Electroless plating method of NI-Al intermetallic compound

A electroless plating method of an Ni--Al intermetallic compound includes steps of a) providing a reducing solution containing a reducing agent and reducing nickel ions, b) adding a proper amount of aluminum powder to the reducing solution, and c) permitting the reducing agent to reduce the reducing nickel ions to be deposited on the aluminum powder. Such electroless plating method permits the Ni--Al compound to be produced inexpensively/efficiently/fastly.

BACKGROUND OF THE INVENTION 
The present invention relates generally to the family of Ni--Al 
intermetallic compounds, and more particularly to a preparing method 
thereof. 
The Ni--Al intermetallic compounds such as Ni.sub.3 Al (.GAMMA.') has 
demonstrated extraordinary properties: high melting point, high ordering 
energy, thermal hardening, good resistance to oxidation and relatively 
small density. Those properties make it attractive for aerospatial and 
structural applications at elevated temperatures. 
One of the techniques for forming the Ni--Al intermetallic compounds is 
obtained by vacuum melting and vacuum investment casting which is mostly 
used by the Metals and Ceramics Division of Oak Ridge National Laboratory, 
U.S.A.. Owing to the following suffered disadvantages: a) this compound 
has a relatively high melting point to be hard to be melted, b) the 
metal-crucible and metal-ceramic interactions are prone to be caused 
during the melting and investment casting, c) the cast is apt to have 
shrinking pores, and d) the cast is too hard to be worked, there are many 
difficulties encountered according to this technique. 
Another technique for forming the Ni--Al intermetallic compound is the 
powder metallurgy (PM). This technique can permit us to obtain a compound 
with a relatively high yield rate, accurate dimensions, and a satisfactory 
microstructure and to easily control the components thereof. 
One of the powder metallurgy techniques is the sintering of pre-alloyed 
powder which mainly processes by the rapid solidification process (RSP), 
the powder or ribbons by hot isostatic pressing or hot extrusion. Although 
the final product is of a high sintering density, there is still a key 
disadvantage: this technique includes too many procedures which have to 
employ many expensive equipments and to operate under a protective 
atmosphere. Besides, the tensility and the hardness of the pre-alloyed 
powder are both so high that the green forged parts cannot be easily 
formed and will wear the mold off easily. 
Another powder metallurgy technique is the mechanical alloying which 
processes the pure metal powder in a protective atmosphere by the 
high-energy ball milling to lower the sintering temperature. According to 
this technique, some dispersion strengthening particles are added to 
achieve grain refining and strength increasing. The disadvantages of this 
technique are a) the procedure takes too much time, b) the obtained powder 
is so hard that the pressure for formation is therefore high, c) the 
ball-milling step causes the pollution problem, and d) the sintering 
density after the ball milling procedure is lowered. 
A further powder metallurgy technique is the reactive sintering. This 
technique uses the inexpensive elemental metal powder which is softer than 
the pre-alloyed powder for the initial material, so there are the 
following disadvantages: a) the formation thereof is easy to be obtained, 
b) the sintering temperature can be lowered down to a large scale, c) the 
sintering time can be shortened. Whereas, there are also disadvantages: a) 
the pores are prone to be generated when the reaction heat and the 
difference of the elemental diffusion rates are high, b) the densification 
is hard to be obtained, c) the protective atmosphere such as argon, 
hydrogen, and helium is necessary for preventing the oxidation of aluminum 
powder, and d) the densified compound is sensitive to the processing 
parameters such as the heating rate, the interfacial quality, the 
temperature, and the particle size. It is also noted that in case a high 
density sintered body is to be obtained, a higher heating rate, a finer 
powder (in .mu.m order) and an externally applied pressure during 
sintering are all needed, but the equipments to meet with above 
requirements are extremely expensive. 
A further technique for forming the Ni--Al compounds is chemical technique. 
The initial material NiCl.sub.2 and AlCl.sub.3 are processed by the 
co-deposition method to obtain a nickel-aluminum organometallic complex. 
After a first thermal treatment lower than 1000.degree. C. to burn off the 
organic function groups to obtain the mixture of Ni.sub.3 C and the 
non-crystalline Al.sub.2 O.sub.3 and free carbon, and after a second stage 
of heat treatment above 1300.degree. C. to obtain the intermetallic 
compound, the Ni.sub.3 Al and NiAl powder whose diameters are below 3 
.mu.m are formed. Whereas, this technique whose cost is too high and whose 
speed is too slow cannot economically meet with the industrial demand. 
