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Joining Technologies
Published in Raghu Echempati, Primer on Automotive Lightweighting Technologies, 2021
Mechanical plating is where the part is tumbled with a metal powder. The tumbling action causes the metal powder to be cold-welded to the part. This process is common for fasteners, such as screws, nails, and washers. Mechanical plating is advantageous because this method avoids hydrogen embrittlement. Hydrogen embrittlement is when a metal becomes brittle due to the diffusion of hydrogen into the metal (common in high-strength steel). Hydrogen embrittlement is a concern with electroplating.
Sources of Stress and Service Failure Mechanisms
Published in Colin R. Gagg, Forensic Engineering, 2020
There is an insidious mode of brittle failure that will often be encountered in service – that of hydrogen embrittlement. When atomic hydrogen enters a metallic material, it can result in a loss of load-carrying ability, loss of ductility or sub-microscopic cracking. Hydrogen embrittlement is an insidious failure mechanism that can cause unexpected and sometimes catastrophic brittle failure at applied stresses well below the yield strength of the material. Hydrogen embrittlement is therefore considered to be the Achilles’ heel of high-strength ferrous steels and alloys. Hydrogen embrittlement does not affect all metallic materials equally; the most vulnerable are high-strength steels, titanium alloys and aluminium alloys. Although the phenomenon is well-known, extensive research has failed to pinpoint the precise mechanism at play. However, hydrogen embrittlement mechanisms are thought to be diffusion controlled, with current thinking suggesting the susceptibility of any material is directly related to the characteristics of its trap population. In turn, the trap population of any material is related to its microstructure, dislocations, carbides and other elements present in the structure. Therefore, diffusion is controlled by the rate of escape of hydrogen from the traps. It follows that the nature and the density of traps will control the diffusion coefficients.
Diffusion
Published in Gregory N. Haidemenopoulos, Physical Metallurgy, 2018
Hydrogen in steel causes hydrogen embrittlement, especially in high-strength steels. For this reason, several engineering parts as well as welds are subjected to a bake out treatment to remove hydrogen. Consider a steel ball of a rolling bearing, with radius 0.5cm. The ball is placed in a laboratory furnace, at 300°C, for bake out. The initial hydrogen concentration is 25ppmw. Assume that heat transfer is so fast that it is not the rate limiting step of the bake out process.
Hydrogen-induced embrittlement of nickel-chromium-molybdenum containing HSLA steels
Published in Journal of the Chinese Institute of Engineers, 2020
Yu-Tung Hsu, He-Ying Jiang, Hung-Wei Yen, Hsin-Chih Lin, Steven Hong
8625-Modified steel (8625M steel) is a representative of the advanced Ni-Cr-Mo HSLA steels developed by our research team. 8625M steel has martensite microstructure and its tensile strength reaches 1600 MPa in as-quenched state. Even after tempering at 400°C, the tensile strength remains above 1200 MPa. Meanwhile, lifting chains and slings made from 8625M steel are often utilized offshore or in corrosive environments. Hydrogen embrittlement requires the simultaneous presence of a threshold level of hydrogen, susceptible microstructure and high restraint or residual stress. If anyone of the above three factors can be eliminated, then hydrogen embrittlement will not occur. In general, hydrogen embrittlement is the mortal enemy of high strength steels. This is because the components made of high strength steels always bear high stress. Besides, these high strength steels often have susceptible microstructures, such as crystal defects, second phases, etc. Hence, it is quite important to understand the phenomenon of hydrogen-induced embrittlement for 8625M steel.
Site stability and pipe diffusion of hydrogen under localised shear in aluminium
Published in Philosophical Magazine, 2019
Y. Wang, D. Connétable, D. Tanguy
An important area of research, within the field of environmental damage of structural metallic alloys, is hydrogen embrittlement. This type of damage is intimately related to the tendency of metallic systems to form a refined dislocation structure, ahead of crack tips [1,2], among which a crack can propagate at low mechanical loads. Hydrogen is not only involved in the crack advance itself but is also responsible for the buildup of the specific dislocation structure. Some related elementary plastic mechanisms (for a review see [3]), such as an enhanced localisation in slip bands, have been recently quantified [4,5]. Also of importance is the modelling of hydrogen diffusion in such a microstructure [6], i.e. to include the presence of dislocations in continuum diffusion. This has essentially been viewed as a stress bias, with an additional trapping at the core of the dislocation [7–9] or at debris produced by plastic strain. Pipe diffusion is not considered and only a limited amount of studies has been devoted to the subject [10]. There is still a need to investigate the details of the diffusion paths provided by the region of imperfect stacking at the core of dislocations and along stacking fault ribbons, in a similar way to what was done in the intergranular case [11].
The Importance of Temperature in Generating ZDDP Tribofilms Efficient at Preventing Hydrogen Permeation in Rolling Contacts
Published in Tribology Transactions, 2018
Vlad Bogdan Niste, Hiroyoshi Tanaka, Joichi Sugimura
Many steel tribological components experience various types of rolling and sliding conditions and are considerably more susceptible to this effect, commonly known as embrittlement. High-strength steels are particularly affected due to their superior mechanical properties and are known to be vulnerable to hydrogen embrittlement, which can cause premature failure. The process is accompanied by the formation of specific white etching cracks, although their role is still debated (Kino and Otani (2); Uyama, et al. (3); Ciruna and Szieleit (4); Ray, et al. (5)). Rolling element bearings are often essential components and their life performance can be the limiting factor in applications such as wind turbines, engines, compressors, etc. (Evans (6); Evans, et al. (7)). It has been previously shown that in hydrogen applications, the rolling contact fatigue (RCF) life of high-strength steel is directly correlated with the amount of hydrogen present in the material (Tanaka, et al. (8); Tanimoto, et al. (9)).