U.S. patent application number 10/906696 was filed with the patent office on 2005-09-08 for method of hardening a beta titanium member.
This patent application is currently assigned to SHIMANO, INC.. Invention is credited to Hayashi, Kentaro, Iwai, Toru, Kashimoto, Yoshikazu, Tsubouchi, Kenji.
Application Number | 20050194075 10/906696 |
Document ID | / |
Family ID | 34747667 |
Filed Date | 2005-09-08 |
United States Patent
Application |
20050194075 |
Kind Code |
A1 |
Iwai, Toru ; et al. |
September 8, 2005 |
METHOD OF HARDENING A BETA TITANIUM MEMBER
Abstract
A method of hardening the surface of a beta titanium member
comprises the step of heating the beta titanium member in a gas
mixture consisting essentially of an inert gas and oxygen.
Inventors: |
Iwai, Toru; (Kitakatsuragi,
JP) ; Tsubouchi, Kenji; (Takarazuka, JP) ;
Kashimoto, Yoshikazu; (Sakai, JP) ; Hayashi,
Kentaro; (Sakai, JP) |
Correspondence
Address: |
DELAND LAW OFFICE
P.O. BOX 69
KLAMATH RIVER
CA
96050-0069
US
|
Assignee: |
SHIMANO, INC.
3-77 Oimatsucho
Sakai
JP
|
Family ID: |
34747667 |
Appl. No.: |
10/906696 |
Filed: |
March 2, 2005 |
Current U.S.
Class: |
148/669 |
Current CPC
Class: |
C23C 8/10 20130101 |
Class at
Publication: |
148/669 |
International
Class: |
C22F 001/18 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 4, 2004 |
JP |
2004-060523 |
Claims
What is claimed is:
1. A method of hardening the surface of a beta titanium member
comprising the step of process heating the beta titanium member in
a gas mixture consisting essentially of an inert gas and
oxygen.
2. The method according to claim 1 wherein the gas mixture has an
oxygen concentration in a range of from approximately 0.05 vol % to
approximately 20 vol %.
3. The method according to claim 2 wherein the gas mixture has an
oxygen concentration in a range of from approximately 1.0 vol % to
approximately 10 vol %.
4. The method according to claim 1 wherein the inert gas comprises
argon.
5. The method according to claim 4 wherein the inert gas consists
of argon.
6. The method according to claim 1 wherein the process heating step
comprises the step of heating the beta titanium member at a
temperature from approximately 700.degree. C. to approximately
1000.degree. C.
7. The method according to claim 6 wherein the process heating step
comprises the step of heating the beta titanium member at a
temperature from approximately 700.degree. C. to approximately
1000.degree. C. for a time period of from approximately 10 minutes
to approximately 30 minutes.
8. The method according to claim 7 wherein the time period is from
approximately 15 minutes to approximately 25 minutes.
9. The method according to claim 6 wherein the process heating step
comprises the step of heating the beta titanium member at a
temperature from approximately 850.degree. C. to approximately
950.degree. C.
10. The method according to claim 9 wherein the process heating
step comprises the step of heating the beta titanium member at a
temperature from approximately 850.degree. C. to approximately
950.degree. C. for a time period of from approximately 10 minutes
to approximately 30 minutes.
11. The method according to claim 10 wherein the time period is
from approximately 15 minutes to approximately 25 minutes.
12. The method according to claim 1 further comprising the step of
subsequently heating the beta titanium member in a temperature
range of from approximately 400.degree. C. to approximately
550.degree. C. after the process heating step.
13. The method according to claim 12 wherein the subsequent heating
step comprises the step of heating the beta titanium member in a
temperature range of from approximately 400.degree. C. to
approximately 550.degree. C. for a time period of from
approximately 6 hours to approximately 16 hours.
14. The method according to claim 13 wherein the time period is
from approximately 10 hours to approximately 14 hours.
15. The method according to claim 12 wherein the subsequent heating
step comprises the step of heating the beta titanium member in a
temperature range of from approximately 450.degree. C. to
approximately 500.degree. C.
16. The method according to claim 15 wherein the subsequent heating
step comprises the step of heating the beta titanium member in a
temperature range of from approximately 450.degree. C. to
approximately 500.degree. C. for a time period of from
approximately 6 hours to approximately 16 hours after the process
heating step.
17. The method according to claim 16 wherein time period is from
approximately 10 hours to approximately 14 hours.
18. A method of hardening the surface of a beta titanium member
comprising the steps of: process heating the beta titanium member
in a gas mixture consisting essentially of an inert gas and oxygen
at a temperature from approximately 700.degree. C. to approximately
1000.degree. C. for a time period of from approximately 10 minutes
to approximately 30 minutes to form an oxygen diffusion layer; and
subsequently heating the beta titanium member in a temperature
range of from approximately 400.degree. C. to approximately
550.degree. C. for a time period of from approximately 6 hours to
approximately 16 hours.
