Laminate

Sliding layers overlays produced by cathode sputtering comprise a matrix-forming metallic material and at least one other material which is substantially insoluble in the matrix have greatly improved mechanical and corrosion resistance properties, if the insoluble material has a lower melting point than the matrix material, and if the diameters of the particles of the insoluble material are statistically normally distributed with mean x<0.8 .mu.m. Such overlays are produced with the temperature of the substrate maintained below 150.degree. C. during the sputtering process. Coating rates of >0.2 .mu.m [of layer thickness] per minute may be used informing such overlays.

BACKGROUND OF THE INVENTION 
Field of the Invention 
This invention relates in general to cathode sputtering techniques in 
particular to a new and useful sliding layer produced by cathode 
sputtering. 
The invention relates to a laminate material having at least one layer for 
sliding a "sliding layer", hereinafter referred to as an "overlay", which 
overlay is applied by cathode sputtering, wherewith said overlay is 
comprised of a mixture of particles sputtered-on in a statistical 
distribution [i.e., of the particle diameters], each of which particles is 
comprised of a metallic material which forms a solidly coherent matrix and 
at least one other metallic material which other metallic material when in 
the solid state is practically insoluble in or undetachable from the 
material of said matrix. The invention further relates to a method of 
manufacturing the inventive laminate, and to a practical application of 
same i.e., use of the laminate. 
Sliding layers as surface layers of laminate materials are used, e.g., for 
bearing seats of internal combustion engines. Such layers must have the 
following properties, among others: lower hardness than the material of 
the shaft, high resistance to dynamic stresses of an alternating nature, 
high shear strength, thermal stability of mechanical properties, and high 
corrosion resistance. These requirements are met by mixtures of lead or 
tin with other metals which lend mechanical strength by forming a coherent 
matrix, and which other metals are themselves corrosion resistant and do 
not dissolve tin or lead (e.g., Al, Cr, or Ni). Laminates with 
lead-containing or tin-containing overlays, and methods of manufacturing 
same by cathode sputtering, are described in Ger. Pats. 2,853,724 and 
2,914,618, and in Ger. OS 34 04 880. When these methods have been used, 
substantial problems have arisen with regard to achieving high adhesive 
strength and bonding strength between the substrate and the applied 
overlay. Furthermore, these methods lead to a relatively coarse structure 
of the overlay, with randomly distributed inclusion particles of Sn or Pb 
of several micron diameter. Such a structure of the overlay leads to 
corresponding degradation of the corrosion resistance properties. 
In addition, according to the state of the art it is considered important 
for an overlay applied by sputtering and based on an alloy composition 
AlSn20 in a conventional steel/Cu/Pb three-layer laminate arrangement to 
have at least a finer distribution of the Sn-containing particles than the 
rolled layers produced by ordinary methods. Nonetheless, even such 
overlays lead to poorly defined, heterogeneous mixtures of Al and Sn. 
Precise data on mean particle size in such overlays, and on reproducible 
reaction conditions (i.e., reaction conditions for producing reproducible 
product quality) for manufacturing such overlays have not been made public 
thus far (see Engle, U., 1986, "Development and testing of new multilayer 
materials for modern engine bearings: Part 2--copper-lead three-layer 
bearings with sputtered overlay", in SAE Tech.Pap. Ser., Int. Cong. and 
Expo., Detroit, Feb. 24-28, pp. 76-77). 
According to the state of the art it has been proposed to harden the matrix 
by appropriate incorporation of oxides ("dispersion hardening"). In 
practice this has also led to major problems. Thus, for a matrix comprised 
of Al, oxide particles in amounts of 0.1-0.5 wt.% have been prescribed 
(Ger. Pat. 2,914,618 Col. 5). Such concentrations are very difficult or 
impossible to control in manufacturing of, e.g., sliding bearings, on a 
large serial production scale. The result again is sharp variations in 
properties of the overlay and unsatisfactory reproducibility of the method 
of producing the overlays. 
SUMMARY OF THE INVENTION 
Accordingly, the underlying problem of the invention is to improve a 
laminate of the type described initially supra, such that its adhesion and 
corrosion resistance are substantially improved, and the method of 
producing it is reproducible. 
