What Causes Intergranular Fracture

Intergranular fracture occurs when a crack propagates along the grain boundaries of a material, usually when these grain boundaries are weakened. The more commonly seen transgranular fracture, occurs when the crack grows through the material grains.

What causes intergranular cracking?

Intergranular cracking is a result of local differences in the composition of a metal as a crack propagates along the grain boundaries of a material, usually where these grain boundaries are weakened.

What conditions promote intergranular fracture?

Intergranular fracture is induced by the transformation of grain boundary bubbles to voids, leading to breakaway growth, cavity coalescence, and rupture in the presence of mechanical stress.

Where do intergranular fractures occur?

Intergranular fractures travel along the grain boundaries, rather than through the actual grains. This usually occurs when the phase in the grain boundary is weak and brittle (such as cementite in iron’s grain boundaries).

Is brittle fracture transgranular?

Higher magnification reveals that transgranular cracking often occurs during brittle fracture, especially at low temperatures. In such cases the crack propagates across and through the grain interiors.

Are quench cracks intergranular?

Usually, quench cracks are intergranular. They look like “rock candy” when viewed with a high enough magnification microscope. It’s a distinctive look.

How do you prevent a brittle fracture?

For new equipment, brittle fracture is best prevented by using the current ASME Boiler and Pressure Vessel Code to specify and incorporate materials designed specifically for low temperature conditions, including upset and auto-refrigeration events.

What is dimple fracture?

A dimple fracture refers to a type of material failure on a metal’s surface that is characterized by the formation and collection of microvoids along the granular boundary of the metal. The occurrence of dimple fractures is directly proportional to increased corrosion rates.

What do you mean by fatigue fracture?

Fatigue fractures (also known as overuse fractures) are a type of stress fracture due to abnormal stresses on normal bone. They should not be confused with an insufficiency fracture, which occurs due to normal stresses on abnormal bone.

What is ductile fracture?

A ductile fracture is a type of fracture characterized by extensive plastic deformation or necking. Cracks that occur in ductile materials are said to be stable, meaning they are able to resist extension without any increase in stress.

What is intergranular and intragranular?

Hi Sankar, based on my knowledge, inter-granular fracture is one which is caused by the crack which follows the grain boundaries, which means the crack is restricted to one particular grain e.g stress cracking ; however trans-granular fracture is caused by crack which does not follow grain boundaries and hence.

What causes hydrogen embrittlement?

Hydrogen Embrittlement occurs when metals become brittle as a result of the introduction and diffusion of hydrogen into the material. This happens when sufficient stress is applied to a hydrogen-embrittled object.

Is transgranular fracture ductile or brittle?

There are two major types of brittle fractures: transgranular and intergranular. With transgranular fractures, the fracture travels through the grain of the material. It changes direction from grain to grain due to the different lattice orientation of atoms in each grain, following the path of least resistance.

What does brittle fracture look like?

Brittle fractures are characterised as having little or no plastic deformation prior to failure. Materials that usually fracture in a brittle manner are glasses, ceramics, and some polymers and metals.

Why do brittle fractures occur?

Brittle fractures occur when the material is subject to stresses that are smaller than the yield limit of the material. Machine design normally is based on ductile material; and the design criteria are meant to avoid plastic deformation and, in certain cases, elastic deformations.

What controls the strength of ceramics and glasses?

What determines or controls the strength of ceramics and glasses? The strength of ceramics and glasses is determined primarily by the size and distribution of defects in the material.

How do you stop quenching cracks?

Steps to prevent cracking in superalloy materials include: reducing (or eliminating) residual surface tensile stresses (e.g., shot peening); modifying or redesigning part geometry (to eliminate stress risers); and addressing surface-roughness issues.

What is cleavage failure?

Cleavage fracture is a fracture, usually of polycrystalline metal, in which most of the grains have failed by cleavage, resulting in bright, reflective facets. It is a type of crystalline fracture and is associated with low-energy brittle fracture. It exhibits a river pattern when examined under an electron microscope.

How does stress corrosion cracking occur?

SCC usually occurs in certain specific alloy-environment-stress combinations. Stress corrosion cracking (SCC) is the cracking induced from the combined influence of tensile stress and a corrosive environment. The impact of SCC on a material usually falls between dry cracking and the fatigue threshold of that material.

How do brittle materials fail?

Brittle materials do not undergo significant plastic deformation. They thus fail by breaking of the bonds between atoms, which usually requires a tensile stress along the bond. Micromechanically, the breaking of the bonds is aided by presence of cracks which cause stress concentration.

How do you know if you have brittle failure?

Brittle fractures have certain characteristics that permit them to be properly identified: There is no gross permanent or plastic deformation of the metal in the region of brittle fracture, although there may be permanent deformation in other locations where relatively ductile fracture has occurred.

What are the three stages of fatigue?

There are three stages of fatigue fracture: initiation, propagation, and final rupture.

What features of the fracture surface indicate ductile fracture?

The characteristic appearance of the surface of a ductile fracture is dull and fibrous. This is caused by deformation on the fracture surface, which will be discussed in the section on the microstructural aspects of ductile fracture.

What is stress intensity factor in fracture mechanics?

The stress intensity factor, , is used in fracture mechanics to predict the stress state (“stress intensity”) near the tip of a crack or notch caused by a remote load or residual stresses.

What is quasi cleavage fracture?

Quasi-cleavage, a common feature of hydrogen-induced fracture surfaces, is generally taken as being cleavage-like but not along a known cleavage plane. It will be demonstrated that the fracture surface arises from the growth and coalescence of voids that initiate at and extend along slip band intersections.