Coating density as the key factor behind hydrogen embrittlement of cadmium-plated 4340 steel
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RESEARCH ARTICLE
Coating density as the key factor behind hydrogen embrittlement of cadmium‑plated 4340 steel J. Bellemare1 · S. Laliberté‑Riverin1 · D. Ménard1 · M. Brochu1 · F. Sirois1 Received: 1 October 2019 / Accepted: 14 July 2020 © Springer Nature B.V. 2020
Abstract The aerospace industry uses 200-h sustained-load test (SLT), described in ASTM F-519, to evaluate hydrogen embrittlement (HE) of their 4340 steel electroplated parts. The cadmium plating used in ASTM F-519 suggest that the coating density may affect HE in an important manner. Therefore, in this work, 4340 steel notched bars were plated with five different cadmium coating densities. Then, the SLT was combined with thermal desorption spectroscopy (TDS) to evaluate: (i) the degree of HE, and (ii) the hydrogen content of the cadmium-plated 4340 steel samples. The results show strong evidences that the major factor causing HE of cadmium-plated 4340 steel is the coating density. Moreover, an advanced analysis of TDS curves using the Hertz–Knudsen equation allows distinguishing hydrogen in steel from hydrogen in the cadmium coating. The advanced analysis also gives an estimation of the coating density, and therefore indicates if the baking will be effective at relieving embrittlement. Finally, TDS could be a good complementary tool to the SLT in evaluating HE. Graphic abstract
Keywords Thermal desorption spectroscopy · Sustained-load test · 4340 steel · Coating density · Cadmium evaporation · Hydrogen embrittlement
1 Introduction
* J. Bellemare [email protected] 1
Polytechnique Montréal, Montréal, QC H3C 3A7, Canada
In the aerospace industry, high-strength steels such as 4340 and 300M are used in critical parts like landing gears and helicopter transmissions. These parts are sensitive to corrosion and need to be plated with cadmium, zinc, nickel or other metals. When electroplated, the parts can suffer from
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hydrogen embrittlement (HE). Hydrogen introduced during the electroplating can be removed by baking the parts, but this is not always effective [1–5]. For the manufacturers, the certification of the parts for HE goes through a 200-h Sustained-Load Test (SLT) and a baking performed within 4 h following the AMS-QQ-P-416 standard. As a result, HE management is costly and puts an important time constraint on the production lines. This motivates the need for a shorter test, able to measure the hydrogen directly in the sample, like thermal desorption spectroscopy (TDS), or a non-destructive test that could evaluate HE indirectly. However, there are two main challenges: (i) the hydrogen distribution in the part is not well known [3, 6–8], and (ii) the critical hydrogen threshold concentration, i.e. the minimum hydrogen concentration leading to HE, is of the order of a fraction of ppm [2, 9], which is very difficult to detect. Cadmium plating, realized in a cadmium-cyanide bath, is used in production and in ASTM F-519 standard as a sensitivity test. In the standard, embrittling platings are produced at a c
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