U.S. patent application number 10/937004 was filed with the patent office on 2006-03-09 for method for processing alloys via high-current density ion implantation.
Invention is credited to Raymond C. Benn, Edward H. Bittner, Clark VanTine Cooper, Harsh Vinayak.
Application Number | 20060048857 10/937004 |
Document ID | / |
Family ID | 35995011 |
Filed Date | 2006-03-09 |
United States Patent
Application |
20060048857 |
Kind Code |
A1 |
Cooper; Clark VanTine ; et
al. |
March 9, 2006 |
Method for processing alloys via high-current density ion
implantation
Abstract
A surface processing method and power transmission component
includes transforming by high current density ion implantation
(high intensity plasma ion processing) a surface region of a metal
alloy into a hardened surface region at a temperature that is less
than a heat treating temperature of the metal alloy. The metal
alloy includes between 1.5 wt % and 15 wt % Ni, between 5 wt % and
30 wt % Co, up to 1.0 wt % carbon, and up to 15 wt % of a
carbide-forming element, such as molybdenum, chromium, tungsten,
vanadium or combinations thereof, that can react with carbon to
form metal carbide precipitates of the form M.sub.2C. The surface
processing temperature, vacuum pressure, precursor gas flow and
ratio, and time of processing are controlled to provide a desirable
hardened surface region having a gradual transition in nitrogen
concentration. A vapor deposition process deposits an amorphous
hydrogenated carbon coating on the hardened surface region of the
metal alloy. An intermediate coating between the coating and the
hardened surface region promotes adhesion between the coating and
hardened surface region.
Inventors: |
Cooper; Clark VanTine;
(Glastonbury, CT) ; Benn; Raymond C.; (Madison,
CT) ; Bittner; Edward H.; (Madison, CT) ;
Vinayak; Harsh; (Meriden, CT) |
Correspondence
Address: |
CARLSON, GASKEY & OLDS, P.C.
400 WEST MAPLE ROAD
SUITE 350
BIRMINGHAM
MI
48009
US
|
Family ID: |
35995011 |
Appl. No.: |
10/937004 |
Filed: |
September 9, 2004 |
Current U.S.
Class: |
148/220 ;
148/222; 148/230; 148/239 |
Current CPC
Class: |
C23C 8/06 20130101; C23C
8/30 20130101; C23C 8/36 20130101; C23C 8/20 20130101; C23C 8/24
20130101; C23C 8/68 20130101 |
Class at
Publication: |
148/220 ;
148/222; 148/230; 148/239 |
International
Class: |
C23C 8/24 20060101
C23C008/24 |
Claims
1. A surface processing method comprising the steps of:
transforming a surface region of a metal alloy into a hardened
surface region at a temperature that is less than a heat treating
temperature of the metal alloy.
2-26. (canceled)
27. The method as recited in claim 1, further comprising the steps
of: applying a heat treatment to said metal alloy; and combining
said step of applying a heat treatment with said step of
transforming said surface region when at least one condition of
said heat treatment corresponds to at least one condition of said
hardened surface.
28. The method as recited in claim 27, wherein said at least one
condition of said heat treatment is a temperature condition.
29. The method as recited in claim 1, further comprising the step
of forming a coating on said hardened surface region.
30. The method as recited in claim 29, further comprising the step
of forming an intermediate coating between said coating and said
hardened surface region.
31. The method as recited in claim 1, wherein said transforming
step includes processes selected from the group consisting of
carburizing, nitriding, carbo-nitriding, nitro-carburizing,
boronizing, and boriding.
32. The method as recited in claim 1, further comprising the step
of transforming the surface region by high current density ion
implantation.
33. The method as recited in claim 1, further comprising the step
of nitriding said metal alloy, said nitriding step including
transforming the surface region into a nitrogen-containing solid
solution surface region.
34. The method as recited in claim 1, further comprising the step
of using a gas atmosphere comprising between about 10% and 100%
nitrogen to transform the surface region.
35. The method as recited in claim 1, further comprising the step
of using a gas atmosphere pressure between 0.5 mtorr and 5.0 mtorr
to transform the surface region.
36. The method as recited in claim 1, further comprising the step
of inducing a bias voltage on the metal alloy between 200V and
1500V to transform the surface region.