19. The method according to claim 18 wherein the time period for
the process heating step is from approximately 15 minutes to
approximately 25 minutes, and wherein the time period for the
subsequent heating step is from approximately 10 hours to
approximately 14 hours.
20. The method according to claim 19 wherein the gas mixture has an
oxygen concentration in a range of from approximately 1.0 vol % to
approximately 10 vol %.
21. A method of hardening the surface of a beta titanium member
comprising the step of heating the beta titanium member in a gas
mixture consisting essentially of an inert gas and oxygen to form a
hardened layer and an oxidized layer above the hardened layer,
wherein the oxidized layer has a thickness less than or equal to
approximately 0.5 .mu.m after the heating has completed.
22. The method according to claim 20 wherein the hardened layer has
a thickness in a range of from approximately 70 .mu.m to
approximately 100 .mu.m.
Description
BACKGROUND OF THE INVENTION
[0001] The present invention is directed to metal hardening
processes and, more particularly, to a method of hardening a beta
titanium member.
[0002] In recent years, products made of titanium or of titanium
alloy, both of which are lightweight and hard, have become widely
used. However, titanium and titanium alloy are active metals and
have low wear resistance. Also, surface processing of either
material is extremely difficult.
[0003] To overcome such problems, methods have been employed to
increase the surface hardness of members formed from such metals.
Such methods include forming an outer hardened layer via surface
plating or hardening the product surface itself via nitriding or
carburizing. However, plating processes encounter the problems of
poor adhesion between the plating layer and the titanium surface
and damage to the appearance of the titanium, and surface hardening
via nitriding or carburizing encounter the problems of coarsening
of the product surface and extended processing times.
[0004] Japanese published patent application nos. 2003-73796,
2002-97914 and 2001-81544 disclose further surface hardening
methods that employ oxygen diffusion to increase the wear
resistance of titanium products. For example, JP 2003-73796
discloses a surface hardening method wherein a titanium member is
heated while buried in a highly oxygen-absorbent powder. The powder
reduces the oxygen concentration of the atmosphere surrounding the
titanium member by physically preventing the titanium surface from
coming into contact with oxygen. As a result, a TiO oxygen
diffusion layer is formed in the surface of the titanium member
while minimizing the formation of an oxidized outer surface
layer.
[0005] Although the surface hardness can be increased using such
methods, because the titanium member must be buried in
oxygen-absorbing powder each time processing is carried out, the
process is relatively inefficient and costly. Furthermore, because
the titanium member is buried in the oxygen-absorbing powder, the
desired cooling rate cannot be obtained following the heat
processing, so an appropriate aging treatment cannot be
performed.
SUMMARY OF THE INVENTION
[0006] The present invention is directed to various features of a
method of hardening a beta titanium member. In one embodiment, a
method of hardening the surface of a beta titanium member comprises
the step of heating the beta titanium member in a gas mixture
consisting essentially of an inert gas and oxygen. Additional
inventive features will become apparent from the description below,
and such features alone or in combination with the above features
may form the basis of further inventions as recited in the claims
and their equivalents.
BRIEF DESCRIPTION OF THE DRAWINGS
[0007] FIG. 1 shows the basic construction of a particular
embodiment of an apparatus for surface hardening a beta titanium
member;
[0008] FIGS. 2A and 2B are graphs of surface hardness for various
heat treating methods;
[0009] FIG. 3 is a bar graph of the results of friction testing
beta titanium members when subjected to the methods shown in FIGS.
2A and 2B; and
[0010] FIG. 4 is a cross sectional diagram of a surface hardened
beta titanium member formed according to the methods taught
herein.
DETAILED DESCRIPTION OF THE EMBODIMENTS
[0011] FIG. 1 shows the basic construction of a particular
embodiment of a beta titanium surface hardening apparatus 10 in the
form of a titanium melting furnace for surface hardening a beta
titanium member 11. In general, beta titanium member 11 is placed
in a processing chamber S of beta titanium surface hardening
apparatus 10, and then beta titanium member 11 is heated in an
atmosphere comprising a gas mixture comprising oxygen and an inert
gas such as argon gas. As a result, heat processing can be carried
out in an atmosphere having a lower oxygen concentration than
ordinary atmospheric air. In this embodiment, the oxygen
concentration ranges from approximately 0.05 vol % to approximately
20 vol % (preferably approximately 1.0 vol % to approximately 10
vol %), the heating temperature ranges from approximately
700.degree. C. to approximately 1000.degree. C. (preferably
approximately 850.degree. C. to approximately 950.degree. C.), and
the heat processing time ranges from approximately 10 minutes to
approximately 30 minutes (preferably approximately 15 minutes to
approximately 25 minutes).
