Transgranular failure

Figure 18.13a shows the fracture surface of polycrystalline AIN. Can you see any evidence of transgranular failure ... 

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... 

No mechanism for cracking in N2O4 has been established . In organic media crack velocities are similar to those obtained in distilled water. Lowering the water content results in lower velocities. Not all authors attribute failures in organic liquids to the residual moisture . Furthermore, part of the fracture may be transgranular . Water additions to methanol increase crack velocities as do halide additions. In oils velocities are similar to those in organic liquids and distilled water. 

Where stress plays a part, the resultant metal failure may be present as either a transgranular (transcrystalline) or an intergranular ( intercrystalline) mechanism. 

Ammonia SCC of Cu-base alloys 02 and C02 accelerate SCC failure in a wide range of NH3/air ratios of 20-80% NH3 Alloys of 60-65% Cu resulted in both intergranular and transgranular SCC predominantly transgranular SCC with alloys of >70% Cu... 

Failures in refineries have shown cracks parallel or normal to welds, depending upon the orientation of principal stresses. Both transgranular and intergranular cracks have been observed. 

Fig. 9. Potential-temperature diagram for sensitized TVpe 304SS in 0.01 m NaCl solution showing regions of different failure modes [29], TGSCC, transgranular stress corrosion cracking. Reproduced from Proc. 9th Int. Congr. Met. Corros., Vol. 2, pp. 185-201 (1984) by permission of the National Research Council of Canada.

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