37. The method as recited in claim 1, further comprising the step
of using a plasma discharge voltage of between 30V and 150V to
transform the surface region by ionizing precursor processing
gases.
38. The method as recited in claim 1, wherein said nitriding step
further comprises the step of removing oxides on the surface region
during the transforming of said surface region into said hardened
surface region.
39. The method as recited in claim 1, wherein said nitriding step
further comprises transforming the surface region of a metal alloy
into the hardened surface region at a temperature between about
700.degree. F. and 1000.degree. F.
40. The method as recited in claim 1, wherein said nitriding step
further comprises the step of forming a coating on the hardened
surface region.
41. A surface processing method comprising the steps of:
solutionizing a metal alloy; quenching said metal alloy; reheating
said quenched metal alloy to age said quenched metal alloy;
transforming a surface region of said metal alloy into a surface
hardened region; and combining said step of reheating with said
step of transforming said surface region when at least one
condition of said reheating step corresponds to at least one
condition of said hardened surface.
42. The method as recited in claim 41, wherein said transforming
step is performed at a temperature that is less than a temperature
of said reheating step.
43. The method as recited in claim 41, further comprising the step
of forming a coating on said hardened surface.
44. The method as recited in claim 43, further comprising the step
of forming an intermediate coating between said coating and said
hardened surface.
45. The method as recited in claim 41, further comprising the step
of nitriding said metal alloy.
46. The method as recited in claim 41, further comprising the steps
of: refrigerating said quenched metal alloy; and reheating said
quenched metal alloy to temper said quenched metal alloy.
47. The method as recited in claim 41, wherein said solutionizing
step includes the step of austenitizing said metal alloy.
48. A surface processing method comprising the steps of: providing
a metal alloy with an associated composition and associated heat
treating conditions; and transforming a surface region of said
metal alloy to a hardened surface region at a temperature that is
less than said heat treating conditions of said metal alloy.
49. The method as recited in claim 48, further comprising the step
of forming a coating on said hardened surface.
50. The method as recited in claim 48, wherein said metal alloy
comprises at least 5 wt % cobalt.
51. The method as recited in claim 48, wherein said metal alloy
comprises at least 1.5 wt % nickel.
52. The method as recited in claim 48, wherein said metal alloy
comprises up to 1.0 wt % carbon.
53. The method as recited in claim 48, wherein said metal alloy
comprises less than 20 wt % of molybdenum, chromium, tungsten, or
vanadium and combinations thereof.
54. The method as recited in claim 48, wherein said forming said
coating step further comprises forming an amorphous hydrogenated
carbon coating on said hardened surface region.
55. The method as recited in claim 49, wherein said forming said
coating step further comprises forming a intermediate coating
between said coating and said hardened surface.
56. The method as recited in claim 49, wherein said forming said
coating step further comprises forming a metallic intermediate
coating between said coating and said hardened surface.
57. The method as recited in claim 48, wherein said metal alloy is
used in a power transmission system, a gear, a shaft, a spring, a
bearing, or as armor plating.
Description
BACKGROUND OF THE INVENTION
[0001] This invention relates to surface processing of a power
transmission component and, more particularly, to methods of
surface processing that minimize dimensional alteration and the
identification of alloys that possess properties and
microstructures conducive to surface processing in such a way that
the processed alloy possesses desirable surface and core properties
that render it particularly effective in applications that demand
superior properties such as power transmission components. Absent
the combination of alloy selection and processing that are taught
herein, such superior properties would be unavailable.
[0002] For iron-based metal alloy components, such as power
transmission components, it is often desirable to form a hardened
surface case around the core of the component to enhance component
performance. The hardened surface case provides wear and corrosion
resistance while the core provides toughness and impact
resistance.
[0003] There are various conventional methods for forming a
hardened surface case on a power transmission component fabricated
from a steel alloy. One conventional method, nitriding, utilizes
gas, salt bath or plasma processing. The nitriding process
introduces nitrogen to the surface of the component at an elevated
temperature. The nitrogen reacts with the steel alloy to form the
hardened surface case while the core of the component may retain
the original hardness, strength, and toughness characteristics of
the steel alloy. This conventional process provides a hardened
surface case, however, the elevated temperatures of the nitriding
process may over-temper the core and diminish its properties and/or
induce dimensional distortion of the component such that additional
grinding or dimensionalizing steps are required to bring the
component into dimensional tolerance.
