Intergranular fracture examples

Fracture surfaces of pure MgO show a large proportion of transgranular cracks, with a few intergranular cracks (Fig. 14.9). At low additions of spinel, transgranular cracks are still present with some intergranular cracks, in the fracture surfaces of each spinel composite. However, at higher additions of spinel (> 20%), mostly intergranular fracture occurs. For example, 20%... 

Examination of the fracture surfaces indicates that samples with the higher fracture toughness values show a predominantly intergranular fracture mode with clear evidence of crack deflection and subsurface fracture of bridging whiskers. The low toughness samples showed a transgranular fracture mode with little crack deflection. Examples of the fracture surfaces are shown in Fig. 4. 

Figure 1. Examples of the two brittle fracture modes found in intermetallic compounds (a) cleavage in NlAl (b) intergranular fracture in NijOe...

Some liquid metals have been observed to cause embrittlement in many titanium alloys. In mercury, for example, Ti-8Al-lMo-lV exhibits both intergranular and transgranular fracture with velocities as high as lOcm/s. Heat treatment affects this behaviour in a manner similar to that observed in aqueous and methanolic solutions. Some alloys are embrittled by liquid cadmium and zinc. More surprising, perhaps, is the observed solid metal embrittlement which has been found on titanium alloy components coated with cadmium, silver or zinc Service failures of cadmium-plated Ti-6A1-4V fasteners have been reported , and cracking of this alloy and... 

Many types of alloy can suffer stress-corrosion cracking (SCC) if subject to external stress or residual stress when in contact with corrosive media. Typically SCC is characterized by a low-ductility or brittle fracture. For example standard austenitic stainless steels, e.g. types 1.4301 or 1.4401, are susceptible to chloride-induced stress-corrosion cracking in a chloride-containing environment at a temperature above 50 C. Depending on the specific environment cracks propagate trans- or intergranularly chloride-induced SCC is characterized by trans-granular cracks (Fig. 1-12). 

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