阅读说明：本技术 一种钛合金表面氮化层的激光修复方法 (Laser repairing method for titanium alloy surface nitride layer ) 是由 姚建华 张天亮 吴国龙 陈智君 董刚 于 2020-11-05 设计创作，主要内容包括：本发明结合选区激光熔化技术和激光气体氮化技术提出一种针对钛合金表面氮化层修复的方法,完成修复后区域无裂纹,且与相临氮化层和基体之间有良好的冶金结合；本发明首先对存在缺陷的氮化层区域进行铣削加工,在加工后的凹槽处预置钛合金粉末,利用小光斑激光器辐照待加工区域,同时沿着工件表面提供一定浓度的氮气源,使钛合金粉末熔化再凝固为金属实体的同时进行气体氮化,以达到填补铣削加工区域并修复氮化层的目的。(The invention provides a method for repairing a titanium alloy surface nitrided layer by combining a selective laser melting technology and a laser gas nitriding technology, so that the repaired area has no crack, and the repaired area has good metallurgical bonding with an adjacent nitrided layer and a substrate; the method comprises the steps of firstly milling a defective nitride layer area, presetting titanium alloy powder at the processed groove, irradiating the area to be processed by using a small-spot laser, and simultaneously providing a nitrogen source with a certain concentration along the surface of a workpiece, so that the titanium alloy powder is melted and then solidified into a metal entity, and simultaneously gas nitriding is carried out, thereby achieving the purposes of filling the milled area and repairing the nitride layer.)

1. A laser repairing method for a titanium alloy surface nitride layer is characterized by comprising the following steps:

(1) pretreatment: milling to remove the defect area of the nitride layer on the surface of the titanium alloy workpiece, cleaning, and airing to obtain an area to be processed;

(2) laser processing: laying preset titanium alloy powder in an area to be processed, carrying out selective laser melting on the powder layer, and simultaneously providing a nitrogen source to enable the powder layer to simultaneously generate a nitride layer in the forming process;

in the selective laser melting process, the focal length of a laser is 510-530 mm, the laser power is 300-500W, the line spacing is 0.16-0.28 mm, and the scanning speed is 100-300 mm/s; the laser is a vibrating mirror continuous fiber laser;

synchronously feeding a nitrogen source in a direction parallel to the surface of the workpiece in the laser processing process, wherein the nitrogen source is a mixed working gas of nitrogen and argon;

(3) and (3) post-treatment: and grinding the repair area to remove the area higher than the original nitride layer, so that the original size precision of the processed part is restored.

2. The laser repairing method of titanium alloy surface nitride layer according to claim 1, wherein in step (1), milling depth is controlled to be 0.2-0.4 mm each time relative to the original surface of the workpiece, and flaw detection is performed after milling is completed to ensure that no crack exists in the area to be processed; and if the defects still exist after flaw detection, continuing milling until the surface defects are removed to obtain a flat area to be processed, and then cleaning and airing the area to be processed by using ethanol.

3. The laser repairing method for titanium alloy surface nitride layer according to claim 1, wherein the titanium alloy in step (1) is Ti-6Al-4V, the titanium alloy powder in step (2) is Ti-6Al-4V, and the Ti-6Al-4V component is Al: 5.5-6.8%; v: 3.5-4.5%; fe is less than or equal to 0.3 percent; c is less than or equal to 0.1 percent; h is less than or equal to 0.015 percent; n is less than or equal to 0.05 percent; o is less than or equal to 0.2 percent; the balance being Ti.

4. The laser repairing method for titanium alloy surface nitride layer according to claim 1, wherein in the step (2), the thickness of the powder layer laid in one time is 0.1-0.2 mm.

5. The laser repairing method of titanium alloy surface nitride layer according to claim 1, wherein step (2) repeats the laser processing step until the repaired area is 0 to 0.2mm higher than the original surface.

Technical Field

The invention belongs to a method for repairing a nitride layer, and particularly relates to a laser repairing method for a nitride layer on the surface of a titanium alloy.