It is therefore attempted by the Applicant to deal with the above situation 
encountered by the prior art. 
SUMMARY OF THE INVENTION 
The primary object of the present invention is to provide an electroless 
plating method for producing the family of Ni--Al compounds (i.e., 
Ni.sub.3 Al, NiAl etc.) inexpensively/effectively/fastly. 
Another object of the present invention is to provide an electroless 
plating method for producing the family of Ni--Al compounds by replacement 
reaction to form a nickel layer on the surface of the aluminum powder as 
an Ni--Al composite powder. 
Another object of the present invention is to provide a preparing method of 
an Ni--Al compound by oxidation and reduction reaction to deposit the 
reduced nickel ions on the nickel layer of the Ni--Al composite powder. 
A further object of the present invention is to provide a method especially 
suitable for executing plating action on the surface of the powder. 
Another object of the present invention is to provide a composite powder 
softer than the both pre-alloyed powder and the mechanical alloying powder 
for being formed easily. Still an object of the present invention is to 
provide an electroless plating method of an Ni--Al compound which can 
shorten the diffusion distance for forming the Ni--Al intermetallic 
compounds. 
One more objective of the present invention is to provide a Ni--Al 
intermetallic compounds having a higher constituent uniformity. 
Furthermore objective of the present invention is to provide a Ni--Al 
intermetallic compound preparing method whose electroless plating solution 
containing boron ions permits boron uniformly distributed in the plating 
layer. 
Further more object of the present invention is to provide an Ni--Al 
intermetallic compound preparing method which can solve the problems of 
processing difficulty and difficult formation for the compounds. 
Once more object of the present invention is to provide an Ni--Al 
intermetallic compounds preparing method which applies inexpensive and 
simple equipments. 
Yet more object of the present invention is to provide an Ni--Al 
intermetallic compounds whose nickel layer can lessen or avoid the 
oxidation of the aluminum powder. 
In accordance with the present invention, a preparing method of an Ni--Al 
intermetallic compounds includes steps of a) providing a reducing solution 
containing a reducing agent and reducing nickel ions, b) adding a proper 
amount of aluminum powder to the reducing solution, and c) permitting the 
reducing agent to reduce the reducing nickel ions to be deposited on the 
aluminum powder. 
Certainly, the aluminum powder can be processed by a pre-treatment 
procedure. The pre-treatment procedure can include steps of defatting, 
flushing with a basic solution, and flushing with a acid solution. The 
pre-treatment procedure can further include a step of subjecting the 
aluminum powder to an ultrasonic vibration to speed up a reaction therefor 
and improve a uniformity of the aluminum powder. 
Alternatively, the pre-treatment procedure can include steps of d) 
providing the aluminum powder, e) providing a replacing solution 
containing replacing nickel ions, and f) permitting the replacing nickel 
ions to replace aluminum ions ionized from the aluminum powder for forming 
a thin nickel layer on a surface of the aluminum powder. 
Certainly, the aluminum powder whose purity can be about 99.5% and whose 
average diameter can be about 22 .mu.m. The replacing solution can include 
a salt and a reducing agent and can further include at least one selected 
from a group consisting of a pH regulator, a buffer, a complexing agent, a 
stabilizer, and an improver. 
Certainly, the replacing solution can include nickel chloride 
(NiCl.sub.2.6H.sub.2 O), sodium citrate (Na.sub.3 C.sub.6 H.sub.5 
O.sub.7.2H.sub.2 O), ammonia chloride (NH.sub.4 Cl), and ammonium water 
(NH.sub.4 OH) regulating the pH value of said replacing solution above 7, 
and the pH value can be properly chosen between about 9 and about 11. The 
replacing solution can include nickel chloride (NiCl.sub.2.6H.sub.2 O), 
sodium citrate (Na3C.sub.6 H.sub.5 O.sub.7.2H.sub.2 O), ammonium chloride 
(NH.sub.4 Cl), sodium fluoride (NaF) and ammonium water (NH.sub.4 OH) 
regulating the pH value of the replacing solution above 7, and the pH 
value can be properly chosen between about 7.5 and about 9.5. 
Certainly, the reducing solution can include a salt and a reducing agent, 
and can further include a pH value regulator, a buffer, a complexing 
agent, a stabilizer, and an improver. 
