GB2291071A

GB2291071A - Wear-resistant thermal sprayed layer

Info

Publication number: GB2291071A
Application number: GB9514312A
Authority: GB
Inventors: Toru Hazano; Hiroto Fukotome; Nobuyuki Yamashita
Original assignee: Teikoku Piston Ring Co Ltd
Current assignee: Teikoku Piston Ring Co Ltd
Priority date: 1994-07-14
Filing date: 1995-07-13
Publication date: 1996-01-17
Also published as: GB9514312D0; JP3244959B2; JPH0827558A

Abstract

A resistant thermal sprayed layer is provided which is suitable for the surface of a sliding member, e.g. the inner circumferential surface of a steel cylinder liner. The thermal sprayed layer is comprised of steel containing 0.25 to 2.2 percent by weight of carbon and 13.0 percent or less by weight of one or more element selected from chromium, molybdenum, tungsten and vanadium. Non-fused particles are dispersed in an area ratio of 10 to 50 percent in the matrix of said layer. The hardness of the non-fused particles differs from the hardness of the matrix, with that of the matrix or of the non-fused particles, whichever is greater, having a Vickers hardness of 400 or more. The layer is produced from a powder mixture comprising two or more types of powder materials having different degrees of hardness after spraying, the said powder of large particle size being the powder material of lesser hardness, and the said powder of small particle size being the powder material of greater hardness.

Description

WEAR-RESISTANT THERMAL SPRAYED LAYER Field of the Invention This invention relates to a wear-resistant thermal sprayed layer which is effective when applied to sliding members such as cylinder liners.

Description of the Related Art Thin-walled steel cylinder liners have become a subject of much attention due to emphasis lately on producing more compact and light-weight engines. A combination of a steel cylinder liner of a specified composition and a piston ring of a specified composition, and soft nitriding treatment performed onone of them are proposed in Japanese Patent Laid-open No. 58-27860.

However the cylinder liner of this method had a weakened resistance to scuffing compared to cast iron cylinder liners.

Conventional methods proposed coating the surface of the sliding member with a thermal sprayed layer to improve slidability. However these proposed conventional methods had the drawback of high cost materials such as ceramic, molybdenum, ferrochrome and nickel-base self-fluxing alloy for the thermal sprayed layer to improve wear resistant characteristics, and were not suited as a surface treatment to improve wear resistant characteristics and scuffing resistant characteristics of the steel cylinder liner.

SUMMARY OF THE INVENTION It is an object of this invention to provide a thermal sprayed layer having superior resistance to scuffing and to wear, as well as a forming method, and a sliding member covered with the thermal sprayed layer.

The resistant thermal sprayed layer of this invention is comprised of steel containing 0.25 to 2.2 percent by weight of carbon and 13.0 percent or less by weight of one, or more than one of chromium, molybdenum, tungsten, and vanadium (total value when two or more types are used).

Non-fused particles are dispersed in an area ratio of 10 to 50 percent in the matrix of said layer. The hardness of the non-fused particles differs from the hardness of the matrix, with the matrix or the non-fused particles, whichever is higher, having a Vickers hardness of 400 or more.

The hardness difference between the non-fused particles and the matrix is preferably a Vickers hardness of 30 or more, and more preferably between 100 and 250.

The Vickers hardness of the non-fused particles or of the matrix, whichever is lower, is preferably 300 or more.

The particle size of the non-fused particles is preferably within a range of 10 to 100 Wm.

The method of forming the wear resistant thermal sprayed layer is characterized by spraying a powder mixture comprising steel powder of small particle size intended for fusing, and steel powder of large particle size not intended for fusing to form the thermal sprayed layer with non-fused particles dispersed in the matrix of said layer.

The powder mixture is comprised of either powder material of the same composition, or two or more types of powder materials having different degrees of hardness after spraying.

When powder material of the same composition is used, the hardness of the non-fused particles is greater than the hardness of the matrix.