[0004] Accordingly, it is desirable to identify a class of alloys
for a surface processing method that minimizes dimensional
alteration of a power transmission component and essentially
eliminates dimensionalizing processes subsequent to the case
hardening process.
SUMMARY OF THE INVENTION
[0005] The surface processing method and power transmission
component according to the present invention includes transforming
a surface region into a hardened surface region at a temperature
less than a tempering temperature of the metal alloy. The Fe-based
metal alloy includes between 1.5 wt % and 15 wt % Ni, between 5 wt
% and 30 wt % Co, up to 1.0 wt % C, and up to 15 wt % of a
carbide-forming element, such as Mo, Cr, W, or V and combinations
thereof, that can react with the C to form a metal carbide
precipitate of the form M.sub.2C. A high current density ion
implantation, also known as high intensity plasma ion processing,
process is one technique that may be used to transform the surface
region into a hardened surface region. The temperature, vacuum
pressure, precursor gas flow and ratio, time of processing, and
bias voltages are controlled during the high current density ion
implantation nitriding process to provide a hardened surface having
a gradual transition in nitrogen concentration. A temperature below
the heat treating temperature of the metal alloy is utilized during
the high current density ion implantation nitriding to maintain the
crystal structure and metal alloy dimensions through the
process.
[0006] A coating deposited on the hardened surface region of the
metal alloy provides lubricity and wear resistance. The deposited
coating is an amorphous hydrogenated carbon or other coating
including a metal or transition metal. Alternatively, the deposited
coating may be a hard or ultra-hard transition-metal compound, such
as a carbide, boride, nitride, or oxide or mixture thereof,
deposited by a vapor-deposition method such as physical vapor
deposition (PVD), chemical vapor deposition (CVD), or
plasma-assisted chemical vapor deposition (PACVD). An intermediate
coating may be deposited between the coating and the hardened
surface region to promote adhesion between the coating and hardened
surface region. The intermediate coating is the transition metal as
is included in the amorphous hydrogenated carbon coating.
[0007] The metal alloy and high current density ion implantation
surface processing method according to the present invention
minimize dimensional alteration of a power transmission component
and essentially eliminate subsequent dimensionalizing
processes.
BRIEF DESCRIPTION OF THE DRAWINGS
[0008] The various features and advantages of this invention will
become apparent to those skilled in the art from the following
detailed description of the currently preferred embodiment. The
drawings that accompany the detailed description can be briefly
described as follows.
[0009] FIG. 1 shows a schematic view of a metal alloy;
[0010] FIG. 2 shows a schematic view of a crystal structure;
[0011] FIG. 3 shows a schematic view of a metal alloy during
surface processing;
[0012] FIG. 4 shows a schematic view of a metal alloy and hardened
surface region;
[0013] FIG. 5 shows a schematic view of a plasma (ion) nitriding
chamber;
[0014] FIG. 6 shows a nitrogen concentration profile over a depth
of a hardened surface region;
[0015] FIG. 7 shows a schematic view of a nitride compound on a
surface region of a metal alloy;
[0016] FIG. 8 shows a schematic view of a coating on a hardened
surface region of a metal alloy; and
[0017] FIG. 9 shows a schematic view of a coating on an
intermediate coating on a surface region of a metal alloy.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
[0018] FIG. 1 shows a schematic view of a metal alloy 10, including
a core 12 and a surface region 14 on the core 12. The metal alloy
10 is an iron-based alloy that is generally nitrogen-free and has
an associated composition and hardening heat treatment, including a
tempering temperature. The tempering temperature is dependent on
the metal alloy 10 composition and is the temperature at which the
metal alloy is heat processed to alter characteristics of the metal
alloy 10, such as hardness, strength, and toughness.