Certainly, the reducing solution can have a pH value ranging from about 7 
to 8 and a reaction temperature about 70.degree. C., and can include 
nickel chloride (NiCl.sub.2.6H.sub.2 O), dimethylamine borane (DMAB), 
sodium acetate (CH.sub.3 COONa.3H.sub.2 O), and lead nitrate 
(Pb(NO.sub.3).sub.2). The reducing solution can have a pH value ranging 
from 7 to 8 and a reaction temperature about 70.degree. C. and can include 
nickel chloride (NiCl.sub.2.6H.sub.2 O), dimethylamine borane (DMAB), 
sodium citrate (Na.sub.3 C.sub.6 H.sub.5 O.sub.7.2H.sub.2 O), ammonium 
chloride (NH.sub.4 Cl), and lead nitrate (Pb(NO.sub.3).sub.2). 
The reducing solution can have a reaction temperature at room temperature, 
and can include nickel chloride (NiCl.sub.2.6H.sub.2 O), dimethylamine 
borane (DMAB), ammonia water (NH.sub.4 OH), and ammonium chloride 
(NH.sub.4 Cl). The reducing solution can have a reaction temperature at 
room temperature, and can include nickel chloride (NiCl.sub.2.6H.sub.2 O), 
dimethylamine borane (DMAB), sodium citrate (Na.sub.3 C.sub.6 H.sub.5 
O.sub.7.2H.sub.2 O), and ammonia water (NH.sub.4 OH). 
The reducing solution can have a pH value ranging from about 6 to about 7 
and a reaction temperature about 70.degree. C., and can include nickel 
chloride (NiCl.sub.2.6H.sub.2 O), dimethylamine borane (DMAB), malonic 
acid (HOOCCH.sub.2 COOH), and thiourea (NH.sub.2 COSC.sub.2 H.sub.5). 
The reducing solution can have a pH value ranging from about 7 to about 8 
and a reaction temperature at room temperature, and can include nickel 
chloride (NiCl.sub.2.6H.sub.2 O), sodium borohydride (NaBH.sub.4), sodium 
citrate (Na.sub.3 C.sub.6 H.sub.5 O.sub.7.2H.sub.2 O), ammonium chloride 
(NH.sub.4 Cl), and lead nitrate (Pb(NO.sub.3).sub.2). The reducing 
solution can have a pH value ranging from about 8 to about 10 and a 
reaction temperature at room temperature, and can include nickel chloride 
(NiCl.sub.2.6H.sub.2 O), sodium borohydride (NaBH.sub.4), ammonia water 
(NH.sub.4 OH), and lead nitrate (Pb(NO.sub.3).sub.2. 
The reducing solution can have a pH value ranging from about 8 to about 10 
and a reaction temperature at room temperature, and can include nickel 
chloride (NiCl.sub.2.6H.sub.2 O), sodium borohydride (NaBH.sub.4), 
ammonium chloride (NH.sub.4 Cl), sodium citrate (Na.sub.3 O.sub.6 H.sub.5 
O.sub.7.2H.sub.2 O), sodium acetate (CH.sub.3 COONa.3H.sub.2 O), and lead 
nitrate (Pb(NO.sub.3).sub.2). The reducing solution can have a pH value 
ranging from about 8 to about 10 and a reaction temperature about 
80.degree. C., and can include nickel acetate (Ni(C.sub.2 H.sub.3 
O.sub.2).sub.2.4H.sub.2 O), hydrazine hydrate (N.sub.2 H.sub.4.H.sub.2 O), 
2 hydroxylacetic acid (HOCH.sub.2 COOH), and ethylenediaminetetraacetic 
acid (EDTA). 
Certainly, the reducing solution can contain boron ions for forming an 
Ni--B--Al composite powder. The present method can further include steps 
of g) providing a pure nickel powder, and h) adding a proper amount of the 
pure nickel powder in the reducing solution at a proper time for forming 
an Ni--B--Ni composite powder, and i) obtaining a mixture of the Ni--B--Al 
composite powder and the Ni--B--Ni composite powder. The proper amount of 
pure nickel powder can further adjust a concentration of the boron ions. 
Certainly, the nickel powder can have a purity is about 99.9% and an 
average diameter can be about 5.mu.m. The reaction temperature of the 
reducing solution can range from about 0.degree. C. to about 100.degree. 
C. 
