Influence of hydrogen on the tarnishing film-induced brittle cracking of brass
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The effects of hydrogen-charging on tarnishing film-induced brittle cracking of brass were studied. The tarnishing film was generated on brass samples with various hydrogen concentrations in Mattsson’s solution, then removed from the solution, dried, and subjected to a slow loading rate (loading speed = 0.5 mm/min) in air. The results indicated that hydrogen caused the film-induced brittle cracking to be more difficult to occur and a considerably high concentration of hydrogen could inhibit completely the film-induced brittle cracking. Elastic modulus test results showed that elastic modulus of the brass substrate decreased and elastic modulus of the tarnishing film increased with increasing the hydrogen concentration. Hydrogen inhibiting the film-induced cracking can be ascribed to the fact that hydrogen changed the elastic modulus of substrate and film.
I. INTRODUCTION
There was a considerable amount of evidence that the oxide film or dealloyed layer could cause brittle cracking of the normally ductile substrate.1–7 For example, Newman et al.1 found that film-induced cleavage fracture occurred when a brass foil with a dealloyed layer was strained rapidly in 15 M NH4+ + 0.05 M Cu(NH3)2+ solution or in air at 77 K. Kelly et al.2 reported that thin Ag–20Au foils had undergone a brittle fracture under a positive polarization in 1 M HClO4 without applied stress. Chen et al.3 showed that Cu–30Au alloy with a dealloyed layer fractured in an intergranular mode under an impact load in 0.6 M NaCl. Devasenapathi et al.4 reported that a Mn substituted stainless steel with thick film showed brittle intergranular stress corrosion cracking (SCC) under impact load in 1 M HCl. Saito et al.5 revealed that filminduced intergranular fracture occurred in Ag–20Au foil after dealloying for 10 s at 1050 mVSCE in 1 M HClO4. Cassagne et al.6 observed Cu3Au single crystal with a dealloyed layer and then bending in air, many cracks formed in the dealloyed layer, some cracks of which developed into the substrate. Our previous work7 showed that the cracks originally initiated on the tarnishing film and then propagated into the brass matrix in a brittle intergranular manner when the tarnishing filmed brass was subjected to a slow loading rate (loading speed = 0.5 mm/min) in air. However, it changed into a ductile mode after removal of deposited film. a)
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2009.0406
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http://journals.cambridge.org
J. Mater. Res., Vol. 24, No. 11, Nov 2009 Downloaded: 13 Mar 2015
On the basis of some of the previous results, Newman et al.1 proposed a film-induced cleavage model to explain SCC, they considered that ductile-brittle transition resulting from the surface was the root cause of SCC. Some experiments have shown that hydrogen would increase the vacancy concentration,8 change the mechanical properties of material,9 and enhance susceptibility to SCC.10 Therefore, hydrogen might have an effect on film-induced brittle cracking. Almost all previous evidence of th
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