Laser nanostructured surface preparation for joining materials

Abstract

A joined article includes a first component having a laser-treated surface portion and a second component having a laser-treated surface portion. An adhesive joins the first component to the second component at the treated surface portion. A method of making a joined article form components and a system for making joined articles are also disclosed.

Claims

1. A joined article, comprising: a first component having an interference laser-treated surface portion; a second component having an interference laser-treated surface portion; and, an adhesive joining the first component to the second component at the interference laser-treated surface portions; wherein the interference laser-treated surface portions comprise ridge features, wherein the ridge features have a periodicity between 0.5-50 μm, and wherein the periodicity varies by no more than ±5%.

2. The joined article of claim 1, wherein the interference laser-treated surface portions comprise features comprising at least one selected from the group consisting of depressions, channels and holes.

3. The joined article of claim 1, wherein the interference laser is a multiple-beam interference laser, wherein an original laser beam is split into at least 2 beams which are then refocused over the same spot on the surface of each component.

4. The joined article of claim 1, wherein the joined article treated according to the invention has a tensile strength that is at least 10% greater than a baseline tensile strength of an untreated article.

5. The joined article of claim 1, wherein the joined article includes a carbon-fiber polymer composite component and has a displacement of failure that is at least 100% greater than a baseline joint of an untreated article.

6. The joined article of claim 1, wherein the interference laser-treated surface portion of the first component and the interference laser-treated portion of the second component are dissimilar materials.

7. A joined article, comprising: a first component having an interference laser-treated surface portion; a second component having an interference laser-treated surface portion; and, an adhesive joining the first component to the second component at the treated surface portions; wherein one of the interference laser-treated surface portions comprises a carbon fiber material having carbon fibers embedded in resin and partially exposed from the resin, and wherein a surface portion of the resin has been removed by the interference laser treatment, and wherein the carbon fibers comprise interference laser-created grooves.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) There are shown in the drawings embodiments that are presently preferred it being understood that the invention is not limited to the arrangements and instrumentalities shown, wherein:

(2) FIG. 1 is a schematic diagram for the optical setup for two-beam interference.

(3) FIG. 2 is a schematic diagram for the optical setup for three-beam interference.

(4) FIG. 3 is a schematic diagram for an alternative optical setup for three or more beams interference.

(5) FIG. 4 is a schematic diagram of the alternating high-power and low-power profile created by wave interference for two-beam interference.

(6) FIG. 5 is a schematic diagram of the alternating high-power and low-power profile created by wave interference for three or more beams interference.

(7) FIG. 6 is a schematic diagram of a laser spot profile for a rastering mode with 5 mm/s rastering speed.

(8) FIG. 7 is a schematic diagram of a laser spot profile for a rastering mode with 10 mm/s rastering speed.

(9) FIG. 8 is a schematic diagram of a laser spot profile for a spot-by-spot mode with a beam size of 4 mm covering an area of 25×25 mm.

(10) FIG. 9 is a schematic diagram of a laser spot profile for a spot-by-spot mode with a beam size of 6 mm covering an area of 25×25 mm.

(11) FIG. 10 is a schematic diagram illustrating the effect of the invention on a carbon fiber polymer composite.

(12) FIG. 11 is a schematic diagram of the adhesive-resin interface for a carbon fiber polymer composite without laser structuring.

(13) FIG. 12 is a schematic diagram of the adhesive-resin interface for a carbon fiber polymer composite with laser structuring at 2 shots per spot.

(14) FIGS. 13 A-D are schematic diagrams illustrating the laser structuring of carbon fibers where A) is a perspective view; B) is a side view; C) is a top view; and D) is a vertical cross section through a vertical carbon fiber.

(15) FIG. 14 is a schematic diagram of the expected surface morphology induced through the laser-structuring of Al.