Certainly, the present method can further include steps of j) drying the 
mixture, k) executing a first heat treatment at about 450.degree. C. in a 
vacuum tube furnace with less than about 10.sup.-5 torr to degas the 
mixture, l) canning the mixture in a stainless steel tube in air, m) 
sealing both ends of the tube, and n) cold-rolling the tube containing the 
mixture to form a composite flake. 
Certainly, the Ni--Al intermetallic compound can be one selected from the 
group consisting of Ni.sub.3 Al, NiAl, Ni.sub.2 Al.sub.3, NiAl.sub.3, 
Ni.sub.3 Al+B, NiAl+B, Ni.sub.2 Al.sub.3 +B, and NiAl.sub.3 +B. 
Certainly, the composite flake can be sintered at about 1200.degree. C. for 
forming a sintered specimen. Alternatively, the composite flake can be 
pre-sintered by a second heat treatment at about 650.degree. C. for 
forming pre-sintered specimens; the pre-sintered specimens are then 
sintered by a third heat treatment at about 1200.degree. C. for forming 
sintered specimens; and the sintered specimens are then released from the 
tube, and cold-rolled, and homogenized at about 1200.degree. C. 
The present invention can be more fully understood by reference to the 
following description and accompanying drawings which form an integral 
part of this application:

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
Generally speaking, there are three ways to reduce metal ions in a solution 
to be deposited on an article: 1) the electro plating, 2) the chemical 
reducing plating, and 3) the replacing plating. According to the present 
invention, there are in fact the chemical reducing plating and the 
replacing plating included. That is to say, first, the nickel ions in the 
replacing plating solution replace the aluminum ions ionized from the 
aluminum powder to form a mono-atomic nickel layer on the surface of the 
powder; secondly, the reducing agent in the reducing solution permits the 
reduced nickel and boron ions to be deposited on the nickel layer. Because 
nickel has a property of spontaneous catalysis, the thickness of the 
nickel layer can be precisely controlled only if the adhesion between the 
surface of the aluminum powder and the nickel layer is satisfactory and 
only if the stability of the plating solution is as desired. 
The electroless plating solution chiefly contains a metal salt and a 
reducing agent. For improving the reducing speed and for prolonging the 
life of the plating bath, the solution further contains a pH regulator, a 
buffer, a complexing agent, a stabilizer, and an improver. 
A preparing method according to the present invention is shown in FIG. 1, 
and the key steps are discussed in detail as follows: 
A) ELECTROLESS PLATING 
The aluminum powder whose purity is above 99.5% and whose average diameter 
is 22 .mu.m is obtained from CERAC Co. Besides, for adjusting the boron 
content of the Ni.sub.3 Al+B intermetallic compound to be about 0.1 wt% 
and for adjusting the nickel content of the compound, a proper amount of 
nickel powder (of 99.9% purity, average diameter 5.mu.mm, marketed by 
CERAC Co.) is added into the electroless plating solution at a proper 
time. 
The electroless plating includes the replacing plating and the reducing 
plating: 
I) REPLACING PLATING 
There are two possible replacing plating conditions shown as follows: 
______________________________________ 
CONDITION A 
nickel chloride (NiCl.sub.2.6H.sub.2 O) 
15 g/l 
sodium citrate (Na.sub.3 C.sub.6 H.sub.5 O.sub.7.2H.sub.2 O) 
20 g/l 
ammonia chloride (NH.sub.4 Cl) 
6 g/l 
ammonium water (NH.sub.4 OH) regulating the 
pH value of the replacing solution to 
about 10 
reaction temperature room temperature 
CONDITION B 
nickel chloride (NiCl.sub.2.6H.sub.2 O) 
30 g/l 
sodium citrate (Na.sub.3 C.sub.6 H.sub.5 O.sub.7.2H.sub.2 O) 
20 g/l 
ammonium chloride (NH.sub.4 Cl) 
7 g/l 
sodium fluoride (NaF) 0.5 g/l 
ammonia water (NH.sub.4 OH) regulating the pH 
value of said replacing solution to about 8.5. 
reaction temperature room temperature 
______________________________________ 
Compared to the conventional pre-treatment procedures such as defatting the 
aluminum powder, flushing the aluminum powder with a basic solution, and 
flushing the aluminum powder with an acid solution, the replacing plating 
procedure performs effectively. Because the conventional defatting, 
flushing with a basic solution, and flushing with an acid solution cause a 
large amount of weight loss of aluminum during the pre-treatment 
procedure, an appropriate replacing plating is more suitable for 
pre-treating aluminum plates, aluminum flakes, and aluminum powder of 
large size. The difference between CONDITION A and CONDITION B is that 
some amount of NaF is added in CONDITION B to etch Al.sub.2 O.sub.3 for 
lowering the pH value of the solution. That is to say, the weak acid NaF 
with Cl-- and F-- can etch away Al.sub.2 O.sub.3 to execute the replacing 
reaction. 
