DE102009031375B4 - Piston ring with adjustable wear characteristics and process for its preparation - Google Patents

Abstract

Disclosed is a piston ring for an internal combustion engine, comprising a substrate; and a coating obtainable by thermal spraying a powder comprising the following elemental proportions: 20-40% by weight of iron, Fe; 0-30 wt% tungsten, W; 20-40 weight percent chromium, Cr; 10-20 weight percent nickel, Ni; 1-5 weight percent molybdenum, Mo; 1-8 weight percent carbon, C; and 0.1-2% by weight of silicon, Si.

Description

The The present invention relates to a piston ring whose wear characteristics can be adjusted during manufacture, as well as the corresponding Manufacturing method thereof.

nowadays are the customer requirements regarding the wear behavior on the piston ring and the cylinder bore differently, d. H. it is partly a possible low wear requires on the other hand need Engine manufacturers sometimes also higher wear rates, from their point of view as possible good run-in behavior for the system "piston ring / cylinder liner lubricated " receive.

The publication DE 101 63 933 B4 discloses a material wire for producing a wear-resistant surface coating for running surfaces of machine parts subject to frictional wear, in particular piston rings of internal combustion engines, by means of thermal spraying methods, wherein the material wire consists of an iron or a nickel base material and fractions of Cr, B, Si, CrC , TiC, WC, MOC and C are included.

The publication DE 10 2008 032 042 B3 describes piston rings with improved tribological properties. On the wear-stressed surface of the components is a wear protection layer with an iron-based alloy, which was applied by means of thermal spraying.

The The object of the invention is, therefore, the tribological properties of thermally sprayed piston rings. this will according to the invention achieved through the use of a previously unused material system as a coating material compared to piston ring coatings Moybden-based. The invention is further intended to manufacture according to customer requirements appropriate tailor made coated piston rings, in particular with regard to their wear behavior and the residual stress, improve the coating over thermal Spraying takes place.

Of Further, the base material matrix should have similar physical properties (in terms of the thermal expansion coefficient and the thermal conductivity) like the underlying substrate as well as sufficient mechanical Properties (re Hardness and ductility) exhibit.

• – ein Substrat; und
• – eine Beschichtung, erhältlich durch thermisches Spritzen eines Pulvers umfassend die Elementanteile

20–40 Gewichtsprozent Eisen, FE;
0–30 Gewichtsprozent Wolfram, W;
20–40 Gewichtsprozent Chrom, Cr;
10–20 Gewichtsprozent Nickel, Ni;
1–5 Gewichtsprozent Molybdän, Mo;
1–8 Gewichtsprozent Kohlenstoff, C; und
0,1–2 Gewichtsprozent Silizium, Si.According to a first aspect of the invention, a piston ring for an internal combustion engine is provided, comprising

• A substrate; and
• A coating obtainable by thermal spraying of a powder comprising the elementary parts

20-40% by weight iron, FE;
0-30 wt% tungsten, W;
20-40 weight percent chromium, Cr;
10-20 weight percent nickel, Ni;
1-5 weight percent molybdenum, Mo;
1-8 weight percent carbon, C; and
0.1-2% by weight of silicon, Si.

To an embodiment is the elemental proportion of iron is at least 25% by weight, preferably between 37 and 40 weight percent.

In one embodiment, the amount of carbides is 20-70 weight percent composed of 0-30 wt% tungsten carbide WC and 20-40 wt% chromium carbide Cr ₃ C ₂ .

To an embodiment are the particle sizes of the Powder in the range of 1-100 microns.

To an embodiment The carbides are embedded in a nickel-chromium matrix and have a Particle size of 0.5-5 microns on.

To an embodiment the layer thickness of the coating is in the range of 20-1000 μm.

To an embodiment The thermal spraying process includes high-speed flame spraying (High Velocity Oxy Fuel, HVOF) or plasma spraying.

To an embodiment the piston ring is a cast or steel piston ring.

