METHOD TO PRODUCE HIGH CORROSION AND WEAR RESISTANT CAST IRON COMPONENTS BY USING LASER CLADDING

Abstract

A method to produce a wear and corrosion resistant coating system onto a surface of a substrate, preferably a brake disc, comprising the following steps: (1) providing the substrate having the surface made of an iron-based material or a steel material, (2) selecting a dedicated material for producing one or more coating layers of the coating system, (3) producing onto the substrate surface one or more coating layers of the coating system by using a laser cladding process, wherein the dedicated material selected in step (2) is used as source material for the production of the coating layers, and positioning a laser beam with respect to the substrate surface in such a manner that a coating angle is formed between the laser beam and the substrate surface, and maintaining this coating angle during the production of the one or more coating layers at a value between 10° and 30°.

Claims

1. A method to produce a wear and corrosion resistant coating system onto a surface of a substrate, the method comprises comprising the following steps: (1) providing the substrate having the surface to be coated with the coating system, (2) selecting a dedicated material for producing one or more coating layers of the coating system, (3) producing onto the substrate surface to be coated one or more coating layers of the coating system by using a laser cladding process, wherein the dedicated material selected in step (2) is used as a source material for the production of the coating layers, wherein for conducting step (3) a laser beam is positioned with respect to the substrate surface to be coated in such a manner that an angle is formed between the laser beam and the substrate surface to be coated and this angle is called a coating angle, and the coating angle is maintained during the production of the one or more coating layers at a value between 10° and 30°, and wherein the substrate or at least the surface of the substrate is made of an iron-based material or a steel material.

2. The method according to claim 1, wherein the substrate material is a cast iron material.

3. The method according to claim 1, wherein the substrate is a brake disc.

4. The method according to claim 1, wherein the laser cladding process in step (3) is conducted by implementation of high laser power levels which are in a range between 10 kW and 30 kW.

5. The method according to claim 1, wherein the laser cladding process in step (3) is conducted by using high process speeds which are in a range between 100 m/min and 200 m/min.

6. The method according to claim 1, wherein the laser cladding process in step (3) is conducted by using a high deposition rate which is in a range between 500 cm.sup.2/min and 1200 cm.sup.2/min.

7. The method according to claim 2, wherein before conducting the step (3), a pre-treatment process is conducted, said pre-treatment process comprising a step in which graphite lamellae are reduced or removed from the substrate for increasing weldability of the substrate material.

8. The method according to claim 7, wherein the pre-treatment process involves surface activation of the substrate material by using a pulsed fluid jet process.

9. The method according to claim 1, wherein the coating system comprises only one coating layer produced by using laser cladding.

10. The method according to claim 1, wherein the coating system comprises two or more coating layers produced by using laser cladding.

11. The method according to claim 9, wherein the coating system consists of the only one coating layer produced by using laser cladding.

12. The method according to claim 10, wherein the coating system consists of the two or more coating layers produced by using laser cladding.

13. The method according to claim 1, wherein after conducting the step (3), a post-treatment process is conducted, said post-treatment process comprising a step in which a diffusion layer is produced by using a nitrocarburizing process, in order to protect the uncoated surfaces of the substrate.

14. The method according to claim 1, wherein after conducting the step (3), a post-treatment process is conducted, said post-treatment process comprising a nitrocarburizing process and oxidation process in order to improve corrosion and wear resistance of uncoated surfaces of the substrate.

Description

DESCRIPTION OF THE FIGURES

[0052] FIG. 1 shows a brake disc of cast iron without any coating. The brake disc surface is therefore significantly exposed to corrosion, wear and consequently fine dust emissions during the performance. For these reasons, a coating solution is recommendable needed to reduce the corrosion and wear and to prolong the lifetime of the brake disc part

[0053] FIG. 2 shows a brake disc of cast iron with a thermal spray coating. The process efficiency is less than 50% and the coating system is complex. Rough surface activation is needed to achieve acceptable adhesion between coating and substrate since in contrast to laser cladding there is no metallurgical bonding in thermal spray process. Laser cladding has two major advantages compared to thermal spray: 1. Process efficiency higher than 90% in laser cladding and 2. Metallurgical bonding between coating and substrate in laser cladding guarantees the enough bond strength of the coating and cast iron

[0054] FIG. 3 shows a brake disc of cast iron with one laser cladding coating deposited as monolayer by using a EHLA process, without pre-treatment and also without post treatment. FIG. 3a) shows the substrate surface with the coating just after deposition of the coating, without being subjected to any subsequent process; FIG. 3b) shows the same coated substrate shown in FIG. 3a but after grinding; FIG. 3c) shows a brake disc of cast iron coated according to the present invention, with one laser cladding coating deposited as monolayer by using a EHLA process, wherein for producing the coating as dedicated material a Metco®Brake powder was used; 3d) shows an augmentation of the picture of the coating shown in FIG. 3c), in which the very uniform hard-phase distribution in the coating structure can be observed.

[0055] FIG. 4 shows a brake disc of cast iron coated according to the present invention with one laser cladding coating deposited in multiple runs, without pre-treatment and also without post treatment.

[0056] FIG. 5 shows a brake disc of cast iron coated according to the present invention with one laser cladding coating deposited in multiple runs with pre-treatment. Interface quality has been significantly improved due to reduction of graphite lamellas by pre-treatment.

[0057] FIG. 6 shows a brake disc of cast iron deposited according to the present invention, with one laser cladding coating deposited as monolayer in one run, wherein a posttreatment was conducted after coating deposition; 6a) shows the substrate surface coated and post-treated; 6b) shows the substrate surface that during coating could not be coated but which was modified during post-treatment, 3 different layers were formed: one oxide layer, one white layer and one diffusion layer, these three layers were formed in the cast iron uncoated substrate surface due to the post-processing to protect the uncoated areas such as ventilation channels.

[0058] FIG. 7 shows a brake disc of cast iron deposited according to the present invention, with one laser cladding coating deposited as monolayer in multiple runs one run, wherein a pretreatment and a posttreatment was conducted previous to coating deposition; 6a) shows the substrate surface coated and a reduction of graphite lamellas at the interface can be observed; 6b) shows the substrate surface that during coating could not be coated but which was modified during post-treatment, 3 different layers were formed: one oxide layer, one white layer and one diffusion layer, these three layers were formed in the cast iron uncoated substrate surface due to the post-processing to protect the uncoated areas such as ventilation channels.

[0059] Break discs of cast iron were deposited with methods according to the present invention.

[0060] In some inventive examples, brake discs of cast iron were coated with monolayers laser cladding coatings having total coating layer thickness in a range between 150 to 500 .Math.m, the porosity according to ASTM E2109-01 was ≤ 0.5%, the average microhardness was about 350 HV, the deposition efficiency by using a EHLA process with process parameters in the inventive ranges was ≥90%, the wear life (AK master) was increased attaining a wear life higher than uncoated gray iron brake discs in more than 10-times, the corrosion resistance (ASTM B117) was ≥ 1000 h. In some of these examples as dedicated material a Metco®Brake powder was used.