Background

The titanium alloy has the advantages of high specific strength, good corrosion resistance and the like. The preparation of the nitrided layer on the surface of the titanium alloy is realized by a certain processing method, so that nitrogen elements are diffused inwards from the surface of a workpiece to be processed, and finally, the nitrided layer with high melting point, high hardness, high temperature chemical stability and good wear resistance and heat conductivity is formed. When a workpiece made of the titanium alloy material faces a severe working environment, the preparation of the nitriding strengthening layer is a surface protection means for strengthening the performance of the workpiece. The conventional processing methods for preparing such nitride layers are solid nitriding and laser gas nitriding, and the latter has higher nitriding efficiency than the former and can selectively control the nitrided area.

Aiming at the titanium alloy workpiece with the surface nitride layer protective layer, under the environment of high use frequency and long working time, the surface coating inevitably has the defects of abrasion, cracks and the like, and finally leads the coating of a part of the area to lose efficacy, thereby damaging the performance of the base part of the part. The laser repairing method of the nitride layer with the selectivity can ensure that the damaged nitride layer is completely repaired, and the nitride layer can achieve good metallurgical bonding, thereby greatly prolonging the service life of the titanium alloy workpiece containing the nitride layer.

Disclosure of Invention

Aiming at the condition that the nitride layer on the surface of the titanium alloy workpiece has defects, the invention provides a laser repairing method for the nitride layer on the surface of the titanium alloy workpiece. The method comprises the steps of firstly milling a nitrided layer area on the surface of the titanium alloy with defects until the defective part is completely removed, then laying preset titanium alloy powder on the milled part, feeding mixed working gas of nitrogen and argon parallel to the surface of the nitrided layer, solidifying the powder layer into an entity by utilizing the laser action, filling the milled area, and simultaneously preparing the required nitrided layer.

The technical scheme of the invention is as follows:

a laser repairing method for a titanium alloy surface nitride layer comprises the following steps:

(1) pretreatment: milling to remove the defect area of the nitride layer on the surface of the titanium alloy workpiece, cleaning, and airing to obtain an area to be processed;

preferably, the milling depth of each time is controlled to be 0.2-0.4 mm relative to the original surface of the workpiece, and flaw detection is carried out after milling is finished to ensure that no crack exists in a region to be processed; if defects still exist after flaw detection, continuing milling until the defects such as surface scratches, cracks and the like are removed to obtain a flat area to be processed, and then cleaning and airing the area to be processed by using ethanol;

the titanium alloy is Ti-6Al-4V, and the components are Al: 5.5-6.8%; v: 3.5-4.5%; fe is less than or equal to 0.3 percent; c is less than or equal to 0.1 percent; h is less than or equal to 0.015 percent; n is less than or equal to 0.05 percent; o is less than or equal to 0.2 percent; the balance being Ti;

(2) laser processing: laying preset titanium alloy powder in an area to be processed, carrying out selective laser melting on the powder layer, and simultaneously providing a nitrogen source to enable the powder layer to simultaneously generate a nitride layer in the forming process;

preferably, the thickness of the powder layer laid once is 0.1-0.2 mm;

the titanium alloy powder is Ti-6Al-4V, and the components are Al: 5.5-6.8%; v: 3.5-4.5%; fe is less than or equal to 0.3 percent; c is less than or equal to 0.1 percent; h is less than or equal to 0.015 percent; n is less than or equal to 0.05 percent; o is less than or equal to 0.2 percent; the balance being Ti; the titanium alloy powder is spherical powder prepared by an aerosol method, the particle size is 45-106 mu m, the powder purity is 99.9%, and the titanium alloy powder is dried in a vacuum drying oven at 120 ℃ for 120min before use;

in the selective laser melting process, the focal length of a laser is 510-530 mm, the laser power is 300-500W, the line spacing is 0.16-0.28 mm, and the scanning speed is 100-300 mm/s; the laser is a vibrating mirror continuous fiber laser;

synchronously feeding a nitrogen source in a direction parallel to the surface of the workpiece in the laser processing process, wherein the nitrogen source is a mixed working gas of nitrogen and argon, and the proportion of nitrogen in the mixed working gas means the nitriding degree and is adjusted according to actual conditions;

preferably, the laser processing step is repeated until the repair area is 0-0.2 mm higher than the original surface;

(3) and (3) post-treatment: and grinding the repair area to remove the area higher than the original nitride layer, so that the original size precision of the processed part is restored.