(16) FIGS. 15 A-C are schematic diagrams of surface profiles of A) unprocessed aluminum; B) aluminum processed using a 2 beam laser interference; and C) a cross section of the aluminum taken along line A-A of FIG. 15 B).

(17) FIG. 16 is a schematic diagram of a system for joining articles according to the invention.

(18) FIG. 17 is a schematic diagram of a joined article according to the invention.

(19) FIG. 18 is a plot of shear lap stress (psi) vs. displacement (in.) for an unstructured joint, a spot-by-spot laser-interference structure, and a laser-interference raster structure.

(20) FIG. 19 is a plot of shear lap strength (psi) for differing joint types (baseline, 2B-raster, 3B-raster and 3C-spot) for a first adhesive.

(21) FIG. 20 is a plot of shear lap strength (psi) for differing joint types (baseline, 2B-raster, 2B-spot(6) and 2B-spot(4)) for a second adhesive.

(22) FIG. 21 is a plot of shear lap strength (psi) for differing joint types (baseline, 2B-raster, and 2B-spot) for a third adhesive.

(23) FIG. 22 is a plot of bond length (mm) for differing joint types (baseline, 3C-spot, 2B-raster and 3B-raster) for a first adhesive.

(24) FIG. 23 is a plot of bond length (mm) for differing joint types (baseline, 2B-raster, 2B-spot(6) and 2B-spot(4)) for a second adhesive.

(25) FIG. 24 is a plot of bond length (mm) for differing joint types (baseline, 2B-raster, and 2B-spot) for a third adhesive.

DETAILED DESCRIPTION OF THE INVENTION

(26) A joined article includes a first component having a laser-treated surface portion and a second component having a laser-treated surface portion. An adhesive joins the first component to the second component at the treated surface portion. The laser-treated surface portions can include features comprising depressions, channels or holes. The features can have a periodicity. The laser-treated surface portion of the first component and the laser-treated portion of the second component can be dissimilar materials.

(27) The laser can be a multiple-beam interference laser, wherein an original laser beam is split into at least 2 beams, which are then refocused over the same spot on the component surface. The laser beam can be split into 3 or more beams.

(28) The laser-treated surface portions can include features or spots comprising depressions. The spots can have a periodicity. The periodicity can be well defined by the wavelength (λ) and the angle (α) between two beams:

(29) $d=\frac{\lambda }{2\sin \left(a/2\right)}$
The periodicity can be between 0.5-50 μm. The periodicity can vary by no more than ±5%. The laser patterns can be dot-, line-, and ring shaped.

(30) The laser treating can include between 1-50 laser pulses per spot. The laser treating can include laser-component translation or rastering with speeds between 1 to 500 mm/s. The wavelength of the laser light can be 180-2000 nm. The pulse duration can be between 10 fs-10 ns. The average power of the laser can be between 0.1-3,000 W.

(31) For example, with only 10 ns the laser pulse duration is very short, creating an extremely high peak power above 100 MW, resulting in greater than 10.sup.12K/s heating rates on a nickel/aluminum composite structure with a photothermal response. Materials showing a photochemical response ablate with minor temperature increase. Laser intensity, wavelength and pulse patterns can be tuned to achieve the optimum surface texture based on crack arrest criteria for preventing interfacial crack growth along the adhesive/aluminum interface.

(32) The invention is useful for joining metals, carbonaceous materials, polymeric materials, and ceramics. Examples of suitable metals include aluminum, titanium, magnesium, steels, and alloys thereof. Examples of carbonaceous materials include CFPCs, as well as other compound materials where a laser ablatable first material such as a resin has embedded therein a reinforcing or other material-property modifying second material that is resistant to laser ablation, such as carbon fiber and glass fiber. Examples of suitable ceramic materials include silicon carbide, hydroxyapatite, and alumina.

(33) The laser-treated surface portion of the first component and the laser-treated portion of the second component can be dissimilar materials. One of the laser-treated surface portions can include a CFPC material having carbon fibers embedded in resin. A surface portion of the resin can be removed by the laser treatment. The laser treatment can also produce laser-created features in the carbon fibers.

