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Polycrystalline alloys with tensile strength (sigma(f)) in Zr-Al-Cu-Pd and Zr-Al-Cu-Pd-Fe systems were formed by partial crystallization of cast glassy alloys. The alloys consist of nanometer scale Zr(2)(Cu,Pd) surrounded by a glassy phase. The particle size and interparticle spacing of the compound are less than 10 and 2 nm, respectively. The crystallization of a ternary Zr(60)Al(10)Cu(30) amorphous alloy occurs by the simultaneous precipitation of Zr(2)Al and Zr(2)Cu with particle size of 200 nm and hence the addition of Pd is essential for formation of the nanostructure (NS). The NS cylindrical alloys of 2-3 mm in diameter keep good ductility in the volume fraction (V(f)) range of the compound below 40%. The sigma(f) and Young's modulus (E) increase from 1760 MPa and 81.5 GPa, respectively, at V(f) = 0% to 1880 MPa and 89.5 GPa respectively, at V(f) = 40% for the Zr(60)Al(10)Cu(20)Pd(10) alloy. The formation of the NS alloys with high sigma(f) in coexistence with the compound is presumably because the remaining glassy phase contains free volumes by quenching from the supercooled liquid. The synthesis of the high-strength bulk NS alloys is important for future development of new high-strength materials. (C) 1999 Elsevier Science B.V. All rights reserved.

Partial crystallization of cast bulk amorphous alloys in Zr-Al-Cu-Pd and Zr-Al-Cu-Pd-Fe systems was found to cause bulk nanocrystalline alloys with high tensile strength to (sigma(f)). The nanostructure alloys consist of nanoscale bct- Zr-2(Cu, Pd) surrounded by the remaining amorphous phase. The particle size and interparticle spacing of the compound are less than 10 and 1 nm, respectively. The crystallization of a ternary Zr60Al10Cu30 amorphous alloy occurs by the simultaneous precipitation of Zr2Cu and Zr2Al phases with large particle sizes of 400 to 500 nm and hence the addition of Pd is essential for formation of the nanostructure. The Pd has much larger negative heats of mixing against Zr and the resulting Zr-Pd atomic pair seems to act as preferential nucleation sites leading to the precipitation of Zr-2(Cu, Pd). The nanostructure alloys in the cast cylinder of 4 to 5 mm in diameter keep good ductility in the volume fraction (V-f) range of the compound below 30 to 40 %. The sigma(f), Young's modulus (E) and fracture elongation (epsilon(f)) increase from 1760 MPa, 81.5 GPa and 2.10 %, respectively, at V-f=0 % to 1880 MPa, 89.5 GPa and 2.17 %, respectively, at V-f=40 % for the Zr60Al10Cu20Pd10 alloy and from 1750 MPa, 81.1 GPa and 2.21 %, respectively, at V-f=0 % to 1850 MPa, 85.6 GPa and 2.28 %, respectively, at V-f=28 % for the Zr60Al10Cu15Pd10Fe5 alloy. The formation of the high-strength bulk nanostructure alloys in coexistence with the compound is presumably due to the reentrance of free volumes into the remaining amorphous phase caused by quenching from the supercooled liquid region.

Bulk nanocrystalline alloys with good ductility and high tensile strength (a,) in Zr-Al-Cu-Pd and Zr-Al-Cu-Pd-Fe systems were formed by partial crystallization of cast bulk amorphous alloys. The nanostructure alloys consist of nanoscale Zr,(Cu, Pd) compound surrounded by the remaining amorphous phase. The particle size and interparticle spacing of the compound are less than 10 and 2 nm, respectively. The crystallization of a ternary Zr60Al10Cu30 amorphous alloy occurs by the simultaneous precipitation of Zr2Al and Zr2Cu phases with large particle size of about 500 nm and hence the addition of Pd is essential for formation of the nanostructure. The nanostructure alloys in the cast cylinder of 2 to 3 mm in diameter keep good ductility in the volume fraction (V-f) range of the compound phase below 20 to 40%. The sigma(f), Young's modulus (E) and fracture elongation (epsilon) increase from 1760 MPa, 81.5 GPa and 2.10%, respectively, at V-f = 0% to 1880 MPa, 89.5 GPa and 2.17%, respectively, at V-f = 40% for the Zr60Al10Cu20Pd10 alloy and from 1750 MPa, 81.1 GPa and 2.21%, respectively, at V-f = 0% to 1850 MPa, 85.6 GPa and 2.28%, respectively, at V-f = 28% for the Zr60Al10Cu15Pd10Fe5 alloy. The formation of the bulk nanostructure alloys with high sigma(f) and good ductility in coexistent with the compound is presumably because the remaining amorphous phase can contain a number of free volumes by water quenching from the supercooled liquid region. The synthesis of the high-strength bulk amorphous alloys containing nanoscale compounds is important for future development of a new type of high-strength material.