II) REDUCING PLATING 
There are nine possible reducing plating conditions shown as follows: 
______________________________________ 
CONDITION 1 
nickel chloride (NiCl.sub.2.6H.sub.2 O) 
72 g/l 
dimethylamine borane (DMAB) 
6 g/l 
sodium acetate (CH.sub.3 COONa.3H.sub.2 O) 
22 g/l 
lead nitrate (Pb(NO.sub.3).sub.2) 
2 ppm 
pH 6-7 
reaction temperature 70.degree. C. 
CONDITION 2 
nickel chloride (NiCl.sub.2.6H.sub.2 O) 
60 g/l 
dimethylamine borane (DMAB) 
10 g/l 
sodium citrate (Na.sub.3 C.sub.6 H.sub.5 O.sub.7.2H.sub.2 O) 
100 g/l 
ammonium chloride (NH.sub.4 Cl) 
50 g/l 
lead nitrate (Pb(NO.sub.3).sub.2) 
2 ppm 
pH 7-8 
reaction temperature 70.degree. C. 
CONDITION 3 
nickel chloride (NiCl.sub.2.6H.sub.2 O) 
50 g/l 
dimethylamine borane (DMAB) 
5 g/l 
ammonia water (NH.sub.4 OH) 
50 ml/l 
ammonium chloride (NH.sub.4 Cl) 
5 g/l 
reaction temperature room temperature 
CONDITION 4 
nickel chloride (NiCl.sub.2.6H.sub.2 0) 
15 g/l 
dimethyl amine borane (DMAB) 
4 g/l 
sodium citrate (Na.sub.3 C.sub.6 H.sub.5 O.sub.7.2H.sub.2 O) 
20 g/l 
ammonia water (NH.sub.4 OH) 
50 ml/l 
reaction temperature room temperature 
CONDITION 5 
nickel chloride (NiCl.sub.2.6H.sub.2 O) 
30 g/l 
dimethylamine borane (DMAB) 
3.5 g/l 
malonic acid (HOOCH.sub.2 COOH) 
40 g/l 
thiourea (NH.sub.2 COSC.sub.2 H.sub.5) 
1 ppm 
pH 6-7 
reaction temperature 70.degree. C. 
CONDITION 6 
nickel chloride (NiCl.sub.2.6H.sub.2 O) 
60 g/l 
sodium borohydride (NaBH.sub.4) 
2 g/l 
sodium citrate (Na.sub.3 C.sub.6 H.sub.5 O.sub.7.2H.sub.2 O) 
100 g/l 
ammonium chloride (NH.sub.4 Cl) 
50 ml/l 
lead nitrate (Pb(NO.sub.3).sub.2) 
5 ppm 
pH 7-8 
reaction temperature room temperature 
CONDITION 7 
nickel chloride (NiCl.sub.2.6H.sub.2 O) 
60 g/l 
sodium borohydride (NaBH.sub.4) 
3 g/l 
ammonia water (NH.sub.4 OH) 
200 ml/l 
lead nitrate (Pb(NO.sub.3).sub.2) 
2 ppm 
pH 8-10 
reaction temperature room temperature 
CONDITION 8 
nickel chloride (NiCl.sub.2.6H.sub.2 O) 
30 g/l 
sodium borohydride (NaBH.sub.4) 
2 g/l 
ammonium chloride (NH.sub.4 Cl) 
5 g/l 
sodium citrate (Na.sub.3 C.sub.6 H.sub.5 O.sub.7.2H.sub.2 O) 
10 g/l 
sodium acetate (CH.sub.3 COONa.3H.sub.2 O) 
20 g/l 
lead nitrate (Pb(NO.sub.3).sub.2) 
5 ppm 
pH 8-10 
reaction temperature room temperature 
CONDITION 9 
nickel acetate (Ni(C.sub.2 H.sub.3 O.sub. 2).sub.2.4H.sub.2 O) 
60 g/l 
hydrazine hydrate (N.sub.2 H.sub.4.H.sub.2 O) 
100 ml/l 
ethyl alcohol 2-hydroxylacetic acid 
60 ml/l 
(HOCH.sub.2 COOH) 
ethylenediamine-tetraacetic acid (EDTA) 
25 g/l 
pH 8-10 
reaction temperature 80.degree.C. 
