Embrittling of glass alloys by hydrogen charging

Metallic glass powder is prepared by charging a solid metallic glass body with hydrogen to effect embrittlement, followed by comminution of the embrittled metallic glass body.

DESCRIPTION 
1. Field of the Invention 
The invention relates to amorphous metal powders and in particular to 
amorphous metal powders having the composition of known glass forming 
alloys. 
2. Description of the Prior Art 
Metallic glasses (amorphous metals), including metallic glasses in powder 
form have been disclosed by Chen et al. in U.S. Pat. No. 3,856,513. They 
prepared amorphous alloy powders by flash evaporation. They further 
disclose that powders of amorphous metal having the particle size ranging 
from about 0.0004 to 0.01 inch can be made by atomizing the molten alloy 
to droplets of this size and then quenching the droplets in a liquid such 
as water, refrigerated brine or liquid nitrogen. 
A method for making metal flakes suitable for making metal powder for 
powder metallurgical purposes is disclosed by Lundgren in German 
Offenlegungsschrift No. 2,555,131 published Aug. 12, 1976. The process 
involves impinging a jet of molten metal against a rotating flat disc. 
Relatively thin, brittle and easily shattered, essentially dentrite free 
metal flakes are obtained with between amorphous and microcrystalline 
structure, from which a metal powder can be obtained by shattering and 
grinding, for instance in a ball mill. In U.S. Pat. No. 063,942 and U.S. 
Pat. No. 4,069 Lundgren discloses a product with amorphous to 
compact-grained structure. 
There remains a need for methods for making amorphous (glassy) metal powder 
having good properties for use in metallurgical processes. 
SUMMARY OF THE INVENTION 
In accordance with the invention a method of producing metallic glass 
powder is provided wherein a solid metallic glass body, usually in 
filamentary form, is charged with hydrogen to effect embrittlement without 
causing formation of a crystalline phase. The embrittled metallic glass 
body is comminuted to powder. In general, removal of hydrogen from the 
comminuted product, as by exposing it to a substantially hydrogen-free 
atmosphere e.g., air, results in reversion to a ductile material. Each 
particle of the ductile glassy metal powder is defined by an irregularly 
shaped outline resulting from fracture. 
DETAILED DESCRIPTION OF THE INVENTION 
Metallic glass alloy powders are prepared according to a process involving 
first exposing a glassy alloy to hydrogen to produce an embrittled state 
and then comminuting the embrittled alloy to a powder. 
A metallic glass is an alloy product of fusion which has been cooled to a 
rigid condition without crystallization. Such metallic glasses in general 
have at least some of the following properties: high hardness and 
resistance to scratching, great smoothness of a glassy surface, 
dimensional and shape stability, mechanical stiffness, strength and 
ductility and a relatively high electrical resistance compared with 
related metals and alloys and a diffuse X-ray diffraction pattern. 
Alloys suitable for use in my process include those known in the art for 
the preparation for metallic glasses, such as those disclosed in U.S. Pat. 
No. 3,856,513; U.S. Pat. No. 3,981,722; U.S. Pat. No. 3,986,867; U.S. Pat. 
No. 3,989,517 as well as many others. For example, Chen and Polk in U.S. 
Pat. No. 3,856,513 issued Dec. 24, 1974 disclose alloys of the composition 
M.sub.a Y.sub.b Z.sub.c, where M is one of the metals: iron, nickel, 
cobalt, chromium and vanadium; Y is one of the metalloids, phosphorus, 
boron and carbon; and Z is aluminum, silicon, tin, germanium, indium, 
antimony or beryllium with "a" equaling 60 to 90 atom percent, "b" 
equaling 10 to 30 atom percent and "c" equaling 0.1 to 15 atom percent 
with the proviso that the sum of a, b and c equals 100 atom percent. 
Preferred alloys in this range comprise those where "a" lies in the range 
of 75 to 80 atom percent, "b" in the range of 9 to 22 atom percent, "c" in 
the range of 1 to 3 atom percent. Furthermore, they disclose alloys with 
the formula T.sub.i X.sub.j wherein T is a transition metal and X is one 
of the elements of the groups consisting of phosphorus, boron, carbon, 
aluminum silicon, tin, germanium, indium, beryllium and antimony and 
wherein "i" ranges between 70 and 87 atom percent and "j" ranges between 
13 and 30 atom percent. However, it is pointed out that not every alloy in 
this range would form a glassy metal alloy. These alloys are rapidly 
quenched from the melt by known procedures to obtain splats or filament 
(e.g. sheets, ribbons, tapes, wires, etc.) of amorphous metal. 
