidence and non-coincidence boundaries, however, was not possible.

Influence of Ni Addition on Mechanical Properties and Fracture Behaviors of Ir-15Nb Two-Phase Refractory Superalloys

1998 ◽  
Vol 552 ◽  
Author(s):  
Yuefeng Gu ◽  
Y. Yamabe-Mitarai ◽  
Y. Ro ◽  
T. Yokokawa ◽  
H. Harada
Keyword(s):  
Mechanical Properties ◽  
Intergranular Fracture ◽  
Coherent Structure ◽  
Room Temperature ◽  
Two Phase ◽  
Ni Content ◽  
Ni Addition ◽  
Fracture Behaviors ◽  
Materials Used ◽  
Brittle Intergranular Fracture

ABSTRACTIr-based alloys with fcc-L12 two-phase coherent structure, which are called “refractory superalloys”, have good potentiality as structure materials used at ultra-high temperatures up to 2000 °C. Preliminary results showed that the refractory superalloys failed predominately by brittle intergranular fracture at room temperature even though they showed higher strength at that temperature. This paper will present the influence of nickel (Ni) addition on mechanical properties and fracture behaviors of one of these alloys, Ir-15at%Nb. The results indicated that Ni addition was beneficial to the compression ductility and strength of two-phase Ir-15at%Nb alloy when Ni content was below the optimum content.

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