Bulk amorphous alloys with thicknesses up to 75 mm and a wide supercooled liquid region reaching 127 K before crystallization have been found to be fabricated in a number of multicomponent systems which satisfy the three empirical rules for the achievement of large glass-forming ability, i.e., (1) multicomponent alloy systems consisting of more than three constituent elements, (2) significantly different atomic size ratios above 12 % among the main constituent elements, and (3) negative heats of mixing among their elements. The scientific significance of the three empirical rules has been proved based on a number of experimental data as well as on the kinetic theories of the nucleation and growth of a crystalline phase. By choosing appropriate compositions which satisfy the three empirical rules, bulk amorphous alloys in Mg-, lanthanide metal-, Zr-, Pd-, Fe- and Co-based systems were produced in cylindrical and sheet forms by various solidification processes. The bulk amorphous alloys exhibit high tensile strength, good ductility, high elastic energy, high impact fracture energy and high corrosion resistance for Zr-based system and good soft magnetic properties for Fe-based system. Furthermore, their bulk amorphous alloys heated in the supercooled liquid region can be deformed into various shapes by viscous flow. The ideal Newtonian flow has been achieved in the supercooled liquid. The utilization of the ideal superplasticity enabled the achievement of an extremely large elongation exceeding 15000 %. These excellent data allow us to expect that the bulk amorphous alloys with a wide thickness range up to 75 mm develop as a new type of engineering material.

Hard magnetic Nd60Fe30Si10 amorphous ribbons with large thicknesses up to 107 mu m were prepared by melt spinning. The hard magnetic properties of this alloy increase with increasing ribbon thickness to 107 mu m, and the largest values of remanence, coercivity (iH(c)) and maximum energy product (BH)(max) are 0.15 T, 412 kA/m and 3.8 kJ/m(3), respectively. The main feature of this amorphous alloy is that the hard magnetic properties with high iH(c) are obtained in the melt-spun amorphous state without crystallinity. The combination of the large glass-forming ability and hard magnetic properties is important for the future development of hard magnetic bulk amorphous alloys.

An amorphous phase in Ln-Fe-Al (Ln=Nd and Pr) systems is formed in dde composition ranges of 0 to 90 at% Fe and 0 to 93 at% Al by melt spinning, Ferromagnetic Ln(90-x)Fe(x)Al(10) bulk amorphous alloys with high coercive force (H-i(c)) at room temperature are obtained by copper mold Easting. The maximum diameter of the cylindrical amorphous samples is 12 mm far the Nd-30%Fe-Al alloy and 3 mn far the Pr-30%Fe-Al alloys and decreases with deviating Fe content. The extremely high T-x/T-m and small Delta T-m(=T-m-T-x), which are evaluated by the crystallization (T-x) temperature (T-x) and melting temperature (T-m), are the reason for the achievement of large glass-forming ability in these systems, The bulk amorphous Ln(60)Fe(30)Al(10) alloys are ferromagnetic with the Curie temperature of 515 to 600 K which are higher than those for Nd-Fe and Pr-Fe binary amorphous ribbons. The remanence and H-i(c) are 0.089 to 0.122 T and 277 to 321 kA/m, respectively, and the crystallization to Ln+Al(2)Ln+delta causes a ferromagnetic- to -paramagnetic transition. Thus, the hard magnetic properties are achieved only in the amorphous state.

