Abstract
A detailed investigation is made of the general laws governing the increase of corrosion resistance of metallic systems by means of alloying. The role of local cells in alloy corrosion is considered briefly. Some attention is given also to the control characteristics of corrosion processes. Other topics discussed include structural heterogeneity and metal alloy corrosion resistance, conditions for development of metal passivity, and methods of increasing metal and alloy corrosion resistance.
It was found that with corrosion controlled by oxygen diffusion, cathodic inclusions do not notably accelerate corrosion. When it is possible to establish prevalent anodic control, cathodic inclusions may promote passivation and consesuently considerably reduce the rate of, corrosion.
The degree of passivity may be regarded as a value equivalent to the degree of anodic control effected in a given process. When this is taken into account it is possible to propose a new method for calculating the degree of passivity of different metals. Approximate calculation of the passivity of metals in aerated 0.5N NaCl solutions gave the following order of reduction of degree of passivity : Ti, Al, Cr, Be, Mo, Mg, Ni, Co, Fe, Mn, Zn, Cd, Sn, Pb and Cu.
The possibility of increasing alloy corrosion resistance by additional cathodic alloying was interpreted by analyzing the polarization diagram. The possibility of increasing the corrosion resistance of readily passivated metallic systems was tested experimentally. 3.7.2