This problem is solved according to the invention as follows: 
(a) The material substantially locked in the matrix has a lower melting 
point than the matrix material; and 
(b) The diameters of the particles of the material substantially locked in 
the matrix are statistically normally distributed, with mean value x&lt;0.8 
.mu.m. 
The problem cannot be solved by merely employing a standard overlay 
produced by cathode sputtering. The inventive overlay employs specific 
techniques to produce specific properties. It has been discovered in 
connection with the invention that, surprisingly, the mechanical 
properties required for sliding bearings are conferred by a distribution 
of the particles containing the insoluble material which distribution 
(i.e., the mean particle size of which distribution) is finer by about 
tenfold than that made public according to the state of the art, and with 
no participation of (i.e., no measures carried out to provide) oxide 
particles. For example, continuous-cast AlSn20Cu has Vickers hardness 35, 
which can be increased to 130 by dispersion hardening with oxide particles 
(Ger. Pat. 2,853,724, Col. 6), whereas the inventive overlays attain a 
Vickers hardness (HV.sub.0.1) of at least 160 without participation of 
oxides. This 180 hardness can be increased to c, 200 by appropriate 
addition of 0.2 wt.% (maximum) of oxides. Further, the inventive overlays 
have substantially improved annealing stability compared to the overlays 
made public in the state of the art. Heat treatment of conventional 
overlays at 170.degree. C. for 300 hr leads to a substantial decrease in 
hardness (see Ger. Pat. 2,853,724), whereas with inventive overlays 
subjected to the same treatment the hardness does not decrease below 170. 
The inventive overlays also have much higher corrosion resistance than 
layers hardened by oxide dispersion. This is attributable to smaller pore 
size between the matrix and the insoluble particles (in the inventive 
overlays). Further, the fine and uniform distribution of the particles 
fixed in the matrix enables one to employ virtually any proportion of the 
fixed material in the overlay without a risk that the particles will be 
torn out of the matrix material by some mechanical stress (in particular, 
alternating dynamic stresses), or that cracks will develop due to internal 
stress concentration in the overlay. These considerations underlay the 
improved resistance of the inventive overlays to alternating dynamic 
stresses in comparison to the resistance of conventional overlays; and the 
improved thermal stability of the mechanical properties of the inventive 
overlays. 
In a refinement of the invention, at least one of the relatively low 
melting elements Sn (m.p. 231.89.degree. C.), Pb (m.p. 327.4.degree. C.), 
or In (m.p. 156.4.degree. C.) may be used in particular as the material 
substantially undetachable from the matrix. For specific applications, 
other low melting metals and their alloys are good candidates--[e.g.,] Cd 
(m.p. 320.9.degree. C.), Bi (m.p. 271.3.degree. C.), T1 (m.p. 302.degree. 
C.), Zn (m.p. 419.5.degree. C.), and Ga (m.p. 29.8.degree. C.). The 
invention is particularly advantageous for laminate materials or laminate 
workpieces in which the matrix-forming material contains a customary 
sliding-bearing alloy the main component of which is at least one of the 
following elements: Al, Cr, Ni Mg, or Cu. In practice, it has proved 
particularly advantageous if the overlay has an overall composition 
comprising one of the following combinations: AlCuSn, AlCuPb, AlCuSnPb, 
AlSiSn, AlSiPb, AlSiSnPb, CuSn, CuPb, or CuSnPb. The inventive overlays 
preferably have layer thicknesses between 10 and 30 micron, the lower half 
of this range (12-16 .mu.m) being sufficient for most application 
situations. Accordingly, it is not necessary to employ the optimal layer 
thickness of 18 .mu.m recommended according to the state of the art for 
conventional two-component overlays (see Engel, loc.cit., p. 76). 
According to another refinement of the invention, the diameters of the 
particles of the material, substantially locked in the matrix have a 
normal distribution, preferably with mean value x=0.05-0.4 .mu.m. 
Experiments have shown that the inventive effects can be achieved with x 
up to &lt;0.8 .mu.m [sic--i.e., x up to slightly less than 0.8 .mu.m]. 
It is known from the state of the art (Ger. Pat. No. 2,914,618, Col. 5; 
Ger. Pat. 2,853,724, Col. 5) that oxide contents between 0.1 and 0.5 vol. 
