An overview of the delamination theory of wear

Different approaches to superhard coatings and nanocomposites

Environmentally Assisted Cracking: Overview of Evidence for an Adsorption-Induced Localised-Slip Process,

T he hydrogen transport problem is studied in conjunction with large deformation elastic—plastic behavior of a material. Oriani's equilibrium theory is used to relate the hydrogen in traps (micro-structural defects) to concentration in normal interstitial lattice sites (NILS). The resulting non-linear transient hydrogen diffusion equations are integrated using a modified backward Euler method. Coupled diffusion and plastic straining is analysed with this numerical procedure in the area around a blunting crack tip. A uniform NILS concentration as dictated by Sievert's law at the pressure and temperature of interest is used as initial condition throughout the body. The crack is initially blunted by plane strain mode I (tensile) loading. The finite element results show that hydrogen residing at NILS is generally very small in comparison with the population that develops in trapping sites near the crack surface. That is, lattice diffusion delivers the hydrogen but it is predominantly the trapping that determines its distribution at temperatures of interest. The predominance of trapped hydrogen over lattice concentration prevails even in the case when hydrogen migrates under steady state conditions. Hence, the hydrostatic stress effect is less important than traps created by plastic straining as far as the creation of high total hydrogen concentration is concerned. The trapping site locations and the temperature determine the amounts and locations of high hydrogen concentrations. Consequently, ahead of a blunting crack tip, the total hydrogen concentration and plastic strain diminish with distance from the crack tip whereas the hydrostatic stress rises. This would seem to have significant consequences for fractures induced by the presence of hydrogen.

Numerical analysis of hydrogen transport near a blunting crack tip

Stress-corrosion cracking

It is now more than 100 years since certain detrimental effects on the ductility of iron were first associated with the presence of hydrogen. Not only is hydrogen embrittlement still a major industri al problem, but it is safe to say that in a mechanistic sense we still do not know what hydrogen (but not nitrogen or oxygen, for example) does on an atomic scale to induce this degradation. The same applies to other examples of environmentally-induced fracture: what is it about the ubiquitous chloride ion that induces premature catastrophic fracture (stress corrosion cracking) of ordinarily ductile austenitic stainless steels? Why, moreover, are halide ions troublesome but the nitrate or sulfate anions not deleterious to such stainless steels? Likewise, why are some solid metals embrit tled catastrophically by same liquid metals (liquid metal embrit tlement) - copper and aluminum, for example, are embrittled by liquid mercury. In short, despite all that we may know about the materials science and mechanics of fracture on a macroscopic scale, we know little about the atomistics of fracture in the absence of environmental interactions and even less when embrittlement phe nomena such as those described above are involved. On the other hand, it is interesting to note that physical chemists and surface chemists also have interests in the same kinds of interactions that occur on an atomic scale when metals such as nickel or platinum are used, for example, as catalysts for chemical reactions."

Atomistics of fracture

Surface effects in crystal plasticity

: The first four days were devoted to introductory and overview lectures on theory of fracture, solid state chemistry and physics of fracture, solution chemistry, and structure and properties of interfaces After a one-day break, three days of workshop sessions and a summary lecture were held Workshop topics included novel aspects of fracture, intergranular embrittlement, hydrogen embrittlement, and stress corrosion and corrosion fatigue Content: Chemistry and Physics of Fracture: Mechanics of Brittle Cracking of Crystal Lattices and Interfaces; Theory of Fracture; Plastic Processes at Crack Tips; Plastic Flow Instabilities at Crack Tips; Distributed Damage Processes in Fracture; A comparison of Void Growth and Ductile Failure in Plane and Axisymmetric States of Strain; Solid State Chemistry and Physics of Fracture; Theoretical Approaches to Materials Design: Intergranular Embrittlement; Interatomic Forces and the Simulation of Cracks; Application of the Embedded Atom Method to Hydrogen Embrittlement; Solution Chemistry; Surface Chemistry in Aqueous Solutions; Crack Tip Electrochemistry: Electrochemical Thermodynamics and Kinetics and Their Application to the Study of Stress Corrosion Cracking; Structure and Properties of Interfaces; Universal Properties of Bonding at Metal Interfaces; Structure of Grain Boundaries and Interfaces; In Situ TEM Studies of Crack Tip Deformation in Molybdenum; Hydrogen Embrittlement; The Role of Hydrogen Transport in Hydrogen Embrittlement

R. M. Latanision

Papers

Atomistics of fracture

Surface effects in crystal plasticity

Chemistry and physics of fracture

Surface Effects in Crystal Plasticity: General Overview

Stress corrosion cracking of iron--nickel--chromium alloys.