When two or more types of powder materials having different degrees of hardness after spraying are used, and the powder of larger particle size not intended for fusing is the powder material having the higher hardness, then the non-fused particles can have a higher degree of hardness than the matrix. Likewise, when the powder of larger particle size not intended for fusing is the powder material having the lower hardness, then the non-fused particles can have a lower degree of hardness than the matrix.

A high strength, thin-walled, light weight cylinder liner with superior sliding characteristics is provided, when the inner circumference of the steel or aluminum alloy cylinder liner is covered with the wear resistant thermal sprayed layer.

Non-fused particles are present in the matrix of the wear resistant thermal sprayed layer of this invention. The hardness of the non-fused particles differs from the hardness of the matrix. As a result of sliding action, recesses are formed in the portions having lower hardness.

Oil tends to be retained in these recesses serving as oil pockets, thus providing superior slidability.

This difference in hardness between the matrix and the non-fused particles functions over a long span of time, to continually form a concave portion in the portion having lower hardness so that favorable sliding characteristics can be maintained over a long period of time.

Since recesses are formed in the matrix when its hardness is lower than that of the non-fused particles, a concave portion tends to be continuously formed in the matrix.

In the same manner, recesses tend to be discontinuously formed in the non-fused particle portions when its hardness is lower than that of the matrix. Thus, a more suitable sliding surface can be provided to match the sliding conditions and the mating member etc.

Resistance to scuffing falls below that of conventional cast iron cylinder liners when the hardness of the non-fused particles or of the matrix whichever is higher, is a Vickers hardness less than 400. Therefore the hardness of the non-fused particles or of the matrix whichever is higher should be a Vickers hardness of 400 or more, with an upper limit preferably of a Vickers hardness of 700 in view of aggression on the mating member. The hardness of the non-fused particles or of the matrix whichever is higher is preferably a Vickers hardness range of 500 to 650.

Resistance to scuffing falls below that of conventional cast iron cylinder liners when the area ratio of the non-fused particles as seen by microscopic observation falls below 10 percent. When this area ratio exceeds 50 percent, the bonding strength of the non-fused particles to the matrix declines and the resistance to wear decreases. Therefore the area ratio of the non-fused particles should be within a range of 10 to 50 percent and preferably within a range of 25 to 40 percent.

Control of the area ratio of the non-fused particles is difficult during thermal spraying when the size of the non-fused particles drops below 10 Wm, and the thermal spraying becomes difficult when particle size exceeds 100 Wm. A non-fused particle size of 10 to 100 pm is preferable, with a size in the range of 30 pm to 80 Hm more preferable.

A carbon content of 0.25 percent or more is preferable for resistance to wear, and a carbon content of 2.2 percent or less is preferable for toughness. A carbon content between 0.4 percent and 1.5 percent is more preferable.

The carbide-producing element content (Cr, Mo, W, V) is preferably 13.0 percent or less for resistance to scuffing. A lower limit of 0.6 percent is preferable for wear resistance. A content within the range of 1.0 percent to 7 percent is a more preferable carbide-producing element (Cr, Mo, W, V) content.

BRIEF DESCRIPTION OF THE DRAWINGS The aforesaid and other objects and features of the present invention will become more apparent from the following detailed description and the accompanying drawings.

Fig. 1 is a photograph taken with a microscope (100 X magnification) showing the structure of the thermal sprayed layer of this invention.

Fig. 2 is a graph showing the results of the wear tests.

Fig. 3 is a longitudinal cross sectional view of the cylinder liner with its inner circumferential surface covered with the thermal sprayed layer of this invention.

Fig. 4 is a longitudinal cross sectional view of a portion of a piston of an engine.

Fig. 5 is a schematic drawing of a reciprocating friction testing machine.

DESCRIPTION OF THE PREFERRED ENBODIMENTS Wear and scuff tests were performed using a reciprocating friction testing machine empirically known to reproduce well the sliding phenomena of the cylinder liner and piston ring, to evaluate the thermal sprayed layer of this invention.

