Ni-based Bulk Research Articles

Nanocrystallization kinetics of Ni-based bulk amorphous alloy

Nanocrystallization kinetics of Ni-based bulk amorphous alloy

Fillability and Imprintability of High-strength Ni-based Bulk Metallic Glass Prepared by the Precision Die-casting Technique

The fillability and imprintability of a Ni-based bulk metallic glass (BMG) prepared by the precision die-casting was investigated. A three-dimensional microgear made of Ni-based BMG is successfully prepared by the precision die-casting technique. The cast Ni-based BMG has excellent fillability against a microindentation formed by Vickers indentation, and the filling area obtained using a confocal scanning microscope reaches 99%. In addition, the cast Ni-based BMG exhibits excellent imprintability of the die surface even on a nanometer scale. It is therefore concluded that the Ni-based BMG is suitable as a material for micromachines due to its superior fillability and imprintability.

Synthesis of Ni-based bulk metallic glass matrix composites containing ductile brass phase by warm extrusion of gas atomized powders

To prevent catastrophic failure by propagating highly localized shear bands and to overcome the limited dimension of metallic glass, centimeter-scale Ni59Zr20Ti16Si2Sn3 bulk metallic glass matrix composites were fabricated by warm extrusion of a mixture of gas-atomized fully amorphous powders and ductile brass powders. After consolidation, the composite retained the fully amorphous matrix found in the gas-atomized powder combined with the brass second phase. The glass-transition and crystallization temperatures of the extruded material were the same as those of the starting powders. The confined ductile brass phase enabled the bulk metallic glass matrix composites to deform plastically under uniaxial compression at room temperature. The combination of strength and ductility in the inherently brittle Ni-based monolithic materials could be obtained by introducing a ductile phase in the bulk metallic glass matrix. However, control of the volume fraction and distribution of the ductile brass phase was important for the proper combination of the strength and plasticity.

New Cu- and Ni-Based Bulk Glassy Alloys with High Strength of 2500 to 3000 Mpa

New Cu- and Ni-Based Bulk Glassy Alloys with High Strength of 2500 to 3000 Mpa

Ni-based bulk metallic glass formation in the Ni–Nb–Sn and Ni–Nb–Sn–X (X=B,Fe,Cu) alloy systems

Refractory Ni-based bulk metallic glasses are formed in the three-component Ni–Nb–Sn system near a ternary eutectic composition located within the three-phase field bounded by the three intermetallics Ni3Nb, Ni6Nb7 (μ-phase), and Ni2NbSn (BiF3-type). Bulk amorphous alloys of composition Ni60Nb40−xSnx with 3<x<9 were prepared by injection-casting the molten alloys into copper models. X-ray diffraction and differential scanning calorimetry studies show the cast strips to be fully amorphous up to thicknesses from 0.5 to 3 mm as x is varied. Maximum glass-forming ability (GFA) observed when x is between 6 and 7. These refractory bulk amorphous alloys exhibit high glass transition temperatures 881<Tg<895 K, a large, stable, undercooled liquid region with ΔT=Tx−Tg, at ∼40–60 K, very high Vickers hardness (VH∼1000–1280 Kg/mm2), and estimated yield strengths in the range of 3 to 3.8 GPa. The effects of small quaternary additions of B and Fe on the GFA of the ternary alloys are also reported.

Ni-Based Refractory Bulk Amorphous Alloys with High Thermal Stability

Enhancement of thermal stability and glass forming ability in Ni 60 Nb 40-x Ta x (x = 0, 3, 5, 10, 20 at%) alloys has been investigated. The crystallization temperature increases from 660°C in binary Ni 60 Nb 40 amorphous phase to 721°C in Ni 60 Nb 20 Ta 20 amorphous phase. The fully amorphous rod with diameter of 2 mm is fabricated in Ni 60 Nb 30 Ta 10 alloy by an injection casting method. The compressive failure strength of the Ni 60 Nb 30 Ta 10 bulk amorphous alloy is 3346 MPa.

Synthesis of Ni-based bulk amorphous alloys by warm extrusion of amorphous powders

A high strength Ni-based bulk amorphous alloy is synthesized by warm extrusion of gas atomized amorphous powder. The Ni 59Zr 20Ti 16Si 2Sn 3 amorphous powder obtained by a high pressure Ar gas atomization method has a wide super-cooled liquid region of 63 K. Warm extrusion of the amorphous powders in the super-cooled liquid state successfully yielded a fully consolidated bulk amorphous Ni 59Zr 20Ti 16Si 2Sn 3 alloy. The processing conditions for extrusion are obtained from the time–temperature-transformation curve for the onset of crystallization of the amorphous powder. Lower extrusion ratio of 5 is preferred for the retention of the single amorphous phase during extrusion at 848 K. The extruded bulk amorphous Ni 59Zr 20Ti 16Si 2Sn 3 alloy exhibits a high strength level (∼2.0 GPa) similar to that of an as-cast bulk amorphous Ni 59Zr 20Ti 16Si 2Sn 3 alloy (∼2.2 GPa). The mechanical behavior of the extruded alloy under the compressive condition shows no anisotropy in the longitudinal and transverse directions to the extrusion direction.