New bulk amorphous alloys exhibiting a wide supercooled liquid region before crystallization were found in Fe-(Co,Ni)-(Zr,Nb,Ta)-(Mo,W)-B systems. The T-g is as high as about 870 K and the supercooled liquid region reaches 88 K. The high thermal stability of the supercooled liquid enabled the production of bulk amorphous alloys with diameters up to 6 mm. These bulk amorphous alloys exhibit a high compressive strength of 3800 MPa, high Vickers hardness of 1360, and high corrosion resistance. Besides, the amorphous alloys exhibit a high magnetic-flux density of 0.74-0.96 T, low coercivity of 1.1-3.2 A/m, high permeability exceeding 1.2 X 10(4) at 1 kHz, and low magnetostriction of about 12 X 10(-6). (C) 1997 American Institute of Physics.

An amorphous single phase was formed in wide composition ranges of rapidly solidified Al-Si-Fe-Ni and Al-Si-Fe-Co alloys. In comparison with Al-Si-Fe system, the composition range of the amorphous alloys is the widest in the Al-Si-Fe-Ni system and becomes narrower in the kr-Si-Fe-Co system in the direction of Fe concentration axis. The extension of the compositional range in the direction of the Si concentration axis leads to the formation of new amorphous alloys with high silicon concentrations: Si45Al31Fe20Ni4 Si45Al36Fe15Ni4 and Si45Al41Fe10Co4. The crystallized structure consists of fee Al, cubic Si and some ternary compounds of AlFeSi, AlSiNi, AlFeNi and AlSiCo depending on their alloy compositions.

The magnetic properties of a partially crystallized Fe90Nd7B3 amorphous alloy were improved by a two-stage crystallization treatment: (I) the first-stage annealing (923 K x 300 s) is employed as an optimal treatment to obtain rather good hard magnetic properties and is followed by water quenching; (2) the second-stage annealing at 723 K for 60-3600 s is followed by water quenching. The remanence (B-r), coercive field (H-i(c)) and maximum energy product ((BH)(max)) are 1.00 T, 200 kA m(-1) and 100 kJ m(-3), respectively, al the first-stage, and increase to 1.16 T, 232 kA m(-1) and 135 kJ m(-3), respectively, by the second annealing stage. The further increase in the hard magnetic properties is presumably due to the increase in the precipitation amount of nanoscale b.c.c.-Fe phase with high saturation magnetization (B-s) and high Curie temperature (T-c) in the retainment of the nanoscale grains of the former b.c.c.-Fe and Ee(14)Nd(2)B phases. The finding of the usefulness of the multistage crystallization treatment leading to the formation of the fully crystallized nanostructure is important because of the expectation of the further improvement of functional properties resulting from the nanoscale mixed structure. (C) 1997 Elsevier Science S.A.

New Fe-based amorphous alloys in Fe-Co-Ni-Zr-B system exhibiting a wide supercooled liquid region before crystallization and good soft magnetic properties were found to be formed by melt spinning. The composition range of the amorphous (Fe1-x-yCoxNiy)(70)Zr10B20 alloys with the wide supercooled liquid region above 50 K extends from 0 to 36 at%Co and 0 to 30%Ni and the largest value of the supercooled liquid region defined by the difference between the glass transition temperature (T-g) and crystallization temperature (T-x), Delta T-x(= T-x - T-g) is 68 K for Fe56Co7Ni7Zr10B20. The crystallization from the supercooled liquid of the Fe56Co7Ni7Zr10B20 alloy upon continuous healing occurs through a single stage and the resulting crystallized structure consists of alpha-Fe, Fe2Zr and Fe3B phases containing Co and Ni elements. These Fe-based amorphous alloys exhibit good soft magnetic properties and the saturation magnetization, coercive force, permeability at 1 kHz and Curie temperature are respectively 0.96 T, 2.41 A/m, 17700 and 567 K for the amorphous Fe56Co7Ni7Zr10B20 alloy annealed for 600 s at 750 K. The finding of the Fe-based amorphous alloys with good soft magnetic properties and high thermal stability of the supercooled liquid is important for future development of ferromagnetic bulk amorphous alloys.

