Amorphous Al-based alloys essentially containing Ni and/or Fe and Si and process for the production thereof
The invention relates to Al-based alloys essentially containing Ni and/or Fe and Si as main alloy elements, which are produced in an essentially amorphous state, by relatively rapid solidification. The term essentially amorphous is used to denote an alloy in which the crystallised fraction by volume is at most equal to 25%. 
     Although amorphous Al-based alloys are already known generally (see French patent application No. 2 529 209), the production thereof at practical and industrial levels falls foul of major difficulties by virtue of the extremely strict production parameters that have to be complied with, in order to produce the essentially amorphous structure. 
     Such parameters are primarily the temperature range for `quenching` from the liquid state and the minimum solidification rate. 
     Industrial development of such alloys is therefore governed by the selection of alloys having a sufficiently wide quenching range (about 100° C. between the temperature of the liquid alloy and the liquidus thereof) and rates of solidification which are not excessively rapid (of the order of 10 4  K/sec). 
     Only a small number of alloys according to the invention fulfil those aims. Such alloys contain (in atomic %): 
     from 5 to 30% of Si 
     from 11 to 22% of Ni 
     Fe+Ni+Si≦42% 
     wherein the (Ni) may be partially substituted by Fe (up to 10%) by V or B (up to 5 atomic %) or totally substituted by Mn (up to 22 atomic %), the balance being formed by Al and the usual production impurities. 
     The alloys preferably contain: 
     from 9 to 25% of Si 
     from 11 to 19% of Ni 
     with 21≦Fe+Ni+Si≦38% 
     the manganese being limited to 5 atomic %. 
     Under those conditions, it is possible reproducibly to obtain amorphous industrial alloys. 
     Those alloys have an array of remarkable properties in the amorphous or essentially amorphous state as well as in the microcrystallised state which is obtained by annealing of the amorphous or essentially amorphous state. Those properties result from the introduction of a substantial amount of alloying elements without detrimental effects in respect of segregation or the formation of fragile intermetallic phases of dimensions greater than 10 μm. The unique combination of the compositions and structures, which is achieved in that way, provides such alloys with high levels of hardness, excellent hot stability for long-term annealing operations and particular tribological properties. 
     The possibility of obtaining essentially amorphous structures with rates of solification of the order of 10 4  K/sec makes it possible to use different processes for producing such alloys. Thus, besides processes involving rapid quenching on a wheel or gaseous atomisation, it is possible to use plasma deposit of pre-alloyed powders on a metal substrate (or a good conductor of heat such as graphite) or chemical or electrochemical surface nickel plating of an Al alloy containing Si (type AS), with preferably from 10 to 25% of Si, followed by fusion of the deposit of nickel and a portion of the substrate by means of a concentrated and localised heat source such as a laser, plasma torch, HF heating, TIG torch, etc. 
     One consolidation process consists of crushing of strips produced by casting on a wheel, sifting at below 100 μm, hot compression at between 350° and 400° C. and hot extrusion at about 400° to 450° C. In that way it is possible to produce solid products. 
    
    
     The invention will be better appreciated by reference to the examples described hereinafter and the accompanying drawings in which: 
     FIGS. 1 to 3 respectively show the diagrams in respect of X-ray diffraction of an amorphous alloy, an essentially amorphous alloy (about 20% in the crystallised state) and a microcrystalline alloy, 
     FIG. 4 shows the limits of composition of the Al-Ni-Si alloys according to the invention, 
     FIG. 5 shows the variation in the Vickers microhardness values of two initially amorphous alloys: Al 70  Ni 15  Si 12  Mn 13  and Al 70  Ni 15  Si 15  after being maintained for 1 hour at various temperatures, 
     FIG. 6 is a diffractogram of the alloy Al 70  Ni 15  Si 15  deposited by atmospheric plasma and produced with CuKα radiation, and 
     FIG. 7 represents the losses in weight (ΔP) observed on a coating of Al 70  Ni 15  Si 15  in comparison with an alloy A-S17U4G which is recognised as being resistant to wear, in dependence on the number of cycles (N) on a TABER abrasimeter. 
    