New Bulk Glassy Ni-Based Alloys with High Strength of 3000 MPa

New Ni-based bulk glassy alloys with high strength and good ductility were synthesized for the first time in Ni–Nb–Ti–Zr base system by the mold-clamp or copper mold casting method. The bulk glassy Ni53Nb20Ti10Zr8Co6Cu3 alloy has a rod shape with diameters up to 3 mm or a sheet shape with thickness up to 1 mm. The glass transition temperature (Tg) and the supercooled liquid region defined by the difference between Tg and crystallization temperature (Tx), ΔTx(=Tx−Tg) are 846 and 51 K, respectively, and no distinct change in Tg, Tx and ΔTx with sample diameter is seen. The Ni-based alloy is located in the vicinity of eutectic composition and has a high reduced glass transition temperature (Tg⁄Tm) of 0.67. The Ni-based bulk glassy alloy also exhibits good mechanical properties, i.e., tensile fracture strength of 2700 MPa, tensile fracture elongation of 2.1%, compressive fracture strength of 3010 MPa and compressive fracture elongation of 2.4%. It is noticed that the tensile fracture strength is the highest among all bulk glassy alloys developed up to date. The success of synthesizing the new Ni-based bulk glassy alloy with good mechanical properties is promising for future uses as a new type of high strength material.

Ni-based bulk amorphous alloys in the Ni–Ti–Zr–Si system

We report on the fabrication and properties of the new Ni-based bulk amorphous alloys in the Ni–Ti–Zr–Si system that have high glass forming ability (GFA) and large undercooled region ( ΔT X), which corresponds to the temperature difference between glass transition temperature and the onset temperature of a first crystallization event. The compositional range for the formation of the amorphous alloys that have large ΔT X (>30 K) is defined in the pseudo-ternary phase diagram Ni–(Ti,Zr)–Si. Some alloys can be fabricated as fully amorphous rods 2 mm diameter through an injection casting method. Si effects on the crystallization behavior of these new Ni-based amorphous alloys are also investigated and related to the GFA and the ΔT X.

Highly corrosion-resistant Ni-based bulk amorphous alloys

Bulk amorphous Ni-Nb-Ta-P alloys were successfully prepared by copper mold casting method. The addition of tantalum is effective in decreasing the corrosion rate. The corrosion rates of the alloys containing certain amounts of tantalum are more than four orders of magnitude lower than that of nickel metal and are almost equivalent to that of tantalum even in aggressive 12 M HCl open to air at 30°C. They are spontaneously passive and are characterized by immune to pitting by anodic polarization. The corrosion behavior of the bulk amorphous alloys is almost the same as corresponding melt-spun amorphous alloy ribbons.

Formation and Mechanical Properties of Bulk Glassy Ni<SUB>57-x</SUB>Ti<SUB>23</SUB>Zr<SUB>15</SUB>Si<SUB>5</SUB>Pd<SUB>x</SUB> Alloys

The glass-forming ability in Ni57−xTi23Zr15Si5Pdx (x=0, 5, 10, 12.5, 15 and 20) alloys as a function of Pd concentration was examined by melt-spinning and copper mold casting methods. All the melt-spun ribbons are in a glassy state. ΔTx(ΔTx=Tx−Tg) and Tg⁄Tm were used to evaluate the glass-forming ability, where Tg,Tx and Tm represent the glass transition, crystallization and melting temperatures, respectively. The observation of large ΔTx and Tg⁄Tm values in the 12.5 at%Pd alloy implies a high glass-forming ability. At this composition, a cylindrical bulk alloy with a diameter of 2 mm was verified to be in a single glassy state. For the bulk cylinder of 3 mm in diameter, the volume fraction of glassy phase is approximately 92%. The compression fracture strength (σ) and Vickers hardness (Hv) of the bulk glassy alloy are 2100 MPa and 620, respectively. These results demonstrate the good mechanical performance of the present Ni-based bulk glassy alloy, which is prominent for future application.

