Abstract:
Methods for applying an amorphous metal alloy to a substrate, comprising the steps of vaporizing an amorphous metal alloy composition, in a plasma spray gun to form a metal alloy vapor plasma plume, directing the metal alloy vapor plume onto a cooled substrate, maintained and condensing and rapidly solidifying the amorphous metal alloy composition vapor on the substrate, to form an amorphous metal layer deposit of high density and strength.

Description:
CROSS-REFERENCE TO RELATED APPLICATION  
       [0001]     This application claims the benefit of the filing date of U.S. Provisional Application No. 60/504,370 filed Sep. 19, 2003. 
     
    
     FIELD OF THE INVENTION  
       [0002]     The present invention is directed to deposition of amorphous metal coatings, layers and forms by thermal spray processes, as well as new aluminum-based amorphous alloys.  
       BACKGROUND OF THE INVENTION  
       [0003]     Thermal spray processes, such as plasma jet and high velocity oxygen fuel (HVOF) processes are conventionally used to apply particles to form surface coatings on appropriate substrates. However, thermal spray processes have some disadvantages, such as the difficulty of producing adherent, porosity-free coatings with a strong bond to the substrate. Typically the substrate surface must be roughened, so that the thermally sprayed particles can form a relatively low-strength mechanical bond with the substrate. The inherent porosity of thermally-sprayed coatings can be reduced by carrying out the process under vacuum, although this does increase the cost and complexity of the process, and by using high particle velocity such as provided by HVOF systems. The bond strength of thermally sprayed coatings with metallic substrates has been improved by making the substrate a continuous cathode for the direct-current plasma plume, but this may increase the resistive heating at the surface where the thermally sprayed particles are being deposited.  
         [0004]     Thermal spray processes are also used to apply amorphous metal coatings to substrates. In these processes, the powder is melted by plasma or HVOF gun, and the molten droplets form “splats” on the substrate which cool to form the surface coating. “Ordinary” amorphous metals must be cooled from the melt at extremely high rates, to prevent crystallization. However, some amorphous metals are more stable to devitrification at much lower cooling rates. Such amorphous alloys, known generally as Bulk Metallic Glasses (“BMG”) can be based on Zr, Ti, Fe, Co, Ni, Mg, La, Pd, and/or Cu as the main element, typically combined with small metalloids (B, C, Si, P) and other transition elements, and/or small amounts of larger refractory or lanthanide metals to form a high-viscosity melts with a low crystallization energy. However, even bulk metal glasses do not generally produce fully dense and fully amorphous coatings when applied with thermal spray processes.  
         [0005]     Thermal spray processes have also been studied for applying particles of ultra hard materials such as AlMgB 14  based compositions to coat substrates, but such HVOF processes will tend to oxidize such materials and have limited substrate and/or interparticle bonding strength.  
         [0006]     In addition, there is a need for lightweight amorphous alloys, such as aluminum and/or silicon-based amorphous alloys which have desirable performance characteristics.  
       SUMMARY OF THE INVENTION  
       [0007]     This invention is directed to thermal spray methods, particularly including plasma processing methods, for vaporizing small powders of metals/metalloids of specific compositions to form a vapor of a desired alloy, such as an amorphous metal alloy composition and/or an ultra hard alloy composition, and for condensing the vapor on a metal or other suitable surface. In the case of amorphous alloys, the substrate is maintained at a temperature below the crystallization temperature of the amorphous metal alloy and preferably in the case of BMG alloys, below the glass transition temperature of the amorphous metal alloy. The amorphous metal vapor condensed on the metal surface can provide a good bond (e.g., compared to the purely mechanical bond which is typical using thermal powder spray using substantially only relatively large powders) and high density of the deposit. The cooled condensed vapor forms a solid amorphous metal alloy, and the vapor may continue to be condensed and cooled onto the previously deposited amorphous alloy to form layers and shapes of arbitrary thickness. If the plasma is a chemically reducing plasma (e.g., with at least some hydrogen content) capable of preventing or removing surface oxide on the metal substrate, a metallurgical bond may be formed between the deposited metal vapor alloy mixture and the substrate.  
         [0008]     While some amorphous metals fully or partially crystallize over a limited period of time at temperatures coextensive with or only slightly above their effective glass transition temperature, a wide variety of amorphous metal compositions are relatively stable at temperatures at or slightly above their glass transition temperature, Tg, and do not initiate substantial crystallization unless raised to a crystallization temperature, Tx, which may be 10 to 100 or more degrees Celsius higher than Tg. By “bulk metal glass” (BMG) is meant an amorphous metal alloy composition having a glass transition temperature, Tg, at which it exhibits a supercooled liquid phase for at least one second, and preferably at least 30 seconds.  
         [0009]     The glass transition temperature Tg (if any) and the crystallization temperature(s) Tx of an amorphous alloy are typically determined by differential scanning calorimetry, in which the temperature of a sample is slowly raised, and correlated, as a function of temperature, with the amount of energy necessary to raise the temperature. The glass transition phase change is typically an endothermic process involving slight volume increase, while crystallization is typically an exothermic process involving slight volume decrease. Many, if not most, amorphous metal compositions do not have a glass transition temperature, but instead crystallize at one or more elevated temperatures without going through a distinct viscous glass transition phase. An amorphous metal composition may have a number of distinct crystallization temperatures Tx(1), Tx(2) . . . at which various components crystallize or recrystallize from components crystallized in a less stable or metastable crystalline phase at a lower crystallization temperature. As will be discussed, a variety of amorphous metal alloys have a distinct glass transition Tg, at which they undergo a slight volume expansion upon phase transition to a viscous glass state, and undergo partial crystallization, typically forming nanoscale crystallites in an amorphous matrix which remains in a viscous glassy state. These partially-nano-crystalline bulk metal glasses retain a viscous glassy matrix above Tg, and are useful in the present methods and are considered to have a supercooled liquid temperature region in which they form a viscous glass, albeit one with nanoscale crystallites at high temperatures, still below their metal temperature Tm, they will fully crystallize and lose their viscous , supercooled glass condition. The determination of glass transition temperature and crystalline temperature(s) is typically a function of the rate at which the temperature of the metal glass foam is increased. For purposes of this disclosure, a rate of temperature increase of 0.25 degrees Celsius per second may be used to determine Tg, although other rates are used in determining reported Tg and Tx values herein.  
         [0010]     Bulk metal glasses (BMGs) used herein preferably have a crystallization temperature, Tx, which is at least 20° C. and more preferably at least 40° C. higher than the glass transition temperature, Tg, of the bulk metal glass.  