[0019] The composition of the metal alloy 10 is essentially a
Ni--Co secondary hardening martensitic steel, which provides high
strength and high toughness. That is, the ultimate tensile strength
of the metal alloy 10 is greater than about 170 ksi and the yield
stress is greater than about 140 ksi and in some examples the
ultimate tensile strength is approximately 285 ksi and the yield
stress is about 250 ksi. High strength and high toughness provide
desirable performance in such applications as power transmission
components. Conventional vacuum melting and remelting practices are
used and may include the use of gettering elements including, for
example, rare earth metals, Mg, Ca, Si, Mn and combinations
thereof, to remove impurity elements from the metal alloy 10 and
achieve high strength and high toughness. Impurity elements such as
S, P, O, and N present in trace amounts may detract from the
strength and toughness.
[0020] Preferably, the alloy content of the metal alloy 10 and the
tempering temperature satisfy the thermodynamic condition that the
alloy carbide, M.sub.2C where M is a metallic carbide-forming
element, is more stable than Fe.sub.3C (a relatively coarse
precursor carbide), such that Fe.sub.3C will dissolve and M.sub.2C
alloy carbides precipitate. The M.sub.2C alloy carbide-forming
elements contribute to the high strength and high toughness of the
metal alloy 10 by forming a fine dispersion of M.sub.2C
precipitates that produce secondary hardening during a conventional
precipitation-heat process prior to any surface processing. The
preferred alloy carbide-forming elements include Mo and Cr, which
combine with carbon in the metal alloy 10 to form M.sub.2C.
Preferably, the metal alloy 10 includes between 1.5 wt % and 15 wt
% Ni, between 5 wt % and 30 wt % Co, up to 1.0 wt % C, and up to 15
wt % of a carbide-forming element, such as Mo, Cr, W, or V and
combinations thereof, which can react with the C to form metal
carbide precipitates of the form M.sub.2C. It is to be understood
that the metal alloy 10 may include any one or more of the
preferred alloy carbide-forming elements.
[0021] The carbide-forming elements provide strength and toughness
advantages because they form a fine dispersion of M.sub.2C. Certain
other possible alloying elements such as Al, V, W, Si, Cr, may also
form other compounds such as nitride compounds. These alloying
elements and the carbide-forming elements influence the strength,
toughness, and surface hardenability of the metal alloy 10.
[0022] Typically, metal alloy 10 is hardened by heat treating above
.about.1500.degree. F. in the austenite phase region
(austenitizing) to re-solution carbides etc. It is then quenched
and refrigerated at approximately -100.degree. F. to transform the
austenite structure to martensite. The latter is a very hard,
brittle, metastable phase having a body centered tetragonal (BCT)
crystal structure because of the entrapped carbon atoms. Hence, at
this stage, the core 12 and surface region 14 of the metal alloy 10
have a generally equivalent tetragonal crystal structure 16 (FIG.
2).
[0023] As illustrated in FIG. 2, the tetragonal crystal structure
16 includes atomic lattice sites 17 forming sides having length 18
which are essentially perpendicular to sides having length 20. In
the tetragonal crystal structure 16, the length 18 does not equal
the length 20. Subsequent aging heat treatments are used to both
soften the martensite structure and also transform the Fe.sub.3C
phase to M.sub.2C which strengthens the structure. The latter
reaction tends to dominate, leading to secondary hardening. These
reactions can lead to concomitant changes in crystal structure as
the metastable martensitic BCT structure transitions to other
phases, such as austenite and/or ferrite depending on the exposure
temperature and time. It is to be understood that the iron-based
alloy may be formed instead with other crystal structures such as,
but not limited to, face centered cubic (e.g. austenite) and body
centered cubic (e.g. ferrite). These phase transitions may lead to
dimensional changes.
[0024] FIG. 3 shows a schematic cross-sectional view of the metal
alloy 10 during transformation of the surface region 14 into a
hardened surface region 28 as illustrated in FIG. 4. A high current
density ion implantation, also known as high intensity plasma ion
processing, process is used to form the hardened surface region,
although other surface hardening processes may be utilized such as,
but not limited to, nitrocarburizing, carburizing, boronizing, and
chromizing.