    
     EXAMPLE 1 
     Table 1 sets out examples of compositions of amorphous alloys which are defined within the scope of the present invention and which were produced in the form of strips of 20 μm in thickness by quenching on a Cu wheel, the linear rate of ejection of the strip being 60 ms -1 . Crystallisation of those alloys was studied by differential enthalpic analysis, by X-ray, by transmission electron microscopy and by measurements in respect of microhardness values. The temperature of the first crystallisation peak is set forth in Table I for each composition. Thus, for the alloy Al 70  Ni 15  Si 15 , that temperature is 190° C. whereas it is 295° C. for the alloy Al 70  Ni 15  Si 12  Mn 3 . For ternary alloys (Al, Ni, Si), that temperature increases: 
     (a) with a constant Al content, for increasing proportions of Ni, 
     (b) for increasing proportions of alloying elements (Ni+Si) 
     FIG. 5 shows the variation in the Vickers microhardness under a load of 10 g of strips as measured at 20° C. after isothermal annealing operations for 1 hour at different temperatures. Generally speaking, crystallisation is accompanied by a substantial increase in hardness. The high levels of microhardness attained (300 HV to 560 HV) will be noted. After annealing for 1 hour at 200° C., the alloy Al 70  Ni 13  Si 17  shows abundant crystallisation of a new metastable intermetallic phase of hexagonal structure (a=0.664 nm and c=0.377 nm) with incipient crystallisation of the Al. After 1 hour at 300° C., the alloy is made up of micrograins of Al and Si and orthorhombic equilibrium phase Al 3  Ni. 
     Investigations by optical and electronic microscopy in the transmission mode show that after the alloy has been maintained for 1 hour at 400° C., the mean size of the grains is between 0.05 μm and 0.5 μm. That very fine microcrystalline structure can be obtained for such compositions only by annealing of an amorphous alloy, and it imparts both high levels of mechanical strength and high levels of ductility to the alloy. 
     Table II gives the intereticular distances and the X-ray diffraction angles θ (radiation Kα of Cu) relating to the hexagonal phase encountered after quenching at about 200° C. in an initially amorphous sample of the alloy Al 70  Si 15  Ni 15  (a=0.6611 nm and c=0.3780 nm). 
     EXAMPLE II 
     We produced 20 kg of strips of Al 70  Ni 15  Si 15  by quenching on a wheel. The strips were finely crushed and the powder produced in that way was hot compressed. The hot compression billet was extruded at 450° C. with an extrusion ratio of 16:1. The extruded bar was characterised by traction at 20° C., 350° C., 450° C. and 500° C. All the hot traction tests were carried out after the alloy had been maintained at 350° C. for 10 hours. The results obtained are set forth in Table III. Up to 350° C., the material is highly fragile and premature ruptures are found at structural defects. However, the level of breaking stress at 350° C. remains very high. At 450° C. and 500° C. the behaviour of the material is totally different, with elevated degrees of elongation, indicating a highly ductile behaviour. 
     EXAMPLE III 
     The alloy Al 70  Ni 15  Si 15  was produced by quenching on a wheel and crushed. The powder obtained was projected by means of an atmospheric plasma on to a substrate of alloy A-S5U3, which gives rise to a rate of solidification of close to 10 4  K/sec. The deposit produced is 75% amorphous according to semi-quantitative X-ray testing (see FIG. 6). The microhardness of the deposit is 500 Vickers. The behaviour of that deposit, when subjected to abrasion, in comparison with that of an uncoated alloy A-S17U4G, which is known for its resistance to abrasion, was studied on a TABER abrasimeter under the following conditions: 
     grinding wheel type C5 17 
     load applied: 1250 g, 
     with measurement of the losses in weight after 300, 500, 1000, 2000 and 4000 cycles. 
     The results obtained are set forth in Table IV and represented in graph form in FIG. 7. 
     It is found that the essentially amorphous alloy according to the invention therefore has a very good level of performance in respect of friction effect and abrasion. 
     