______________________________________ 
After the replacing plating and reducing plating procedures, a mixture of 
Ni--B--Ni and Ni--B--Al composite powders is formed. Owing to the high 
activity of aluminum, the aluminum is prone to react with H+ and OH- in 
the solution to form an aluminum hydroxide, so the pH value of the 
reducing solution is chosen to the neutral point and the reaction rate is 
chosen higher to lessen the time of the aluminum contacting with the 
solution. FIG. 2 shows a composite powder obtained through an improper 
plating condition (having a too high pH value). As shown in FIG. 2, there 
is a gray middle layer with fractures formed between aluminum and nickel. 
The fractures can be caused by the shrinkage of a glutinous aluminum 
hydroxide after the aluminum hydroxide is dried. FIG. 3 obtained by an SEM 
(CamScan) shows a composite powder through a proper plating condition 
allowing the aluminum particle to be covered by an uniform nickel layer. 
Comparing FIG. 2 with FIG. 3, we can find that there is no middle layer 
between nickel and aluminum in FIG. 3, and the subsequent steps such as 
forming and sintering ones show that this composite powder obtained in a 
proper plating condition performs well. Thus, the excellent Ni--Al 
interface quality is indirectly proved. The small white particles in FIG. 
3 are a proper amount of nickel powder added into the reducing solution at 
five minutes before the reducing plating procedure is completed, and the 
object is to control the Ni and Al ratio of the Ni--Al compound and the 
concentration of boron. Although the boron content of the Ni--B alloy 
layer obtained by using DMAB as a reducing agent varies as the plating 
condition varies, the lowest boron content thereof is about 1% is much 
higher than the most proper boron content 0.1%. So, to add therein the 
nickel powder permits the boron content to be reduced to 0.1%. Table 1 
shows the analysis results by ICP AES. The boron contents of different 
Ni--Al powder portions are all about 0.1%, and the contents of other 
metals such as Fe and Cu coming from the impurities in the reducing 
plating solution are relatively few. FIG. 4 shows the relation between the 
Al content of the Ni--Al compound and the weight of the added aluminum 
powder by varying the weight of added aluminum powder at a certain plating 
condition 4. 
B) FORMING 
The mixture of Ni--B--Ni and Ni--B--Al composite powders is first canned in 
a 304 stainless steel tube in air, then both ends of the tube are 
mechanically sealed to form a canister. Thus, the mixture is processed by 
a first thermal treatment with less than 10.sup.-5 torr at 450.degree. C. 
in a vacuum tube furnace to be degassed, and a cold rolling to about 60% 
reduction in area is followed to form test flakes. It is noted that the 
TABLE 1 
______________________________________ 
Added Concentration of Aluminum Powder 
______________________________________ 
Al 7.10 g/l 7.30 g/l 7.45 g/l 7.60 g/l 
Ni balance balance balance balance 
Al 21.23 at % 22.04 at % 23.89 at % 
24.62 at % 
B 0.119 wt % 0.107 wt % 0.125 wt % 
0.122 wt % 
S 0.002 wt % 0.002 wt % 0.002 wt % 
0.002 wt % 
Fe 0.0051 wt % 
0.0054 wt % 
0.0056 wt % 
0.0057 wt % 
Cu 0.0003 wt % 
0.0003 wt % 
0.0003 wt % 
0.0003 wt % 
______________________________________ 
composite powders absorb therein the hydrogen atoms generated during the 
electroless plating procedure because of the excellence in the 
hydrogen-absorbing behavior of nickel, then the degassing procedure is 
therefore very important. 