Charging the metallic glass body with hydrogen to effect embrittlement can 
be carried out in any desirable manner, for example by subjecting it to a 
hydrogen atmosphere under pressure in a closed container or, in another 
aspect of the present invention, by electrolytic charging by employing the 
material to be embrittled as a cathode in a hydrogen producing 
electrolytic bath. 
The hydrogen pressure (or hydrogen partial pressure, if other gases are 
present) necessary to effect embrittlement depends on the alloy. Generally 
required the hydrogen pressure is at least about 0.1 kg/cm.sup.2, 
preferably to at least about 1 kg/cm.sup.2. Pressures of between about 1 
kg/cm.sup.2 and 200 kg/cm.sup.2 are preferred for reasons of convenience 
(tank pressure). There is no upper limit to the pressure, other than 
imposed by limits of apparatus design. 
Electrolytic charging is obtained by forming a cathode of glassy metal 
alloy and placing the cathode in an electrolyte solution capable of 
forming hydrogen at the cathode under electrolysis conditions. Suitable 
solutions have an electrolyte concentration of from about 0.01 to 10 
moles/liter and a pH of from about 1 to 12. Such solutions include e.g. 
aqueous sulfuric acid, aqueous hydrochloric acid and aqueous ammonia 
solutions. Anodes useful include inert metals such as platinum, stainless 
steel, etc. Preferably a diaphragm is employed for separating cathode and 
anode space. The gas pressure in the cathode is at least 0.1 kg/cm.sup.2 
and preferably from about 1 kg/cm.sup.2 to 1000 kg/cm.sup.2. The current 
density at the cathode surface is at least about 0.001 amp/cm.sup.2 and 
preferably from about 0.005 amp/cm.sup.2 to 0.05 amp/cm.sup.2. The 
electrolytic charging time can be from about 1/4 hour to 100 hours. Alloys 
suitable for electrolytic hydrogen charging include for example TiCu, 
Be.sub.40 Ti.sub.50 Zr.sub.10, Be.sub.35 Zr.sub.65, Ni.sub.40 Fe.sub.40 
P.sub.14 B.sub.6. 
The hydrogen charging temperature may be within the range of from room 
temperature or lower to just below the glass transition temperature and up 
to the glass transition temperature, and preferably is within the range of 
from 350.degree. C. below the glass transition temperature to 50.degree. 
C. below the glass transition temperature. While processes such as 
annealing may embrittle glassy metal alloys, such processes are 
substantially irreversible regarding the loss of ductility of the glassy 
alloy. Hydrogen charging temperatures well below the glass transition 
temperature are preferred to avoid structural relaxation resulting in 
property changes of the glass and to provide for a reversible 
embrittlement process. For the sake of convenience, charging at room 
temperature is preferred. The charging time to achieve the desired 
embrittlement varies depending on temperature, composition of the glass 
and hydrogen pressure and may range from about 1 minute to 100 hours, and 
is preferably from about 10 minutes to 10 hours. 
Whether the metallic glass body has acquired a sufficient degree of 
brittleness can be tested by bending procedures. Depending upon the 
thickness of the ribbon employed initially a suitable radius can be 
selected for bending the embrittled ribbon. If the ribbon fails when bent 
around an adequately sized radius, the embrittlement process has been 
carried far enough. The larger the radius of breaking, the better 
embrittled the material. For ease of subsequent comminution, materials 
embrittled according to the present invention should fail when bent around 
a radius of about 0.1 cm and preferably of about 0.5 cm. 
In addition, it is possible to integrate the process of charging of a 
glassy alloy to produce embrittlement and of comminuting the embrittled 
glassy alloy. This can be done by comminuting of ribbons under hydrogen 
pressure. After the glassy material is embrittled by charging with 
hydrogen, it is relatively easy to comminute same to flake or fine powder, 
as desired. 
Milling equipment suitable for comminution of the embrittled metallic glass 
includes rod mills, ball mills, impact mills, disc mills, stamps, 
crushers, rolls and the like. To minimize contamination of the powder, the 
wearing parts of such equipment are desirably provided with hard and 
durable facings. Undue heating and ductilization of the powder may be 
prevented by water cooling of the grinding surfaces. Suitably, but not 
necessarily, the comminution process is performed in a hydrogen atmosphere 
to maintain the metallic glass in the hydrogen charged embrittled state as 
it is being comminuted. 