• – Bereitstellen eines Substrats;
• – Beschichten des Substrats durch thermisches Spritzen eines Pulvers umfassend die Elementanteile

20–40 Gewichtsprozent Eisen, Fe;
0–30 Gewichtsprozent Wolfram, W;
20–40 Gewichtsprozent Chrom, Cr;
10–20 Gewichtsprozent Nickel, Ni;
1–5 Gewichtsprozent Molybdän, Mo;
1–84 Gewichtsprozent Kohlenstoff, C; und
0,1–2 Gewichtsprozent Silizium, Si.According to a second aspect of the invention, there is provided a method of manufacturing a piston ring for an internal combustion engine, comprising

• - Providing a substrate;
• - Coating of the substrate by thermal spraying of a powder comprising the elementary parts

20-40 weight percent iron, Fe;
0-30 wt% tungsten, W;
20-40 weight percent chromium, Cr;
10-20 weight percent nickel, Ni;
1-5 weight percent molybdenum, Mo;
1-84 weight percent carbon, C; and
0.1-2% by weight of silicon, Si.

To an embodiment is the elemental proportion of iron is at least 20% by weight, preferably between 37 and 40 weight percent.

In one embodiment, the amount of carbides is 20-70 weight percent composed of 0-30 wt% tungsten carbide WC and 20-40 wt% chromium carbide Cr ₃ C ₂ .

To an embodiment are the particle sizes of the Powder in the range of 1-100 microns.

To an embodiment The carbides are embedded in a nickel-chromium matrix and have a Particle size of 0.5-5 μm.

To an embodiment the layer thickness of the coating is in the range of 20-1000 μm.

To an embodiment The thermal spraying process includes high speed flame spraying or Plasma spraying.

Short description of the drawing

1 shows the microstructure of a thermally sprayed FeWCrNiMoCSi layer according to an embodiment of the invention;

2 Microstructure of a thermally sprayed FeWCrNiMoCSi layer according to another embodiment of the invention;

3 shows an X-ray diffractometer (XRD) analysis of the material system used of an embodiment of the invention;

4 shows a crystallographic image of the FeWCrNiMoCSi coating of one embodiment of the invention prior to performing a wear test;

5 FIG. 12 shows a crystallographic image of the FeWCrNiMoCSi coating of the embodiment. FIG 4 after carrying out the wear test.

Detailed description the invention

Iron-based Coatings applied by means of arc wire spraying (LDS) previously found only in the range of the crank mechanism on the cylinder bore Application.

The Production of wear protection layers by thermal spraying is a known method. Today's for it powder materials used are based on the substances molybdenum, tungsten carbide, Nickel-chromium and chromium-carbide.

In order to achieve the object described above, the invention proposes a layer system consisting of a base system with similar physical properties to the substrate to be coated and of sufficient strength, combined with a wear-resistant portion. At the Her depending on the wear-resistant component, the desired different wear rates at the ring and the bushing in the lubricated state occur.

As well is the type and strength the residual stresses due to the addition of defined amounts of the wear-resistant Proportion adjustable. in principle are compressive stresses in thermally sprayed coatings too prefer, as this an emerging crack and crack growth counteract in the vertical direction.

The solution is thus in accordance with the invention a new iron-based coating system reinforced by carbides.

Regarding the physical properties (thermal conductivity, thermal expansion coefficient) arises at a preferred minimum proportion of the iron-containing base system 20 percent by weight, a quasi-homogeneous system between substrate and coating. As a result, during the mixed friction, in particular in the OT or UT area, resulting thermal energy better dissipated and a uniform thermal Relaxation process ensured by the temperature fluctuations present in the engine become.

The Application of iron-based alloys as a piston ring base coating material together with a carbidic system produced by HVOF or plasma spraying, results in the production of a new type of piston ring. The too Coating piston ring can be a casting, but also a steel piston ring be.

Basically, the whole system consists of the following elements:
Iron (Fe), tungsten (W, as WC), chromium (Cr, as Cr and Cr3C2), nickel (Ni), molybdenum (Mo), silicon (Si) and carbon (C, partially bound in Fe, W and Cr as carbide). For the presentation of the new material system, the following element concentrations must be observed:
20-40 weight percent iron, Fe;
0-30 wt% tungsten, W;
20-40 weight percent chromium, Cr;
10-20 weight percent nickel, Ni;
1-5 weight percent molybdenum, Mo;
1-8 weight percent carbon, C; and
0.1-2% by weight of silicon, Si.

