Abrasion resistant copper alloy for build-up cladding on engine cylinder head

Abstract: The copper alloy contains: 6 - 15 wt% Ni; 1 - 5 wt% Si; 1 - 5 wt% (total) Mo, W, Ta, Nb, and/or V. The alloy may also contain 0.5 - 1.5 wt% Fe, 1 - 5 wt% Cr, 0.5 - 0.9 wt% Al, and 0.1 - 1.0 wt% P, which are obligatory when Ni is above 9 wt%. The alloy may also contain 1 - 10 wt% Mn and 0.01 to 0.1 wt% rare earth metal. A valve seat (2) is formed by build-up cladding by irradiating a laser beam on a powder (4) of the copper alloy, provided in the rim of a port (3) formed in an engine cylinder head (1). Due to the composition of the copper alloy, the valve seat (2) has few microcracks and excellent abrasion resistance.

Description: This invention relates to an abrasion resistant copper alloy. This invention also relates to build-up cladding of a copper alloy for forming a valve seat in an engine cylinder head. A method of forming a valve seat for an engine intake valve or exhaust valve is known wherein copper alloy powder is dissolved by a laser beam and accumulated on a cylinder head base metal along a rim of an intake port or exhaust port. As an example of such a powdered copper alloy, JP-A-08-35027 published by the Japanese Patent Office in 1996 discloses a powder material of a copper alloy excellent in high temperature wear resistance. According to tests performed by the inventors, a valve seat formed using this powder material displayed superior abrasion resistance, but microcracks occurred sporadically in the valve seat after cladding. JP-A-02-179839 discloses a hot-workable copper alloy containing 3-10 wt% Ni, 0.7-2.5 wt% Si, 2-6 wt% Al, 0.1-1.0 wt% Cr, and optionally 0.05-0.5 wt% of at least one of Zr, Ti, and Nb EP-A-0 320 195 discloses a wear resistant copper alloy containing 10-40 wt% Ni, 1-7 wt% Si, 0.5-5 wt% B, and 1-20 wt% Cr. EP-A-0 727 501 discloses a wear resistant copper alloy containing 10-30 wt% Ni, 2-15 wt% Fe, 2-15 wt% Co, 0.5-5.0 wt% Si, and 1-10 wt% Cr. It would be desirable to be able to provide an abrasion resistant copper alloy in which microcracks rarely form. It would also be desirable to be able to improve the quality of an engine valve seat. The present invention provides an abrasion resistant copper alloy as set forth in claim 1. This invention preferably provides an abrasion resistant copper alloy consisting of copper (Cu), 9-15 wt% nickel (Ni), 1-5 wt% silicon (Si), 0.5-1.5 wt% iron (Fe), 1-5 wt% chromium (Cr), 0.5-0.9 wt% aluminum (Al), 0.1-1.0 wt% phosphorus (P), and 1-5 wt% of a material selected from molybdenum (Mo), tungsten (W), tantalum (Ta), niobium (Nb),and vanadium (V). The preferred material is vanadium. This invention also provides an abrasion resistant copper alloy consisting of copper (Cu), 9-15 wt% nickel (Ni), 1-5 wt% silicon (Si), 0.5-1.5 wt% iron (Fe), 1-5 wt% chromium (Cr), 0.5-0.9 wt% aluminum (Al), 0.1-1.0 wt% phosphorus (P), 1-10 wt% manganese (Mn), and 1-5 wt% of a material selected from molybdenum (Mo), tungsten (W), tantalum (Ta), niobium (Nb),and vanadium (V). This invention also provides an abrasion resistant copper alloy consisting of copper (Cu), 9-15 wt% nickel (Ni), 1-5 wt% silicon (Si), 0.5-1.5 wt% iron (Fe), 1-5 wt% chromium (Cr), 0.5-0.9 wt% aluminum (Al), 0.1-1.0 wt% phosphorus (P), 1-10 wt% manganese (Mn), 0.01-0.1 wt% rare earth metal, and 1-5 wt% of a material selected from molybdenum (Mo), tungsten (W), tantalum (Ta), niobium (Nb),and vanadium (V). The above copper alloys are preferably provided in the form of powder for build-up cladding using a laser beam. Such build-up cladding is preferably used for forming a valve seat of intake and exhaust valves arranged in an engine cylinder head. The details as well as other features and advantages of this invention are set forth in the remainder of the specification and are shown in the accompanying drawings. Fig. 1 is a perspective view of a valve seat portion of an engine cylinder head. Fig. 2 is a table showing the composition of samples of copper alloy powder materials proposed by the inventors, only samples #13-15 being according to this invention. Fig. 3 is a table showing the composition of comparative samples set by the inventors for the purpose of comparison. Fig. 4 is a table showing the characteristics of the valve seats made of the powder materials of Fig. 2. Fig. 5 is a table showing the characteristics of the valve seats made of the powder materials of Fig. 3. Referring to Fig. 1 of the drawings, valve seats 2 for intake valves and exhaust valves are formed in an engine cylinder head 1. The valve seat 2 is formed by build-up cladding of copper alloy powder 4 having the composition of Samples #1 - #15 in Fig. 2 in the rim of a port 3 in the base material of the precast cylinder