[0025] The high current density ion implantation nitriding process
is conducted in an appropriate reactor, an example of which is
illustrated schematically in FIG. 5. The metal alloy 10 is placed
in the reactor 34. The metal alloy 10 is placed in the high current
density ion implantation chamber 36 on a cathode 38. The cathode 38
provides a voltage bias to the metal alloy 10, thereby heating the
metal alloy 10 to a desired temperature that is below the heat
treating temperature, such as an aging or tempering temperature, of
the metal alloy 10.
[0026] Heating the metal alloy 10 to a temperature above the heat
treating temperature may alter the incumbent crystal structure 16,
relieve residual stresses in the metal alloy 10, otherwise
undesirably alter the microstructure and properties of the core,
and undesirably alter the dimensions of the metal alloy 10. By
utilizing a temperature that is below the heat treating temperature
of the metal alloy 10, the strength, toughness, incumbent crystal
structure 16, and dimensions of the metal alloy 10 are maintained
through the high current density ion implantation and process.
Subsequent processes to dimensionalize the metal alloy 10 or a
power transmission component formed from the metal alloy 10 are
eliminated. For the preferred metal alloy 10 composition, the heat
treating temperature is between 700.degree. F. and about
1000.degree. F. For other compositions, the heat treating
temperature may be different.
[0027] The chamber 36 includes a vacuum pump 40 which maintains a
vacuum in the chamber 36 of the reactor 34. A sample bias device 42
provides a bias voltage of between 200V and 1500V to the cathode
38. Preferably, the bias voltage is between 700V and 1000V. A
thermocouple 44 attached to the cathode 38 detects the cathode 38
temperature and a cooling system 46 provides cooling capability to
control the chamber 36 temperature. The chamber 36 is in fluid
communication with precursor gases in storage tanks 48. The
precursor gas storage tanks 48 may include gases such as nitrogen,
hydrogen, and methane, although it should be noted that these gases
are not all necessarily utilized during the high current density
ion implantation nitriding process. The conduit 50 connects the
precursor gas storage tanks 48 to the inner chamber 40 and includes
a gas metering device 52 to control the gas flow from the gas
storage tanks 48. A plasma discharge voltage device at the filament
54 provides an ionizing voltage to a filament 56, which ionizes
incoming gas from the conduit 50. The plasma discharge voltage at
the filament is preferably between 30V and 150V and even more
preferably is about 100V. It is to be understood that the
configuration of the reactor 34 is not meant to be limiting and
that alternative configurations of high current density ion
implantation reactors as well as reactors utilizing alternative
surface processing processes may be used.
[0028] The temperature, vacuum pressure in the chamber 36,
precursor gas flow and ratio, time of processing, filament bias
voltage, and sample bias voltage are controlled during the high
current density ion implantation nitriding process to provide a
hardened surface region 28 (FIG. 4) on the metal alloy 10. The
preferred conditions include a temperature between 700.degree. F.
and about 1000.degree. F., a pressure between about 0.5 mtorr and
5.0 mtorr in the chamber 36, a precursor gases mixture of nitrogen
and hydrogen in the range 10 to 100% nitrogen and a preferred range
of 80 to 100% nitrogen and a time in the range of about 5 to 200
hours and a preferred range of 10 to 40 hours. Even more
preferably, the conditions are controlled to a temperature of about
850.degree. F., a pressure of 0.75 mtorr in the chamber 36, as
illustrated in FIG. 5, and for a time of about twelve hours.
Additionally, when the high current density ion implantation
process conditions, such as temperature and time, are essentially
equal to the tempering/aging heat treatment conditions, then the
two processes may be combined into one process.
[0029] Under the preferred conditions, nitrogen from the nitrogen
atmosphere 26 (FIG. 3) in the chamber 36 diffuses into the surface
region 14 of the metal alloy 10. The nitrogen interstitially
diffuses into the surface region 14, thereby hardening the surface
region 14 and transforming the surface region 14 into the hardened
surface region 28. During this process, ions from the chamber 36
also bombard the surface region 14 without diffusing into the
surface region 14. That is, the ions sputter the surface region 14
and thereby remove oxides and other impurities that may be present
on the surface region 14. Additionally, the bias voltages utilized
for the sample bias and filament voltage may provide the benefit of
more favorable processing kinetics compared to other nitriding
processes that utilize lower operating voltages, such as plasma
(ion) nitriding.
