Hydrogen embrittlement is a serious issue. Hydrogen can induce damage to metals and alloys, such as blistering, hydrogen embrittlement, cracking, hydrogen attack. In high strength materials such as steel, hydrogen embrittlement (HE) is quite common. HE refers to the phenomena that the strength of a material is reduced significantly when hydrogen is somehow introduced in the material, and subsequently the material become more brittle. it's not until a series of serious accidents that we learned how serious HE is.
Therefore, it quite natural that when I was looking at hardmetals such as tungsten carbides, I got the following question in my mind, "Can hydrogen embrittlement happen in such hardmetals?" Surprisingly, I found NO INFORMATION on this! Any ideas regarding this question? Thank you.
Hydrogen embrittlement for hard metals based on tungsten carbide does not exist. Evidence of this is that these materials are sintered under hydrogen.
For a very long time, the essential role of interfaces has been suspected, where reactions depend on the viscosity or elastoplasticity of the materials in contact, the work function, the contact potential, the surface energy and the rate of stress change. The reactions in the interfaces are usually considered redox and the stress variation is similar to that of the imaginary part of the permittivity. The reactions occur with variation of the polarization, temperature and conductivity. The energy storage properties of interfaces make them behave as thermal, electrical and particle generators. The three functions are simultaneous but only the battery function has been exploited so far. These observations are not sufficient to explain the phenomena of aging, thermal drift, fracture and explosion, we sought the missing elements to arrive at a damage model applicable to all the problems encountered. For this, we used gravimetry, calorimetry, the coupling of the two and electron beam techniques to study the similar effects of the adsorption of polar molecules and of the localization of charges, on the internal energy and on the deformations. These techniques were chosen because the processes at the interfaces are similar under mechanical and electrical stresses or in the presence of trapped charges. Thus, an equation of state under stress was derived which applies to the phenomena at the interfaces and allows the prediction of the lifetime of the generators according to their operating conditions. To facilitate the dissemination of these results, they are grouped on a website in a 250-page book, an unpublished publication on the equation of state, an invited article in Journ.Appl.Physics/PERSPECTIVE/surface coating, 2023, and a training course in 14 videos of about 3 hours. For more information contact me at [email protected]
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Hello
To explain my answer I propose you what guided it;
It is difficult to know on which form the hydrogen is in the metal, that is to say it is in hydride form, atomic or molecular. The next difficulty is to measure its concentration. I approached these questions by studying the adsorption of incondensable gases on metals, atomically clean (Ta and Al (111)) at very low H2 partial pressure, of the order of 10^-3 Pascal and at room temperature. While the residence time of the molecules should be extremely short of the order of 10^- 10 seconds or less, it is much larger and depends on the polarity of the molecules and the presence of defects, impurities and dislocations. These defects create local variations of the crystal field and internal stresses while the adsorbed molecules create image charges that modify the electronic and vibrational structure at the surface of the solid. This is verified by electron spectrometry and is expressed by the dielectric function. Even at very low coverage, the adsorbed molecules become unstable due to the relaxation of internal stresses of entropic origin. This scheme is parallel to that of the effects of adsorbed charges on insulators and is expressed by an equation of state and expresses the surface barrier deformation by defects and the resulting physical/chemical adsorption and ion diffusion processes. On the basis of these elements, the hydrogen concentration of the order of ppm would not be measurable by weight but fatal to the cohesion. One can imagine several experiments to verify this scheme.
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Claude
Thank you Vadim and Claude. I look forward to read Claude's paper, preferably in the published format. One thing I want to point out is that hardmetals such as tungsten carbide are mostly "composite" materials. What I mean by the term "composite" is that because of the high melting point of tungsten carbide, there seems no other way than using the typical powder metallurgy approach, so microscopically the final texture of the material is tungsten carbide particles "dissolved" in Co. Co is chosen because of it's low melting point and good affinity with Tungsten carbide. So being a composite material may change the whole scenario. Based on my rough understanding of hydrogen embattlement, it's strongly related to two facts. First, hydrogen is easy to diffuse in the material. Second, this diffusion cause thing like stress concentration or perhaps even local weakening of chemical bonds. In composite materials, there is a good chance that neither of these can be a concern. Look forward for further comments.
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