CN107858680B

CN107858680B - Method for reducing residual stress of laser cladding metal coating

Info

Publication number: CN107858680B
Application number: CN201710947554.6A
Authority: CN
Inventors: 赵剑峰; 王冠军; 谢德巧; 梁绘昕; 田宗军; 沈理达
Original assignee: Nanjing University of Aeronautics and Astronautics
Current assignee: Nanjing University of Aeronautics and Astronautics
Priority date: 2017-10-12
Filing date: 2017-10-12
Publication date: 2021-02-05
Anticipated expiration: 2037-10-12
Also published as: CN107858680A

Abstract

The invention discloses a method for reducing the residual stress of laser cladding metal coating. Before cladding, the invention prefabricates regularly arranged groove microstructures on the base material, and the laser focus falls on the center of two adjacent grooves where the melting channel and the groove are parallel to each other. The invention is suitable for the laser cladding technology, and is characterized in that the residual stress of the formed parts is low, cracks, cracks and warpage deformation are effectively avoided, no additional equipment is required, and the operation is simple.

Description

Method for reducing residual stress of laser cladding metal coating

Technical Field

The invention relates to the field of laser processing, in particular to a method for reducing residual stress of a laser cladding metal coating.

Background

Laser cladding is a method for cladding metal powder on a base material by using high-energy laser beams to prepare a metal coating, and the method has the advantages of high bonding strength with the base material, low dilution rate, high hardness, wear resistance, corrosion resistance and the like. In recent years, the surface modification and reinforcement of key metal parts based on the technology is becoming a research hotspot and showing wide application prospects. However, due to factors such as uneven laser energy distribution, large temperature gradient and large solidification rate in the cladding process, the laser-clad cermet layer has the defects of cracks and the like due to residual stress, and the cladding layer is easy to crack, so that the further popularization and application of the laser-clad cermet layer to the industrial field are severely restricted.

To solve this problem, researchers have taken the following four approaches:

firstly, optimizing process parameters from the aspects of laser power, spot diameter, scanning speed, lap joint rate, scanning strategy and the like, and changing the stress distribution in a workpiece so as to reduce residual stress, but the mechanical property of the workpiece cannot be considered;

secondly, a preheating module is added on the forming base material, and the bottom of the base material is heated before the base material is scanned by laser, so that the temperature gradient between the forming part and the base material workpiece is reduced, and the residual stress caused by overlarge temperature gradient is reduced, but the complexity of equipment and the difficulty of control are increased by preheating the base material;

thirdly, post-treatment such as hot isostatic pressing and stress relief annealing is carried out on the formed part to eliminate residual stress in the formed part, and although the residual stress can be reduced to a certain extent, the formed part still deforms and cracks after being processed, so that the prevention effect cannot be achieved;

fourthly, oxides such as MgO, CeO2 and Y2O3 are doped in the cladding process to reduce residual stress, but the oxide doping causes complex process, low production efficiency and high processing cost.

In summary, the prior art lacks a simple and low-cost method for effectively reducing residual stress and preventing the metal melt layer from cracking.

Disclosure of Invention

The invention provides a method for reducing the residual stress of a laser cladding metal coating, which can reduce the residual stress of the metal melting coating and avoid the problem of cracking of the metal melting layer by a simple and easy method with low cost.

A method of reducing residual stress of a laser clad metal coating, comprising:

s1, fixedly mounting the base material on the processing bottom plate;

s2, scanning the surface of the base material by laser and ablating a groove;

s3, starting a powder feeding system, and paving metal powder in the groove;

and S4, enabling the laser focus to fall on the center of the adjacent groove, solidifying the metal powder after laser melting to form a melting channel, and coating the metal powder on the surface of the base material after cladding to form a cladding layer.

Further, the dimensions of the trench are: the depth d is 1-3 mm, the width b is 1-2 mm, and the distance a is 1-5 mm.

Further, the grooves are parallel to each other and to the direction of the laser scanning.

Further, the metal powder comprises the following materials: copper-based materials, iron-based materials, cobalt-based materials, nickel-based materials, aluminum-based materials, intermetallic-based materials.

Furthermore, the granularity of the metal powder is-100 to +300 meshes

Furthermore, the laser power is 500-10000W, the scanning speed is 1-10 mm/s, the spot diameter is 1-5 mm, and the protective gas is inert gas.

Furthermore, when the substrate is a plane type, the groove is of a grid type and a boundary offset type; when the base material is a multi-surface type, the groove is of a boundary offset type; when the substrate is a revolving body, the groove is spiral.

The invention has the beneficial effects that: the groove structures which are regularly distributed are prefabricated on the base material, the uniform grooves can effectively release the constraint of thermal strain of the cladding layer, the residual stress accumulation is reduced, the residual stress level is reduced, the generation of cracks is inhibited, and the problems of cracks and cracking are effectively avoided.

Drawings

In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings needed to be used in the embodiments will be briefly described below, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and it is obvious for those skilled in the art that other drawings can be obtained according to the drawings without creative efforts.

FIG. 1 is a schematic diagram of an apparatus suitable for use in accordance with an embodiment of the present invention;

FIG. 2 is a schematic view of the structure between cladding channel trenches;

FIG. 3 is a schematic view of a trench structure;

FIG. 4 is a graph comparing example cladding track cracks;

FIG. 5 is a metallographic comparison of a cross section of a cladding layer according to an example;

FIG. 6 is a statistical chart of the dry sliding wear resistance of the cladding layer of the examples.