The details of the reciprocating friction testing machine and the test conditions are as follows.

(1) Reciprocating Friction Testing Machine Fig. 5 shows a schematic drawing of the reciprocating friction testing machine. A plate test piece 10 of Fig. 5 is mounted on a test stand 11 and secured. The tip of a pin test piece 12 is pressed on the top surface of the test piece 10 by a hydraulic unit 13. The wear test is performed in this state moving the test stand 11 back and forth in a horizontal plane with a crank mechanism 14. The number 15 denotes a hydraulic pressure load gauge. The number 16 denotes a load cell for detecting the friction force. The number 17 denotes a recorder for recording the friction force.

(2) Sliding Mating Member (pin test piece 12) The material is of carbon tool steel (Japanese Industrial Standard SK5). The tip of the pin test piece 12 is machined into a hemispherical shape with a diameter of 18 mm, plated with hard chromium and then ground. The thickness of the hard chromium plating is 100 pm with a Vickers hardness of 900.

(3) Test piece (Plate test piece 10) The material is carbon steel (Japanese Industrial Standard S45C). The dimensions are 17 x 14 x 70 (mm).

After thermal spray of one side (sliding side) of the piece with steel materials of various compositions, the piece is then ground.

(4) Thermal Spraying method A test piece is secured on the inner circumferential surface of a cylindrical jig having an inner diameter of 108 mm. The jig rotates at a speed of 300 rpm. The spray gun sprays to a distance of 40 mm. The spray gun stroke is 190 mm with reciprocating speed of 500 mm/min. The spray application is performed by a high velocity oxy-fuel spraying method in accordance with the above conditions.

Table 5 shows more detailed information on thermal spray conditions (5) Scuffing Test A lubricant with a viscosity equivalent to that of light oil was prepared and the scuffing test was performed, raising the load imposed by the reciprocating friction testing machine from an initial 2 kilograms in increments of 2 kilograms every 60 seconds.

(6) Wear Test A lubricant with a viscosity equivalent to that of light oil was prepared and the test pieces were then subjected to testing with the reciprocating friction testing machine under conditions of 2kg(load) x 100c.p.m.

(speed) x 5 minutes (time) for break-in period, and conditions of lOkg(load) x 600c.p.m.(speed) x 60 minutes (time) for test period; the amount of wear was then measured.

(7) Measuring the area ratio of non-fused particles After the thermal spray application, the surface was ground and the area ratio of the non-fused particles was measured by means of an image processor-analyzer.

Scuffing Test The scuffing test was performed using the various test pieces shown in Tables 1 and 2. In embodiments 1 through 3, and comparative examples 2 and 3, after spraying, heat treatments were performed to adjust the hardness of the non-fused particles, and the effect of the hardness of the non-fused particles on scuffing was then investigated.

In Table 1 the meanings of the symbols in the particle size distribution column in thermal spray powder, the heat treatment column, and thermal spray conditions column are given respectively in Tables 3, 4 and 5.

The scuffing loads obtained are also shown in Table 2.

According to this table, when the hardness of the non-fused particles is a Vickers hardness of 400 or more, a scuffing load greater than that of the cast iron for cylinder liners of comparative example 1 was obtained.

The effect of the area ratio of the non-fused particles on the scuffing load was investigated. Results showed that when the ratio of the surface area occupied by the non-fused particles was 10 to 50 percent, a scuffing load higher than that of the cast iron for cylinder liners of comparative example 1 was obtained.