% [sic] lead to so-called dispersion hardening. It has been found, 
surprisingly, that the inventive overlays produced by appropriate 
techniques ([e.g.,] target maintained in an inert gas atmosphere) whereby 
their oxygen content is reduced (i.e., in comparison to customary 
overlays) to &lt;0.2 wt. % have much better mechanical properties than 
dispersion-hardened overlays according to the state of the art. Thus, 
hardening by reducing the diameters of the implanted particles can be 
advantageously substituted for hardening accomplished by providing 
dispersed oxide particles. The inventive overlays are particularly 
suitable as surface layers of three-layer sliding bearings, wherein a 
support layer comprised of a material with good "emergency running 
properties" is disposed between the base material (bearing backing) and 
the overlay. There are various possibilities for the composition of this 
"underlay" material; the important criterion is that they be less hard 
than the overlay. In particular, these "underlays" may contain elements as 
Sn, Pb, Sb, and Cu, or known alloys such as tin bronzes, tin-lead bronzes 
(see DINs 1705, 1716, 1718, and 17 662) or babbitt metals (see Neale, M. 
J. (Ed.), 1975, "Tribology Handbook", pub. in London, Table C-1). The 
Brinell hardness of these supporting underlays should be between 30 and 
100 kp/sc .mu.m. 
It has also proven advantageous to provide a thin blocking layer which is 
applied between the overlay and the base material. Like the overlay, this 
layer is also applied by cathode sputtering. Its function is to prevent 
diffusion of material from the overlay into the base material or/and the 
supporting underlay. This diffusion-blocking layer advantageously has a 
thickness of c. 2 .mu.m, and may employ as its main component any of the 
matrix-forming materials of the overlay. Compositions comprising Cr and Ni 
together have proven particularly suitable. The diffusion-blocking layer 
is advantageously applied between the overlay and the support layer 
disposed below the overlay. However, for special applications it is 
possible to apply the blocking layer between the said support layer and 
the base material (bearing backing). Also, a plurality of superposed 
sliding layers (overlays) may be employed, for special applications. 
The invention further relates to a method of manufacturing the proposed 
laminate materials, wherein the overlay is applied by sputtering. 
The underlying problem of the method part of the invention is to devise 
manufacturing techniques which are reproducible (in contrast to the 
techniques publicized in the state of the art) and thereby are capable of 
producing products which have constant [i.e. uniformly controllable] 
mechanical and corrosion-resistance properties. 
This problem is solved according to the method aspect of the invention in 
that the temperature of the substrate to be coated is kept below 
150.degree. C. during the coating. It has been discovered (in connection 
with the invention) that, surprisingly, such a reduction of the substrate 
temperature during sputtering leads to an unexpectedly large reduction of 
the mean diameter of the particles insoluble in the matrix, from several 
microns to a value between 0.05 and 0.8 .mu.m, and thereby leads to the 
inventive properties of the applied overlay (e.g. higher strength under 
alternating [dynamic stresses], and higher corrosion resistance). Another 
factor, beside reduction of the coating temperature, which other factor 
also contributes to the inventive fine particle size distribution of the 
insoluble component is increased coating speed (in comparison to the state 
of the art), namely&gt;0.2 .mu.m [of thickness] per minute. This discovery 
can be applied advantageously in situations in which insufficient amounts 
of cooling water are available for carrying out the method. 
According to a refinement of this method, the various materials of the 
overlay, i.e. the matrix-forming material and the material insoluble in 
the matrix, are applied simultaneously to the substrate by sputtering, 
whereby the inventive fine particle size distribution is further improved. 
In an advantageous technique for this, more than half of the targets 
employed in the method contain both the main component of the matrix and 
the material insoluble or locked in the matrix. Depending on the 
composition of the desired overlay, alloys of the following types may be 
employed: AlCuSn, AlCuPb, AlSiSn, AlSiPb, AlSiSnPb, CuSn, CuPb, [or] 
CuSnPb. In order to keep the oxygen (or oxide) content of the overlay 
under 0.2 wt. % it is necessary to cast the target in vacuum or under a 
practically oxygen-free inert atmosphere. 