1-bottom plate, 2-base material, 3-groove, 4-deposition layer, 5-powder feeding system, 6-laser system, 7-powder conveying pipeline, 8-laser conveying pipeline, 9-powder feeding groove, 10-powder feeding nozzle and 11-laser.

Detailed Description

In order that those skilled in the art will better understand the technical solutions of the present invention, the present invention will be further described in detail with reference to the following detailed description.

The device suitable for the embodiment of the invention is shown in fig. 1, and comprises: the powder feeding device comprises a bottom plate 1, a base material 2, a groove 3, a deposition layer 4, a powder feeding system 5, a laser system 6, a powder conveying pipeline 7, a laser conveying pipeline 8, a powder feeding groove 9 and a powder feeding nozzle 10.

The base plate 1 is fixedly provided with a base material 2, and the base material 2 is provided with a groove 3 by burning. The powder feeding system 5 and the laser system 6 are connected with a powder feeding groove 9 through a powder conveying pipeline 7 and a laser conveying pipeline 8, and a powder feeding nozzle 10 is arranged at the tail end of the powder feeding groove 9. The powder feeding nozzle 10 sprays metal powder to cover the surface of the base material 2, the laser 11 melts the metal powder to form a cladding channel, and as shown in fig. 2, the molten metal powder in the cladding channel and the groove forms a deposition layer 4.

A method of reducing residual stress of a laser clad metal coating, comprising:

s1, fixedly mounting a 316L stainless steel base material on the processing bottom plate, wherein the size of the base material is 100 multiplied by 10 mm.

S2, scanning and ablating a groove on the surface of the base material by laser, wherein in the drawing, the groove is 1mm in depth, 1mm in width, 5mm in spacing and 100mm in length, as shown in FIG. 3; the laser power is 2300W, the scanning speed is 10mm/s, and the shielding gas velocity is 25L/min.

S3, starting a powder feeding system, wherein the powder feeding rate is 60g/min, and tungsten carbide metal powder WC/Ni60 (60% WC) is paved in the groove, and the powder particles are 200 um.

And S4, enabling the laser focus to fall at the center of the adjacent groove, enabling the diameter of a light plate of the laser to be 5mm, enabling the lap joint rate to be 5%, and cladding the metal powder by the laser to obtain a cladding layer.

Performing dye penetrant inspection on the cladding sample piece, and analyzing the number of macrocracks; fig. 4(a) is a distribution diagram of the cracks of the cladding channel when the substrate has no groove, and fig. 4(b) is a distribution diagram of the cracks of the cladding channel when the substrate has a groove.

Comparing and observing the microstructure of the cladding layer by using an optical microscope; fig. 5(a) is a cross-sectional metallographic image of the cladding channel when the substrate has no groove, and fig. 5(b) is a cross-sectional metallographic image of the cladding channel when the substrate has a groove.

And (3) carrying out a dry sliding wear test, comparing the friction resistance of the pure laser cladding layer with that of the texture laser cladding layer by adopting a weighing method, wherein fig. 6 is a statistical graph of the dry sliding wear resistance of the cladding layer, and under the same laser process condition, the wear quality of the texture cladding layer is about 7/10 of that of the laser cladding layer, namely the wear resistance of the texture cladding layer is about 1.4 times that of the laser cladding layer.

To sum up: the groove structure can effectively release the constraint of thermal strain of the cladding layer, reduce residual stress accumulation, reduce the level of residual stress and inhibit the generation of cracks, and compared with the cladding layer of a non-groove base material, the wear resistance is obviously improved.

The invention has the beneficial effects that:

(1) the residual stress of a formed part can be obviously reduced, and the phenomena of cracks, cracking and warping deformation are effectively avoided;

(2) the bonding strength between the cladding layer and the base material is high;

(3) the invention is realized without complex equipment and is simple to operate.

The above description is only for the specific embodiment of the present invention, but the scope of the present invention is not limited thereto, and any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope of the present invention are included in the scope of the present invention. Therefore, the protection scope of the present invention shall be subject to the protection scope of the claims.

Claims

1. a method for reducing residual stress of laser cladding metal coating, characterized in that, comprising:

S1. Fix the base material on the processing base plate;

S2, the laser scans and ablates grooves on the surface of the substrate;

S3, open the powder feeding system, and cover the metal powder in the groove;

S4. The laser focus falls on the center of the adjacent groove, and the laser clads the metal powder to obtain a cladding layer.

2. The method for reducing residual stress of laser cladding metal coating according to claim 1, wherein the dimensions of the groove are: depth d=1～3mm, width b=1～2mm, spacing a=1~5mm.

3 . The method for reducing residual stress of laser cladding metal coating according to claim 1 , wherein the grooves are parallel to each other and parallel to the scanning direction of the laser. 4 .

4. The method for reducing residual stress of laser cladding metal coating according to claim 1, wherein the material of the metal powder comprises: copper-based material, iron-based material, cobalt-based material, nickel-based material , aluminum-based materials, intermetallic compound-based materials.

5. The method for reducing residual stress of laser cladding metal coating according to claim 4, wherein the particle size of the metal powder is -100～+300 mesh, and the laser power is P=500～ 10000W, the scanning speed is v=1~10mm/s, the spot diameter is D=1~5mm, and the protective gas is inert gas.

6. The method for reducing residual stress of laser cladding metal coating according to claim 1, wherein when the base material is a plane type, the grooves are a grid type and a boundary offset type; When the base material is a polygonal type, the groove is a boundary offset type; when the base material is a gyratory body, the groove is a spiral shape.