Table 1 SCUFFING TEST

Particle Thermal Heat Thermal Spray Powder Composition Size Spray Treat Test (% by weight ) Distri- Condi- ment No. bution tions after in Thermal Thermal Spray - Spray ins C Si Mn Cr Mo V Fe Powder resl resi 2 0.35 0.2 0.75 1.1 0.2 - dual A a I resi 3 0.35 0.2 0.75 1.1 0.2 - dual A a II resi < 4 0.4 1.0 0.3 5.0 1.3 1.0 dual C a a resi o 5 0.4 1.0 0.3 5.0 1.3 1.0 dual D a resi 6 0.4 1.0 0.3 5.0 1.3 1.0 dual A a resi 7 0.4 1.0 0.3 5.0 1.3 1.0 dual F a resi 8 0.4 1.0 0.3 5.0 1.3 1.0 dual E a resi " 1 3.15 2.20 0.75 0.25 B: 0.06 dual - - resi X 2 0.35 0.2 0.75 1.1 0.2 - dual A a III a) resi 3 0.35 0.2 0.75 1.1 0.2 - dual A a IV resi o 4 0.4 1.0 0.3 5.0 1.3 1.0 dual B a o Note 1: The material for comparative example 1 is cast iron for cylinder liners, with other portions comprising 0.2% phosphorus, 0.038 sulfur, and 0.4t copper. The Rockwell hardness is 96 on the B scale.

Table 2 SCUFFING TEST

Test Non-fused Particles Matrix Scuffing No. Vickers Area Vickers Load (kg) Hardness Ratio (*) Hardness 1 560 30 450 34 2 490 30 420 32 c 3 400 30 350 22 a) t 4 600 10 380 22 0 5 610 18 390 28 6 610 32 400 32 7 610 42 400 32 8 630 50 420 30 a) (d x w 2 380 30 340 10 a, 3 3 240 30 210 6 A g 4 0 450 14 Table 3 Particle Size Distribution in Thermal Spray Powder (% by weight)

Particle Size ( m) Symbol 5 - 15 15 - 25 25 - 37 37 - 45 45 - 53 A 70 - - 30 - 3 100 - - - - C 90 - - 10 D 80 - - 20 - E 60 - - 40 F 50 - - 50 G 31 16 19 21 13 Table 4 HEAT TREATMENT CONDITIONS

Symbol Heat treatment conditions I 3000C x 1 hour II 4000C x 1 hour III 5800C x 1 hour IV 7000C x 1 hour Table 5 THERMAL SPRAY CONDITIONS

Thermal Spray Symbol Conditions a b Gas Flow Rate Propylene 15 20 (l/min) Oxygen 100 150 Air 250 290 Powder Supply Rate (g/min) 40 20 Thermal Sprayed Layer 200 200 Thickness (Am) (Wear Test) The wear test was performed using the various test pieces shown in Tables 6 and 7. The results of the test are shown in Fig. 2.

Powder material intended for fusing has the same composition as powder material not intended for fusing in embodiments 9 through 17.

In embodiment 18, a powder material intended for fusing has the different composition compared with powder material not intended for fusing. In embodiment 18, the matrix hardness was made higher than the hardness of the non-fused particles by making the carbon content of the powder material of larger particle size which constitutes the non-fused particles, less than the carbon content of the powder material of smaller particle size intended for fusing.

Incidentally, when the carbon content of the powder material of larger particle size which constitutes the nonfused particles, is increased to a quantity larger than the carbon content of the powder material of smaller particle size intended for fusing, then a thermal sprayed layer having non-fused particles with hardness higher than that of the matrix can be obtained.

As shown by the test results in Fig. 2, all embodiments of this invention had lower wear values for the plate test pieces 10 and the pin test piece 12 than the cast iron for cylinder liners of comparative example 5.

