On the stability of surface martensite in β-phase CuZn alloys

• Published in: Scripta metallurgica 1983-04, Vol.17 (4), p.501-504
• Main Authors: Lovey, F.C., Ferron, J., De Bernardez, L.S., Ahlers, M.
• Format: Article
• Language: English
• Subjects: Cross-disciplinary physics: materials science; rheology; Exact sciences and technology; Materials science; Metals, semimetals and alloys; Phase diagrams and microstructures developed by solidification and solid-solid phase transformations; Physics; Specific materials
• ISSN: 0036-9748
• DOI: 10.1016/0036-9748(83)90340-X

In many beta phase noble metal alloys, surface martensite of approx 10 nm thickness is frequently observed. This surface martensite is stable at temp. well above the temp. M sub S below which martensite forms in the bulk. For Cu--Zn and Cu--Zn--Al the temp. difference amounts to approx 500K. Although the rules underlying the selection of the martensite variants and their structures could be determined, it is not yet clear what the reasons are for the higher stability of the surface martensite. Since M sub S is strongly composition dependent, only a small decrease in Zn content, by approx 6 at.-%, is required to account for the difference of 500 deg C in Cu--Zn. For an evaluation of the martensite stability it would be desirable therefore to know the composition of the subsurface layers. An attempt has been made for binary Cu--Zn, by combining Auger emission spectroscopy (AES), which permits the determination of the composition of the surface layer, with an ion beam bombardment, by which the surface layers are continuously sputtered off. The results show that the most likely reason for the formation of a surface martensite is a compositional change of the near-surface region due to the oxide layer which acts as a sink for Zn atoms. 17 ref.--AA