[0030] Preferably, the hardened surface region 28 has a gradual
transition in nitrogen concentration over a depth D between an
outer surface 30 of the hardened surface region 28 and an inner
portion 32 of the hardened surface region 28.
[0031] The line 62 in FIG. 6 illustrates a gradual nitrogen
concentration profile over the depth D. By comparison, the line 64
represents the nitrogen concentration profile of a generally abrupt
nitrogen concentration. For the line 62, at a shallow depth into
the hardened surface region 28 such as near the outer surface 30,
the nitrogen concentration is relatively high compared to the
nitrogen concentration in the core 12. At a deeper depth, such as
near the inner portion 32, the nitrogen concentration is relatively
low and approaches the nitrogen concentration of the core 12. It is
to be understood that a variety of nitrogen concentration profiles
may result from varying the preferred conditions.
[0032] FIG. 7 shows a schematic view of a metal alloy 10 after
another high current density ion implantation nitriding process.
Utilizing a temperature towards the ends of the preferred range of
700.degree. F. and about 1000.degree. F. or utilizing an additional
gas such as methane may result in the formation of a compound 68 of
iron and nitrogen, such as the .gamma.' or .epsilon. compounds, on
the surface region 14. Formation of the compound 68 is generally
not preferred if a coating will be subsequently deposited over the
compound 68, however, the compound 68 may provide corrosion
resistance for the metal alloy 10.
[0033] Additionally, alloying elements such as Al, V, W, Si, and Cr
may be present in the metal alloy 10. Nitride compounds containing
the alloying elements may form during the high current density ion
implantation nitriding process. The presence of the nitride
compounds is generally detrimental to the mechanical properties of
the metal alloy 10 and are particularly detrimental in a complex
with iron nitride compounds that may be formed under certain high
current density ion implantation nitriding processing conditions,
however, the presence of these alloying elements may be required to
acquire other characteristics in the metal alloy 10.
[0034] FIG. 8 shows a schematic view of a metal alloy 10 after a
high current density ion implantation nitriding process. The metal
alloy 10 includes a coating 84 on the hardened surface region 28,
which preferably has a gradual nitrogen concentration profile and
essentially does not include an iron and nitrogen compound, such as
the .gamma.' or .epsilon. compounds. The coating 84 is deposited on
the hardened surface region 28 in a thickness between 0.5
micrometers and 10 micrometers by a vapor deposition or magnetron
sputtering process, although other thicknesses may be desirable.
Known chemical vapor deposition, physical vapor deposition, and
plasma-assisted chemical vapor deposition are preferred vapor
deposition processes, however, it is to be understood that other or
hybrid deposition processes may be utilized.
[0035] The deposited coating 84 is a solid lubricious coating such
as an amorphous hydrogenated carbon, although other coatings may be
used. The amorphous hydrogenated carbon coating has a biaxial
residual stress less than 800 MPa in compression at room
temperature, is thermally stable at temperatures over 400.degree.
F., and has an abrasive wear rate less than 3.times.10.sup.-15
m.sup.3m.sup.-1N.sup.-1 in a slurry of Al.sub.2O.sub.3. The
amorphous hydrogenated carbon coating may include a metal or
transition metal such as titanium, chromium, tungsten or other
transition metal to alter the lubricious characteristics of the
coating 84.
[0036] Referring to FIG. 9, an intermediate coating 86 may be
deposited between the coating 84 and the hardened surface region 28
to strongly bond the coating 84 to the hardened surface region 28.
The intermediate coating 86 bonds strongly to both the hardened
surface region 28 and the coating 84. Preferably, the intermediate
coating 86 is a metal and even more preferably it is the same
transition metal as is included in the amorphous hydrogenated
carbon coating. Generally, like materials, such as two metals, form
stronger bonds than unlike materials, such as a metal and a
non-metal. Therefore, the metal of the intermediate coating 86
strongly bonds to the metal hardened surface region 28 and to the
transition metal in the amorphous hydrogenated carbon coating.
[0037] Although a preferred embodiment of this invention has been
disclosed, a worker of ordinary skill in this art would recognize
that certain modifications would come within the scope of this
invention. For that reason, the following claims should be studied
to determine the true scope and content of this invention.
* * * * *