One type of mill suitable for the comminution of embrittled metallic glass 
is the conventional hammer mill, having impact hammers pivotably mounted 
on a rotating disc. Disintegration of the metallic glass is effected by 
the large impact forces created by the very high velocity of the rotating 
hammers. Another example of a suitable type of mill is the fluid energy 
mill. 
Ball mills are preferred for use in the comminuting step, inter alia 
because the resultant product has relatively close particle size 
distribution. 
Following comminution, the powder may be screened, for instance, through a 
100 mesh screen, if desired, to remove oversize particles. The powder can 
be further separated into desired particle size fractions; for example, 
into 325 mesh powder and powder of particle size between 100 mesh and 325 
mesh. 
Powder of metallic glass made according to the invention process may 
comprise fine powder with particle size under 100 micron, coarse powder 
with particle size between 100 micron and 1000 micron and flake with 
particle size between 1000 and 5000 micron, as well as particles of any 
other desirable particle size, and of any particle size distribution, 
without limitation. 
After milling the hydrogen can be removed from the glassy metal alloy. 
Hydrogen removal is associated with subsequent return of ductility of the 
glassy metal alloy (reversible embrittlement). Methods for removing the 
hydrogen include releasing the hydrogen pressure, removal of hydrogen by 
evacuation at room temperature and, in some cases, evacuation while 
heating to a temperature below the glass transition temperature to 
facilitate the removal. 
A material is called ductile when considerable deformation occurs before 
fracture. Such deformation can be for example an elongation of a specimen 
or a bending deformation of a specimen. 
While glassy metal alloys upon tempering turn irreversibly brittle and 
loose their ductility permanently, hydrogen charging of glassy metal 
alloys reversibly embrittles the glassy metal alloy and upon release of 
the hydrogen the original ductility substantially returns. 
The dissolved hydrogen in the glassy metal alloys reduces temporarily the 
ductility of the glassy metal alloy over a certain temperature range and 
at certain deformation rates. 
While I do not wish to be bound by any theory, it is believed that a 
suitable choice of temperature provides a mobility rate of the hydrogen in 
the glassy metal alloy compatible with the deformation rate whereby the 
movement of the glassy metal alloy atoms is hampered and brittleness 
results. 
This process produces a new glassy metal alloy powder which exhibits an 
irregularly shaped outline resulting from fracture but which is 
nevertheless ductible based on the reversibility of the hydrogen charging 
process on the ductile properties. 
The powder prepared according to the present invention in general does not 
exhibit sharp edges with notches as typically found in glassy metallic 
powders prepared according to the process involving chill casting of an 
atomized liquid as disclosed in commonly assigned copending applications 
Ser. No. 023,413 and Ser. No. 023,412 filed Mar. 23, 1979. A particular 
advantage of a powder with less rough edges and good ductility is that the 
particles can slide against each other and as a result can be compacted to 
higher density at equivalent pressure compared with an analogous chill 
cast atomized alloy. A compact of higher density is often a more desirable 
starting material for powder metallurgical applications. The metallic 
glass powder of the present invention is useful for powder metallurgical 
applications.

The examples as set forth below further illustrate the present invention 
and set forth the best mode presently contemplated for its practice. 
EXAMPLE 1 
A metallic glass in the form of short pieces of ribbon, 2-5 mm long and 2 
mm wide, of composition Fe.sub.84 B.sub.16 was exposed at room temperature 
to hydrogen at 135 kg/cm.sup.2 pressure in a modified 300 ml stainless 
steel, commercial hydrogenation apparatus. (Magna Dash unit, made by 
Autoclave Engineers, Erie, Pa.). The modification consisted of replacing 
the actuated dasher with a tungsten carbide ball which was brazed to the 
actuating rod. The impact of the carbide ball, falling under gravitational 
forces, provided the grinding action. After grinding for 13/4 hours the 
resulting powdered sample was removed for analysis. The following particle 
size distribution was determined: -100 to +200 mesh 44.7%; -200 to +325 
mesh 39.2%; -325 mesh 16.1%. From X-ray diffraction analysis it was 
concluded that no crystallization had taken place and that the glassy 
state was preserved. Thermogravimetric analysis to 900.degree. C. showed 
no weight loss indicating that any hydrogen absorbed under high pressure 
was released when the hydrogen pressure was removed. Differential thermal 
analysis of the powder showed no change in T.sub.g or crystallization 
behavior from the original sample. 