Ni-based bulk amorphous alloys in the Ni–Ti–Zr–(Si, Sn) system

New Ni-based bulk amorphous alloys in the alloy system Ni–Ti–Zr–(Si,Sn) were developed through systematic alloy design based upon the empirical rules for high glass forming alloys. Small additions of Si and/or Sn significantly improved the glass forming ability (GFA) of the alloys Ni57Ti23−xZr20 (Si,Sn)x leading to a Ni-based bulk amorphous alloy. The amorphous ribbons of the alloys Ni57Ti23−xZr20 (Si,Sn)x exhibited very high glass transition temperatures (Tg > 823 K), crystallization temperatures (Tx > 883 K), and large undercooled liquid regions (δTx > 50 K) implying the high GFA of the alloys. Fully amorphous rods with the diameter of up to 2 mm can be fabricated by a copper mold casting method. Development of the new Ni-based bulk amorphous alloys having high Tg,Tx, and δTx expands the practical applications of amorphous alloys as structural materials.

Quaternary and Quinary Ni-based Amorphous Alloys in the Ni-Zr-Ti-X (X=Al, Si, P) and Ni-Zr-Ti-Si-Y (Y=Sn, Mo, Y) Systems

AbstractNew Ni-based bulk amorphous alloys in the alloy system Ni-Zr-Ti-X (X=Al, Si, P) and Ni-Zr- Ti-Si-Y (Y=Sn, Mo, Y) were developed through systematic alloy design based upon the empirical rules for high glass forming ability (GFA). Additions of a small amount of Si and/or Sn to a ternary Ni-Ti-Zr alloy are very effective to increase GFA as well as the undercooled liquid region (ΔTX). Changes in crystallization mode during continuous heating of amorphous phase and lowered liquidus temperature by quaternary and quinary additions are associated with the enhanced GFA and the enlarged ΔTx. Development of new Ni-based amorphous alloys with high GFA and large ΔTx expands structural application of amorphous alloys.

Preparation of New Ni-based Amorphous Alloys with a Large Supercooled Liquid Region

A distinct glass transition and a rather wide supercooled liquid region before crystallization were found in Ni76M5P19 (M=Ti, Zr, Hf or Nb) ternary amorphous alloys. The glass transition temperature (Tg) and the temperature interval of the supercooled liquid region defined by the difference between crystallization temperature (Tx) and Tg, ΔTx(=Tx−Tg) are 659 and 48 K for the M=Ti alloy, 675 and 34 K for the Zr alloy, 687 and 34 K for the Hf alloy, and 668 and 21 K for the Nb alloy, respectively. The reduced glass transition temperature (Tg⁄Tm) shows high values higher than 0.60 for the Ni76M5P19 (M=Ti and Hf) alloys. The high stability of the supercooled liquid against crystallization is due to the satisfaction of the three empirical rules for achievement of high glass-forming ability, i.e., (1) multi-component alloy systems consisting of more than three elements, (2) significant atomic size ratios above 10% among the main three elements, and (3) negative heats of mixing among the main three elements. The tensile fracture strength (σf) and Vickers hardness (Hv) of the Ni-based amorphous alloys are in the ranges of 950 to 1500 MPa and 410 to 455, respectively, which are considerably higher than those for the conventional Ni-based crystalline alloys. The finding of the Nibased amorphous alloys with a wide supercooled liquid region reaching about 50 K is promising for the future development of Ni-based bulk amorphous alloys with high strength and good ductility.

Bulk Amorphous Ni<SUB>75−<I>x</I></SUB>Nb<SUB>5</SUB>M<I><SUB>x</SUB></I>P<SUB>20−<I>y</I></SUB>B<I><SUB>y</SUB></I> (M=Cr, Mo) Alloys with Large Supercooling and High Strength

Bulk amorphous Ni-based alloys with high strength were formed in the diameter range up to 1.0 mm for Ni 65 Nb 5 Cr 5 Mo 5 P 14-16 B 4-6 alloys by copper mold casting. The T g and Δ T x (= T x -T g ) of the bulk amorphous alloys are 703 and 50 K, respectively, for the 4%B alloy and 701 and 61 K, respectively, for the 6%B alloy. There is no difference in thermal stability between the bulk and ribbon alloys. The crystallization takes place through a single exothermic reaction in which crystalline phases of Ni, Ni 3 P, Ni 3 B, Ni 6 Mo 2 P 3 , Cr 3 P and Cr 0.75 Ni 0.25 P precipitate almost simultaneously. The necessity of the long-range atomic rearrangement leading to the simultaneous precipitation of the six crystalline phases seems to be the reason for the high glass-forming ability of the Ni-based alloys. The Ni-based bulk amorphous alloys exhibit high tensile fracture strength (σ f ) of 2690 to 2760 MPa, Young's modulus (E) of 95 to 103 GPa, fracture elongation (e f ) of 2.8% and Vickers hardness (H v ) of 840 to 880. The ratios of 9.8H v /3E and σ f /E are nearly the same as those for the corresponding melt-spun amorphous ribbons. The synthesis of the Ni-based bulk amorphous alloys with the same thermal and mechanical properties as those for the alloy ribbons is encouraging for the future development of bulk amorphous nonferrous alloys with high strength.