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Transformation elasticity in polycrystaline Cu-Zn-Sn alloy

University of British Columbia

A study has been made of the elasticity associated with the martensite transformation in the polycrystalline β-phase alloy of composition Cu-33.6 wt. % Zn-4 wt. % Sn tested at room temperature. The mechanical properties of the material undergoing the stress induced martensite transformation have been examined. These properties are influenced by the elastic anisotropy of the bcc β-phase, the development, preferential distribution and morphology and the mechanical properties of the transformation product. The elastic shape change associated with the elastically accommodated, stress-induced martensitic transformation was always found to be accompanied by some plastic deformation. A relationship between the β-grain size, the sample thickness and the deformation response was observed. Specimens with grains extending through the sample thickness exhibited large reversible strains (∼2.5%), whereas specimens with a much smaller grain size/thickness ratio (<1) exhibited only limited transformation elasticity. The morphology of the thermal martensite and the Ms temperature was also found to be influenced by the ratio grain size/thickness (g.s./t). A lower Ms temperature was associated with a decreasing g.s./t ratio; only self-accommodating burst martensite was observed in very fine grained material. The Af temperature increased with a decreasing g.s./t ratio. Repeated loading (cycling) reduced the hysteresis of the stress strain curve for all g.s./t ratios tested, but was always accompanied by plastic deformation of the matrix and the development of non-reversible deformation martensite. The experimentally determined habit plane for the thermal and the stress induced martensite were in moderate agreement with the planes predicted by the phenomenological martensite theory (W.L.R.) assuming a {110} <1Ī0> microscopic shear.

Text

2011-03-29

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http://hdl.handle.net/2429/33042

Metals and Materials Engineering

University of British Columbia

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