EXAMPLE 2 
Glassy metal alloy of the composition Fe.sub.5 Ni.sub.45 B.sub.16 Mo.sub.4 
Cr.sub.10 Co.sub.20 (atom percent) was ground at room temperature for 1 
hour in the Magna Dash Unit under 125 kg/cm.sup.2 hydrogen pressure. The 
particle size distribution was: -20 to +100 mesh 53.8%; -100 to +200 mesh 
29.3%; -200 to +325 mesh 11.6%; -325 mesh 5.3%. Hydrogen was not retained 
by the glass when the pressure was released. 
EXAMPLE 3 
Glassy metal alloy Fe.sub.40 Ni.sub.40 P.sub.14 B.sub.6 (atom percent) was 
ground for 4 hrs. in the Magna Dash Unit under approximately 155 
kg/cm.sup.2 hydrogen pressure at room temperature. Particle size 
distribution analysis gave: -100 to +200 mesh 81.5%; -200 to +325 mesh 
14.1%; -325 mesh 4.4%. Again, no retention of hydrogen was observed when 
the pressure was released. 
EXAMPLES 4-8 
Metallic glass in ribbon form of composition indicated in the Table, below, 
was ground in a hydrogen atmosphere at temperatures and for times given in 
the table. The resulting powder had a fine particle size between about 45 
and 850 microns, as given in the table, and the powders were found to be 
amorphous by X-ray analysis and differential scanning calorimetry. The 
hydrogen which had been absorbed under high pressure was released when the 
hydrogen pressure was removed except in the case of TiCu which required 
prolonged evacuation and heating to remove absorbed hydrogen. The powder 
size is given in the Table in weight percentages for some ranges in size. 
Nickel, cobalt and iron base metallic glass alloys containing chromium and 
molybdenum in powder form as obtained by the method of my invention are 
fabricated by powder metallurgical techniques into structural parts with 
excellent properties desirable for wear and corrosion resistant 
applications. Such materials will find uses in pumps, extruders, mixers, 
compressors, valves, bearings and seals especially in the chemical 
industry. 
EXAMPLE 9 
A metallic glass ribbon of composition TiCu was electrolyzed in an aqueous 
solution containing 0.1 moles/liter of H.sub.2 SO.sub.4. The anode was 
platinum, the potential 10 volts and the current 0.567 amps; the time of 
electrolysis 1 hour. Upon completion of electrolysis a portion of the 
ribbon, which had become quite embrittled, was easily ground to &lt;200 mesh 
powder and an X-ray pattern taken. The pattern showed that the amorphous 
structure was retained. Another portion of the ribbon was analyzed for 
hydrogen and a composition TiCuH.sub.0.98 was indicated. The removal of 
hydrogen was difficult and required prolonged evacuation and gentle 
heating. 
The results of Examples 1 through 8 are summarized in the Table, below. 
TABLE 
______________________________________ 
Char- 
ging Char- Milled 
Pres- ging Powder 
Composition sure Time Size 
Ex. (atom percent) kg/cm.sup.2 
[h] [microns] 
______________________________________ 
1 Fe.sub.84 B.sub.16 
135 1.75 Less than 
45:16.1% 
45-75:39.2% 
75-150:44.7% 
2 Ni.sub.45 Co.sub.20 Cr.sub.10 Fe.sub.5 Mo.sub.4 B.sub.16 
125 1 45-75:11.6% 
75-150:29.3% 
150-1850:53.8% 
3 Fe.sub.40 Ni.sub.40 P.sub.14 B.sub.16 
155 4 Less than 
45:4.4% 
45-75:14.1% 
75-150:81.5% 
4 Fe.sub.83 P.sub.16.5 Si.sub.0.5 
130 4 Less than 
75:100% 
5 Fe.sub.40 Ni.sub.38 Mo.sub.4 B.sub.18 
146 3 Less than 
75:6% 
75-150:22.1% 
150-850:71.9% 
6 Co.sub.60 Fe.sub.7.5 Ni.sub.7.5 Mo.sub.2 Si.sub.8 B.sub.15 
145 5 Less than 
75:11.6% 
150-850:44.9% 
7 Fe.sub.80 Si.sub.10 B.sub.10 
143 5 Less than 
75:3.9% 
75-150:23.8% 
150-850:72.4% 
8 CuTi* 1 6 Less than 
200:100% 
______________________________________ 
*Hydrogen highly bound in this sample. Prolonged evacuation necessary for 
the removal of hydrogen.