Intergranular fracture

Some manufacturers have experienced die above mentioned Ni3S2 scale formation phenomenon under certain gas conditions, which led to die failure of a rotating blade. One such experience involved a fracture dial was distinctly intergranular with evidence of secondary intergranular cracks or grain separation across die fracture. Intergranular facets of die fracture were sharp and distinct with little evidence of any ductile mode. The fracture appeared to have occurred in a brittle intergranular mode. 

B. The direct identification of such microscopic fracture modes as transgranular cleavage, radial fracture, intergranular separation or ductile dimpled rupture, was shown to be considerably more dependable by SEM than by OM... 

Not all metal.s and alloys can be persuaded to fracture in an intergranular manner by impact at low temperature. However, a whole group of metals and alloys will fracture in that mode if they are first embrittled by charging with hydrogen. Some will then fracture intergranularly by impact, but others require to be fractured by a slow tensile pull. This group includes the au.stenitic stainless steels [4], nickel [12], the nickel-base superalloys [14] and nickel aluminum alloys [45]. 

All alloys tested deformed by slip and twinning at 300, 76, and 20 K in both tension and impact. Specimens tested at 195 K were not examined metallographi-cally. Only the HK31A-T6 cast alloy tended to fracture intergranularly in tension and impact, and this tendency continued down to 20 K. 

HK31A-T6 tended to fracture intergranularly, while the remaining five alloys fractured transgranularly. 

To explain the mechanism by which the formation of Ni3S2 scale can result in the fatigue failure of the blade disc, the effect of sulfur on the mechanical properties of nickel base alloys must be understood. Since the fracture modes are totally intergranular with evidence of... 

Stickler, R. and Vinckier, A., Electron Microscope Investigation of the Intergranular Corrosion Fracture Surfaces in a Sensitised Austenitic Stainless Steel , Corros. Sci., 3, 1 (1963) von Schwenk, W. and Buhler, H.-E., Beoboshtungen an einem Kornzerfallsen falligen Austenitischen Cr-Ni-Stahl im Aktivzustand , Corros. Sci., 3, 145 (1963)... 

Intergranular corrosion Carbon steels in NO solns Some Al alloys in Cl Cu-Zn alloys solns, high in NH7 solns potentials Fe-Cr-Ni steels in Cl solns Cu-Zn alloys Mg-A alloys in NO in CrO + solns Cl solns Ti alloys in High methanol. A strength alloys, low steels in Cl potentials solns Brittle fracture... 

Intergranular fracture along pre-existing paths Transgranular fracture along straingenerated paths Mixed crack paths by adsorption, decohesion or fracture of brittle phase ... 

The fracture mode of stress-corrosion cracks in austenitic stainless steels can be transgranular, intergranular or a mixture of both. One of the earliest environments found to cause problems was solutions containing chlorides or other halides and the data due to Copson (Fig. 8.30) is very informative. The test solution for that data was magnesium chloride at 154°C the alloys contained 18-20alloy with a composition of approximately 18Cr-8Ni has the least resistance to cracking in this environment. 

There are four possible contributions to intergranular fracture that can arise from sensitisation. In addition to the previously mentioned effect on... 

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... 

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