Abstract
The limits of occurrence and the morphology of martensite in Cu-Zn-Al alloys with 30 to 50 wt pct Zn and ≤ 1.5 wt pct Al have been investigated. In samples with concentration gradients, various conditions for the competition between martensitic and massive transformation have been observed. Microstructural details of martensite were obtained by combining vibration polishing, chemical or plasma etching and polarized light, backscattered electron channeling contrast or electron backscatter diffraction analysis. Depending on the cooling rate, martensite undergoes a morphological change from self-accommodating thin plates to lenticular shaped plates, which is documented for the first time in Cu-based alloys. The number of martensite twins in the investigated compositional range was found to be significantly smaller than that in commercial Cu-Zn-Al alloys that are used as shape memory alloys.
Highlights
IN Cu-Zn(-Al) alloys, two different types of concentration invariant phase transformations are observed at high quenching rates, massive and martensitic transformation
The martensite morphology in Cu-Zn-Al alloys was observed be only plate martensite,[8,9,10,11] which represents a distinct difference to other alloy systems in which several different types of martensite morphologies are
The combination of the presented preparation methods offers the possibility to systematically scan the system for suitable concentrations for different types of phase transformations and potential applications as, e.g., shape memory alloys
Summary
IN Cu-Zn(-Al) alloys, two different types of concentration invariant phase transformations are observed at high quenching rates, massive and martensitic transformation. Typical transformation rates in Cu-Zn-based alloys are in the order of 10À2 m/ s[2] and are not accompanied by long-range diffusion, but only by diffusion in the interfacial region. The martensitic transformation is diffusionless and characterized by a cooperative movement of atoms across an interface, transferring a parent into a product crystal structure while retaining atomic neighborhoods.[5,6] The growth rates are in the order of 103 m/ s[7] and among the highest rates observed in solids.
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