Table 6 WEAR TEST

Particle Thermal Thermal Spray Powder Composition Size Spray Test (% by weight ) Distribu- Condi No. tion in tions Thermal Spray C Si Mn Cr Mo V Fe Powder Resi 9 0.35 0.2 0.75 1.1 0.2 - dual A a Resi 10 1.0 0.20 0.30 1.5 - - dual A a Resi 11 0.4 1.0 0.3 5.0 1.3 1.0 dual A a Resi 12 1.0 0.3 0.8 5.0 1.0 0.3 dual A a Resi 13 1.0 1.0 0.8 7.0 2.0 - dual A a Resia) . 14 0.55 0.8 0.60 13.0 - - dual A a o Resi E 15 0.25 0.20 0.75 1.0 - - dual A a Resi 16 2.2 0.20 0.60 13.0 - - dual A a Resi 17 0.35 0.20 0.75 0.60 - - dual A a Resi 18 0.40 1.0 0.3 5.0 1.3 1.0 dual A a Resi 0.25 0.20 0.5 0.60 dual Res i 6 0.20 0.20 0.70 1.10 0.4 - dual A a Resi a) H 7 0.70 0.40 0.30 13.5 0.3 - dual A a E Resi x 8 1.0 0.30 0.30 16.0 0.5 - dual A a Resi a) > 9 0.35 0.20 0.75 1.1 0.20 - dual G b Resi 10 1.0 0.20 0.30 1.5 - - dual G b k Resi o 11 1.0 1.0 0.80 7.0 2.0 - dual G b 0 U Resi 12 0.55 0.8 0.60 13.0 - - dual G b Note 1: The powder composition of embodiment 18 is a mixture at a ratio of 7 parts of the powder composition of the upper row, to 3 parts of the powder composition of the lower row in Table 6.

Note 2: The material for comparative example 5 is cylinder liner cast iron, with other portions comprising 0.2% phosphorus, 0.03% sulfur, and 0.4% copper. The Rockwell hardness is 96 on the B scale.

Note 3: The meanings of the symbols in the particle size distribution column in thermal spray powder, and the thermal spray conditions column are given respectively in Tables 3 and 5.

Table 7 WEAR TEST

Test No. Non-fused Particles Matrix Vickers Area Vickers Hardness Ratio (%) Hardness 9 560 30 450 10 570 30 470 11 610 32 400 12 620 29 410 13 610 33 410 E o 14 430 32 400 15 550 30 460 16 470 28 430 17 580 31 460 18 370 34 450 5 - - 6 520 33 490 " 7 450 34 400 '(S X 8 480 32 440 a) 9 9 ~ 0 520 (d 10 10 - 0 540 '(S E 11 ~ 0 480 U 12 - 0 460 The results of the scuffing tests and wear tests described above clearly show that the thermal sprayed layer of this invention has sliding characteristics superior to those of conventional cast iron for cylinder liners and can provide superior sliding characteristics when used as a thermal sprayed layer for cylinder liners.

Figure 1 is a sample photograph taken with a microscope of the surface in the thermal sprayed layer of this invention. The surface portion of the atomized powder may possibly be fusing during thermal spraying. The nonfused portions are softened and have a slightly crushed shape due to the impact during spraying. This explains why the particle size of the atomized powder and the size of the non-fused particles do not match each other in a 1 to 1 ratio. As shown by the photograph taken with a microscope in Fig. 1, the non-fused particles have a circular shape making them readily distinguishable from the surrounding fused matrix.

Figure 3 is a longitudinal cross section of a cylinder liner coated on the inner circumferential surface with the thermal sprayed layer of this invention. Figure 4 is a longitudinal cross section showing a portion of the piston of an engine. A cylinder liner 1 is inserted in the bore of a cylinder block 2 and secured in place. A piston 3 is inserted in the cylinder liner 1. A piston ring 5 is mounted in a piston ring groove 4 formed on the piston 3.

The outer circumferential surface of the piston ring 5 is in contact with the inner circumferential surface of the cylinder liner 1.

The piston ring 5 is of such materials as steel, cast iron, titanium or titanium alloy and may be for instance of martensitic stainless steel. The outer circumferential surface of the piston ring 5 may be covered with for example a hard chromium plating 6.

The cylinder liner 1 is of such materials as steel, cast iron or aluminum alloy and may be for instance of carbon steel. A thermal sprayed layer 7 on the inner circumferential surface of the cylinder liner 1 is made of for instance a steel of any of embodiments 1 through 18 as shown in the above-mentioned scuffing test and wear tests.

