Method for producing amorphous metal layer

A method metallurgically bonds a thin film of easily amorphized material on a metallic substrate having a large thermal conductivity, and then irradiates all or selected portions of the thin film with a pulse laser. The irradiated portions become amorphous by rapidly heating and cooling. Therefore, a whole surface which is an amorphous layer or a part of a surface which is an amorphous layer is obtained. In the latter, a porous amorphous metal layer is obtained by subsequent acid elution and by removing the non-amorphous part.

BACKGROUND OF THE INVENTION 
The present invention relates to a method for producing an amorphous metal 
layer and an amorphous alloy layer having small sized pores. The use of 
amorphous metal layers, which possess excellent mechanical, physical and 
chemical properties such as corrosion resistance, strong toughness, 
optical properties and magnetic properties, is rapidly expanding. An 
amorphous metal is non-crystalline, and is obtained by methods such as the 
metal gas condensation method, the rapid cooling method of liquid metal, 
or the fault introducing method for crystals for the purpose of producing 
an amorphous state. Of the methods, the method of rapidly quenching liquid 
metal is suited to continuously produce large amounts of materials and is 
generally used. Many papers report that in one rapid quenching method, an 
amorphous surface is rapidly heated and fused by giving laser irradiation 
to a metal material having a high amorphous-formation ability, and the 
surface layer part becomes amorphous. However, there are problems such as 
that the amorphous state or layer becomes crystallized again. The 
heterogeneity of the composition and the shape of the amorphous layer is 
observed at the part of overlapped laser irradiation. Cracks are further 
observed. In order to take advantage of amorphous metals, materials having 
a uniform thickness amorphous metal are required for use as electrode 
material, contacts, wear-resistant material or magnetic material. Also, 
there are many cases requiring that an amorphous metal having the 
abovementioned many advantages be formed as a wire net or a porous sheet, 
or such formed objects are joined and rested on a base plate depending on 
the use. Also, when making a form where the amorphous layer itself has 
fine pores, uses as a filter for corrosive material or a printing negative 
increase. Therefore, in the existing state of the art, an amorphous metal 
is difficult to work to the form of a wire net or a porous sheet because 
amorphous metal itself is tough. 
SUMMARY OF THE INVENTION 
It is an object of the present invention to provide a method in which an 
amorphous metal not having cracks and having a uniform thickness is easily 
produced on a base material surface. It is also another object of the 
present invention to provide a method in which the object alloy layers are 
made amorphous and are simultaneously formed as a wire net or a porous 
sheet.

DETAILED DESCRIPTION OF THE INVENTION 
The following embodiments are a detailed description of the present 
invention. 
EMBODIMENT 1 
Experiments using a Cu substrate and a Ni substrate constitute Embodiment 
1. 
Fe.sub.78 Si.sub.9 B.sub.13 for magnetic materials was bonded as a 25 mm 
wide and about a 40 .mu.m thick thin film on 50 mm.times.50 mm and 10 mm 
thickness Cu and Ni substrates by hot isostatic pressure (hereinafter 
HIP), and then, the thickness of the thin film was finished to 20 .mu.m. 
The HIP condition and a schematic view of a specimen section in this case 
are shown in FIG. 1. 
For such specimens, concerning the relationship of the fused part shaped by 
laser irradiation and the condition of laser irradiation, the defocused 
distance(fd) and laser energy(Eo) were changed, the condition of obtaining 
a plain surface was required, pulse laser irradiation was applied under 
such condition, and the forming condition of the amorphous surface layer 
was examined. Also, pulse laser was applied under an Ar gas atmosphere, 
the structure of the surface and a section of a laser irradiation molten 
part was observed by optical microscope and scanning electron microscope, 
and the condition of the amorphous layer formation was further examined by 
X-ray diffractometer. 
As for results, the surface condition of various kinds of molten parts was 
observed and the surface conditions were classified into five groups: 
formations having pores(Type H), formations having unevenness of 
surface(Type R), formations having a smooth surface(Type S), formations 
having a non-uniform molten surface(Type I) and formations having an 
insoluble surface(Type N). FIG. 2(Cu substrate) and FIG. 3(Ni substrate) 
show schematically the relationship of the above-mentioned five types and 
the laser irradiation condition. 
An amorphous layer not having cracks was classified as Type S. From the 
results of FIG. 2 and FIG. 3, when a Cu substrate was used in an area 
having a high energy density, the substrate did not fuse and only the 
surface of the amorphous metal thin film had pores. When using a Ni 
substrate, the substrate fused at the same time, and cracks were observed 
in the central part. 
The reason for the above-mentioned result is that Fe.sub.78 Si.sub.9 
B.sub.13 was used as an easily amorphized material thin film. If the 
materials having a low thermal conductivity are used for the easily 
amorphized material, a sufficiently uniform amorphous metal without cracks 
is obtained even using a Ni substrate. Furthermore, in the Cu substrate 
shown in FIG. 2, if fd is not changed, and Eo is lowered in an area of 
Type H, or Eo is not changed and fd is lowered, then Type H is easily 
moved into an area of Type S. However, in the Ni substrate shown in FIG. 