Compared with the prior art, the invention has the beneficial effects that:

1. the repair area can achieve good metallurgical bonding with the workpiece and the nitride layer.

2. All processes are not required to be carried out in a sealed environment, the requirement on the processing environment is low, and the efficiency of the processing process is high.

3. The repaired nitrided layer has no crack defect, the wear resistance, corrosion resistance and high-temperature chemical stability of the repaired nitrided layer can meet the original requirements, the original protective effect of the nitrided layer can be well replaced, the use cost is low, and the service life of a workpiece is prolonged.

Drawings

FIG. 1 is a schematic view of the process of the present invention.

Detailed Description

The present invention is further illustrated by the following specific examples, but the scope of the invention is not limited thereto.

Powder selection: the laid preset powder is Ti-6Al-4V titanium alloy powder prepared by an aerosol powder preparation process, and comprises the following components (5.5-6.8% of Al, 3.5-4.5% of V, less than or equal to 0.3% of Fe, less than or equal to 0.1% of C, less than or equal to 0.015% of H, less than or equal to 0.05% of N, less than or equal to 0.2% of O, and the balance of Ti), the particle size is 45-106 microns, and the shape of the powder is spherical.

Laser selection: IPG continuous fiber laser model YLR-1500-MM-WC.

Pretreatment: milling to remove the defect area of the nitride layer on the surface of the titanium alloy workpiece, and cleaning and airing the area to be processed by using ethanol on the assumption that no crack is detected after the milling depth is 0.4mm relative to the original surface of the workpiece.

And (3) post-treatment: and grinding the repair area to remove the area higher than the original nitride layer, so that the original size precision of the processed part is restored.

Example one

Laser processing: and laying preset titanium alloy powder in the area to be processed, wherein the thickness of the powder layer laid once is 0.1 mm. In the selective laser melting process, the focal length of a laser is 520mm, the laser power is 300W, the line spacing is 0.16mm, the scanning speed is 100mm/s, and the scanning strategy is reciprocating scanning. And repeating the powder paving and laser processing steps for 5 times. And synchronously feeding mixed working gas of nitrogen and argon in a direction parallel to the surface of the workpiece in the laser processing process, wherein the total flow of the mixed gas is 15L/min. Wherein the nitrogen accounts for 20%, 40%, 80% and 40% of the mixed gas in sequence in the processing layer from bottom to top.

Example two

Laser processing: and laying preset titanium alloy powder in the area to be processed, wherein the thickness of the powder layer laid once is 0.15 mm. In the selective laser melting process, the focal length of a laser is 520mm, the laser power is 400W, the line spacing is 0.22mm, and the scanning speed is 200 mm/s. And repeating the steps of powder paving and laser processing for 3 times. And synchronously feeding mixed working gas of nitrogen and argon in a direction parallel to the surface of the workpiece in the laser processing process, wherein the total flow of the mixed gas is 15L/min. Wherein the nitrogen accounts for 20 percent, 40 percent and 80 percent of the mixed gas in the processing layer from bottom to top in sequence.

EXAMPLE III

Laser processing: and laying preset titanium alloy powder in the area to be processed, wherein the thickness of the powder layer laid once is 0.2 mm. In the selective laser melting process, the focal length of a laser is 520mm, the laser power is 500W, the line spacing is 0.28mm, and the scanning speed is 100 mm/s. The powder spreading and laser processing steps are repeated for 3 times. And synchronously feeding mixed working gas of nitrogen and argon in a direction parallel to the surface of the workpiece in the laser processing process, wherein the total flow of the mixed gas is 15L/min. Wherein the nitrogen accounts for 20 percent, 80 percent and 40 percent of the mixed gas in the processing layer from bottom to top in sequence.