         [0011]     Amorphous metal alloys may have exceptionally high impact resistance and strength, which are important qualities for various metal product, coatings and components. For example, Bulk Metal Glasses (BMGs) based on Fe, Zr, Ti, Cu, Mg and/or Al metal systems can exhibit unique combinations of high hardness, strength, toughness and corrosion resistance. BMG alloys such as Fe—(Zr,Ti,Ni,Co,Mo)—(B,C,Si,P); Zr—Ni—Al—Cu; and Zr—Ti—Cu—Ni—(Si,Be) exhibit very good bulk glass-forming ability with high thermal stability in the supercooled glass state, and low critical cooling rates. [See, e.g., U.S. Pat. No. 6,258,185, “Methods of Forming Steel” to Branagan et al (2001); A. Inoue, et al.,  Mater. Trans. JIM,  31 (1991), p. 425; T. Zhang, et al.,  Mater. Trans. JIM,  32 (1991), p. 1005; A. Inoue et al.,  Mater. Trans. JIM,  32 (1991), p. 609; A. Peker, et al.,  Appl. Phys. Lett.,  63 (1993), p. 2342.  
         [0012]     The toughness of amorphous metals, including bulk metal glasses (BMGs) can increase with increasing impact or shear rates, to relatively high levels. The more stable BMG alloys typically form dense, deep eutectic liquids with relatively small free volume, and relatively high melt viscosity, above their glass transition temperature, Tg. They typically comprise three, and preferably four or more components having negative heats of mixing and at least 12% difference in atomic size, in proportions which permit high packing density and short-range order. Being energetically close to the crystalline state in this manner, can provide slow crystallization kinetics, with high viscosity and high glass forming ability. R. Busch, “The Thermophysical Properties of Bulk Metallic Glass-Forming Liquids”,  JOM,  52:7 (2000), pp. 39-42. However, the thickness of amorphous metal alloys which can be formed directly by casting from the melt is generally limited by the cooling rate and thermal conductivity. By condensing plasma-vaporized amorphous metal alloys on a suitable substrate in accordance with the present disclosure, relatively thick coatings and product shapes may be manufactured.  
         [0013]     In conventional thermal spray processes, relatively large metal particles (e.g., 30-150 micron-sized particles) are introduced into a fast-moving plasma or HVOF jet, and at least partially melted while being accelerated toward a target surface.  
         [0014]     The (partially) molten particles “splat” on the surface and are solidified. The speed at which the “splats” can cool is limited by their thickness, and even BMG thermally sprayed alloys may slow some crystallization under such standard conditions, particularly if “splatted” on a crystalline surface. In accordance with the present disclosure, small metal/metalloid particles of particle size less than about 10 microns, and preferably about 6 mircons or less, are introduced into a very hot plasma (e.g., at least 10,000° K., and preferably over 15,000° K. to as much as 25,000° K. or more) where they are substantially vaporized in view of their high surface area to volume ratio. Inert gas-vacuum or other suitable atomization processes may be used to produce amorphous metal alloy powders of small particle size for vaporization in accordance with the present disclosure. Inert gas atomization is particularly preferred in which the metal/metalloid alloy components are melted to form a uniform amorphous or BMG alloy mixture in an induction furnace, arc furnace or other suitable furnace, and the homogeneous liquid metal melt is dispersed into individual particles in an atomizing chamber where it is contacted by a high velocity stream of the atomizing inert gas. The molten metal stream is disintegrated into fine droplets which may solidify from the direct cooling effects of the atomizing gas, or more indirectly during their fall through an atomizing tank. It is not necessary that the small alloy particles be in an amorphous state, because they will be vaporized in the deposition process. Particles are collected at the bottom of the tank. Alternatively, centrifugal force can be used to break up the liquid as it is removed from the periphery of a rotating electrode or spinning disk/cup. Powders used for spraying may be prepared by vacuum gas atomization and then crushed by a centrifugal mill, ball mill, attention mill, or other suitable comminution.  
         [0015]     Similarly, mechanical powder forming methods, such as milling may also be used for reducing the size of larger particles and particle agglomerates and for making uniform blends. Ball, hammer, vibratory, attrition, and tumbler mills are some of the commercially available comminuting devices. Impact, attrition, shear, and compression all influence powder particle size composition and crystal (or amorphous) structure. Liu, Y. J. and I. T. H. Chang (2002). “The correlation of microstructural development and thermal stability of mechanically alloyed multicomponent Fe—Co—Ni—Zr—B alloys.” Acta Materialia 50(10 June 12): 2747-2760 describe formation of multicomponent Fe70-x-yCoxNiyZr10B20 (x=0, 7, 21; y=7, 14, 21, 28) alloys by high energy ball milling. Zhang, L. C., E. Ma, et al. (2002). “Mechanically alloyed amorphous Ti50(Cu0.45Ni0.55)44-xAlx Si4B2 alloys with supercooled liquid region.” Journal of Materials Research 17(7 July): 1743-1749 describe production of amorphous Ti50(Cu0.45Ni0.55)44-xAlx Si4B2 (x=0, 4, 8, 12) alloy powders with a well-defined glass transition and a supercooled liquid region (delta-Tx=64 K). In this regard, see also Zhang, L. C. and J. Xu (2002). “Formation of glassy Ti50Cu20Ni24Si4B2 alloy by high-energy ball milling.” Materials Science Forum Proceedings of the International Symposium on Metastable, Mechanically Alloyed and Noncrystalline Materials (ISMANAM), Jun. 24-29, 2001 386-388: 47-52.  
         [0016]     Chemical and electrochemical methods may also be used to produce suitable small particle amorphous alloy powders. Included are the production of metal powders by the reduction of metallic oxides, precipitation from solution (hydrometallurgy), and thermal decomposition of metal carbonyl compounds. Precipitation of metal alloys from aqueous or nonaqueous solutions can be accomplished by using electrolysis and/or chemical reduction. 
     
    
     DESCRIPTION OF THE DRAWINGS  
       [0017]      FIG. 1  is a schematic illustration of thermal spray apparatus for carrying out certain embodiments of the present invention; and  
         [0018]      FIG. 2  is a cross-sectional view of the plasma gun of the apparatus of  FIG. 1 . 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0019]     Alloys and/or blends of small powder components are fed into a plasma gun to vaporize the powders to form BMG amorphous metal vapor mixtures. By condensing these vapor mixtures on a cool (preferably metal) substrate, the condensate can immediately cooled below its glass transition temperature before crystallizing, and can remain amorphous. It is preferable to limit or avoid oxidation, particularly when vaporizing highly reactive elements, and to control the substrate-surface-cooling temperature. Desirably, if an amorphous alloy layer is to be deposited, the substrate will be maintained during the deposition at a temperature at least 50° C. and more preferably at least 100° C. below the crystallization temperature of the alloy being deposited on the substrate. If the alloy being deposited is a Bulk Metal Glass, the substrate is preferably cooled to a temperature at least 50° C., and more preferably at least about 100° C. below the glass transition temperature Tg of the alloy being deposited.  
         [0020]     The vapor is cooled rapidly enough to a temperature below the Tx or Tg of the condensed amorphous or BMG alloy, that the appropriate amorphous metal alloy composition is condensed and deposited on the substrate and solidified in an amorphous state. Amorphous metal coatings are strong, resist corrosion, and can be converted to hard, wear resistant surfaces upon appropriate nanocrystallization conditions.  