3, cracks are caused in Type H, and an area of Type R containing 
non-amorphous layer parts exists between Type H and Type S by dilution of 
the substrate. Therefore, it is hard to move directly from Type H to Type 
S, and it is also found that the condition set points become complex. 
Next, for the condition that a smooth plain surface such as the 
above-mentioned is obtained, the surface of the specimen in which the 
Fe.sub.78 Si.sub.9 B.sub.13 thin film layer is bonded on the Cu substrate 
of the embodiment of the present invention was given repetitive overlapped 
irradiation with laser, the whole area of the surface was fused and 
solidified, and the surface condition of the melt-in condition was 
examined. When the above-mentioned results wee observed by surface 
microstructure and section-scanning electron microscope, it was found that 
a smooth surface condition and uniform melt-in depth are obtained in the 
case of overlapped irradiation with a laser. 
Next, concerning the specimen after the above-mentioned overlapped laser 
irradiation treatment, the formation of the amorphous alloy layer was 
examined. 
Examination revealed that there are laser irradiated molten part (1), 
non-molten part (2) and substrate (3). As shown in FIG. 4, the laser 
irradiation molten part has a low degree of etching compared with the 
non-molten part in microscopic observation, and the amorphous phase is 
almost a single layer. 
The results of the above-mentioned observation by X-ray diffractometer are 
shown in FIGS. 5(a), (b) and (c). FIG. 5(a) shows X-ray diffraction when 
Fe.sub.78 Si.sub.9 B.sub.13 is bonded on a Cu substrate before laser 
irradiation. FIGS. 5(b) and (c) show X-ray diffraction when specimens of 
Fe.sub.78 Si.sub.9 B.sub.13 bonded on a Cu substrate and a Ni substrate in 
the present embodiment are treated by laser. In FIG. 5(a), the specimen is 
heated to 1073K by HIP treament, and the compounds of Fe and Fe.sub.2 B 
metals are produced as a thin film and are crystallized. However, in FIGS. 
5(b) and (c), a broad X-ray diffracted peak which is the characteristic of 
an amorphous condition is confirmed. And partly, a non-molten part at a 
lower part and a peak showing a crystal structure of Cu and Ni are 
observed. 
From the above-mentioned results, in laser treatment condition where a 
plain surface is obtained without fusing the substrate, it is found that a 
non-molten part of the thin film stays as a crystal structure, but a 
molten part attains the amorphous condition. 
As mentioned above, from the examinations and results in Embodiment 1, it 
is possible to form an amorphous layer having uniform depth. However, as 
found by comparing FIG. 2 and FIG. 3, a Cu substrate obtains a good 
surface condition much more than a Ni substrate and is easily controlled 
to that condition. This is because Cu has good thermal conductivity, and 
the surface of Cu easily reflects laser irradiation, even if the Cu 
surface is exposed during irradiating and is hardly fused. These 
properties are the same with Ag or copper-silver alloys. 
Additionally, as for amorphous alloys, an examination in which the alloys 
shown in the following Table 1 are laser-irradiated at the block condition 
was conducted similarly to the abovementioned Fe.sub.78 Si.sub.9 B.sub.13. 
Table 1 shows the structure and cracks-evolving situation. In the items of 
the structures in Table 1, A indicates an amorphous structure, C indicates 
a crystal structure, (A) indicates a partly amorphous structure, and (C) 
indicates a partly crystal structure. 
From the results of Table 1, even given an easily amorphized material, it 
is found that a uniform amorphous layer is hardly obtained, and a lot of 
cracks are evolved using laser irradiation at the block state excepting a 
small number of alloys. 
TABLE 1 
______________________________________ 
Material 
No. (at %) Structure cracks 
______________________________________ 
1 Pd.sub.40 Ni.sub.40 P.sub.20 
A none 
2 Pb.sub.78 Cu.sub.6 Si.sub.16 
A none 
3 Ni.sub.53 Pb.sub.27 P.sub.20 
A none 
4 Ni.sub.63 Nd.sub.37 
A + (C) exist 
5 Ni.sub.60 Nd.sub.40 
A + (C) exist 
6 Pd.sub.82 Si.sub.18 
A + (C) partly exist 
7 Cu.sub.56 Zr.sub.44 
A + C partly exist 
8 Ni.sub.64 Zr.sub.36 
A + C exist 
9 Fe.sub.41.5 Ni.sub.41.5 B.sub.17 
C exist 
10 Au.sub.78 Ge.sub.14 Si.sub.8 
C exist 
11 Ni.sub.80 P.sub.20 
C + (A) exist 
12 Pd.sub.40 Ni.sub.40 P.sub.10 Si.sub.10 
A none 
13 Fe.sub.78 Si.sub.9 B.sub.13 
A + (C) exist 
14 Fe.sub.73 Si.sub.12 B.sub.5 
A + (C) exist 
15 Fe.sub.79 Si.sub.14 B.sub.14 
A + (C) exist 
16 Fe.sub.83 P.sub.10 C.sub.7 
C exist 
17 Fe.sub.40 Ni.sub.40 P.sub.14 B.sub.6 
C exist 
18 Ti.sub.70 Ni.sub.30 
C exist 
______________________________________ 
Additionally, in the present invention, the substrate and easily amorphized 
material at an upper face of the substrate have to be metallurgically 
bonded before laser irradiation. This is because the amorphous condition 
is not sufficiently achieved due to bad thermal conductivity. For 
metallurgical bonding, there can be used coating, press-bonding and other 
kinds of methods including HIP bonding as employed in the above-mentioned 
embodiment. 