                       TABLE I                                                     
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                     TEMPERATURE                                          
                     OF THE FIRST                                         
            CRYSTAL- CRYSTALLISATION                                      
            LINITY   PEAK (in °C.)                                 
______________________________________                                    
    TERNARY                                                               
    ALLOYS                                                                
    Al.sub.75 Ni.sub.12.5 Si.sub.12.5                                     
                  0          159                                          
    Al.sub.75 Ni.sub.15 Si.sub.10                                         
                  0          199                                          
    Al.sub.75 Ni.sub.17 Si.sub.8                                          
                  0          219                                          
    Al.sub.70 Ni.sub.13 Si.sub.17                                         
                  0          157                                          
    Al.sub.70 Ni.sub.15 Si.sub.15                                         
                  0          190                                          
    Al.sub.70 Ni.sub.17 Si.sub.13                                         
                  0          226                                          
    Al.sub.65 Ni.sub.15 Si.sub.20                                         
                  0          217                                          
    Al.sub.65 Ni.sub.17.5 Si.sub.17.5                                     
                  0          260                                          
    Al.sub.70 Mn.sub.13 Si.sub.17                                         
                  &lt;25        --                                           
    QUATERNARY                                                            
    ALLOYS                                                                
    Al.sub.70 Ni.sub.10 Fe.sub.3 Si.sub.17                                
                  0          159                                          
    Al.sub.70 Ni.sub.3 Fe.sub.10 Si.sub.17                                
                  0          248                                          
    Al.sub.70 Ni.sub.15 Si.sub.12 Mn.sub.3                                
                  0          295                                          
    Al.sub.70 Ni.sub.15 Si.sub.12 B.sub.3                                 
                  0          216                                          
    Al.sub.70 Ni.sub.15 Si.sub.12 Fe.sub.3                                
                  &lt;25        --                                           
    Al.sub.70 Ni.sub.15 Si.sub.12 V.sub.3                                 
                  &lt;25        --                                           
    Al.sub.80 Ni.sub.8.5 Si.sub. 8.5 V.sub.3                              
                  &lt;25        --                                           
    Al.sub.80 Ni.sub.8.5 Si.sub.8.5 Fe.sub.3                              
                  &lt;25        --                                           
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                       TABLE II                                                    
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Experimental       Theoretical                                            
d(nm)       σ.sup.o                                                 
                   d(nm)        σ.sup.o                             
                                     h-k-l                                
______________________________________                                    
0.57488      7.70  0.57253       7.73                                     
                                     100                                  
0.57055     13.48  0.57055      13.48                                     
                                     110                                  
0.57595     14.11  0.57575      14.13                                     
                                     101                                  
0.57859     18.05  0.57883      18.03                                     
                                     111                                  
0.57807     19.74  0.57821      19.73                                     
                                     201                                  
0.57592     20.90  0.57540      20.85                                     
                                     210                                  
0.57040     23.86  0.57084      23.80                                     
                                     300                                  
0.57745     24.26  0.57780      24.21                                     
                                     211                                  
0.57488     27.85  0.57407      18.00                                     
                                     112                                  
0.57838     29.10  0.57879      29.02                                     
                                     310                                  
0.57098     30.68  0.57143      30.57                                     
                                     221                                  
0.57597     31.85  0.57640      31.74                                     
                                     311                                  
0.57219     32.80  0.57235      32.76                                     
                                     212                                  
0.57404     35.07  0.57429      35.00                                     
                                     302                                  
0.57455     38.20  0.57441      38.25                                     
                                     222                                  
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                       TABLE III                                                   
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ALLOY Al.sub.70 Ni.sub.15 Si.sub.15 EXTRUDED A 450° C.             
TRACTION TEST                                                             
(lengthwise direction)                                                    
T test   R.sub.p 0.2   Rm      A                                          
(°C.)                                                              
         (MPa)         (MPa)   (%)                                        
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20       --            227     ˜0                                   
         --            320     ˜0                                   
         --            240     ˜0                                   
350*     --            286     ˜0                                   
         --            246     ˜0                                   
450*     23             30      35                                        
500*     10             13      40                                        
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 *Testpieces annealed for 10 hours at 350° C. and then brought to  
 the test temperature in about 1 hour.                                    
 
    
     
                       TABLE IV                                                    
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                          Weight loss (P)                                 
Alloy        No of cycles (N)                                             
                          (in g)                                          
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Al.sub.70 Si.sub.15 Ni.sub.15                                             
              300         4.6 · 10.sup.-3                        
(according to the                                                         
              500         8.7 · 10.sup.-3                        
invention)   1000         1.3 · 10.sup.-2                        
             2000         1.9 · 10.sup.-2                        
             4000         3.1 · 10.sup.-2                        
A-S17U4G      300         7.4 · 10.sup.-3                        
uncoated      500         9.7 · 10.sup.-3                        
(reference)  1000         1.1 · 10.sup.-2                        
             2000         1.5 · 10.sup.-2                        
             4000           2 · 10.sup.-2                        
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