head 1. Copper alloy powder 4 is supplied to the rim of the port 3 from a powder feed nozzle 5. The building of copper alloy is formed with a thickness of 3mm or more on the rim of the hole 3 by irradiating this powder by a laser beam from a carbon dioxide laser element 6 under the following conditions. Laser output = 5.0 kW Working speed = 1.0 m/min Shielding gas = Ar Shielding gas flow rate = 20 liter/min The base metal of the cylinder head 1 is cast in Al-Cu-Mg type alloy specified by AC2A, which is an aluminum casting alloy specified by JIS-H-5202. This cylinder head 1 is for an in-line type four-cylinder double overhead cam (DOHC) engine, and comprises four holes 3 for intake valves and exhaust valves in each cylinder. The copper alloy powder 4 is formed as follows. First, molten copper alloy corresponding to one of Samples #1 - #15, shown in the table of Fig. 2, is prepared in a graphite pot of a high frequency induction furnace. Next, the molten copper alloy is allowed to flow down from the bottom of the pot, and "gas atomization" is performed wherein a gas is blown into the molten copper alloy which is flowing down to pulverize the alloy to a powder. Dehydration, degassing,and particle grading is then performed to obtain a cladding powder. A common feature of the copper alloy powders shown in Samples #1 - #15 of Fig. 2 is that they comprise 6-15 wt% nickel (Ni), 1-5 wt% silicon (Si), and 1-5 wt % of at least one of molybdenum (Mo), tungsten (W), tantalum (Ta), niobium (Nb) and vanadium (V). Nickel (Ni) is a useful element for improving the abrasion resistance of the valve seat 2. By suppressing nickel (Ni) to 9 wt% or less, microcracks formed sporadically in the cladding layer can be reduced. When the content of nickel (Ni) is higher than 9 wt%, the number of microcracks increases, but by further adding phosphorus (P) or manganese (Mn), 9-15 wt% of nickel (Ni) may improve the abrasion resistance of the alloy while suppressing the number of microcracks to within an acceptable range as shown by Samples #13 - #15. Nickel (Ni) and silicon (Si) cause deposition of hard silicides, but when nickel (Ni) is less than 6 wt%, deposition of hard silicides is reduced and high abrasion resistance is no longer obtained. Silicon (Si) is required for deposition of hard silicides and is useful for improving the abrasion resistance of the valve seat 2. When the silicon (Si) content is less than 1 wt%, the deposition amount of hard silicides decreases, but if the content exceeds 5 wt%, abrasion resistance does not greatly improve and microcracks actually tend to form more easily. By adding 0.5-1.5 wt% of iron (Fe) or 1-5 wt% chromium (Cr), abrasion resistance can be improved as shown by Samples #4 - #15 of Fig. 2. Both of these raise room temperature hardness and high temperature hardness of the cladding of a valve seat. When the addition amount is less than the lower limits mentioned above, a marked effect cannot be obtained from either iron (Fe) or chromium (Cr). However, when the upper limits are exceeded, there is not much improvement of hardness while microcracks form easily. When 0.5-0.9 wt% of aluminum (Al) is added, room temperature hardness is enhanced and an improvement of abrasion resistance is obtained as shown by Samples #6, #7, and #12 - #15. However, when aluminum (Al) is less than 0.5 wt%, the effect is small. Above 0.9 wt %, e.g. at 1.3 wt%, room temperature hardness decreases and microcracks form easily. When 5-15 wt% of cobalt (Co) is added, lumps of hard silicides are deposited and room temperature hardness is mainly enhanced as shown by Samples #7 and #10 - #12. This is effective for abrasion resistance improvement of a valve seat of the exhaust valve. However, when the cobalt (Co) content is less than 5 wt% the effect is small, and when it exceeds 15 wt%, microcracks form easily. Note that Samples #13-15 contain no cobalt. When 0.1-1.0 wt% of phosphorus (P) is added, the viscosity decreases when the powder melts as shown by Samples #8 - #15, so lumps of hard silicides are uniformly deposited when the cladding is formed by irradiation with the laser beam, and the formation of microcracks is suppressed. However, when the phosphorus (P) content is less than 0.1 wt% the effect is small, and when it exceeds 1.0 wt%, no further advantage is obtained. When 1.0-10.0 wt% manganese (Mn) is added, the formation of microcracks is suppressed as shown by Samples #9 - #12, #14,and #15. However, when the manganese (Mn) content is less than 1 wt% the effect is small, and when it exceeds 10 wt%, no further advantage is obtained. When 0.01-0.1 wt% of rare earth metals (REM) comprising misch metal is added, the formation of microcracks is suppressed as shown by Samples #10 - #12 and #15. However, when