The effect of Si additions on the thermal stability of the supercooled liquid before crystallization, glass-forming ability (GFA) and soft magnetic properties was examined for amorphous alloy series Fe72-xAl5Ga2P11C6B4Si2, Fe72Al5-xGa2P11C6B4Six, Fe72Al5Ga2P11-xC6B4Six and Fe72Al5Ga2P11C6-xB4Sx. The increases in the thermal stability and GFA and the improvement of soft magnetic properties were recognized in the replacements of P by 1 to 2 at%Si and of C by 1 at%Si. The supercooled liquid region (Delta T-x) defined by the difference between crystallization temperature (T-x) and glass transition temperature (T-g) increases from 53 K for Fe72Al5Ga2P11C6B4 to 58 K for Fe72Al5Ga2P11C5B4Si1. The maximum thickness for glass formation (t(max)) by copper mold casting increases from 1 mm for the Fe-Al-Ga-P-C-B alloy to 2 mm for the Fe72Al5Ga2P10C6B4Si1 alloy. The increases in Delta T-x and t(max) are presumably because of the increase in the degree of the satisfaction of the three empirical rules for the achievement of large glass-forming ability, i.e., (1) multicomponent alloy systems consisting of more than three elements, (2) significantly different atomic size ratios above about 12% and (3) negative heats of mixing. The soft magnetic properties are also improved by the replacement of 1 at%Si for P or C through the increase in the squareness ratio of B-H loop (B-r/B-s) and the decrease in coercive force (H-c). The best soft magnetic properties for the bulk amorphous alloys are obtained for the Fe72Al5Ga2P10C6B4Si1 alloy and the saturation magnetization (B-s), H-c, B-r/B-s, and Curie temperature are 1.14 T, 1.5 A/m, 0.45 and 594 K, respectively. The success of forming the Fe-based bulk amorphous alloys of 2 mm in thickness exhibiting the good soft magnetic properties is promising for future development as a new type of soft magnetic material.

The amorphous phase in the Nd-Fe-Al and Pr-Fe-Al systems is formed in extremely wide composition ranges of 0 to 90 at% Fe and 0 to 93 at% Al by melt spinning. Ferromagnetic Ln(90-x)Fe(x)Al(10) (Ln=Nd or Pr) bulk amorphous alloys with high coercive force at room temperature are obtained by a copper mold casting method. The maximum diameter of the cylindrical amorphous samples is 12 mm for the Nd-30%Fe-Al alloy and 3 mm for the Pr-30%Fe-Al alloys and decreases with deviating Fe content. Neither glass transition nor supercooled liquid region is observed in the temperature range before crystallization (T < T-x), which is different from other bulk amorphous alloys exhibiting wide supercooled liquid regions. The extremely high T-x/T-n and small Delta T-m(=T-m-T-x) values are the reason for the achievement of large glass-forming ability in these systems. The bulk amorphous Ln(60)Fe(30)Al(10) alloys are ferromagnetic with the Curie temperature (T-c) of 515 to 600 K which are much higher than those for Nd-Fe and Pr-Fe binary amorphous ribbons. The remanence (B-r) and intrinsic coercive force (H-i(c)) are 0.089 to 0.122 T and 277 to 321 kA/m, respectively, and the crystallization to Ln+Al(2)Ln+delta phases causes a ferromagnetic- to -paramagnetic phase transition. Thus, the hard magnetic properties are achieved only in the amorphous state.

The local ordering structure of amorphous Fe89Nd7B4 and Fe89Zr7B4 alloys has been determined by anomalous X-ray scattering (AXS) coupled with the conventional X-ray diffraction method using Mo K-alpha radiation. The atomic distance and its coordination number in the nearest neighbor region obtained by a least-squares variational method indicate that the local ordering structure of both amorphous alloys appears to be no closer to the crystalline precipitates than a random packing of the present alloy composition and then any specific different structural feature could not be suggested in these two as-quenched amorphous alloys.