         [0021]     As indicated, the vaporized alloy components are condensed on the substrate. However, because different metal and metallized components of various alloys have different vaporization and condensation characteristics, depending on factors including the temperature of the substrate (which is much lower than the vaporized alloy components), pressure and the volume of inert gas carrying the alloy vapor, the composition of the alloy condensed on the substrate may differ from the composition of the vaporized components.  
         [0022]     In this regard, the following table lists the temperature in degrees Celsius at which the vapor pressure of selected metal and metallized elements is, respectively, 1×10 −2  Torr, and 1 Torr.  
         [0023]     Vapor Pressure Data for Selected Elements  
                                                               Element   10 −2  Torr   1 Torr                           Al   Aluminum   1,217° C.   1,557° C.           B   Boron   2,027° C.   2,507° C.           Ba   Barium     610° C.     852° C.           Be   Beryllium   1,227° C.   1,557° C.           C   Carbon   2,457° C.   2,897° C.           Ca   Calcium     597° C.     802° C.           Co   Cobalt   1,517° C.   1,907° C.           Cr   Chromium   1,397° C.   1,737° C.           Cu   Copper   1,257° C.   1,617° C.           Dy   Dysprosium   1,117° C.   1,437° C.           Fe   Iron   1,477° C.   1,857° C.           Ge   Germanium   1,397   1,777° C.           La   Lanthanum   1,727° C.   2,177° C.           Li   Lithium     537° C.     747° C.           Mg   Magnesium     439     605° C.           Mn   Manganese     937° C.   1,217° C.           Mo   Molybdenum   2,527° C.   3,117° C.           Nb   Niobium   2,657° C.   3,177° C.           Ni   Nickel   1,527° C.   1,907° C.           P   Phosphorus     185° C.     261° C.           Re   Rhenium   3,067° C.   3,807° C.           Sb   Antimony     533° C.     757° C.           Si   Silicon   1,632° C.   2,057° C.           Sn   Tin   1,247° C.   1,612° C.           Sr   Strontium     537° C.     732° C.           Ta   Tantalum   3,057° C.   3,707° C.           TI   Thallium     609° C.     827° C.           Ti   Titanium   1,737° C.   2,177° C.           W   Tungsten   3,227° C.   3,917° C.           Y   Yttrium   1,632° C.   2,082° C.                      
 
         [0024]     A variety of amorphous, BMG metal alloys with their Tg, Tx and supercooled liquid region are listed in the following Table (with compositions given at atomic %):  
                                           TABLE 1                       Major                                   element   Alloy Composition   Tg (K)   Tx (K)   Tx − Tg   S   H   Ref.                   Mg—   Mg80Ni10Nd10   454   471   17           k           Mg75Ni15Nd10   450   470   20           k           Mg60Cu30Y10   419   466   47           c           (Mg99Al1)60Cu30Y10   419   459   40           c           (Mg98Al2)60Cu30Y10   421   454   33           c           (Mg96Al4)60Cu30Y10   411   455   44           c           (Mg95Al5)60Cu30Y10   415   453   38           c           (Mg93Al7)60Cu30Y10   411   445   34           c           Mg70Ni15Nd15   467   489   22           k           Mg65Ni20Nd15   459   501   42           k           Mg65Cu25Y10   425   479   54           k           Mg60Cu30Y10   400   450   50           Mg65Y10Cu15Ag5Pd5   437   472   35    770        1       Zr—   Zr66Al8Ni26   672   708   36           k           Zr66Al8Cu7Ni19   662   721   59           k           Zr66Al8Cu12Ni14   655   733   78           k           Zr66Al9Cu16Ni9   657   736   79           k           Zr65Al7.5Cu17.5Ni10   657   736   79           k           Zr57Ti5Al10Cu20Ni8   677   720   43           k           Zr41.2Ti13.8Cu12.5Ni10Be22.5   623   672   49           k           Zr38.5Ti16.5Ni9.75Cu15.25Be20   630   678   48           k           Zr39.88Ti15.12Ni9.98Cu13.77Be21.25   629   686   57           Zr42.63Ti12.37Cu11.25Ni10 Be23.75   623   712   89           k           Zr44Ti11Cu10Ni10Be25   625   739   114            k           Zr55Al10Ni5Cu30   683   748   65           d           Zr45.38Ti9.62Cu8.75Ni10Be26.25   623   740   117            Zr65Al10Ni10Cu15   652   757   105            e           Zr65Al7.5Cu17.5Ni10   633   749   116            i           (Zr65Al7.5Cu17.5Ni10)95Fe5   650   725   75           i           (Zr65Al7.5Cu17.5Ni10)90Fe10   670   730   60           i           (Zr65Al7.5Cu17.5Ni10)85Fe15   675   735   60           i           (Zr65Al7.5Cu17.5Ni10)80Fe20   680   740   60           i           Zr52.5Cu17.9Ni14.6Al10Ti5   686   725   39           j           (Zr67Hf33)52.5Cu117.9Ni14.6Al10Ti5   708   753   45           j           (Zr50Hf50)52.5Cu17.9Ni14.6Al10Ti5   722   767   45           j           (Zr33Hf67)52.5Cu17.9Ni14.6Al10Ti5   737   786   49           j           Zr52.5Cu17.9Ni14.6Al10Ti5   767   820   53           j           Zr52.2Ti16.7Cu17.7Ni8.7B4.7   564   668   104            l           Zr50.2Ti16.7Cu17.7Ni8.7B6.7   646   719   73           l           Zr48.2Ti16.7Cu17.7Ni8.7B8.7   682   720   38           l           Zr54.9Ti16.7Cu17.7Ni8.7P2.0   578   686   108            l           Zr53.9Ti16.7Cu17.7Ni8.7P3.0   636   722   86           l           Zr52.9Ti16.7Cu17.7Ni8.7P4.0   698   734   36           l           Zr54.9Ti16.7Cu17.7Ni8.7Si2.0   562   681   119            l           Zr53.9Ti16.7Cu17.7Ni8.7Si3.0   563   681   118            l           Zr52.9Ti16.7Cu17.7Ni8.7Si4.0   639   742   103            l           Zr41.2Ti13.8Cu12.5Ni10Be22.5   633   741   108            l           Zr70Fe20Ni10   646   673   27           o           Zr60Al10Cu30   680   750   70           p           Zr65Al7.5AlCu1017.5   625   750   125            z           Zr70Ni23Ti7           30            2           Zr65Al10Cu15Ni10           95            3       La—   La55Al25Ni10Cu10   467   547   80           k           La55Al25Ni5Cu15   459   520   61           k           La55Al25Cu20   456   495   39           k           La55Al25Ni5Cu10Co5   465   542   77           