According to another refinement of the method, the various components of 
the overlay are applied to the substrate in sequence. For this purpose, 
advantageously targets are used comprised of the main components of the 
overlay, thus e.g., targets comprised of pure Al and (i.e., "or") pure Sn, 
and the sputtering is carried out at various positions of the coating 
[(sputtering)] apparatus. It can be particularly advantageous to use the 
same target for the diffusion-blocking layer and the overlay, and to form 
the different layers one immediately after the other on the workpieces 
which are to be coated. 
In another variant (i.e., refinement) of the inventive method, the 
temperature of the substrate is varied such that the matrix-forming 
component is applied at a higher temperature than the component which is 
insoluble in the matrix. In another variant, this is achieved in that the 
matrix-forming component of the overlay is applied at a higher substrate 
temperature and prior to (the application of) the insoluble or locked 
component, with the temperature being reduced during the coating process. 
Other variation possibilities for the inventive method lie in varying the 
voltage applied to the substrate, to suit the requirements of the given 
use situation. In a technique of this type, the components with the higher 
melting points, e.g. the matrix-forming component or the main component of 
the diffusion-blocking layer, may be applied at a higher voltage than the 
component which is insoluble or locked in the matrix (which component has 
a lower melting point). 
The inventive overlays can be successfully employed in sliding bearings of 
any type. They have proven particularly advantageous in so-called 
three-material (or three-layer) bearings having bearing loads between 80 
and 120 N/sq mm, and at bearing backing temperatures of between 
150.degree. and 200.degree. C. Under these conditions the inventive 
overlays have shown zero measurable wear after 720 hr in extended load 
tests. 
Accordingly, it is an object of the invention to provide an improved 
laminate material. 
A further object of the invention is providing method manufacturing 
laminate material in which an overlay is applied by cathode sputtering and 
the temperature is kept under 150.degree. centigrade during the coating 
produced by the sputtering. 
A further object of the invention is to provide a laminate which is 
inexpensive to make, and is rugged in construction and economical to use. 
The various features of novelty which characterize the invention are 
pointed out with particularity in the claims annexed to and forming a part 
of this disclosure. For a better understanding of the invention, its 
operating advantages and specific objects attained by its uses, reference 
is made to the accompanying drawings and descriptive matter in which 
preferred embodiments of the invention are illustrated.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
Referring to the drawings in particular, the invention embodied therein 
comprises an approved laminate construction and method of making the 
laminate. 
In the embodiment of FIG. 1, a support layer 2 of a material with good 
emergency running properties has been applied with layer thickness 200-700 
.mu.m to a steel backing (base material) 1. If a lead bronze of lead-tin 
bronze is used for this support layer, the layer achieves a Brinell 
hardness of 50-100 kp/sq mm. 
A thin diffusion-blocking layer 3 with layer thickness of the usual few 
microns (2-4 .mu.m) has been applied to this support layer by sputtering. 
This diffusion-blocking layer 3 advantageously is comprised of one or more 
elements comprised in the matrix-forming material of the overlay, e.g. Ni, 
Cr, or an alloy of these two. The inventive overlay 4 has been applied 
over this blocking layer 3, by sputtering. The extremely fine particle 
size distribution of the insoluble or undetachable phase in comparison to 
the insoluble phase in ordinary overlays is seen in FIG. 2 from the 
scanning electron micrographs, which shows an overlay with a weight ratio 
80:20:1 of the components of the overlay. 
The following reaction conditions are used to produce the inventive 
laminate materials: 
EXAMPLE 1 
A cathode sputtering apparatus of a type which is per se known was used for 
the sputtering, wherein a ring-shaped, dense plasma is concentrated by a 
magnetic field immediately ahead of the cathode. The apparatus has a 
cylindrical processing chamber, on the external side of which up to four 
sources can be mounted vertically, each such source having an area of 
322.6 sq cm. The substrates to be coated were also mounted vertically, on 
a support which can be rotated by drive means controllable at between 0.2 
and 24.5 rpm, (see, e.g., Blazers product information bulletins BB 800 246 
PD (August 1985) and BB 800 039 RD (July 1985)). 