The amorphous phase in the Pr-Fe-Al system is formed in an extremely wide composition range of 0 to 90 at% Fe and 0 to 93 at% Al by melt spinning. Ferromagnetic Pr90-xFexAl10 bulk amorphous alloys with high coercive force at room temperature are obtained by a copper mold casting method. The maximum diameter of the cylindrical amorphous samples with a length of 50 mm is 3 mm for the 30%Fe alloy and 1 mm for the 20%Fe, 40%Fe and 50%Fe alloys. Neither the glass transition nor the supercooled liquid region is observed in the temperature range before crystallization (T < T-x), which is different from other bulk amorphous alloys exhibiting wide supercooled liquid regions. The extremely high T-x/T-m and small Delta T-m (= T-m-T-x) values are the reason for the achievement of large glass-forming ability in this system. The bulk amorphous Pr60Fe30Al10 alloy is ferromagnetic with the Curie temperature (T-c) of 515 K which is higher than the highest T-c of 470 K for Pr-Fe binary amorphous ribbons. The remanence (B-r) and intrinsic coercive force (H-i(c)) are 0.089 T and 300 kA/m, respectively, and the crystallization to Pr+Al2Pr+delta phases causes a ferromagnetic-to-paramagnetic phase transition. Thus, the hard magnetic properties are achieved only in the amorphous state.

Fe-based amorphous alloys in Fe- (Al,Ga)-(P,B,C,Si) system were found to exhibit a wide supercooled liquid region exceeding 50 K before crystallization. The high stability of the supercooled liquid enabled the production of cylindrical bulk amorphous alloys with diameters up to 2 mm by copper mold casting. The Pe-based bulk amorphous alloys exhibit ferromagnetism with the Curie temperature of about 600 K. The saturation magnetization (Bs), coercivity (Hc) and permeability (mu(e)) at 1 kHz in as-quenched state are 1.07 T, 12.7 A/m and 3600, respectively, for Fe73Al5Ga2P11C5B4 and 1.14 T, 0.5 A/m and 3200, respectively for Fe72Al5Ga2P10C6B4Si1. Besides, the use of the Fe-based amorphous alloys enabled the production of thick amorphous ribbons above 100 mu m in thickness and the thick samples also exhibit good soft magnetic properties. The success of synthesizing the bulk Fe-based amorphous alloys with good soft magnetic properties is promising for future development as a new type of soft magnetic materials.

Bulk amorphous Nd70Fe20Al10, Nd65Fe25Al10 and Nd60Fe30Al10 alloys with hard magnetic properties were produced in a cylindrical form with a diameter of 12 mm and a length of 70 mm by sucking their molten alloys into a copper mold. The sucking force was generated from the rapid movement (5.0 m/s) of piston with a diameter of 12 mm which was set at the center of the copper mold. The casting velocity was evaluated to be as high as 3.5 kg/s. Neither cavity nor hole is seen on the outer surface of the bulk amorphous alloy and the crystallization temperature (T-x) and melting temperature (T-m) are 761 and 866 K, respectively, for the bulk amorphous Nd70Fe20Al10 alloy. Consequently, the temperature interval of supercooled liquid defined by the difference between T-m and T-x, Delta T-m(= T-m-T-x) is as small as 105 K and the reduced crystallization temperature (T-x/T-m) is as high as 0.88. The small Delta T-m and high T-x/T-m values are presumed to be the origin for the achievement of the large glass-forming ability for the Nd-Fe-Al alloys. The bulk amorphous Nd70Fe20Al10, Nd65Fe25Al10 and Nd60Fe30Al10 cylinders exhibit hard magnetic properties of 0.076 to 0.086 T for remanence, 291 to 321 kA/m for intrinsic coercive held and 13 to 16 kJ/m(3) for maximum energy product at 298 K which are nearly the same as those for the corresponding bulk amorphous cylinders with diameters of 1 to 5 mm prepared by conventional casting. The hard magnetic properties for the Nd-Fe-Al amorphous alloys with large glass-forming ability are promising for future progress as a new type of hard magnetic materials.