k           La66Al14Cu20   395   449   54           k           La60Al20Ni10Co5Cu5   451   523   72           g       Pd—   Pd40Cu30Ni10P20   577   656   79           k           Pd81.5Cu2Si16.5   633   670   37           k           Pd79.5Cu4Si16.5   635   675   40           k           Pd77.5Cu6Si16.5   637   678   41           k           Pd77Cu6Si17   642   686   44           k           Pd73.5Cu10Si16.5   645   685   40           k           Pd71.5Cu12Si16.5   652   680   28           k           Pd40Ni40P20   590   671   80           k       Nd—   Nd60Al15Ni10Cu10Fe5   430   475   45           k           Nd61Al11Ni8Co5Cu15   445   469   24           k       Cu—   Cu60Zr30Ti10   713   763   50           k           Cu54Zr27Ti9Be10   720   762   42           k           Cu48Ti34Zr10Ni8   —   —   —           Cu47Ti34Zr11Ni8   688   743   55            4           (Cu60Zr30Ti10)99Sn1                        5       Ti—   Ti34Zr11Cu47Ni8   698   727   29           k           Ti50Ni24Cu20B1Si2Sn3   726   800   74           h           Ti45Ni20Cu25Sn5Zr5           Ti50Cu25Ni25   713   753   40           m           Ti50Ni22Cu25Sn3   715   765   50           m           Ti50Ni20Cu25Sn5   710   770   60           m           Ti50 Ni20Cu23Sn7   710   759   49           m           Ti50Ni24Cu25Sb1   707   740   33           m           Ti50Ni22Cu25Sb3     763 ??   718   45           m           Ti50Cu35Ni12Sn3   —   —   —           Ti74Ni20Si4B2   700   752   52            6           T64Ni30Si4B2   700   774   74                                 Ti64Cu10Ni20Si4B2   700   758   58                                 Ti74Cu10Ni10Si4B2   700   761   61                                 Ti50Ni20Cu25Sn5   710   770   60           Z           Ti50Ni24Cu20Si4B2   735   800   65           Z           Ti—Cu—Ni—B—Sn—Si           &gt;70     2100   620    7           Ti50Cu20Ni24Si4B2   742                    8       Fe—   Fe63Ni7Zr10B20   553   579   26           b       and/or   Fe56Ni14Zr10B20   579   601   22           b       Co—   Fe49Ni21Zr10B20   589   611   22           b           Fe42Ni28Zr10B20   602   619   18           b           Fe42Co7Ni21Zr10B20   580   611   30           b           Fe72Hf8Nb2B18   856   932   76           f           (Fe, Co)85 Zr7B6(Nb, Nd)2           Fe 74.5Si13.5B9Nb3           Fe58Co7Ni7Zr8B20   821   899   78           n           Fe52Co10Nb8B30   907   994   87           n           Fe62Co9.5RE3.5B25 (RE = Pr, Nd, Sm, Gd, Tb, Dy, Er)           &gt;50             (22.5-30 at % B, 0-30 at % Co and 2.5-6 at % RE)           Co63Fe7Zr6Ta4B20   858   895   37           n           Co40Fe22Nb8B30   895   976   81           n           Co43Fe20Ta5.5B31.5   910   980                9           Fe75-x-yCoxNiySi8B17 (7.5-45% Co and 7.5-60% Ni)           Up to 54           s           Fe30Co30Ni15Si8B17   780   834   54   2800       10           Fe90-xNb10Bx   —   —   —           t           Fe85.5Zr2Nb4B8.5   —   —   —           Fe70B20Zr8Nb2           91           u           Fe62Co6Zr6Nb4Cr2B20           85           11           Fe63Co7Nb4Zr6B20           79           12           (Fe0.75B0.15Si0.1)99Zr1   815   867   52           13           Fe—Cr—Mo—C—B—P           90           14           Fe75Ga5P12C4B4   761   768   37           15           Fe70Al5Ga2P9.65 C5.75B4.6Si3           60           16           Fe66.5Co10Nd3.5B20           40           17           Fe75Ga5P12C4B4   731   768   37           18           Fe47Co30Sm3B20           41           19           Fe66.5Co10Nd3.5B20   802   842   40           20           Fe70Al5Ga2P9.65C5.75B4.6Si3           60           21           Fe—Co—Ni—Hf—B             80+           22           (Fe70Mn20Cr10)68Zr7Nb3B22   595       75   3000+       23           (Fe69Mn26Cr5)68Zr10C3B19   580       70   3000+       Poon 3           (Fe69Mn26Cr5)70Zr4Nb4B22   595       78   3000+       Poon 3           (Fe69Mn26Cr5)68Zr4Nb4B24   613       85   3000+       Poon 3           (Fe66Mn29Mo5)68Zr4Nb4B24   605       87   3000+       Poon 3           (Fe66Mn29Cr5)68Zr4Nb4B24   600       100    3000+       Poon 3           (Fe69Mn26Cr5)68Zr4Ti4B24   560       60   3000+       Poon 3           (Fe66Mn29Mo5)68Zr4Nb4B22Si2   ˜595         75   3000+       Poon 3           (Fe60Mn25Cr5Ni10)68Zr7Nb3B22   572       75   3000+       Poon 3       Al—   Al85Ni5Y8Co2   538   570   32           a           Al87(La,Nd,Pr)8Ni5   500   553   53           r           Al92(La,Nd,Pr)4Ni4   525   608   83           r           Al—Ti—M (M = V, Fe, Co and/or Ni) alloys, such as                       v           Al94V4Fe2, Al93Ti4Fe3, Al93Ti4V3           Al94V2Ti2Fe2           Al93Ti5Fe2           Ta55Zr10Ni10Al10Cu15   834   1004    170            24           Ni76Ti5P19   659   707   48           z           Ni65Nb5Cr5Mo5P14B6   701   762   61           z           Ni57Zr20Ti18Al5   800   841   41           z           Ni60Nb20Ti12.5Hf7.5           60   3180       25           Ni—Nb—Sn—X (X = B, Fe, Cu)   881-895       40-60    3-3800   1000-1280   26           Ni57Zr20Ti20Si3               788-830    88   27           Ni65Nb5Cr5Mo5P14-16B4-6   703   753   50   2690   840   28           Cu40Zr30Ti30           61           29           Cu40Ti30Ni15Zr10Sn5   735   780   45           30           La55Al25Ni20   483       65           31                 a. Kawamura, Y., et al., “Nanocrystalline Aluminum Bulk Alloys with a High Strength of 1420 MPa Produced by the Consolidation of Amorphous Powders”, Scripta mater., 44; 1599-1604 (2001)            b. Liu, Y. J., et al., “The correlation of microstructural development and thermal stability of mechanically alloyed multicomponent Fe—Co—Ni—Zr—B alloys”, Acta Materialia, 50, 2747-2760 (2002)            c. Linderoth, S., et al., “On the stability and crystallization of bulk amorphous Mg—Cu—Y—Al Alloys”, Materials Science and Engineering A304-306, 656-659 (2001)            d. deOliveira, M. F., et al., “Effect of oxide particles on the crystallization behaviour of Zr 55 Al 10 Ni 5 Cu3 0  Alloy”, Materials Science &amp; Engineering A304-306, 665-6659 (2001)            e. Kawamura, Y., et al., “Newtonian and non-Newtonian viscosity of supercooled liquid in metallic glasses”, Materials Science &amp; Engineering, A304-306, 674-678 (2001)            f. Kawamura, Y., et al., “Superplasticity in Fe-based metallic glass with wide supercooled liquid region”, Materials Science &amp; Engineering, A304-306, 674-678 (2001)            g. Saotome, Y., et al., “Superplastic micro/nano formability of La 60 Al 20 Ni 10 Co 5 Cu5 amorphous alloy in supercooled liquid state”, Materials Science &amp; Engineering, A304-306, 716-720 (2001)            h. Zhang, T., et al., “Ti-based amorphous alloys with a large supercooled liquid region”, Materials Science &amp; Engineering, A304-306, 771-774 (2001)            i. Mattern, N., et al., “Influence of iron additions on structure and properties of amorphous Zr 65 Al 7.5 Cu 17.5 Ni 10 ”, Materials Science and Engineering A304-306, 311-314 (2001)            j. Glass-forming ability and crystallization of bulk metallic glass (HfxZr1-x)52.5Cu17.9Ni14.6Al10Ti5”, Journal of Non-Crystalline Solids”, 311 77-82 (2002)            k. Lu, Z. P., et al., “A new glass-forming ability criterion for bulk metallic glasses”, Acta Materialia, 50, 3501-3512 (2002)            l. Choi, et al., “Effect of Additive Elements on the Glass Forming Ability and Crystallization of Zr—Ti—Cu—Ni Metallic Glasses”, Journal of Metastable and Nanocrystalline Materials, Vols. 343-346, pp. 109-115 (2000)            m. Inoue, A., “Synthesis and Properties of Ti-Based Bulk Amorphous Alloys with a Large Supercooled Liquid Region”, Journal of Metastable and Nanocrystalline Materials, Vols. 2-6 (1999), pp. 307-314            n. Inoue, et al., “Ferromagnetic Bulk Glassy Alloys with Useful Engineering Properties”, Journal of Metastable and Nanocrystalline Materials, Vols. 343-346, pp. 81-90 (2000)            o. Saida, et al., “Nano-Icosahedral Quasicrystalline Phase Formation from a Supercooled Liquid State in Zr—Fe Ternary Metallic Glass”, Applied Physics Letters, Vol. 76, No. 21, pp. 3037-3039 (May 22, 2000)            p. Inoue, et al., “Synthesis of High Strength Bulk Nanocrystalline Alloys Containing Remaining Amorphous Phase”, Journal of Metastable and Nanocrystalline Materials, Vol. 1, pp. 1-8 (1999)            q. Eckert, J., “Mechanical Alloying of Highly Processable Glassy Alloys”, Materials Science and Engineering, A226-228, pp. 364-373 (1997)            r. Tong, et al., “Microstructure and Thermal Analysis of Amorphous Al87RE8Ni5 and AL92RE4Ni4 Alloys”, Materials Letters, Vol. 28, pp. 133-136 (1996)            s. Zhang et al, “Bulk glassy alloys in (Fe, Co, Ni)—Si—B system”, Materials Transactions, v 42, (2001)            t. Imafuku et al, “Structural variation of Fe—Nb—B metallic glasses during crystallization process”, Scripta Materialia, v 44 (2001)            u. Ma et al, “Fe-based metallic glass with significant supercooled liquid region of over 90 K”, Journal of Materials Science Letters, v 17 (1998)            v. Kimura et al, “Formation of nanogranular amorphous phase in rapidly solidified Al—Ti—M (M = V, Fe, Co or Ni) alloys and their mechanical strength”, Nanostructured Materials, v 8, p 833-844 (1997)             
 
         [0025]     While this table lists certain primarily BMG alloys, other amorphous alloys may also be used. The amorphous metal powder blend may also include other components such as reinforcing and/or alloying fibers or powders. Such fibers or powders may be densely consolidated within the condensed and solidified amorphous alloy layer(s) deposited on the substrate.  
         [0026]     If it is desired to include “intact” powders and/or (short) fibers, these components should best be substantially larger than the approximately 10 million or less metal/metallized powders which are intended to be vaporized. For example, amorphous metal alloy powders of the same or similar composition to the alloy being deposited from the vapor, but a diameter of, for example, about 45 to about 150 microns, may be introduced in to the plasma gun nozzle to be applied to the substrate with the condensing alloy vapor. Amorphous alloy powders to be co-deposited on the substrate, as “splats” with the condensing alloy vapor should be fully melted in the plasma before implact on the substrate, and then rapidly cooled on the substrate before crystallization, if it is desired to maintain the amorphous characteristic of the “splats”.  
         [0027]     In such processes, the mass ratio of the vaporized small-particle alloy component to the relative large particle size component should be at least about 0.25 to 1.00, and preferably, at least about 0.5 to 1.0.  
         [0028]     It should be noted that even for larger 45-150 micron particles, some of the surface of these particles may be vaporized in the plasma gun plume as they are heated to a temperature about the melting point. As shown in the preceding table, different elements of these surface components may have significantly different vaporization rates, which will change the composition of the molten particles.  
         [0029]     For example, magnesium and aluminum have relatively high vaporization rates in an ultrahot plasma plume, while iron and boron have relatively slower vaporization rates. However, in accordance with the present method, such differential vaporization (and condensation rate) may be compensated for by controlling the composition of the vapor phase to include an excess of the higher-volatility components.  
         [0030]     As indicated, many BMG alloys with a broad supercooled liquid region may be vaporized for deposition in accordance with the present disclosure. However, aluminum-based alloys tend to have marginal glass-forming ability, and do not readily form BMG alloys with a wide supercooled liquid range. A few Al-based alloys have small supercooled liquid regions (such as Al85Y8Ni5Co2 Tx-Tg˜30° K.), which have been spray formed with some degree of amorphous phase retention, but most amorphous aluminum alloys have no Tg, and progressively crystallize with increasing temperature.  