The thickness of the thermal sprayed layer 7 is 30 to 300 pm, and preferably in the range of 50 to 100 Wm.

As seen above, when the base material of the cylinder liner 1 is carbon steel, the machining is simple and production is inexpensive, providing a cylinder liner with thin walls of high strength, that is light-weight and compact with excellent sliding characteristics. When the base material of the cylinder liner 1 is of an aluminum alloy, then a high-strength, light-weight cylinder liner with excellent sliding characteristics can be provided.

The thermal sprayed layer need not necessarily be formed with the high velocity oxy-fuel spraying method but may also be formed with the plasma spraying method or electric arc spraying method, etc.

The resistant thermal sprayed layer of this invention need not be limited to covering at least the sliding surface of the cylinder liner, but is also suitable for use on at least sliding surfaces of other sliding members (for instance on at least the inner circumferential surface of bores in cylinder blocks of cast iron or aluminum alloy without cylinder liners).

Although the present invention has been described with reference to the preferred embodiments, it is apparent that the present invention is not limited to the aforesaid preferred embodiments, but various modification can be attained without departing from its scope.

Claims

CLAIMS:

1. A wear-resistant thermal sprayed layer of steel containing 0.25 to 2.2 percent by weight of carbon and 13.0 percent or less by weight of one or more element selected from chromium, molybdenum, tungsten and vanadium, wherein non-fused particles are dispersed in an area ratio of 10 to 50 percent in the matrix of said layer, the hardness of said non-fused particles differing from the hardness of said matrix, and the Vickers hardness of said matrix or of said non-fused particles, whichever is greater, being 400 or more.

2. A wear-resistant thermal sprayed layer as claimed in claim 1 in which said non-fused particles have a greater hardness than said matrix.

3. A wear-resistant thermal sprayed layer as claimed in claim 1 in which said matrix has a greater hardness than said non-fused particles.

4. A wear-resistant thermal sprayed layer as claimed in any one of claims 1 to 3 in which the difference in hardness between said non-fused particles and said matrix is a Vickers hardness of 30 or more.

5. A wear-resistant thermal sprayed layer as claimed in any one of claims 1 to 4 in which the size of said non-fused particles is within the range of 10 ssm and 100 pm.

6. A method of forming a wear-resistant thermal sprayed layer comprising spraying a powder mixture comprising steel powder of small particle size intended for fusing, and steel powder of large particle size not intended for fusing, to form a thermal sprayed layer having non-fused particles dispersed in the matrix of said layer.

7. A method of forming a wear-resistant thermal sprayed layer as claimed in claim 6 in which said powder mixture comprises powder material of uniform chemical composition.

8. A method of forming a wear-resistant thermal sprayed layer as claimed in claim 6 in which said powder mixture comprises two or more types of powder materials having different degrees of hardness after spraying, the said powder of large particle size being the powder material of greater hardness, and the said powder of small particle size being the powder material of lesser hardness.

9. A method of forming a wear-resistant thermal sprayed layer as claimed in claim 6 in which said powder mixture comprises two or more types of powder materials having different degrees of hardness after spraying, the said powder of large particle size being the powder material of lesser hardness, and the said powder of small particle size being the powder material of greater hardness.

10. A sliding member having on at least one sliding surface a wear-resistant thermal sprayed layer as claimed in any one of claims 1 to 5.

11. A sliding member as claimed in claim 10 which is a cylinder liner or a cylinder block.

12. A sliding member as claimed in claim 11 in which the base material of said cylinder liner is steel, cast iron or aluminium alloy.

13. A sliding member as claimed in claim 11 in which the base material of said cylinder block is cast iron or aluminium alloy.

14. A wear-resistant thermal sprayed layer of steel substantially as described herein with reference to any one of Embodiments 1 to 18 shown in the Tables.

15. A sliding member substantially as described herein with reference to any one of Embodiments 1 to 18 shown in the Tables.