Environment Sensitive Fracture Of Metals And Alloys

The stress corrosion cracking of alloys is markedly sensitive to the environment to which they are exposed, so that an alloy developed to have low susceptibility to such failure in a particular environment will not necessarily show such behavior in a different environment, as illustrated by a number of examples. It is also possible for results from tests using standard environments to lead to the exclusion of the use of materials that may behave satisfactorily in service. While it is obvious that tests should be conducted, whenever possible, in environments relevant to particular service conditions, these are not necessarily known when alloy development programs are being undertaken in the laboratory, hence the need for standardized or synthetic solutions. Evidence for the cracking domains for ferritic steels and ?-brasses suggests that stress corrosion cracking in a range of environments occurs at potentials and pH's where the lower oxide of the relevant metal can form. This suggests that laboratory tests should involve more than a single standardized environment, and that variation from test to test of potential and pH, guided by the potential pH diagram, may provide a more reliable guide to stress corrosion cracking propensities than that obtained from tests in a single solution.

Advances in Research on the Strength and Fracture of Materials: Volume 1s—An Overview contains the proceedings of the Fourth International Conference on Fracture held at the University of Waterloo, Canada, in June 1977. The papers review the state of the art with respect to fracture in a wide range of materials such as metals and alloys, polymers, ceramics, and composites. This volume is comprised of 40 chapters and opens with a discussion on progress in the development of elementary fracture mechanism maps and their application to metal deformation processes, along with micro-mechanisms of fracture and the fracture toughness of engineering alloys. The next section is devoted to the fracture of large-scale structures such as steel structures, aircraft, cargo containment systems, nuclear reactors, and pressure vessels. Fracture at high temperatures and in sensitive environments is then explored, paying particular attention to creep failure by cavitation under non-steady conditions; the effects of hydrogen and impurities on brittle fracture in steel; and mechanism of embrittlement and brittle fracture in liquid metal environments. The remaining chapters consider the fracture of non-metallic materials as well as developments and concepts in the application of fracture mechanics. This book will be of interest to metallurgists, materials scientists, and structural and mechanical engineers.

Papers included topics of phenomena, basic mechanisms, modeling, test methodologies, materials performance, engineering applications and service experience and failures and reflects the current emphasis with regard to material/environment systems.

The effects of surface and environmental conditions on the plastic flow and fracture of metals and alloys are reviewed, with particular emphasis on topics of current controversy. These include the effects of surface films and the hard-vs-soft surface layer controversy in the plastic deformation of metal monocrystals, and the influence of crack-tip chemistry, cathodically-produced hydrogen, brittle films and other parameters in stress-corrosion cracking. (Author).

For many years it has been recognized that engineering materials that are-tough and ductile can be rendered susceptible to premature fracture through their reaction with the environment. Over 100 years ago, Reynolds associated hydrogen with detrimental effects on the ductility of iron. The "season cracking" of brass has been a known problem for dec ades, but the mechanisms for this stress-corrosion process are only today being elucidated. In more recent times, the mechanical properties of most engineering materials have been shown to be adversely affected by hydrogen embrittlement or stress-corrosion cracking. Early studies of environmental effects on crack growth attempted to identify a unified theory to explain the crack growth behavior of groups of materials in a variety of environments. It is currently understood that there are numerous stress-corrosion processes some of which may be common to several materials, but that the crack growth behavior of a given material is dependent on microstructure, microchemistry, mechanics, surface chemistry, and solution chemistry. Although the mechanism by which various chemical species in the environment may cause cracks to propagate in some materials but not in others is very complex, the net result of all environmentally induced fracture is the reduction in the force and energy associated with the tensile or shear separation of atoms at the crack tip.