                           TABLE 2                       Conventional Al-based                   Alloy Amorphous       New Al-based Alloy with (Ca,Ba)-Si2   New Al-based Alloy with (Zr, Ti)-(B,Si)       At %   Ref.   Backbone At %   Backbone At %                   Al73Cu16Ni5Mg8   32   (Al73Cu16Ni5Mg8)70(Ca,Ba)10Si20   (Al73Cu16Ni5Mg8)70(Zr,Ti)10(B,Si)i20       Al93Ti4Fe3   33   (Al93Ti4Fe3)70(Ca,Ba)10Si20   (Al93Ti4Fe3)70(Zr,Ti)10(B.Si)20       Al90Fe7Nb3   34   (Al90Fe7Nb3)70(Ca,Ba)10Si20   (Al90Fe7Nb3)70(Zr,Ti)10(B.Si)20       Al-4Ni-6Ce   35   (Al-4Ni-6Ce)70(Ca,Ba)10Si20   (Al-4Ni-6Ce)70(Zr,Ti)10(B.Si)20       Al85Ni5Y4Mm4Co2   36   (Al85Ni5Y4Mm4Co2)70(Ca,Ba)10Si20   (Al85Ni5Y4Mm4Co2)70(Zr,Ti)10(B.Si)20       Al85Y8Ni5Co2.       (Al85Y8Ni5Co2)70(Ca,Ba)10Si20   (Al85Y8Ni5Co2)70(Zr,Ti)10(B.Si)20       Al84Ni8Co4Y3Zr1   37   (Al84Ni8Co4Y3Zr1)70(Ca,Ba)10Si20   (Al84Ni8Co4Y3Zr1)70(Zr,Ti)10(B.Si)20       Al75Ni21Y4   38   (Al75Ni21Y4)70(Ca,Ba)10Si20   (Al75Ni21Y4)70(Zr,Ti)10(B.Si)20       Al90Fe5Ce5   39   (Al90Fe5Ce5)70(Ca,Ba)10Si20   (Al90Fe5Ce5)70(Zr,Ti)10(B.Si)20       Al84Ni5Y9Co2   40   (Al84Ni5Y9Co2)70(Ca,Ba)10Si20   (Al84Ni5Y9Co2)70(Zr,Ti)10(B.Si)20       Al92V3Fe3Zr2   41   (Al92V3Fe3Zr2)70(Ca,Ba)10Si20   (Al92V3Fe3Zr2)70(Zr,Ti)10(B.Si)20       Al93Fe3Ti2V2   42   (Al93Fe3Ti2V2)70(Ca,Ba)10Si20   (Al93Fe3Ti2V2)70(Zr,Ti)10(B.Si)20       Al93Fe3Ti2Cr2       (Al93Fe3Ti2Cr2)70(Ca,Ba)10Si20   (Al93Fe3Ti2Cr2)70(Zr,Ti)10(B.Si)20       Al94.5Cr3Co1.5Ce1   43   (Al94.5Cr3Co1.5Ce1)70(Ca,Ba)10Si20   (Al94.5Cr3Co1.5Ce1)70(Zr,Ti)10(B.Si)20       Al86V14   44   (Al86V14)70(Ca,Ba)10Si20   (Al86V14)70(Zr,Ti)10(B.Si)20       Al84.6Cr15.4       (Al84.6Cr15.4)70(Ca,Ba)10Si20   (Al84.6Cr15.4)70(Zr,Ti)10(B.Si)20       Al77.5Mn22.5       (Al77.5Mn22.5)70(Ca,Ba)10Si20   (Al77.5Mn22.5)70(Zr,Ti)10(B.Si)20       Al94Cr5Ce1Al93Ti4Fe3       (Al94Cr5Ce1Al93Ti4Fe3)70(Ca,Ba)10Si20   (Al94Cr5Ce1Al93Ti4Fe3)70(Zr,Ti)10(B.Si)20       Al90Fe5Nd5   45   (Al90Fe5Nd5)70(Ca,Ba)10Si20   (Al90Fe5Nd5)70(Zr,Ti)10(B.Si)20       Al56Si30Fe10Cr4   46   (Al56Si30Fe10Cr4)70(Ca,Ba)10Si20   (Al56Si30Fe10Cr4)70(Zr,Ti)10(B.Si)20       Al44Si30Ge12Fe10Cr4       (Al44Si30Ge12Fe10Cr4)70(Ca,Ba)10Si20   (Al44Si30Ge12Fe10Cr4)70(Zr,Ti)10(B.Si)20       Al89Fe10Zr1   47   (Al89Fe10Zr1)70(Ca,Ba)10Si20   (Al89Fe10Zr1)70(Zr,Ti)10(B.Si)20       Al90Ti10   48   (Al90Ti10)70(Ca,Ba)10Si20   (Al90Ti10)70(Zr,Ti)10(B.Si)20       Al87Ni10Ce3   49   (Al87Ni10Ce3)70(Ca,Ba)10Si20   (Al87Ni10Ce3)70(Zr,Ti)10(B.Si)20       Al87Ni10Zr3       (Al87Ni10Zr3)70(Ca,Ba)10Si20   (Al87Ni10Zr3)70(Zr,Ti)10(B.Si)20       Al87Ni7Cu3Ce3       (Al87Ni7Cu3Ce370(Ca,Ba)10Si20   (Al87Ni7Cu3Ce370(Zr,Ti)10(B.Si)20       Al94V4Fe2   50   (Al94V4Fe2)70(Ca,Ba)10Si20   (Al94V4Fe2)70(Zr,Ti)10(B.Si)20       Al94V2Ti2Fe2       (Al94V2Ti2Fe2)70(Ca,Ba)10Si20   (Al94V2Ti2Fe2)70(Zr,Ti)10(B.Si)20       Al94V2Ti2Fe2       (Al94V2Ti2Fe2)70(Ca,Ba)10Si20   (Al94V2Ti2Fe2)70(Zr,Ti)10(B.Si)20       Al94.5Cr3Ce1Co1.5   51   (Al94.5Cr3Ce1Co1.5)70(Ca,Ba)10Si20   (Al94.5Cr3Ce1Co1.5)70(Zr,Ti)10(B.Si)20       Al96.7Cr3Mo0.3   52   (Al96.7Cr3Mo0.3)70(Ca,Ba)10Si20   (Al96.7Cr3Mo0.3)70(Zr,Ti)10(B.Si)20       Al93.1Ti2.5Fe2.3Cr2.3   53   (Al93.1Ti2.5Fe2.3Cr2.3)70(Ca,Ba)10Si20   (Al93.1Ti2.5Fe2.3Cr2.3)70(Zr,Ti)10(B.Si)20       Si45Al31Fe20Ni4   54   (Si45Al31Fe20Ni4)90(Ca,Ba)10   (Si45Al31Fe20Ni4)80 Zr5B10       Si45Al36Fe15Ni4       (Si45Al36Fe15Ni4)90(Ca,Ba)10   (Si45Al36Fe15Ni4)80 Zr5B10       Si45Al41Fe10Co4       (Si45Al41Fe10Co4)90(Ca,Ba)10   (Si45Al41Fe10Co4)80 Zr5B10       Si55-45Al20Fe10Ni5Cr   55   (Si55-45Al20Fe10Ni5Cr)90(Ca,Ba)10   (Si55-45Al20Fe10Ni5Cr)80 Zr5B10       5Zr5Ge0-10       (5Zr5Ge0-10)90(Ca,Ba)10   (5Zr5Ge0-10)80 Zr5B10       Si55Al20Fe10Ni5Cr5Zr5   56   (Si55Al20Fe10Ni5Cr5Zr5)90(Ca,Ba)10   (Si55Al20Fe10Ni5Cr5Zr5)80 Zr5B10       Si45Al31Fe20Ni4   57   (Si45Al31Fe20Ni4)90(Ca,Ba)10   (Si45Al31Fe20Ni4)80 Zr5B10       Si45Al36Fe15Ni4       (Si45Al36Fe15Ni4)90(Ca,Ba)10   (Si45Al36Fe15Ni4)80 Zr5B10       Si45Al41Fe10Co4       (Si45Al41Fe10Co4)90(Ca,Ba)10   (Si45Al41Fe10Co4)80 Zr5B10       Si55Al20Fe10Ni5Cr5Zr5   58   (Si55Al20Fe10Ni5Cr5Zr5)90(Ca,Ba)10   (Si55Al20Fe10Ni5Cr5Zr5)80 Zr5B10       Si50Al25Fe10Ni5Cr5Zr5       (Si50Al25Fe10Ni5Cr5Zr5)90(Ca,Ba)10   (Si50Al25Fe10Ni5Cr5Zr5)80 Zr5B10                  
 
         [0031]     Accordingly, new aluminum-based amorphous alloys with improved amorphous properties are desirable, and are also described in accordance with the present disclosure. The new Al-based amorphous alloys are MSL class alloys with midsize atoms “M” as the majority component (60-70 at. %), small atoms “S” as the next-majority component (20-30 at %), and large-size atoms “L” as the minority component (10 at. %). The “L/S” pairs have high negative heats of mixing to stabilize the glass.  
