La Amorphous Alloys Research Articles

Crystallization behaviors of Al–Ni–La amorphous alloys with trace Ti and B

Abstract Effects of the single or simultaneous addition of trace Ti and B (⩽1 at.%) on the glass-forming ability (GFA) and crystallization behaviors of Al88Ni6La6 and Al89Ni6La5 amorphous alloys were investigated by X-ray diffraction and differential scanning calorimetry. The addition of trace Ti and B deteriorates the GFA, but improves the thermal stability especially if Ti is added singly. The crystallization onset temperature Tx1 of the first exothermic peak increases by 29.5 and 18.0 K when 1% of the Al atoms in Al88Ni6La6 and Al89Ni6La5 are replaced by Ti, respectively. However, the primary phase during annealing remains unchanged.

Effects of replacing Ni by Co on the crystallization behaviors of Al–Ni–La amorphous alloys

Effects of replacing Ni by Co on the crystallization behaviors of three Al–Ni–La amorphous alloys, i.e. Al 85Ni 9La 6, Al 86Ni 9La 5 and Al 87Ni 8La 5 were investigated by X-ray diffraction and differential scanning calorimeter. The results show that the glass-forming ability decreases when Ni is replaced by excessive Co. Meanwhile replacing Ni by Co improves the thermal stability, enlarges the supercooled liquid region Δ T x and promotes the precipitation of the metastable phase(s) as the primary phase. The apparent activation energy E a1 of the first reaction changes complicatedly during the replacement and is strongly dependent on the type of the primary phase, i.e. diffusion of atoms.

Dependences of the crystallization behavior of Al–Ni–La amorphous alloys on La and Ni contents

Crystallization behaviors of Al–Ni–La amorphous alloys with a fixed Ni (La) content of 6at.% were investigated by X-ray diffraction and differential scanning calorimeter when the La (Ni) content changes from 3 to 9at.%. The results show that the thermal stability of the amorphous alloys monotonically increases with increasing the La (Ni) content. Glass transition only exists in the alloys with the La (Ni) content higher than 6at.%. La plays a more significant role than Ni in promoting the glass-forming ability, improving the thermal stability, stabilizing the supercooled liquid region, depressing the precipitation of fcc-Al in the first crystallization process and increasing the apparent activation energy of the first reaction.

Thermal stability and primary phase of Al–Ni(Cu)–La amorphous alloys

Abstract Thermal stability and primary phase of Al 85+ x Ni 9− x La 6 ( x = 0–6) and Al 85 Ni 9− x Cu x La 6 ( x = 0–9) amorphous alloys were investigated by X-ray diffraction and differential scanning calorimeter. It is revealed that replacing Ni in the Al 85 Ni 9 La 6 alloy by Cu decreases the thermal stability and makes the primary phase change from intermetallic compounds to single fcc-Al as the Cu content reaches and exceeds 4 at.%. When the Ni and La contents are fixed, replacing Al by Cu increases the thermal stability but also promotes the precipitation of single fcc-Al as the primary phase.

Effects of La content on the glass transition and crystallization process of Al–Ni–La amorphous alloys

Effects of La content on the glass transition and crystallization process of Al 94− x Ni 6La x ( x = 3–9) amorphous alloys were investigated by X-ray diffraction and differential scanning calorimeter. The results show that the thermal stability increases with increasing the La content. The crystallization changes from a two-stage process without glass transition at x = 3–6 to a three-stage one with obvious glass transition at x = 7–9. The first crystallization process results in precipitation of single fcc-Al at x = 3–5, fcc-Al plus metastable phase(s) at x = 6 and 7, and single metastable phase at x = 8 and 9. The first crystallization process at x = 4 and 5 is the growth of quenched-in nuclei, whereas that at x = 6, 7 and 9 is the diffusion-controlled growth with a decreasing, constant and increasing nucleation rate, respectively. The activation energy for the first crystallization process is larger in the eutectic reaction than that in the primary reaction, and is the highest when the number of the products is the most.

