A New Thermodilatometric Instrument for Thin Metallic Ribbons

Abstract

A thermodilatometer was designed allowing metallic specimens in the form of thin ribbon to be heated at slow heating rates (1 to 5°C min-1) from room temperature up to 1000°C in an ultra-high vacuum (10-7 Pa). This dilatometer is a direct type and highly sensitive; amplification coefficient is 25 000. The transparent silica specimen holder is of the tensile type and allows the specimen to be fixed in a unique plane of the space. The specimen is 40 mm in length and ≈50 μm thick. A tensile stress of ≈5×104 Pa is applied during the experiment. One or more strips can be used for each experiment. This device was used for studying metallic glasses: Fe78B13Si9 and CuxZr(100-x) (x = 33, 40, and 46). Thermal expansion coefficients were determined on heating and cooling. Isothermal annealings were also performed in situ in the dilatometer. On heating, the “as-quenched” ribbons, structural relaxation, Curie point, glass transition, and crystallization are successively evidenced on the dilatometric curves. Structural relaxation results in a progressive and small shrinkage of the specimens (ΔL/L < -4 × 10-4). Curie point results in sharp shrinkage. Glass transition is manifested by the creep of the specimen (ΔL/L ≈ +2.0 × 10-3), and crystallization of the amorphous phase results in a large shrinkage (ΔL/L ≈ - 1.00 × 10-3). Relaxation rate, Curie point, glass transition, and crystallization of the specimens were also determined by differential scanning calorimetry (DSC). The irreversibility of structural relaxation below glass transition is well evidenced by DSC and thermodilatometry.