         [0032]     The aluminum alloys based on aluminum as the midsize component and (Ca, Ba)—Si and/or (Zr,Ti)—B as the L/S pairs. In the proposed MSL alloys, the negative heats of mixing are large for enhancement of the stability of the undercooled melt. The concentration of the L atoms is from 3-12, preferably about 10 at. %, and the “S” atom content is about 20-30 at. %. Smaller amounts, however, can still improve the glass-forming-ability (GFA) properties of Al-based alloys.  
         [0033]     The first L/S pair relies on Calcium, Strontium and/or Barium as the inexpensive “large” atom, and Silicon as the “small” atom component. The Ca—Si2 pair has a large negative heat of mixing, as does the Ca—Al interaction with the base Aluminum “M” component. Moreover, Al and Si are fully compatible in amorphous compositions, and also have a large negative heat of mixing. Calcium is a relatively large atom, and very light, and Ba and Sr are even larger, while still having reasonably low density. The atomic size ratio of Ca/Al is 1.37, as shown in the following Table 3.  
                                                 TABLE 3                                       Atomic   Density           Element   Size nm   gm/cm3                                        B   0.098   2.34           Ni   0.124   8.9           Co   0.125   8.9           Fe   0.126   7.86           Cu   0.128   8.96           Cr   0.130   7.19           Si   0.132   2.33           V   0.134   5.8           Mn   0.135   7.43           Al   0.143   2.7           Ti   0.145   4.5           Mg   0.160   1.74           Zr   0.161   6.49           Y   0.178   4.5           Nd   0.182   7           Ca   0.197   1.55           Sr   0.215   2.6           Ba   0.222   3.5                      
 
         [0034]     Al—Ca binary alloys (and mixtures with Mg, Zn, Fe, Ga, Ni and Cu additions) can be amorphized in the composition range of 9 to 11 at % Ca by melt spinning. 59  Amorphous Mg70Al20Ca10 alloys with density of 1.80 g/cm3 can have a yield strength up to 930 MPa and a plastic strain up to 9.2% 60 , which is almost twice as strong as Beryllium, at approximately the same weight. New Al-based compositions in which (Ca,Ba)—Si are added to known amorphous aluminum alloys in accordance with the present disclosure, are listed in the middle column of Table 1, above. The multinary nature of most of these compositions is favorable to amorphous property development, as most pairs have large mixing heats, and a smoother size progression is provided than with a smaller number of elements.  
         [0035]     The second L/S pair for use in MSL Aluminum-based BMG alloys disclosed herein relies on Zr and/or Zr—Ti, Hf blends as the large atom component, and Boron and/or Silicon as the small atom component. Zr—B pair has a very large negative heat of mixing, and B and Si are both compatible with amorphous Al-alloys. The density of Zr is not prohibitive for lightweight alloys in minor amounts, and the atomic size ratio of Zr/Al is large enough at 1.13 to facilitate BMG formation.  
         [0036]     Al-based compositions in which (Zr,Ti)—B are combined with known amorphous aluminum alloys in accordance with the present disclosure are listed in the middle column of Table 1, above. In both the Ca,Ba compositions, and the Zr,Ti compositions, a mixture of B and Si can be beneficial in fostering larger-cluster formation, thereby increasing viscosity and reducing diffusion of Al and smaller atoms.  
         [0037]     In the apparatus of  FIG. 1 , small metal/metalloid particles are vaporized in a hot plasma. Preferably, the particles have a uniform bulk metal glass composition. However, powder blends of different alloy components may also be used. The metal/metalloid vapor is condensed on a suitable metal substrate to form an intimate bond with the substrate. Preferably, the substrate is cooled to enhance the solidification of the deposited vapor, and keep the surface below the glass transition temperature of the amorphous metal vapor composition being condensed on the surface. Conventional, larger (˜25-100 micron) metal thermal spray particles can be included, which may have an enhanced bond in the coating because of the condensing vapor. A reducing plasma can be used to keep the metal substrate clean and even help reduce a thin oxide surface layer to assist formation of a good, preferably metallurgical, bond. By forming appropriate vapor compositions, the vapor-condensed layer can be an amorphous metal composition, and preferably a bulk metal glass composition. The condensed-deposited amorphous (including partially nano-crystallized) layer can be retained as is, or can subsequently be treated to further crystallize or nanocrystallize it, to obtain specific properties, such as increased hardness.  
         [0038]     The illustrated apparatus  100  comprises a conventional plasma gun  102 , and a conventional inert gas shield  104 . As shown in  FIG. 1 , the plasma gun  102  produces an ultrahigh temperature plasma plume  106  which is directed toward a suitable substrate  108 , such as cooled steel, stainless steel, aluminum or titanium alloy substrate.  
