Environment Induced Embrittlement

This research program has included two thrusts. The first addressed environment-induced embrittlement in a parallel study of stress corrosion cracking and metal-induced embrittlement. This work has examined (1) mechanical properties as influenced by embrittling environments, (2) fractography and crystallography or transgranular cracking, (3) the mechanics of cracking, (4) the extent and role of local plastic flow, and (5) local chemistry within stress corrosion and metal-induced cracks. The embrittlement of iron aluminide alloys by air was addressed by determining the effect of water and hydrogen upon the mechanical properties. Slow strain rate testing in aqueous environments was carried out at controlled anodic and cathodic potentials. The effect of cathodically charged hydrogen and the effect of subsequent baking were measured. Environmental susceptibility was measured as affected by alloy composition, microstructure and degree of ordering.

This research program has included two thrusts. The first addressed environment-induced embrittlement in a parallel study of stress corrosion cracking and metal-induced embrittlement. This work has examined (1) mechanical properties as influenced by embrittling environments, (2) fractography and crystallography or transgranular cracking, (3) the mechanics of cracking, (4) the extent and role of local plastic flow, and (5) local chemistry within stress corrosion and metal-induced cracks. The embrittlement of iron aluminide alloys by air was addressed by determining the effect of water and hydrogen upon the mechanical properties. Slow strain rate testing in aqueous environments was carried out at controlled anodic and cathodic potentials. The effect of cathodically charged hydrogen and the effect of subsequent baking were measured. Environmental susceptibility was measured as affected by alloy composition, microstructure and degree of ordering.

Treatise on Materials Science and Technology, Volume 25: Embrittlement of Engineering Alloys is an 11-chapter text that describes some situations that produce premature failure of several engineering alloys, including steels and nickel- and aluminum-base alloys. Chapters 1 to 3 consider situations where improper alloy composition, processing, and/or heat treatment can lead to a degradation of mechanical properties, even in the absence of an aggressive environment or an elevated temperature. Chapters 4 and 5 examine the effect of elevated temperatures on the mechanical properties of both ferrous and nonferrous alloys. Chapters 6 and 7 discuss the effects of corrosive environments on both stressed and unstressed materials. In these environments anodic dissolution is the primary step that leads to failure. Chapters 8 to 10 deal with the effects of aggressive environments that lead to enhanced decohesion or embrittlement of the metal, such as hydrogen, liquid metal, and irradiation-induced embrittlement. Chapter 11 looks into the embrittlement phenomena occurring during welding, one of the most common processing conditions to which a material could be subjected. This book will prove useful to materials scientists and researchers.

In order to predict when and how a material will crack under environmental conditions, engineers used to subject it to pressure for a long time, up to a year in cases; about 20 years ago, a testing method was developed that slowly but inexorably increases the pressure, which seems to cut down the ti

An experiment designed to study the effect of several variables on the subcritical crack growth rate of a high-strength steel in a water environment was conducted. Double cantilever beam specimens of an AISI 4340 steel were employed to study crack extension rates. The environmental variables included temperature, pH of the liquid environment, electric charging and the combined effect of pH and electric charging. (Author).

Ordered intermetallics based on aluminides and silicides possess many promising properties for elevated-temperature applications; however, poor fracture resistance and limited fabricability restrict their use as engineering material. Recent studies have shown that environmental embrittlement is a major cause of low ductility and brittle fracture in many ordered intermetallic alloys. There are two types of environmental embrittlement observed in intermetallic alloys. One is hydrogen-induced embrittlement occurring at ambient temperatures in air. The other is oxygen-induced embrittlement in oxidizing atmospheres at elevated temperatures. In most cases, the embrittlements are due to a dynamic effect involving generation and penetration of embrittling agents (i.e., hydrogen or oxygen) during testing. Diffusion of embrittling agents plays a dominant role in fracture of these intermetallic alloys. This chapter summarizes recent progress in understanding and reducing environmental embrittlement in these alloys.