Premartensitic anelasticity in indium-thallium alloys

The linear and nonlinear low frequency internal friction of In-24 at. pct T1 displays a Curie-Weiss type behavior in the temperature range above the transformation temperature. The critical temperature equals the martensite start temperature. It is proposed that the origin of the observed internal friction is the diffusion controlled interaction of substitutional atoms with the premartensitic strain modulation, tweed. This paper is based on a presentation made in the symposium “Pretransformation Behavior Related to Displacive Transformations in Alloys” presented at the 1986 annual AIME meeting in New Orleans, March 2–6, 1986, under the auspices of the ASM-MSD Structures Committee.     

Electron diffuse scattering studies of premartensitic alloys: β' Cu-Zn, β' Ni-Al,In-TI,and Fe-Ni

Electron diffuse scattering patterns obtained from β' Cu-Zn, β' Ni-Al, In-TI, and Fe-Ni alloys in their premartensitic conditions have been analyzed and compared with Kohn constructions which map Fermi surface segments into the scattering plane. Because of the close correlations between these patterns and constructions, it appears likely that the diffuse electron scattering may be viewed as arising from conduction-electron energy effects on the structure of these alloys. A comparison of the diffuse scattering observations will be made and the possible role of Kohn anomalies as a precursive phenomenon discussed. This paper is based on a presentation made in the symposium “Pre-transformation Behavior Related to Displacive Transformations in Alloys≓ presented at the 1986 annual AIME meeting in New Orleans, March 2–6, 1986, under the auspices of the ASM-MSD Structures Committee.     

Neutron scattering studies of pretransitional phenomena in structural phase transformations

Materials exhibiting structural phase transformations are well known to possess pretransitional phenomena. Below the transition temperature, T_c, an order parameter appears and the pretransitional effects are associated with the fluctuations of the order parameter. Neutron scattering techniques have proved invaluable in studying the temporal and spatial dependence of these fluctuations. SrTiO₃ is the prototypical example of a structural phase transformation exhibiting features observable in other transformations such as martensitic and order-disorder. The experimental evolution of the understanding of the phase transformation in SrTiO₃ will be reviewed and the features observed will be shown to typify other systems. This paper is based on a presentation made at a symposium on “Pretransformation Phenomena, Fluctuations and Related Effects” held at the annual meeting of The Metallurgical Society of AIME, New Orleans, Louisiana, February 18-22, 1979, under the sponsorship of the Structures Activity, Materials Science Division, ASM.     

Premartensitic time dependent X-ray scattering and stress relaxation in an indium-thallium alloy

Synchronous time dependent X-ray scattering and anelastic stress relaxation experiments were carried out to investigate the dynamic premartensitic properties of an In-24 at.% Tl alloy. The relaxation of the X-ray intensity, 0.2 degrees off the 220 Bragg diffraction peak, has been observed under a uniaxial [001] tensile strain of the order of 10⁻⁴ as the temperature approaches the martensitic transformation temperature. The activation energy calculated from the Arrhenius plot of the relaxation times obtained from the X-ray diffraction is 0.78 eV which is equal to the one found previously in the course of an internal friction experiment. However, the activation energy obtained from the anelastic stress relaxation is 0.11 eV. It is proposed that the high activation energy of 0.78 eV represents the energy of formation of a premartensitic strain embryo. The much smaller activation energy of 0.11 eV is interpreted as the activation energy of stress assisted growth of this embryo.     

Structural transformations and mechanical behavior in the premartensitic state of titanium nickelide-based alloys

The premartensitic structural evolution in and the mechanical properties of alloys based on titanium nickelide and other titanium-based intermetallics with a B2-type lattice are studied. The unique mechanical properties of titanium nickelide (anomalously high plasticity, superelasticity) are found to be caused by the realization of specific structural states (SRDO, IDS, R phase) and the formation of a domain nanostructure in the premartensitic state. The dynamics and crystallographic geometry of premartensitic phenomena determine the fine structure of the B2 phase and, quite often, the radical differences in the properties of intermetallic-based alloys with different degrees and systems of alloying.     

X-ray study of the premartensitic phenomena in AuCd

An X-ray study has been carried out in order to investigate the premartensitic phenomena in AuCd alloys. We observed diffuse satellite reflections nearq =(1/3, 1/3,0) and Huang scattering around funda-mental Bragg reflections above the transition temperature to the martensite phase. Satellites observed on (H, K, 0) plane shift off from the commensurate positions, and the shift or the 'incommensurability' forms swirl patterns. These features are the same as the results reported by S. M. Shapiroet al. in a NiTi(Fe) alloy. The results have been discussed in terms of the MLR (modulated lattice relaxation) model and a heterogeneous two phase model. M. Takimoto, formerly with Osaka University     

Neutron radiography of unidirectionally solidifying Sn−Cd alloys

The use of neutron radiography in revealing the solidification process in Sn?Cd alloys is described. It is shown that segregation of cadmium in the liquid and solid as well as in front of the solid-liquid interface occurs. From the respective neutron radiographs an easy evaluation of the partition and diffusion coefficient is possible. An estimate has been made of the temperature of the solid-liquid interface using the observed solute concentrations and the Sn?Cd phase diagram.