[0012] After this processing, titanium member 11 undergoes an aging
treatment at an ambient temperature of from approximately
400.degree. C. to approximately 550.degree. C. (preferably
approximately 850.degree. C. to approximately 950.degree. C.) for a
time of from approximately 6 hours to approximately 16 hours
(preferably approximately 10 hours to approximately 14 hours).
[0013] FIGS. 2A and 2B are graphs of surface hardness for various
heat treating methods. In FIG. 2A, one line represents an
unprocessed beta titanium member, another line represents a beta
titanium member subjected to an Argon-Oxygen atmosphere of 5 vol %
oxygen at 850.degree. C. for 10 minutes, and another line
represents a beta titanium member subjected to an Argon-Oxygen
atmosphere of 10 vol % oxygen at 850.degree. C. for 10 minutes. In
FIG. 2B, one line represents an unprocessed beta titanium member,
another line represents a beta titanium member subjected to an
Argon-Oxygen atmosphere of 1.7 vol % oxygen at 900.degree. C. for
10 minutes, another line represents a beta titanium member
subjected to an Argon-Oxygen atmosphere of 5 vol % oxygen at
900.degree. C. for 10 minutes, and another line represents a beta
titanium member subjected to an Argon-Oxygen atmosphere of 10 vol %
oxygen at 900.degree. C. for 10 minutes.
[0014] As shown in FIG. 2A, a beta titanium member that was
processed at a temperature of 850.degree. C. for 10 minutes in an
atmosphere having an oxygen concentration of 5 vol % exhibited an
HV hardness of 570-400 down to a depth of 0.10 mm (100 .mu.m) below
the surface, as compared to the more or less fixed HV hardness of
400 for an unprocessed beta titanium member. In particular, the HV
hardness increased to 570-400 from the surface down to a depth of
0.05 mm (50 .mu.m) below the surface. A beta titanium member that
was processed at a temperature of 850.degree. C. for 10 minutes in
an atmosphere having an oxygen concentration of 10 vol % also
exhibited an HV hardness of 570-400 down to a depth of 0.10 mm (100
.mu.m) below the surface. In particular, the HV hardness increased
to 570-450 from the surface down to a depth of 0.05 mm (50 .mu.m)
below the surface.
[0015] As shown in FIG. 2B, a beta titanium member that was
processed at a temperature of 900.degree. C. for 10 minutes in an
atmosphere having an oxygen concentration of 1.7 vol % exhibited an
HV hardness of 590-420 from the surface down to a depth of 0.10 mm
(100 .mu.m) below the surface, as compared to the more or less
fixed HV hardness of 450 for an unprocessed beta titanium member.
In particular, the HV hardness increased to 590-495 from the
surface down to a depth of 0.05 mm (50 .mu.m) below the surface. A
beta titanium member that was processed at a temperature of
900.degree. C. for 10 minutes in an atmosphere having an oxygen
concentration of 5 vol % exhibited an HV hardness of 580-470 from
the surface down to a depth of 0.10 mm (100 .mu.m) below the
surface. In particular, the HV hardness increased to 585-515 from
the surface down to a depth of 0.05 mm (50 .mu.m) from the surface.
A beta titanium member that was processed at a temperature of
900.degree. C. for 10 minutes in an atmosphere having an oxygen
concentration of 10 vol % exhibited an HV hardness of 545-395 down
to a depth of 0.10 mm (100 .mu.m) from the surface. In particular,
the HV hardness increased to 545-490 from the surface down to a
depth of 0.05 mm (50 .mu.m) below the surface.
[0016] It should be readily apparent from the graphs in FIGS. 2A
and 2B that, with respect to the temperature parameter, a
temperature of 900.degree. C. resulted in a greater increase in
hardness over a greater range than a temperature of 850.degree. C.
More specifically, when the beta titanium member was subjected to a
processing temperature of 900.degree. C., the HV hardness declined
more gradually beyond a depth of 0.02 mm (20 m) below the surface
than it did when the beta titanium member was subjected to a
processing temperature of 800.degree. C. Therefore, taking into
consideration the melting temperature of beta titanium, it is
preferable that processing be carried out at a temperature in the
range of from approximately 850.degree. C. to approximately
950.degree. C.
[0017] With respect to the oxygen concentration parameter, FIG. 2B
shows that HV hardness increases to a greater degree when the
oxygen concentration is 1.7 vol % than when it is 5 vol %. The same
is true when the oxygen concentration is 5 vol % than when it is 10
vol %. Therefore, in order to minimize the formation of an oxidized
layer while increasing HV hardness, it is preferable that
processing be carried out within an oxygen concentration in a range
of from approximately 1 vol % to approximately 10 vol %.