(34) The CFPC surface can be prepared by selectively ablating the resin rich surface layer and also ablating, to a pre-determined depth, the resin in the top fiber layers of the composite. The ablation depth can be between 3-50 μm. Laser intensity and wavelength can be tuned to remove resin without damaging the fibers. Thus, the untreated sharp adhesive/resin rich interface of the CFPC is replaced by a rough, fiber-reinforced interface through which the adhesive would bond more effectively. Additionally, the method of the invention will clean contaminants such as mold release agents, lubricant oils and oxides from the surface. After the laser scanning of contacting surfaces, CFPC composites would be joined to the opposing surface of the second component using an adhesive, interlocking the materials to form a joint between the CFPC of the first component and other material, for example aluminum, of the second component.

(35) The adhesive can be any suitable adhesive. Suitable adhesives include those based on epoxy, polyurethane, and acrylic, which are commonly used in the industry.

(36) The joined article treated according to the invention can have: (a) a tensile strength that is at least 10% greater than a baseline tensile strength of an untreated article, and/or (b) have an 100% increase in ductility, i.e., a 100% increase in the displacement at failure during shear-lap testing.

(37) FIG. 1 is a schematic depiction of three alternative optical setups for the two-beam interference. The optical components are: MS—mechanical shutter, BS—beam splitter, M—mirror, and L—lens. FIG. 2 is a schematic depiction of the optical setup for the multiple-beam interference.

(38) FIG. 3 is a schematic depiction of the optical setup for a femtosecond laser in which the interference patterns were produced using a diffractive beam splitter (DBS) and confocal imaging system with two convex lenses.

(39) FIG. 4 illustrates the alternating, high-power and low-power profile created by 2-beam wave interference, which yields localized melting and surface structuring. FIG. 5 illustrates the alternating, high-power and low-power profile created by multiple-beam wave interference (more than 3 beams), which yields localized melting and surface structuring.

(40) FIGS. 6-9 are schematic illustrations of the laser spots for a 25×25 mm coverage area. FIG. 6 is a depiction of features or spots created by a 5 mm/s rastering speed. FIG. 7 is a depiction of the feature pattern for a 10 mm/s rastering speed. The overlap distance of rows in FIGS. 6-7 is 1 mm. FIG. 8 is a depiction of the feature pattern created by the laser in spot-by-spot mode with a beam size of 4 mm. FIG. 9 is a depiction of the feature pattern created by the laser in spot-by-spot mode with a beam size of 6 mm.

(41) The optical micrographs of laser ablated CFPC specimens show that carbon fibers are directly exposed on both top surface and on side surfaces, creating an improved bonding surface for the adhesive. The laser structuring of CFPC addresses the prior problems related to CFPC joining with Al in which adhesive does not directly contact the CFPC but instead the resin rich layer on the CFPC and the inherent poor mechanical strength of that resin. The resin rich surface layer on the composite is also susceptible to Mode I fracture (delamination) sensitivity as the adhesive/resin interface relies only upon chemical bonding and is planar in nature. FIG. 10 illustrates the expected effects due to laser-structuring of CFPC, in which the resin rich near surface is removed along with mold release agents and surface contaminants to expose the carbon fibers to the adhesive. FIG. 11 is a rendering of the adhesive-resin interface of a baseline joint without laser structuring, and FIG. 12 illustrates the adhesive-resin interface of a joint in which the CFPC was laser-structured with 2 shots per spot. The adhesive directly contacts and engages the roughened surface created by the exposed carbon fibers.

(42) FIG. 13 illustrates the laser structuring of the carbon fibers themselves. FIG. 13A illustrates a fiber arrangement in which the carbon fibers at the surface are structured and those behind them are not structured. FIG. 13B is a side view illustrating the depth of the features relative to the fibers. FIG. 13C is a top view of the carbon fiber surface that is exposed to the adhesive. FIG. 13D is cross-section through a carbon fiber showing the periodic structuring. The depth of the grooves can be varied by increasing the laser power, and the periodicity can be changed by varying the angles between the beams.