With a carbide content of 20-70% by weight, the following carbide concentrations must be observed:
0-30 wt% tungsten carbide WC,
20-40% by weight Cr3C2.

A Iron-based alloy without carbide content is not recommended since the wear resistance (measured as described below) today's requirements are not Fulfills. The material system according to the invention therefore comprises at least 20% by weight of carbide. A increase of the total carbide content above 70% by weight is for the application as piston ring coating but also not too recommend, since too high a carbide content, the layer too strong gets ceramic character (too high modulus of elasticity) and thus the thermal cycling in the engine does not withstand. The material system according to the invention therefore, comprises a maximum of 70% by weight of carbide.

The Particle sizes of Powders used are in the range 1-100 microns, with the individual, in a NiCr matrix embedded carbides have a particle size of 0.5-5 microns.

Experiments performed:

The powder was thermally sprayed and, for various variants, the chemical composition (see Table 1), the carbide content (see Table 2), the microstructure (see 1 ), the crystal structure (see 2 ), the porosity, the residual stresses (by Almentest) and the hardness (see Table 3) of the coating produced. For the experiments 1 to 4 different carbide concentrations were used. For experiment 3, two different injection process parameters were set (FIGS. 3a, 3b), whereby for variant 3b an approximately 10% higher O2 volume flow than for variant 3a was set (from 800 l / min to 900 l / min).

table 1 shows the chemical composition of the layer system produced FeWCrNiMoCSi after the different experiments.

table 2 shows the carbide content of the samples used.

The microstructural micrograph of the FeWCrNiMoCSi coating according to experiment # 2 (corresponding to Table 1), which in 1 shows homogeneously distributed carbides, no unmelted particles and a very dense layer with a very low porosity of <1%.

The microstructural micrograph of the FeWCrNiMoCSi coating according to experiment # 3a (corresponding to Table 1), which in 2 is shown, shows a thicker layer. This was achieved by a comparatively longer coating time.

at The investigations showed that by means of the diffractogram Although the carbide phases detected, but no differentiation between a carbide concentration of 20% by weight or 40% by weight could be.

As Table 3 shows, first experiments have shown that the layers a porosity of <1-2% at a hardness from about 695 HV0.1 for the carbide-free Fe base material up to 1178 HV0.1 for the Fe base Have material with a carbide content of 60 wt.%. Additionally were measured the residual stresses occurring during the coating. The addition of up to 40% by weight of carbides causes a change the residual stresses with hardly changed Hardness values. The roughness data refer to the layer roughness directly after spraying.

Around the tribological properties of the respective system were examined wear tests on the internal standard test system carried out. The test conditions were as follows:

Running Partner: Gray cast iron cylinder liner segment with a standard finish
Duration: 23 h
Frequency: 10 Hz
Path length: 20 mm
Oil temperature: 190 ° C
Lubricant: unadditized oil

Table 4 shows the relative improvement in wear by the addition of different carbide levels, each after completion of the experiment. The addition of carbides thus allows a targeted adjustment of the hardness, the compressive residual stresses and the wear properties of the ring and the cylinder liner. In addition, despite the high loads during the wear test, the microstructure is largely retained, which basically points to a wear-resistant piston ring produced by this coating according to the invention for the system "ring / bushing lubricated" ( 4 and 5 ).

4 shows a cross-section of an HVOF-sprayed FeWCrNiMoCSi layer according to experiment # 3a from Table 1 on a piston ring before carrying out the wear test.

5 shows a cross-section of a HVOF sprayed FeWCrNiMoCSi layer according to experiment # 3a on a piston ring after the wear test.

The Layer system of the invention is for all common piston ring geometries suitable.

Also are by means of the invention layer thicknesses in the range 20-1000 microns for a finished machined piston ring feasible.

The Invention further offers the following advantages. The new powder is about 25-40% better as that conventional to disposal asked Mo-based powder, so that the production of the piston rings and the end products cheaper fail. The separation efficiency (DE value) of layer systems according to the invention is 50-59%.