Thermal stabilities and discharge capacities of melt-spun Mg–Ni-based amorphous alloys

Mg–Ni–M (M=Ca, La or Pd) ternary alloys were synthesized by the melt-spinning technique. All as-solidified alloys possessed an amorphous single phase by the additional effect of the third element, though it was difficult to obtain an amorphous Mg 67Ni 33 binary alloy by melt-spinning. We examined the thermal stability and electrochemical cyclic life property of the ternary amorphous alloys. The crystallization temperature of the amorphous alloys increases with increasing M content. All the alloys except Mg 67Ni 28Pd 5 examined in the present study maintain the amorphous structure even after hydrogen absorption at 373 K for Mg–Ni–Ca and Mg–Ni–Pd and at 423 K for Mg–Ni–La. The crystallization temperature increases by absorbing hydrogen, indicating that the alloys are thermally stabilized by hydrogen absorption. In the electrochemical cyclic life measurements up to five cycles, the Mg–Ni–Pd amorphous alloys exhibit high discharge capacities ranging from 100 to 400 mA h/g as well as small cyclic life degradation tendency, though the Mg–Ni–Ca and Mg–Ni–La amorphous alloys possess small discharge capacities of 10–100 mA h/g with significant cyclic life degradation. It is thus concluded that the good cyclic life property of the amorphous hydrogen storage alloys can be obtained by application of the melt-spinning technique to Mg-based alloys with appropriate alloy compositions.

Nanocrystalline Mixed Structure Prepared by Crystallization of Cu–Ag–La Amorphous Alloys

New amorphous alloys in the Cu-Ag-La system were found to form in a wide composition range of 20 to 70 at% Ag and 3 to 10%La by melt spinning, despite that the Cu-Ag binary system is an insoluble type and no fcc single phase could be obtained in the binary system by melt spinning. The origin of the remarkable effect of La on the glass formation is probably due to the difficulty of the precipitation of a crystalline phase from the supercooled liquid containing La. The liquid consisting of the three constituent elements with significantly different atomic sizes (La>Ag>Cu) is expected to have a highly dense random packed structure which inhibits the precipitation. These ternary amorphous alloys have good bending ductility. The Vickers hardness is in the range of 310 to 330 and tends to increase with increasing La content. The amorphous alloys containing less than 6 at% La subjected to continuous heating crystallized through two stages of Am → Am + fccCu(Ag) + fccAg(Cu) → Cu + Ag + unknown compound. The Cu(Ag) and Ag(Cu) phases are in a metastable state enriched with Ag and Cu, respectively. Particles of these phases have an ellipsoidal morphology with a diameter of about 3 nm and a length of about 8 nm. This study emphasizes the synthesis of the nanoscale mixed structure consisting of two kinds of fcc phases by the crystallization of the Cu-Ag-La amorphous alloys containing the insoluble elements as main constituent components.

Fabrication and Mechanical Properties of Mg–Zn–La Amorphous Alloys Containing Nanoscale hcp-Mg Particles

An amorphous single phase and coexistent amorphous and hcp-Mg phases in the Mg-Zn-La system were found to form in the composition ranges of 20 to 40%Zn and 0 to 12%La and 12 to 20%Zn and 0 to 4%La, respectively. The hcp phase has an ellipsoidal morphology and the particle size and interparticle distance are in the range of 5 to 10 nm and 3 to 10 nm, respectively. The mixed phase alloys exhibit high mechanical strength combined with good ductility and the tensile strength (σ B ) and fracture elongation (∈ f ) at 288 K are 675 MPa and 4.3% for Mg 85 Zn 12 La 3

Mg–Ni–La Amorphous Alloys with a Wide Supercooled Liquid Region

Mg–Ni–La Amorphous Alloys with a Wide Supercooled Liquid Region