The effect of quenching treatment on the reversible martensitic transformation in CuAlBe alloys

The metastable beta phase, retained on rapid cooling of CuAlBe alloys, subsequently undergoes a diffusionless transformation to martensite over a temperature range that strongly depends on composition. Experiments have been conducted on CuAlBe alloys that involved close control of the quenching variables to examine the effect of quenching temperature, quenching medium, and specimen mass and thickness on the characteristics of the first reverse transformation, and subsequent forward and reverse transformations. The martensite formed on quenching was found to be stabilised with respect to reverse transformation during the first heating cycle, with reversion occurring over two distinct temperature ranges. The relative volume fractions of parent phase formed over these two ranges was found to depend on the quenching conditions. Monitoring of the transformation was performed by DSC and it was found that stabilisation is also sensitive to the heating rate through the reverse transformation range. Both stabilisation effects were eliminated by transformation cycling, indicating that they are transient effects arising from the initial quench. It is proposed that the lower temperature transient stabilisation effect is due mainly to vacancy pinning and the higher temperature effect ('hyperstabilisation') is a result of suppression of DO3 ordering by rapid quenching. (C) 2004 Elsevier B.V. All rights reserved.