C) SINTERING, COLD-ROLLING, AND HOMOGENIZING 
The test flakes are processed by a second heat treatment at 650.degree. C. 
to form a pre-sintered specimens, which are then reduced 30% in area by 
cold-rolling in a DBR-250 rolling mill and sintered at 1200.degree. C. for 
two hours in the same furnace. After being released from the canister, the 
sintered specimens are cold-rolled to another 26% reduction in area and 
homogenized at 1200.degree. C. for four hours in the same furnace. The 
X-ray diffraction patterns of the specimen in various steps in the 
sintering process are shown in FIG. 5. Comparing the two situations at 
650.degree. C. for 15 minutes and at 650.degree. C. for 60 minutes, we can 
find that the prolongation of the specimen in the pre-sintering period 
from 15 minutes heat-treatment to 60 minutes heat-treatment does not 
significantly affect the relative intensity of each phase in the X-ray 
diffraction spectrum. FIG. 6 shows the metallograph of the specimen after 
a heat treatment at 650.degree. C., and we can find that the black 
portions are pores being as large as the aluminum particle, so the 
portions should be pores generated from the reaction of aluminum and 
nickel. Around the pores there is an area of a gray thick layer, and 
according to the XRD patterns in FIG. 5 we can know that this gray area 
consists of Al.sub.3 Ni.sub.2. From above discussions, we can get that the 
reaction mechanisms for forming the composite flakes at 650.degree. C. are 
as follows: the atomized aluminum powders reacting with the nickel layer 
to form a new phase so that the compound Al.sub.3 Ni.sub.2 and a large 
amount of reaction heat are generated, and the reaction heat in turn 
elevates the local temperature of the flakes so that there is a transient 
liquid existing between the powder to speed up the reaction; whereas the 
formed compound whose melting point is higher and the diffusion rate of 
nickel and aluminum in the compound is slower so that the rate of nickel 
reacting with Al.sub.3 Ni.sub.2 is slowed down, thus the composition at 
650.degree. C. heat-treatment for 15 minutes and 650.degree. C. for 60 
minutes are almost the same; the reaction of aluminum and nickel to form 
the Ni--Al compound is one which causes the entire volume to be shrunk, so 
there are generated pores whose sizes are similar to the ones of the 
aluminum particles, and by the fact that a gray layer of a second phase 
developing around the inner wall of each pore has a uniform thickness and 
that there is no un-reacted aluminum left, it can be proved that the 
interface quality between nickel and aluminum is satisfactory. From FIG. 
5, we can also be informed that the reacting mechanisms of the 
transformation from Ni and Al to Ni.sub.3 Al are Ni+Al.fwdarw.Ni+Al.sub.3 
Ni.sub.2 .fwdarw.Ni+NiAl+Al.sub.3 Ni.sub.2 .fwdarw.Ni+NiAl+Ni.sub.3 
Al.fwdarw.Ni3Al. In other words, the intermetallic compound containing 
higher content of aluminum is first formed in the entire reaction, and the 
formation rate (especially of Al.sub.3 Ni.sub.2) is very fast which is 
achieved chiefly by means of a fast diffusion rate made possible by a 
transient liquid state. The post solid in this stage diffuses into a 
homogenized mechanism gradually formed into an intermetallic compound 
having a higher nickel content as the temperature is raised and the time 
passes to finally obtain the Ni.sub.3 Al of a mono-phase. 
In addition, the physical properties of the specimen are discussed now. The 
tensile tests were performed on specimens of gauge length 25.4 mm (ASTM 
standard) at room temperature, and a testing machine (MTS 810) with an 
initial strain rate 1.0.times.10.sup.-4 s.sup.-1 was employed. The test 
record is obtained from a X-Y recorder and a personal computer. FIG. 7 is 
a typical tensile test stress-strain curve for an air test specimen. 
The test is conducted on a specimen obtained by a composite powder 
metallurgy (CPM) where the aluminum content ranges from 23 a/o to 25 a/o. 
Its elasticity ranges from 160 GPa to 200 GPa which respectively 
correspond to theoreticle values. Its yield strength ranges from 420 MPa 
to 580 MPa which is twice that of a vacuum molten test piece. Its 
elongation percentage ranges only from 12% to 17% which is higher than 
that of most Ni.sub.3 Al+B compounds produced by other powder metallurgy 
methods. FIG. 8 shows a metallograph of a test piece processed by a 
homogenizing procedure at 1200.degree. C. for eight hours. 
While the present invention has been described in connection with what are 
presently considered to be the most particle and preferred embodiments, it 
is to be understood that the invention is to be limited to the disclosed 
embodiments but on the contrary, is intended to cover various 
modifications and equivalent arragements included within the spirit and 
scope of the appended claims which scope is to be accorded the brodest 
interpretation so as to encompass all such modification and equivalent 
structures.