[0018] FIG. 3 is a bar graph of the results of friction testing
beta titanium members when subjected to the methods shown in FIGS.
2A and 2B. The beta titanium member that was heated at 850.degree.
C. for 10 minutes in an oxygen concentration of 5 vol % is referred
to as a first sample, the beta titanium member that was heated at
900.degree. C. for 10 minutes in an oxygen concentration of 10 vol
% is referred to as a second sample, a beta titanium member that
was heated at 900.degree. C. for 10 minutes in an oxygen
concentration of 5 vol % is referred to as a third sample, and a
beta titanium member that was heated at 900.degree. C. for 10
minutes in an oxygen concentration of 1.7 vol % is referred to as a
fourth sample.
[0019] As shown in FIG. 3, the average amount of wear was 0.15 mm
for the unprocessed beta titanium member, 0.138 mm for the first
sample, 0.132 mm for the second sample, 0.110 mm for the third
sample, and 0.104 mm for the fourth sample. Clearly, the average
wear amount was lower for the processed beta titanium members than
for the unprocessed beta titanium member. The average wear amount
for the third and fourth samples in particular, which were
processed at 900.degree. C. for 10 minutes, was approximately 30%
lower than the wear amount for the unprocessed beta titanium
member. Thus, processing at a temperature in a range of from
approximately 850.degree. C. to approximately 900.degree. C.
results in wear resistance and surface hardness values that are
higher than the equivalent values for an unprocessed beta titanium
member.
[0020] From a comparison between the first sample and the third
sample, it may be seen that the average amount of wear can be
reduced when heating is carried out at 850.degree. C. than at
900.degree. C. Accordingly, heating at a temperature of 850.degree.
C. may be preferred in some applications. Moreover, from a
comparison of the second through fourth samples, it may be seen
that the average amount of wear can be reduced by reducing the
oxygen concentration from 10 vol % to 1.7 vol %, so such oxygen
concentration reduction also may be preferable in some
applications.
[0021] FIG. 4 is a cross sectional diagram of a surface hardened
beta titanium member 11 formed according to the methods taught
herein. In this condition, beta titanium member 11 comprises a
topmost oxidized layer 11a, a hardened oxygen diffusion layer 11b
having a thickness of approximately 100 .mu.m below oxidized layer
11a, and an unprocessed layer 11c below hardened layer 11b.
Oxidized layer 11a has a thickness of from approximately 0 .mu.m to
approximately 5 .mu.m. Such a layer is significantly thinner than
the oxidized layers formed in the prior art processes that heat the
titanium member in atmospheric air. Thus, removal of oxidized layer
11a created by the teachings herein is very easy.
[0022] In other words, because hardened layer 11b can be formed to
a thickness of at least 70 .mu.m (preferably 100 .mu.m) while
minimizing the thickness of oxidized layer 11a, a beta titanium
member 11 having increased surface hardness can be efficiently
obtained. When the same processes as described above are performed
in atmospheric air, a hardened layer may be formed to a thickness
of 300 .mu.m with an increased HV hardness of 500, but an oxidized
layer having a thickness of 100 .mu.m is formed on top of the
hardened layer. An oxidized layer on the surface of the product is
undesirable because it tarnishes the product's appearance. Since
the oxidized layer is hard and brittle, removal of such a thick
layer is extremely cumbersome and impairs production
efficiency.
[0023] The processes described above have particular benefit when
applied to beta titanium members. When the process was applied to
pure titanium and alpha-beta titanium alloys, a hardened oxygen
diffusion layer did not form. This is thought to be due to the fact
that an oxygen diffusion layer cannot be formed via melting of the
surface of pure or alpha-beta titanium, whereas such a layer can be
formed in beta titanium by surface melting.
[0024] While the above is a description of various embodiments of
inventive features, further modifications may be employed without
departing from the spirit and scope of the present invention. For
example, while argon gas was used solely as the inert gas, other
inert gases could be used alone or in combination argon in addition
to the oxygen. The size, shape, location or orientation of the
various components may be changed as desired. Components that are
shown directly connected or contacting each other may have
intermediate structures disposed between them. The functions of one
element may be performed by two, and vice versa. The structures and
functions of one embodiment may be adopted in another embodiment.
It is not necessary for all advantages to be present in a
particular embodiment at the same time. Every feature which is
unique from the prior art, alone or in combination with other
features, also should be considered a separate description of
further inventions by the applicant, including the structural
and/or functional concepts embodied by such feature(s). Thus, the
scope of the invention should not be limited by the specific
structures disclosed or the apparent initial focus or emphasis on a
particular structure or feature.
* * * * *