Ductility, origin

Alloy Compositions and Product Forms. The nominal compositions of various cobalt-base wear-resistant alloys are Hsted in Table 5. The six most popular cobalt-base wear alloys are Hsted first. SteUite alloys 1, 6, and 12, derivatives of the original cobalt—chromium—tungsten alloys, are characterized by their carbon and tungsten contents. SteUite aUoy 1 is the hardest, most abrasion resistant, and least ductile. 

The surface from which the cracks originate may not be apparent without a microstructural examination. Stress-corrosion cracks invariably produce brittle (thick-walled) fractures regardless of the ductility of the metal. 

The embrittlement effect can be largely removed by ageing the steel at about 150 C, but even then the original ductility is not entirely restored. 

Kikuchi Y., Eukui T., Okada T., and Inoue T. Origin of rubber elasticity in thermoplastic elastomers consisting of crossUnked rubber particles and ductile matrix, J. Appl. Polym. Sci., Appl. Polym. Symp., 50, 261, 1992. 

Yielding is a manifestation of the possibility that some of the atoms (or molecules) in the stressed material may slip to new equilibrium positions due to the distortion produced by the applied tensile force. The displaced atoms can form new bonds in their newly acquired equilibrium positions. This permits an elongation over and above that produced by a simple elastic separation of atoms. The material does not get weakened due to the displacement of the atoms since they form new bonds. However, these atoms do not have any tendency to return to their original positions. The elongation, therefore, is inelastic, or irrecoverable or irreversible. This type of deformation is known as plastic deformation and materials that can undergo significant plastic deformation are termed ductile. 

Sulfur dioxide was the major volatile product and was used as a probe to correlate the radiation resistance with polymer structure. The use of biphenol in the polymer reduced G(SO ) by 60% compared with bisphenol A based systems (Bis-A PSF). Surprisingly, the isopro-pylidene group was shown to be remarkably radiation resistant. The ultimate tensile strain decreased with dose for all polysulfones investigated and the rate of decrease correlated well with the order of radiation resistance determined from volatile product measurements. The fracture toughness (K ) of Bis-A PSF also decreased with irradiation dose, but the biphenol based system maintained its original ductility. 

For metals, the percent reduction in area provides additional information about the material s deformation or its ductility. It is calculated by dividing the change in the cross-sectional area by the original cross-sectional area ... 

Tensile testing or a hardness test is a basic requirement of most metal specifications. Some product specifications also require impact-testing, bend and other ductility tests, proof testing, flange or flare tests. The size of the sample may limit which tests can be performed. Macro, superficial, and micro-hardness tests are routinely done in failure analysis even if the original product specification did not require them. 

The elongation measured over a fixed gage length, and the reduction of area of the section at the fracture are measures of ductility. In cylindrical specimens, the area is readily determined from the final diameter at the fracture. The percent reduction of area is then determined as original area minus final area, divided by original area. 

When GBS is accommodated by some of the mechanisms involving dislocation movement or diffusion of point defects, the grains retain almost the original size and shape even after large deformations. This GBS, as the primary mechanism for deformation, is the basis for the high ductility exhibited... 

The study of surface behavior is not of recent origin. In the 1920s, Joffe (1928) observed an increase in the ductility in the presence of water on solid potassium chloride. In 1930s, Roscoe (1926) published that the presence of oxides on certain metals, such as cadmium, produced a surface hardening effect. 

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