• ^(*)bezogen auf den maximalen Verschleiß in axialer Richtung

Initial machining experiments on piston rings produced according to the invention have shown that the rings coated with the HVOF layer are at least as good machinable as conventionally Mo-based plasma-sprayed rings. attempt Carbide content target Chemical composition Fe W Cr Ni Not a word C Si # (Wt%) (Wt.%) 1 0 47.5 0 28 17 4.6 1.8 1.1 2 20 35.7 11.2 30.2 15.2 3.8 3.1 0.8 3a 40 23.9 22.5 33.2 12.4 2.6 4.9 0.5 3b 40 23.9 22.5 33.2 12.4 2.6 4.9 0.5 4 60 11.4 33.8 34.8 11.7 2.3 5.7 0.3 Table 1 attempt carbide Individual carbides WC Cr3C2 Should is is # (Wt.%) (Wt.%) 1 0 0 0 2 20 9 13 3a 40 17.5 25 3b 40 17.5 25 4 60 26 37.5 Table 2 attempt Carbide content target HV0.1 porosity Residual stress # (Wt.%) % [.Mu.m] 1 0 695 <1 -110 2 20 760 <1 -18 3a 40 824 <1 -26 3b 40 841 <1 57 4 60 1178 <2 102 Table 3 Wear value - relative improvement ^(*) comment ring liner Development layer 1 from experiment 1 1 1 without carbides Development layer 2 from experiment 2 3.9 1.2 20% by weight of carbides Development Layer 3 From Experiment 3a 13.1 1.1 40% by weight of carbides Table 4

• ^(*) related to the maximum wear in the axial direction

Claims (15)

Piston ring for an internal combustion engine, comprising A substrate; and A coating, available by thermal spraying of a powder comprising the elementary parts 20-40 weight percent Iron, Fe; 0-30 Weight percent tungsten, W; 20-40 weight percent chromium, Cr; 10-20 Weight percent nickel, Ni; 1-5 weight percent molybdenum, Mo; 1-8 weight percent Carbon, C; and 0.1-2 Weight percent silicon, Si. Piston ring according to claim 1, wherein the element portion of iron is at least 25 percent by weight. A piston ring according to claim 1 or 2, wherein the content of carbides is 20-70% by weight composed of 0-30% by weight of tungsten carbide, WC, and 20-40% by weight of chromium carbide, Cr ₃ C ₂ . Piston ring according to one of the preceding claims, wherein the particle sizes of the Powders are in the range of 1-100 microns. Piston ring according to one of the preceding claims, wherein the carbides are embedded in a nickel-chromium matrix and a Particle size of 0.5-5 microns have. Piston ring according to one of the preceding claims, wherein the layer thickness of the coating is in the range of 20-1000 microns. Piston ring according to one of the preceding claims, wherein the thermal spraying process high-speed flame spraying or plasma spraying. Piston ring according to one of the preceding claims, wherein the piston ring is a cast or steel piston ring. Method for producing a piston ring for an internal combustion engine, full - Provide a substrate; - coating of the substrate by thermal spraying a powder the elementary parts 20-40 Weight percent iron, Fe; 0-30 wt% tungsten, W; 20-40 weight percent Chromium, Cr; 10-20 Weight percent nickel, Ni; 1-5 weight percent molybdenum, Mo; 1-8 weight percent Carbon, C; and 0.1-2 Weight percent silicon, Si. The method of claim 9, wherein the element portion of iron is at least 25 percent by weight. A method according to claim 9 or 10, wherein the content of carbides is 20-70% by weight composed of 0-30% by weight of tungsten carbide, WC, and 20-40% by weight of chromium carbide, Cr ₃ C ₂ . Method according to one of claims 9 to 11, wherein the particle sizes of the Powders are in the range of 1-100 microns. Method according to one of claims 9 to 12, wherein the carbides in a nickel-chromium matrix are embedded and have a particle size of 0.5-5 microns. Method according to one of claims 9 to 13, wherein the layer thickness of the coating in the range of 20-1000 microns. Method according to one of claims 9 to 14, wherein the thermal Spray method High-speed flame spraying or plasma spraying includes.