(43) FIG. 14 is a schematic depiction of the expected surface morphology/topology induced through laser-structuring of Al. The shape including the aspect ratio, the periodicity and the distribution of the features can vary.

(44) FIG. 15 is a schematic depiction of 3-D surface profiles of an aluminum surface. FIG. 15A is a depiction of an as-received unprocessed aluminum surface. FIG. 15B and FIG. 15C are schematic depictions of a laser structured aluminum surface using a 2 beam laser interference technique with 10 pulses.

(45) A system for joining articles having at least first and second components is shown in FIG. 16. The system can include an interference laser 30, wherein an original laser beam is split into at least 2 beams, which are then refocused over the same spot on the component surface 34. A support 38 is provided for rigidly fixturing each of two or more components to be joined, and for registering the position of the first component and subsequent components relative to the laser 30. A drive 42 is provided for moving at least one of the laser 30 and the component support 38 relative to each other to apply features to a surface portion of each component. The system can further include a device for cleaning the surfaces of each component prior to adhesive application. The device can be a blower 44 for blowing air over the laser processed component surface.

(46) A joined article 50 according to the invention is shown in FIG. 17. The article 50 includes a first component 54 and a second component 58. The first component 54 can be a CFPC in which a surface portion has been removed to expose carbon fibers 62. The carbon fibers 62 that extend from the ablated resin surface 64 can have laser-structured features 66 formed therein. Spaces 68 between the exposed carbon fibers 62 also provide features for engaging the adhesive. The second component 58 can have features 70. An adhesive 74 is interposed between the first component 54 and the second component 58 and contacts the carbon fibers 62 and feature bordering the spaces 68, and also contacts the second component 58 and features 70.

(47) A method of making a joined article from components can include the step of treating a surface of a first component with a laser to create a treated surface portion. A surface of a second component can be treated with a laser to create a treated surface portion. An adhesive can be applied between the treated surface portion of the first component and the treated surface portion of the second component, and the treated surface portion of the first component can be joined to the treated surface portion of the second component.

(48) Experimental Setup

(49) Baseline joints were made without involving laser structuring by using Al and CFPC samples that were abraded using a ScotchBrite® pad and ultrasonically cleaned using ethanol. The baseline joints were used to assess the improvements in the joint strength for the joints produced with the laser-structured Al and CFPC. Both CFPC and Al specimens were laser-structured using the interference technique in as-received condition, without any additional surface preparation steps. Prior to joining, the laser-structured samples were not cleaned with any solvents. Two types of laser structuring were employed: (1) rastering, in which the laser beam was translated over the sample surface while the laser was on, and (2) spot-by-spot, in which the laser beam was held over each spot for a certain amount of time in order to allow multiple laser shots over the same area.

(50) A 10 Hz Q-switched Nd:YAG laser (Quanta-Ray PRO 230, Spectra Physics) was used to process specimens. The pulse width was 10 ns and the beam diameter was varied from 2 to 8 mm. The fundamental emission with the wavelength of 1064 nm was transformed to 355 nm and 266 nm using non-linear crystals. The maximum laser energy per pulse was 0.35 J at 355 nm and 0.04 J at 266 nm. The number of pulses is selected by a mechanical shutter. The primary laser beam was split into two beams and guided with mirrors onto the specimen surface. The laser interference power profile was created by guiding those beams to the sample surface by overlapping each other with defined angles to each other. The coherent beams create an interference pattern instead of adding their intensity. This allows a microscopic modulation and creates a light pattern without any loss of energy during the interference process.