the rare earth metal (REM) content is less than 0.01 wt% the effect is small, and when it exceeds 0.1 wt%, no further advantage is obtained. The remaining components of Samples #1 - #15 of Fig. 2 are copper (Cu) and impurities. The inventors prepared 100 of the cylinder heads 1 for each Sample, and performed build-up cladding in sixteen ports 3 in each of the cylinder heads 1. Build-up cladding was performed also using Comparative Samples #1 - #12 which are not according to this invention and which have the compositions shown in Fig. 3. Comparative Sample #11 corresponds to the copper alloy disclosed in the aforesaid prior art Tokkai Hei 8-35027. Comparative Samples #1 - #10 and #12 were arranged by the inventors for purposes of comparison, and do not necessarily conform to the prior art. The remainder of the compositions of Comparative Samples #1 - #12 of Figs. 3 also comprises copper (Cu) and impurities. The cylinder head 1 obtained by the above process was finished to predetermined dimensions and surface roughness via mechanical machining. Twenty of the cylinder heads 1 which respectively have sixteen valve seats thus formed using the same powder were selected corresponding to each of the above Samples and Comparative Samples, and the number of microcracks was examined by performing a color check on the cladding layer of 320 of the holes 3 in total for each case. The results are shown in Figs. 4 and 5. The Vickers' hardness of the cladding, which has a significant correlation with the abrasion resistance of the valve seat formed, was measured at room temperature and at a high temperature of 400°C. As for Samples #1 - #3 and Comparative Samples #1 - #4 which have a Vickers' hardness less than Hv150, the cladding was performed only in the valve seat of the intake valve. The measurement results are shown in Figs. 4 and 5. For each Sample and Comparative Sample, cylinder heads for which microcracks had not been found were subjected to the following engine test. Engine = 1998cc in-line type four cylinder DOHC engine Fuel = regular clear gasoline Engine rotation speed = 6,000rpm Intake valve material = heat-resistant steel corresponding to JIS SUH11 Exhaust valve material = heat-resistant steel corresponding to JIS SUH36 Engine load (throttle opening) = 4/4 Test time = 100 hours After the test, the abrasion depth of the valve seat and valve face were measured. The measurement results are shown in Figs. 4 and 5. From the test results, the number of valve seats with microcracks decreased for Samples #1 - #15 compared to Comparative Samples #1 - #12. The depth of abrasion of the valve seat and valve face after the engine test was also less for Samples #1 - #15 than for Comparative Samples #1 - #12. For a valve seat formed using Samples #1 - #15, the external appearance of the frictional sliding parts was almost smooth, and no abrasion defects or pits which would cause loss of sealtightness of the valve seat were observed. On the other hand for Comparative Sample #1 wherein the nickel (Ni) content was less than 6 wt%. the hardness Hv200 at room temperature was extremely low, and the abrasion depth of the valve seat was very high as the abrasion resistance was incomplete. The abrasion depth of the valve face was also large due to repeated sticking and peeling of the abrasive powder on the valve face. In a valve seat according to Comparative Sample #2 wherein the nickel (Ni) content was 10 wt% or more and neither phosphorus (P) nor manganese (Mn) were present, there were a large number of microcracks and the abrasion depths of the valve seat and valve face due to the test were high. Further, in a valve seat according to Comparative Sample #12 wherein phosphorus (P) and manganese (Mn) are added, but the nickel (Ni) content exceeds 15 wt%, high abrasion resistance was obtained, but a considerable number of the valve seats had microcracks. For a valve seat according to Comparative Sample #3 wherein the molybdenum (Mo) and tungsten (W) content was less than 1 wt%, there was little deposition of hard silicides and adequate abrasion resistance was not obtained. This valve seat therefore had a large abrasion depth, and a ring-shaped groove was formed in the valve seat. The abrasion depth of the corresponding valve face was also large. For a valve seat according to Comparative Sample #4 wherein the total amount of molybdenum (Mo), tungsten (W) tantalum (Ta), niobium (Nb), and vanadium (V) exceeded 5%, there were a large number of microcracks as in the case of the valve seat according to Comparative Sample 2. Although engine tests were performed using cylinder heads wherein microcracks had not been detected, the abrasion depth of the valve seat and valve face due to the test was high. For a valve seat