         [0039]     As shown in the cross-sectional view of  FIG. 2 , the plasma gun  102  has an axially aligned cathode  110 , typically of a refractory metal with a low work function such as tungsten or thoriated tungsten, and a water cooled anode  112  through which powdered metals to be vaporized and deposited on the substrate  108  may be introduced through appropriate passageways  114 ,  116 . If desired, the thermal spray apparatus  100  ( FIG. 1 ) may be enclosed in a controlled-atmosphere chamber or vacuum chamber  118  if it is desired to exclude reactive gas such as oxygen or nitrogen, and/or to operate in subatmospheric pressure. In operation, an inert gas such as an argon-helium mixture  103 , which may include a small amount of hydrogen, is introduced into the plasma gun  102 , while direct-current is applied from a suitable power source to the cathode and anode of the gun to heat the inert gas to a temperature of 10-30 thousand degrees Kelvin to form a high-velocity plasma plume  106 . A selected amorphous metal alloy, which is preferentially a bulk metal glass alloy, having a largest dimension of about five microns or less, is introduced into the plasma gun  102  through conventional introduction port  114 , with an inert gas and/or hydrogen. The more volatile elements such as magnesium, boron and aluminum can be in relatively larger particles, while refractory elements such as Zr are heat volatilized from a smaller particle form. The metal powder may be a homogenous alloy of the specific alloy which is desired to be deposited on the substrate  108 , or may be a mixture of alloy powders or elemental metals which are proportioned to form the desired alloy upon vaporization and deposition. Because of their small size, and the intensity of the plasma thermal spray operation, the metal powder is substantially fully vaporized in the plasma plume  106 . In operation, a shielding gas  109  such as argon or helium may be introduced into the zone  104  surrounding the plasma plume  106 , in order to protect the metal components of the plasma plume from external reactive atmosphere components such as oxygen and nitrogen. Preferably, however, the entire thermal spray process is carried out in a controlled atmosphere or vacuum zone  118 , in which reactive gases such as oxygen and nitrogen are substantially excluded.  
         [0040]     As indicated, the amorphous metal coating is deposited on the selected substrate  108 . In this regard, it is important that the substrate be maintained at a temperature below the glass transition temperature or the crystallization temperature of the amorphous metal composition which is being deposited. Preferably, the substrate will be maintained at a temperature of at least 25 degrees Kelvin, and preferably at least 100 degrees Kelvin below the half crystallization temperature of the amorphous metal composition being applied thereto.  
         [0041]     In order to facilitate the formation of a strong, metallurgical bond between the metallic substrate  108  and the amorphous metal layer being deposited on the substrate, a pulsed power supply  120  may be provided in electrical contact with the plasma gun anode  112  and the substrate  108 . While a continuous current, which is a substantial fraction of that between the cathode  110  in the anode  112 , could tend to heat the surface of the metal substrate in deposited layer, a short duty-cycle discharge as optionally provided in accordance with the present methods can be utilized to enhance surface bonding, while limiting surface heat generation.  
         [0042]     In this regard, a capacitively-pulsed power supply, with a capacitance of 100,000 microfarads is charged to a DC voltage of 100-220 volts, and in connection with its positive (cathodic) voltage terminal to the substrate and its negative (anodic) voltage terminal to the cooled metal anode  112  of the plasma gun  102 . The pulsed power supply is periodically discharged at a rate of above once per second and a duty cycle of about 0.1 to 1 percent (1 to 10-milliseconds per pulse) during the initial pass of the amorphous metal vapor phase over the substrate, to enhance the bond with the substrate by removing any oxide surface layer. By a cathodic pulse to its electrically-conducting substrate  108 , cations from the plasma plume  106  are accelerated to impact and clean the substrate surface. In addition, the substrate tends to be “cooled” by the evaporation of electrons compared to being heated by their impact if connected to the anode.  
       EXAMPLE 1  
       [0043]     An iron-based BMG having a composition of (Fe66Mn29Cr5)68Zr4Nb4B24 (atomic percent) is vaporized in the plasma gun  102 , and condensed and solidified on a steel substrate  108  which is actively cooled to −10° C. by a glycol cooling stream and refrigeration unit. The feed rate of the alloy powder having a particle size of less than 3 microns is 1 pound per hour with 5-10 scfh of argon  103 . Argon is fed to the plasma spray gun  102  at a rate of about 75 scfh, and DC power is fed to the plasma spray gun to produce a plasma temperature of over 20,000° K. The vapor plasma plume is moved along the substrate at a rate of about 2 meters/second at a distance from the end of the gun to the substrate of 5-15 cm. The deposition is carried out in a vacuum in the chamber of approximately 0.01 to 0.1 atmosphere. A slight excess (e.g., 5 atom percent) of the more volatile boron component may be included in the small diameter powder, to produce the desired BMG stoichiometry in the condensed vapor deposit on the substrate. This may be determined empirically. The alloy vapor condenses on the substrate and rapidly solidifies to form a BMG coating of substantially full density with good adherence to the substrate.  
       EXAMPLE 2  
       [0044]     In this example, an aluminum-based alloy from Table 2 having a composition of (Al85Y8Ni5Co2)70Ba8Ca210Si20 or (Al85Y8Ni5Co2)70(Zr,Ti)10B18Si2 (atomic percent) is applied to a cooled, clean copper sheet as described in Example 1, with a similar result. Excess Ca and Al may be used in the input powders, as empirically determined, to obtain the desired atomic ratio in the deposit.  
       EXAMPLE 3  
       [0045]     In this example, a copper-based BMG having a composition Cu40Ti30Ni15Zr10Sn5 (atomic percent) is applied to a cooled copper sheet as described in Example 1, with a similar result  
       EXAMPLE 4  
       [0046]     In this example, a nickel-based BMG having the composition Ni60Nb20Ti12.5Hf7.5 is applied to a rotating, cooled steel mandrel, as generally described in Example 1, with a similar result.  
       EXAMPLE 5  
       [0047]     In this example, a zirconium-based BMG alloy, Zr65Al7.5Ni10Cu17.5 is applied to a cooled steel alloy substrate as in Example 1. Excess aluminum may be vaporized, as indicated, to achieve the desired deposit ratios.  
       EXAMPLE 6  
       [0048]     In this example, a titanium-based amorphous alloy, Ti50Ni24Cu20B1Si2Sn3 (atomic percent, is applied to a cooled, aluminum 2519-T87 or TiAl6V4 alloy sheet.  
       EXAMPLE 7  
       [0049]     In a series of test runs, aluminum, magnesium and boron powders of diameters less than 10 microns are introduced in to the apparatus of  FIGS. 1 and 2  as generally described in Example 1, in proportions to deposit an ultra hard composition ranging from AlMgB 10 to AlMgB 24  on a titanium alloy substrate maintained at 200° C. The deposits are dense, and substantially amorphous and adherent on the substrate. Deposits of nominal composition AlMgB 14  (atomic percent) are heated to 1100° C. in a vacuum to crystallize the composition to form an ultra hard material.  
         [0050]     Up to 30 atomic percent of TiB 2  powder of less than 5 micron diameter may be vaporized and then condensed with the AlMgB 14  to enhance hardness of the deposited composition. [Tian, Y., M. Womack, et al. (2002). “Microstructure and nanomechanical properties of Al—Mg—B—Ti films synthesized by pulsed laser deposition.” Thin Solid Films 418(2): 129-35]
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