Bearing seats of unalloyed tool steel (e.g., [German] Material No. 1,162, 
Short Name C80W2) were coated for 8 hr in this sputtering apparatus at a 
substrate temperature of 60.degree. C., and a pressure of 1.2 Pa (argon, 
with oxygen mixed in at 0.8 vol.%). To maintain this substrate 
temperature, 0.024 cu m cooling water per hour per bearing seat being 
coated was required. The targets used were: 
pure (99.99%) Al, at 470 V; and 
a zinc bronze (SnCu5), at 620 V. 
The substrate was rotated at a constant 15 rpm. The coating thickness at 
the end of the treatment was c. 150 .mu.m, corresponding to a coating rate 
of c. 0.3 .mu.m/min. 
The overlay produced by this technique had a weight ratio Al:Sn:Cu of 
80:20:1 (corresponding to AlSn20Cul) and an oxide content of 0.2 wt.%. The 
Brinell hardness of the overlay was 83, and was unchanged after heat 
treatment at 170.degree. C. for 200 hr. In a test on a bearing testing 
machine for 250 hr under a load of 70 N/sq mm and a bearing backing 
temperature of 160.degree. C., there was no wear on the overlay. 
EXAMPLE 2 
Bearing seats of the same tool steel [as in Example 1] (Ger. Material No. 
1,1625 with a 200 .mu.m thick support layer of CuPb23Sn4 (lead bronze) 
applied in a dipped process were coated at a substrate temperature of 
30.degree. C. and in complete absence of oxygen, with the other conditions 
being the same as in Example 1. The amount of cooling water required was 
0.035 cu m per hour per bearing seat being coated. The following targets 
and power densities were used for applying the overlay: two targets of 
AlSi (with 20 kW/322 sq cm), one target of Sn (with 10.3 kW/322 sq cm), 
and one target of Pb (with 11 kW/322 sq cm). The result was an overlay 
with composition AlSi4Sn15Pb10, having Vickers hardness (HV.sub.0.1 )=175. 
EXAMPLE 3 
Bearing seats with a support layer comprised of lead bronze as described in 
Example 2 were provided with a thin diffusion-blocking layer before 
application of the overlay. For this purpose, only the two AlSi alloy 
targets were employed (12 min, 30.degree. C. [substrate temperature], 322 
sq cm [target area]). The layer thickness of the diffusion-blocking layer 
produced in this manner was c. 2 .mu.m. The two other targets were then 
activated and the coating was completed under the same conditions as in 
Example 2. 
EXAMPLE 4 
The process conditions of Example 3 were varied in that for a 12 minute 
period no cooling was applied to the substrate during application of the 
diffusion-blocking layer comprised of AlSi alloy, resulting in development 
of a temperature of 200.degree. C. The two other targets were then 
activated and the cooling was regulated to reduce the substrate 
temperature to 80.degree. C. In all other respects the coating was carried 
out as in Example 2. 
EXAMPLE 5 
The conditions of Example 1 were varied in that the temperature was 
continuously increased from 20.degree. to 190.degree. C. during the 
application of the overlay, by appropriate regulation of the cooling. The 
result was an overlay with a mean particle size of the insoluble component 
which increased toward the surface, with a corresponding decrease in 
hardness [as the surface was approached]. 
EXAMPLE 6 
The process conditions of Examples 2 and 3 were varied in that the 
diffusion-blocking layer was applied by sputtering at 50.degree. and a 
substrate voltage of -200 V, while the overlay was applied with the aid of 
the 4 different targets at a substrate voltage of -40 V. The overlay 
composition corresponded to that of Example 2 (AlSi4Sn15Pb10), with 
slightly increased hardness (Vickers hardness HV.sub.0.1 =180). 
EXAMPLE 7 
A diffusion-blocking layer comprising of NiCu30 [was applied] at a layer 
thickness of 1.5 .mu.m, followed by an overlay of approximate composition 
AlSn20Cul, under the conditions of Example 1 [but] in the complete absence 
of oxygen. To reduce the porosity of the overlay, a substrate temperature 
of 130.degree. C. was maintained during the [sputtering], and the 
substrate voltage was increased continuously during [i.e., over] the 50 
min duration of the treatment from -40 V to -180 V. The overlays produced 
thereby had higher corrosion resistance than those of Example 1. 
While specific embodiments of the invention have been shown and described 
in detail to illustrate the application of the principles of the 
invention, it will be understood that the invention may be embodied 
otherwise without departing from such principles.