Method for producing oxide layers which protect against wear and/or corrosion

Abstract

Method for producing oxide layers which protect against wear and/or corrosion on barrier layer-forming metals, preferably aluminum, magnesium and titanium, alloys and mixtures thereof by means of laser treatment, characterized in that on the surface a continuous near-surface oxygen-plasma is produced to form the oxide layer.

Claims

1. A method for producing oxide layers which protect against wear and/or corrosion on barrier layer-forming metals, comprising: irradiating a surface of a metal with a laser within an atmosphere to produce a continuous and near-surface oxygen plasma on the surface of said metal to form an oxide layer in which irradiation of said surface takes place with an interaction time between 0.0001 s and 0.1 s and a laser intensity between 510.sup.5 W/cm.sup.2 and 510.sup.6 W/cm.sup.2, and wherein the position of the workpiece does not deviate by more than 1/20 of focal width from focus, and also does so only in a negative focus direction.

Description

DRAWINGS

(1) FIG. 1 is a schematic drawing showing how the laser and oxygen interact and the basic material to form the plasma.

(2) FIG. 2 is a cross-section showing the difference of the influence of the plasma with the plasma-free regions.

(3) FIG. 3 is a schematic drawing showing a process for functional layer production using the plasma.

(4) FIG. 4 and FIG. 5 show surfaces achieved by interleaved or hatched laser interaction with the surface.

(5) FIG. 6 is a section view with the distance between strips of laser interaction of 0.175 mm.

(6) FIG. 7 is a section view of strips of laser interaction with the distance between the strips of 0.075 mm according to this disclosure.

(7) FIG. 8 is a diagram of intensity in W/cm.sup.2 of an interaction time in seconds with a logarithmic scale showing the region I in accordance with this disclosure.

DETAILED DESCRIPTION

(8) An exemplified method is intended to serve hereinunder to illustrate implementation in accordance with this disclosure: The laser used is a commercially available 400 W fibre laser from IPG-Laser with a wavelength of 1070 nm and a spot diameter in the focus of 0.1 mm. The laser beam is controlled by a scan head of the RHINO type with a focal width of 26 cm from the company Arges.

(9) The method is carried out within a chamber so that an oxygen atmosphere of 95%-100% is used.

(10) The component is in the focus and in order to ensure stable plasma its position should deviate at most by 1/20 of the focal width (in this case 1.3 cm).

(11) The substrate used is AlSi12 with a commercially available ground surface. With this alloy, intensities of 510.sup.5 W/cm.sup.2 to 1.510.sup.6 W/cm.sup.2 can be applied. Below this intensity no plasma is produced and above it the material begins to burn, the plasma is discoloured to white and a rough non-uniform layer is produced. For the example, an intensity of 1.510.sup.6 W/cm.sup.2 was used.

(12) Possible interaction times are 0.1 s to 0.0001 s, wherein in this case an interaction time of 0.0004 s was applied. The interaction time influences the duration of the process and the layer thickness to be achieved. If the interaction time is too short, no plasma is produced or it breaks down during the process or a very thin (<1 m) defective layer is produced.

(13) The distance between the individual strips when travelling down the surface of the substrate with the laser is 0.075 mm for this example in order to produce a closed layer (cf. FIG. 7).

(14) When selecting these parameters, 6400 J/cm.sup.2 laser power is applied to the material, whereby plasma is generated which produces a closed layer on the substrate by conversion of oxygen and aluminium to form corundum, the layer having a thickness between 3 and 6 m and a roughness depth <2 m.

COMPARATIVE EXAMPLE

(15) If, when using the same laser parameters, an interaction time of 0.00002 s is selected, no oxygen plasma is produced over the substrate and only remelting of the aluminium alloy takes place despite sufficient oxygen and sufficient laser intensity.