This paper reviews our recent results of the soft and hard magnetic properties of nanocrystalline Fe-rich Fe-M-B (M=Nd or Zr) base alloys containing an intergranular amorphous phase. Based on the previous results that the soft magnetic alloys in Fe-Si-B-Nb-Cu and Fe-Zr-B systems do not have zero magnetostriction (lambda(s)), the effect of the additional Al or Si on the lambda(s) and magnetic properties was examined for the nanocrystalline Fe-Zr-B Al and Fe-Zr-B-Si alloys. The soft magnetic properties of high Bs above 1.5 T and high mu(e) above 1.5x10(4) combined with zero lambda(s) were obtained for the Fe88Zr7B3Al2 and Fe86Zr7B3Si4 alloys annealed for 3.6 ks in the annealing temperature (Ta) range of 823 to 923 K. This is in contrast to the previous result that the good soft magnetic properties of the nanocrystalline Fe90Zr7B3 alloy are obtained in the narrow Ta range around 923 K. The remarkable extension of the Ta range seems to be attributed to the zero lambda(s). The replacement of Zr by Nd in the Fe(90)M(7)B(3) alloys was found to cause rather good hard magnetic properties of 1.3 T for Br. 260 kA/m for iHc and 146 kJ/m(3) for (BH)(max) in a tripler nanostructure of bcc-Fe with a size of 20 nm, tetragonal Fe14Nd2B with a size of 15 nm and intergranular amorphous phase with a thickness of 5 to 10 nm. The hard magnetic properties are obtained for the nanostructure containing 80 % soft magnetic phases and 20 % Fe14Nd2B in volume. The notable result is presumably due to the effective action of the intergranular amorphous network phase which can act as a resistance against the nucleation of the reversion of magnetic domain walls leading to the increase in iHc as well as an exchange magnetic coupling medium between bcc-Fe and bcc-Fe or tetragonal Fe14Nd2B phases leading to the high Br. This presumption is also supported from the result that no good hard magnetic properties are obtained for the over annealed sample without intergranular amorphous phase as well as for the use of the sample which does not consist of a mostly single amorphous phase in the as-quenched state. Thus, the soft and hard magnetic properties for the Fe-M-B alloys are obtained only in the optimal nanostructures. The fabrication of a new nanostructure is expected to cause the appearance of other function properties el en at compositions where no useful properties have not been obtained.

An amorphous phase in Nd-Fe-Al system was formed in an extremely wide composition range of 0 to 90 at% Fe and 0 to 93 at% Al by melt spinning. Based on the information on the amorphous formation, ferromagnetic Nd90-xFexAl10 bulk amorphous alloys with high coercive force at room temperature were obtained by a copper mold casting method. The maximum diameter of the cylindrical amorphous samples with a length of 50 mm is about 7 mm for the 20%Fe alloy and about 4 mm for the 30%Fe alloy. Neither glass transition nor supercooled liquid region is observed in the temperature range before crystallization, being different from previous bulk glassy alloys exhibiting a wide supercooled liquid region before crystallization. The onset temperature of crystallization (T-x) and melting temperature (T-m) are measured to be 778 and 863 K, respectively, for the Nd70Fe20Al10 alloy. The resulting reduced ratio of T-x/T-m is as high as 0.90 and the temperature interval between T-x and T-m is as small as 85 K. The extremely high T-x/T-m and small Delta T-m(=T-m-T-x) values are the reason for the achievement of the large glass-forming ability. The bulk amorphous Nd70Fe20Al10 alloy has a ferromagnetism with the Curie temperature (T-c) of about 600 K which is much higher than the highest T-c (about 480 K) for the Nd-Fe binary amorphous alloy ribbons. The remanence (B-t) and intrinsic coercive force (H-i(c)) for the bulk Nd60Fe30Al10 alloy are 0.122 T and 277 kA/m, respectively, in the as-cast state and 0.128 T and 277 kA/m, respectively, in the annealed state for 600 s at 600 K. The B-r and H-i(c) decrease to 0.045 T and 265 kA/m, respectively, for the crystallized Nd60Fe30Al10 sample consisting of Nd+Al2Nd+delta phases and the maximum hard magnetic properties are achieved in the amorphous state. The hard magnetic properties for the bulk amorphous alloys are presumably due to the homogeneous development of ferromagnetic clusters with large random magnetic anisotropy. The finding of the bulk amorphous alloys exhibiting hard magnetic properties at room temperature is promising for the future development as a new type of metallic amorphous permanent magnet.

