Extension Of Supercooled Liquid Region Research Articles

Thermal stability, crystallization and soft magnetic properties of Fe-P-C-based glassy alloys

Thermal stability, crystallization and magnetic properties of Fe80P11C9, Fe80P9B2C9, and Fe77Al3P9B2C9 glassy alloys were investigated. The relationships of glass-forming ability (GFA) with thermal properties and crystallization, magnetic properties with crystallization were also discussed. The variation trend of GFA for these glassy alloys is in agreement with the reduced glass transition temperature. The annealing experiment shows that the primary precipitation phase both for the Fe80P11C9 and Fe80P9B2C9 glassy alloys is α-Fe, and the addition of small amounts of Al is effective for suppression of the formation of α-Fe phase, resulting in the extension of supercooled liquid region and significant enhancement of GFA. The activation energy for primary crystallization calculated by Kissinger's equation indicates the addition of B in Fe–P–C alloy or Al in Fe–P–B–C alloy makes nucleation more difficult, which is responsible for the enhancement of GFA. In addition, it was found that the crystallized Fe80P9B2C9 specimen with ultrafine α-Fe grains exhibits high saturation magnetic polarization of up to 1.60T and low coercive force of about 3.0A/m.

Effect of B Addition on Extension of Supercooled Liquid Region before Crystallization in Pd–Cu–Si Amorphous Alloys

The supercooled liquid region defined by the difference between glass transition temperature (T g ) and crystallization temperature (T x ), ΔT x (= T x - T g ) for a Pd 76 Cu 6 Si 18 amorphous alloy was found to be significantly extended by the replacement of 3 at%B for Si. The replacement causes a decrease in T g and an increase in T x , leading to the maximum value of 70 K for ΔT x . The Pd 76 Cu 6 S 15 B 3 alloy crystallizes through a single-stage exothermic reaction which leads to simultaneous precipitation of Pd 4 Si, Pd 3 Si and Pd 2 S i phases. With further increasing replacement amount of B, the ΔT x decreases significantly, accompanying the change in the crystallization mode to two stages including the primary precipitation of metastable supersaturated Pd solid solution. The crystallized structure after the two-stage reaction for the Pd 76 Cu 6 Si 13 B 5 alloy consists of five phases of Pd, Pd 4 Si, Pd 3 Si, Pd 2 Si and Pd 2 B. By the dissolution of an appropriate amount (about 3 at%) of B element with smaller atomic size and negative heats of mixing against the other constituent elements, the amorphous structure is presumed to change into a higher degree of dense random packed state. As a result, the long-range atomic rearrangement for crystallization required for the precipitation of the three compound phases in the single-stage exothermic reaction becomes difficult, leading to the extension of the supercooled liquid region. The increase in the thermal stability of the supercooled liquid in the Pd 76 Cu 6 Si 15 amorphous alloy is important because of the increase in the ease of the formation of bulk amorphous alloy.

Effect of B Addition on the Extension of Supercooled Liquid Region in Zr–Cu–Al Base Amorphous Alloys

The replacement of Al by B for Zr 65 Cu 27.5 A1 7.5 - x B x amorphous alloys was found to cause an extension of the supercooled liquid region before crystallization. The largest value of the supercooled liquid region(ΔT x ) defined by the difference between crystallization temperature (T x ) and glass transition temperature (T g ) is 100 K for Zr 65 Cu 27.5 B 4 Al 3.5 . The Δ T x value is much larger than that (72 K) for the Zr 65 Cu 27.5 Al 7.5 alloy. The increase is due to the significant increase in T x by the addition of B exceeding the degree of the increase in T g . The crystallization from the supercooled liquid takes place through a single exothermic reaction in the B concentration range less than 4 at%. The crystallized structure consists of Zr 2 Cu, Zr 2 Al and Zr 5 Al 3 for the Zr-Cu-Al alloy and changes into more multiple phases of Zr 2 Cu, Zr 2 Al, Zr 3 Al, Zr 5 Al 3 and ZrB 2 for the Zr 65 Cu 27.5 B 4 Al 3.5 alloy. Besides, the temperature dependence of the storage and loss moduli (E' and E) in the supercooled liquid also changes from the single stage for the Zr-Cu-Al alloy to the two stages for the Zr-Cu-Al-B alloy. The first-stage changes in the E'(T) and E(T) fit between both alloys and the second-stage change for the B-containing alloy takes place in the temperature range above T x of the Zr-Cu-Al ternary alloy. It is therefore concluded that the generation of Zr-B atomic pair with stronger bonding nature and longer relaxation time by the addition of B causes the increase in the thermal stability of supercooled liquid region through the retardation of the crystallization reaction. Furthermore, this is the first evidence on the synthesis of the amorphous alloy with the large Δ T x above 100 K for the Zr-Cu-B-Al alloy containing higher B content as compared with Al content.