Also, for an easy amorphization material, it is possible to use an alloy 
which is once changed to the amorphous condition by a different manner or 
to use an alloy of a fusion-produced crystal structure as shown in the 
embodiment. 
EMBODIMENT 2 
In Embodiment 2, an Fe.sub.78 Si.sub.9 B.sub.13 thin film layer was bonded 
on a Cu substrate and Ni substrate which are the same as in Embodiment 1 
under the condition of a smooth Type S structure as shown in the 
above-mentioned Embodiment 1. The bonded specimen was laser-irradiated and 
was fused and solidified under the condition that a lot of non-laser 
irradiated parts exist, and the surface condition and the melt-in 
condition or depth of melting, under laser irradiation were examined. The 
results were observed by using a photomicrostructure and scanning electron 
microscope at the section of the specimen. A nearly round-shape white 
color and a non-amorphous part having a nearly round-shape black color 
were observed. The laser-irradiated parts were only changed to an 
amorphous condition, and a nice surface condition and uniform melt-in 
depth were observed in these parts. 
Next, concerning the specimen after the above-mentioned laser-irradiated 
treatment, the formation of an amorphous alloy layer was examined. 
Similar to the results shown in FIG. 4 in the above-mentioned Embodimennt 
1, a laser-irradiated fused part, non-fused part and substrate were formed 
from the surface in order, but it was also found that the laser-irradiated 
fused part had a low degree of etching compared with the non-fused part 
and was nearly a single layer. Also, in the specimen in Embodiment 2, the 
product was confirmed by X-ray diffractometer, and a result the same as 
the result shown in FIG. 5 was observed. 
Additionally, in Type H shown in the above-mentioned Embodiment 1, in the 
case of using Cu as the substrate, nearly uniform pores were observed over 
the whole depth of the thin film, and pores were not observed in the Cu 
substrate. This is because Cu has good thermal conductivity compared with 
Ni, and rapidly attains an edothermic condition, and Cu itself reflects 
laser light. It is considered that the size of pores on the thin film 
becomes almost the same at an upper part and a lower part by the 
reflective strength at the time of reflection, i.e., at the time when the 
laser is reflected by the copper plate. 
Concerning the results of Embodiments 1 and 2 synthetically, it is found 
that an easily amorphized material bonded on such a substrate as Cu having 
a large degree of thermal conductivity results in an amorphous metal 
having many pores obtained by being partially fused by laser irradiation 
and being defective because of spatter (a) or an amorphous metal having 
non-pores(b) and uniform thickness by irradiating with a controlled pulse 
laser. 
Accordingly, by pulse laser irradiating under the condition such as (b), it 
is easy to form an amorphous metal having uniform thickness on the surface 
of a metallic material having a large degree of thermal conductivity such 
as copper, silver, or their alloys. Such an amorphous metal is 
metallurgically bonded with the substrate in advance. Therefore, it is 
suitable for many uses by working the amorphous metal to the necessary 
shape. 
Also, the parts where the laser does not reach remain as the condition for 
an amorphous metal having many pores such as (a). By laser irradiating 
such that an amorphous metal having uniform thickness such as (b) is 
obtained, there are many parts where the laser does not reach. As a 
result, in both methods, an amorphous metal layer in which non-amorphous 
metal parts exist a lot is obtained. Next, only the non-amorphous part 
which is unnecessary, depending on the use, or both the non-amorphous part 
and substrate are eluted and dissipated using an acid. The kind of acid in 
this case is chosen by considering acid elution of amorphous metal versus 
non-amorphous metal or substrate. However, amorphous metal has remarkably 
excellent corrosion resistance, so that it is difficult to select the kind 
of acid. 
By using the above-mentioned method, it is possible to obtain a porous 
metal layer having various shapes which are decided upon depending on the 
laser irradiation at an early step. Laser irradiation is possible for 
microcontrol. Therefore, it is also possible to produce a filter-like 
metal plate having a lot of fine pores. 
Also, in the method of the present invention, it is possible to wholly 
produce an amorphous layer on the surface of a solid-shaped object, to 
form an amorphous layer having many pores, or to produce a solid-shaped 
amorphous metal body regardless of non-pores or pores. It is already 
possible to use laser irradiation for a three-dimensional effect and to 
produce many shapes which were hitherto difficult.