Fe-rich Fe-Nd-B amorphous alloys containing 88 to 90 at% Fe annealed for 60-300 s at 923-1023 K have the nanostructure consisting of bcc-Fe, Fe14Nd2B and remaining amorphous phases, and exhibit rather good hard magnetic properties, i.e., remanence (Br) of 1.28 T, coercive field (iHc) of 252 kA/m and maximum energy product ((BH)(max)) of 146 kJ/m(3) for Fe89Nd7B4. The nanoscale Fe14Nd2B particles with a size of about 30 nm are surrounded by the bcc-Fe and amorphous phases which act as a magnetic exchange-coupled medium. The nanoscale coexistence of the three ferromagnetic phases is important for the achievement of the rather good hard magnetic properties. The simultaneous achievement of the high Br and (BH)(max) values and the residual existence of the amorphous phase for the Fe-rich alloys containing about 90 at% Fe has significant engineering importance because of the expectations of high deformability and low cost.

When Fe-rich Fe-Nd-B amorphous alloys containing 88 to 90 at% Fe are annealed for 60-300 s at 923-1023 K, the annealed alloys have the nanostructure consisting of bcc-Fe, Fe14Nd2B and remaining amorphous phases and exhibit rather good hard magnetic properties. The best hard magnetic properties of remanence (B-r), coercive field (H-i(c)) and maximum energy product ((BH)(max)) are 1.14 T, 260 kA/m and 117 kJ/m(3), respectively, for Fe90Nd7B3, 1.28 T, 252 kA/m and 146 kJ/m(3), respectively, for Fe89Nd7B4 and 1.22 T, 240 kA/m and 130 kJ/m(3) for Fe89Nd8B4. The mean particle sizes of these crystallites in the optimum annealing treatment are 20 to 40 nn and the thickness of the intergranular amorphous layer is 10 to 30 nm. The amorphous layer contains Nd concentrations much higher than the nominal concentration and the enrichment seems to be the reason for the residual existence of the amorphous phase at the high temperatures. The nanoscale Fe14Nd2B particles are surrounded by the bcc-Fe and amorphous phases. The three constituent phases have ferromagnetism and their Curie temperatures for the Fe89Nd7B4 alloy annealed for 300 s at 923 K are about 1040 K for bcc-Fe and 630 K for Fe14Nd2B. The further increase in annealing temperature and time causes the decrease in hard magnetic properties presumably because of the grain growth of bcc-Fe and Fel4N2B phases resulting from the disappearance of the residual amorphous phase. The coexistence of bcc-Fe, Fe14Nd2B and amorphous phases on a subnanoscale is important for the achievement of the rather good hard magnetic properties and hence the bcc-Fe and amorphous phases seem to act as an effective magnetic exchange-coupled medium. The simultaneous achievement of the high B-r and (BH)(max) values in the residual existence of the amorphous phase for the Fe-rich alloys containing about 90 at% Fe is believed to be the first evidence and has significant engineering importance because of the expectations of high deformability and high cost performance.

When an amorphous Fe90Nd7B3 alloy subjected to annealing for 60 to 180 s at temperatures between 923 and 1023 K consists of a mixed structure of bcc-Fe, Fe3B, Fe14Nd2B and remaining amorphous phases, the (BH)(max) and remanence were found to have maximum values of 113 kJ/m(3) and 1.17 T, respectively. Their crystallites which precipitated through the process of Am-->Am'+bcc-Fe-->Am''+bcc-Fe+Fe3B-->Am'''+bcc-Fe+Fe3B+Fe14Nd2B have the particle sizes of 20 to 60 nm and the thickness of the intergranular amorphous layer is 5 to 30 nm. The Fe14Nd2B phase is surrounded by the bcc-Fe and remaining amorphous phase in the optimally annealed state because it precipitates from the remaining amorphous phase which surrounds the bcc-Fe particles. The further increase in annealing temperature and annealing time causes the increase in particle size of their precipitates as well as the disappearance of the residual amorphous phase, leading to the significant decrease in (BH)(max). The existence of the residual amorphous phase was also recognized for all other Fe-Nd-B alloys with maximum (BH)(max) values obtained by annealing the amorphous phase. The intergranular amorphous phase as well as the bcc-Fe phase is presumed to act as an effective magnetic exchange-coupled medium. This information is extremely important for the subsequent development of permanent magnet materials by the utilization of magnetic exchange-coupled state as well as for the interpretation of the appearance of hard magnetism in the use of the rapidly solidified Fe-rich amorphous phase as a precursor.