(51) In some experiments, two identical focal lenses were used in each path of the splitted beam to focus laser beams from 8 mm to smaller sizes, hence increasing the laser pulse fluences. For the laser structuring of Al and CFPC nano-second lasers, the optimum pulse fluence of the laser can be 0.2 to 3 J/cm.sup.2. Periodic lines structures were formed on the surface by laser interference. The specimen was fixed on a translation stage capable of moving in horizontal and vertical directions. A LabVIEW based computer program was used to automatically control the location of the translation stage and the shutter opening time. During the experiments, the specimen attached to the translation stage was firstly moved to a predefined coordinate origin, followed by a shutter opening to transmit a certain number of laser pulses. For spot-by-spot structuring, the specimen was moved to the next position followed by another shutter opening. By repeating this procedure, an entire surface area of the specimen was processed. For the rastering mode, the shutter was open while the specimen was translated over the laser spot and laser fired shots with a 10 Hz frequency. After a horizontal line was completed, the shutter was closed and the specimen was moved to the start of the next line.

(52) A WYKO 9100 surface profilometer was used to obtain surface roughness data for the as-received CFPC. WYKO surface profilometer systems are non-contact optical profilers that use two methods to measure a wide range of surface topographical features. Phase-shifting interferometry mode allows the measurement of smooth surfaces and small steps, while vertical scanning interferometry mode allows the measurement of rough surfaces and steps up to several mm high. The surface profile shown of the as-received CFPC exhibited some grooves on its surface, approximately 9 μm deep, which may be generated from a previous processing step such as rolling. The average roughness, or arithmetical mean deviation of the roughness profile, Ra, root-mean-square deviation of the roughness profile, Rq, and maximum height of the roughness profile, Rt, were estimated.

(53) The examples utilize Al 5182 as one component and as the other component carbon fiber polymer composites (CFPC) made from Prepreg-T83 resin (epoxy) and T700S Carbon Fiber, supplied as 5 ply thick, 0/90° plaques from Clearwater Composites Inc. (Duluth Mich.). The dimensions of the Al samples were 1.5 mm thick, 100 mm width, and 300 mm long. The dimensions of the CFPC samples were 1.08 mm thick, 100 mm width, and 300 mm long. The diameter of one carbon fiber (CF) was approximately 6.7 μm. The adhesives that were used included DP460—an epoxy, DP620—a polyurethane, and DP810—a low-odor acrylic, all from 3M (St. Paul Minn.).

(54) The surface roughness increased from 226 nm (as-received) to 392 nm for the laser interference structured surface of Al 5182 with 10 pulses/spot (A=355 nm, pulse fluence of 1.2 J/cm.sup.2), as shown in Table 1. The following data was obtained with an optical surface profilometer: arithmetical-mean deviation of the roughness profile (Ra), root-mean-square deviation of the roughness profile (Rq), and total height of the roughness profile (Rt). The laser-interference structuring increased the surface area that would be in contact with the adhesive.

(55) TABLE-US-00001 TABLE 1 Condition Ra [μm] Rq [μm] Rt [μm] Untreated 0.226 0.286 3.21 Laser treated 0.391 0.493 4.68

(56) The results from mechanical testing on the lap shear strength are shown in FIG. 18. Shear lap stress data was obtained for Al-CFPC joints for a baseline joint (24.8×26.65), a spot-by-spot laser-interference structured Al and CFPC (24.87×25.18), and laser-interference raster of joint surfaces (25.08×26.45). The width and the length of the actual joined area are indicated in parenthesis as (W×L) in mm. Laser-structured joints are more ductile, indicating an enhanced adhesion of adhesive to both Al and CFPC. The displacement at failure increasing from 0.145 in for the baseline joint to more than 0.26 in for the laser-structured joints. Laser structured joints can absorb approximately 50% more energy than baseline joints.

(57) There is shown in FIGS. 19-21 the single-lap shear strength results for minimum, mean, and maximum values for baseline and laser-interference structured surfaces for both CFPC and Al for the DP810 adhesive (FIG. 19), the DP460NS adhesive (FIG. 20), and the DP620NS adhesive (FIG. 21).