according to Comparative Sample 5 wherein the iron (Fe) content exceeded 1.5% and the chromium (Cr) content exceeded 5%, the abrasion depth of the valve seat was large as in the case of valve seats according to Comparative Samples #2 and #4. It appears that a high iron (Fe) or chromium (Cr) content is not effective in improving hardness and abrasion resistance. For a valve seat according to Comparative Sample #6 wherein the aluminum (Al) content was 1-3%, the same result was obtained as for valve seats according to Comparative Samples #2 and #4. The number of microcracks was highest for this Comparative Sample #6. For the valve seat according to Comparative Sample #6, the high temperature hardness fell considerably compared to the room temperature hardness, as shown in Fig. 5. Therefore, the abrasion depth of the valve seat and valve face of the exhaust valve which reaches a high temperature, was fairly large. For a valve seat according to Comparative Sample #7 wherein the cobalt (Co) content exceeded 15%, the same characteristics were obtained as for a valve seat according to Comparative Samples #2, #4, #5, and #6. Comparative Sample #8 was a copper alloy powder wherein the nickel (Ni), silicon (Si), molybdenum (Mo), iron (Fe), and chromium (Cr) content was that of the copper alloy according to this invention, to which less than 0.1% phosphorus (P), less than 1% manganese (Mn) and less than 0.01% rare earths (REM) had been added. In a valve seat formed using this copper alloy powder, there was no particular decline of abrasion resistance, but there were numerous microcracks. For a valve seat according to Comparative Sample #9 having an identical composition to that of Comparative Sample #8 wherein the phosphorus (P) content had been increased to more than 1.0 wt%, there were few microcracks but the abrasion resistance was not high enough. For a valve seat according to Comparative Sample 10 having an identical composition to that of Comparative Sample 8 wherein the manganese (Mn) content had been increased to more than 1.0 wt%, there was also no great improvement compared to Comparative Sample 8. For a valve seat according to Comparative Sample 11 corresponding to the copper alloy disclosed in Tokkai Hei 8-35027 of the aforementioned prior art, there were a considerable number of microcracks. In a valve seat formed with the copper alloy of Samples #13-#15 according to the present invention, excellent quality is obtained both in terms of the number of microcracks and the abrasion depth.

Claims: An abrasion resistant copper alloy consisting of: 9-15 wt% nickel (Ni); 1-5 wt% silicon (Si); 1-5 wt% of a material selected from molybdenum (Mo), tungsten (W), tantalum (Ta), niobium (Nb), and vanadium (V); 0.5-1.5 wt% iron (Fe); 1-5 wt% chromium (Cr); 0.5-0.9 wt% aluminum (Al); 0.1-1.0 wt% phosphorus (P); optionally 1-10 wt% manganese (Mn); optionally 0.01-0.1 wt% rare earth metal; and the balance copper (Cu) and impurities. An alloy as claimed in claim 1, in which the nickel (Ni) content is at least 12.1 wt%. An alloy as claimed in claim 1 or 2, in which the silicon (Si) content is about 3 wt%. An alloy as claimed in any preceding claim, in which the content of the said selected material is about 2.1 wt%. An alloy as claimed in any preceding claim, in which the said selected material is vanadium alone. An alloy as claimed in any preceding claim, in which the vanadium (V) content is 1.5-2.5 wt%. An alloy as claimed in any preceding claim, in which the iron (Fe) content is at least 1 wt%. An alloy as claimed in any preceding claim, in which the chromium (Cr) content is about 2 wt%. An alloy as claimed in any preceding claim, in which the aluminum (Al) content is at least 0.8 wt%. An alloy as claimed in any preceding claim, in which the phosphorus (P) content is 0.4-0.8 wt%. An alloy as claimed in any preceding claim, containing hard silicides. An alloy as claimed in any preceding claim, in the form of a powder. A method of build-up cladding in which a copper alloy powder is irradiated by a laser beam, characterised in that the copper alloy is an abrasion resistant copper alloy in accordance with any of claims 1 to 11. An engine cylinder head having a valve seat clad with an abrasion resistant copper alloy in accordance with any of claims 1 to 11.

Inventors: KANO MAKOTO, MATSUYAMA HIDENOBU, MIYAKE KOICHI, NINOMIYA RYUJI, OJIRO TAKESHI, SUZUKI KENJI, TSUSHIMA KENJI, KANO, MAKOTO, MATSUYAMA, HIDENOBU, MIYAKE, KOICHI, NINOMIYA, RYUJI, OJIRO, TAKESHI, SUZUKI, KENJI, TSUSHIMA, KENJI
Applicants: MITSUI MINING & SMELTING CO, NISSAN MOTOR, MITSUI MINING AND SMELTING CO., LTD, NISSAN MOTOR COMPANY LIMITED
Application year: 1999
Main classification: C22C9
IPC codes: B23K26, B23K35, C22C1, F02B77, F01L3, C22C9