Ultrafine composite particles consisting of hexagonal AlN and hexagonal (Cr, M)2N, bcc Fe(Cr), fcc Co(Cr) or fcc Ni(Cr) phases were found to form by the reaction between nitrogen plasma and molten Al-Cr-M (M = Fe, Co or Ni) liquid. The AlN and (Cr, M)2N phases in the AlN + (Cr, M)2N particles have a hexagonal prism and hexagon dipyramid shapes in the Al- and Cr-rich alloys, respectively, but their shapes change with increasing M content into a cone for the AlN and a sphere for the M(Cr) particles. The average diameters of the (Cr, M)2N and M(Cr) are in the range of 50 to 150 nm and the average diameter and length of AlN are about 100 and 300 nm for the hexagonal prism and 150 and 150 nm for the cone. The change in the shape for the AlN particles reflects the change from the (Cr, M)2N to M(Cr). The change from (Cr, M)2N to M(Cr) and the decrease in the formation amount of AlN with increasing M content and decreasing Cr content are due to the decrease in nitrogen content in the alloy vapor and ultrafine liquid droplets. The composite AlN and M(Cr) particles are also thought to form through the vapor-liquid-solid (VLS) growth mechanism in which alloy vapors containing Al, Cr, M and nitrogen are preferentially condensed in the remaining liquid M(Cr) region in a coexistent state with AlN solid phase. The composite ceramic and metallic particles prepared by the unique formation mechanism are important for the expectation of unique characteristics which are not obtained for single phase particles.

Ultrafine ceramic composite particles with a matchstick-like shape consisting of hexagonal AlN and Cr2N phases were found to form at approximately 100% fraction by the reaction between nitrogen plasma and molten Al50Cr50 liquid. The AlN phase has a hexagonal prism shape with a transverse size of about 50 nm and a length of about 200 nm while the Cr2N phase has hexagon-pyramids with an edge size of about 100 nm and connects with the AlN hexagonal prism. The two phases have a close crystal orientation relationship of [001]AlNparallel-to[001]Cr2N and [110]AlNparallel-to[100]Cr2N which has low misfit strains of about 11%. The ultrafine composite AlN + Cr2N particle is presumed to form through the following process; (i) the formation of Al-Cr liquid containing large amounts of dessociated nitrogen (N) and hydrogen (H) by the plasma reaction, (ii) the formation of ultrafine supercooled Al-Cr-N liquid particles by condensation of alloy vapor, (iii) the faceted growth of AlN phase along the preferential direction of [001], and (iv) the solidification of the remaining liquid to Cr2N in the close orientation relationship with AlN phase. In the coexistent state of AlN solid and Cr-Al-N liquid, the vapor condensation occurs preferentially at the liquid region which lies on the AlN phase, leading to the preferential growth of AlN phase. The vapor-liquid-solid (VLS) growth mechanism is thought to be the origin for the formation of the matchstick-like composite particles with radially elongated and tree-like morphologies.

Computer simulations of phase decomposition were performed for the Cu-Co alloy system on the basis of the non-linear diffusion equation. In the calculations, the modified regular solution approximation was adopted, i.e. the composition and temperature dependences of the interaction parameter, Ω, between the nearest neighbour atoms were taken into account and the mobility of atoms was defined as a function of solute composition. The phase decompositions were successfully computed for the Cu-Co alloys. The calculation method proposed here is applicable to many actual alloy systems. © 1992 Chapman &amp Hall.

A new Fourier expression of the Cahn-Hilliard's flux equation is proposed, where the regular solution approximation is adopted as the chemical free energy of solid solution and the mobility of atoms is defined as a function of solute composition. The computer simulations of phase decomposition are successfully performed on the basis of the new method. This calculation method is applicable for the phase decompositions in the actual alloy systems, because the thermodynamical characteristics of the alloys have usually been evaluated on the basis of the regular solution model or the modified regular solution model.