(58) The effect of laser structuring for different adhesives was assessed with a total of sixty Al and carbon fiber polymer composite (CFPC) joints. The joints were bonded using the three adhesives, as follows: 24 joints for DP810, 18 joints for DP460, and 18 joints for DP620 (Table 2). Six joint specimens were made for each joint type to assess the effect of adhesive for laser structured surface preparation over conventional surface preparation. The conditions for laser rastering and laser spot-by-spot processing modes were selected based on a sensitivity study for DP810 adhesive. Six specimens were used for each joint type. Thus, the single-lap shear increase was not due to the variation in the bond length but solely due to laser structuring.

(59) TABLE-US-00002 TABLE 2 Adhesive Joint Type Preparation of CFPC Preparation of Al DP810 Baseline abraded and ethanol abraded and ethanol cleaned cleaned DP460NS baseline abraded and ethanol abraded and ethanol cleaned cleaned DP620NS baseline abraded and ethanol abraded and ethanol cleaned cleaned DP810 2B-raster Laser raster #2 Laser raster B DP810 3B-raster Laser raster #3 Laser raster B DP810 3C-spot Laser spot-by-spot #3 Laser spot-by-spot C DP460NS 2B-raster Laser raster #2 Laser raster B DP460NS 2B-spot Laser spot-by-spot #2 Laser spot-by-spot B DP620NS 2B-raster Laser raster #2 Laser raster B DP620NS 2B-spot Laser spot-by-spot #2 Laser spot-by-spot B

(60) Raster #2 indicates 5 mm/s @ 3.5 W, spot size 4 mm, and overlap between successive rows of 1 mm. Raster #3 indicates 10 mm/s @ 3.5 W, spot size 4 mm, and overlap between successive rows of 1 mm. Raster B indicates 5 mm/s @ 3.5 W, spot size 4 mm, and overlap between successive rows of 1 mm. Spot-by-spot #2 indicates 4 shots/spot @ 3.5 W, spot size 6 mm, and overlap between successive rows of 1 mm. Spot-by-spot B indicates 4 shots/spot @ 2.86 W, spot size 6 mm, and overlap between successive rows of 1 mm. Spot-by-spot C indicates 2 shots/spot @ 2.86 W, spot size 6 mm, and overlap between successive rows of 1 mm.

(61) The bond length data shown in FIGS. 22-24 illustrate the minimum, mean, and maximum for baseline and laser-interference structured surfaces for both CFPC and Al for DP810 adhesive (FIG. 22), the DP460NS adhesive (FIG. 23), and the DP620NS adhesive (FIG. 24).

(62) Table 3 shows the increase in mean shear-lap strength (from FIGS. 19, 20, and 21) in percentage for the laser-structured joint components with respect with their corresponding baselines. The results show that the shear-lap strength of Al-CFPC joints has increased by 12-35% using laser-interference structuring.

(63) TABLE-US-00003 % increase by % increase by Adhesive laser-raster laser spot-by-spot 810 12.7-14.8 16.3 460NS 12.8 8.2-12.8 620NS 35.3 25.4

(64) Ranges: throughout this disclosure, various aspects of the invention can be presented in a range format. It should be understood that the description in the range format is merely for convenience and brevity and should not be construed as an inflexible limitation on the scope of the invention. Accordingly, the description of a range should be considered to have specifically disclosed all the possible subranges as well as individual numerical values within that range. For example, description of a range such as from 1 to 6 should be considered to have specifically disclosed subranges such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6 etc., as well as individual numbers within that range for example, 1, 2, 2.7, 3, 4, 5, 5.3 and 6. This applies regardless of the bread of the range.

(65) This invention can be embodied in other forms without departing from the spirit or essential attributes thereof, and accordingly, reference should be had to the following claims to determine the scope of the invention.