Impact fracture intergranular

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. 

The concept of in vacuo fracture as a means of sample preparation for adhesion studies has been developed in the author s laboratory in a gradual manner over many years. Initial studies made use of an impact fracture stage designed to provide an Izod (three-point bend) geometry for use with metallic samples that yielded intergranular fracture at cryogenic temperatures. This was modified for composites research. And small samples that are 30 mm in length and some 2 mm square (with fibers oriented in the 2 mm direction) could be accommodated in the... 

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