Pulsed Nd:YAG laser was used to microtexture AISI-O1 cold work steel to control the substrate surface characteristics for later thermal spray coating to enhance the wearability. Influence of microtexturing parameters on the 3D surface morphology was studied by Atomic Force Microscopy (AFM), Scanning Electron Microscopy (SEM), and Optical Microscopy (OM). Results show that when AISI-O1 specimens are irradiated with various parameters the morphology of AISI-O1 cold work steel is changed correspondingly. It demonstrates that for a given laser the influence of laser microtexturing parameters on the morphology of the machined surface could be established successfully attractive to the thermal spray world. In the meantime, the wearability and antifatigue of the succedent thermal spray coating are significantly increased with the appropriate microtextured surface.
In recent years, microtechnology has become one of the key disciplines, having a significant effect on the development of new products and production technologies, as well as on the introduction of new methods for medical treatment and diagnostics. Moreover, due to the enormous potential for new applications, in future, microtechnology will increasingly affect our daily life with an impact, comparable to that of the industrial revolution in the 19th century, or the development of information technologies in the 20th century [
To date, a key issue associated with thermal spray coating is controlling the substrate characteristics, such as surface preparation. Therefore, knowledge of surface machining from the micrometer scale is of critical importance to future thermal spray technological growth. Consequently, the complicated problems due to micromachining should be overcome.
It is well known that laser has been widely used as a machine tool to modify the surface of the engineering materials, such as laser surface alloying, laser cladding, surface texturing, laser physical vapor deposition, and so forth, [
By considering the unique characteristics of the laser radiation and excellent noncontact micromachining possibility with the laser, an attempt has been made to microtexture AISI-O1 employing the concepts of microprocessing in this research to overcome current problems in the thermal spray technology.
The chemical composition of AISI-O1 is shown in Table
Chemical composition of AISI-O1.
Element | C | Si | Mn | Cr | W | V | Fe |
---|---|---|---|---|---|---|---|
(wt.%) | 0.9 | 0.3 | 1.2 | 0.5 | 0.5 | 0.1 | Bal. |
The materials were machined into 10 mm
Morphology and its corresponding SEM of the initial surface.
Microstructure of AISI-O1.
A GSI Lumonics Model JK702H pulsed Nd:YAG TEM00 mode laser system, with wavelength of 1.06
Laser processing parameters.
Processing parameters | Laser input energy | Feed rate | Pulse duration | Frequency |
PD (ms) | ||||
1, 2, 3 | 100, 200, 300, 400 | 2, 3, 4 | 15, 20, 25, 30 |
After processed, the surface morphology was observed by Atomic Force Microscopy (AFM), Scanning Electron Microscopy (SEM) JEOL/JSM-5600 and Optical Microscopy (OM).
The initial microtexture of AISI-O1 measured by AFM is shown in Figure
3D morphologies of initial microtexture of AISI-O1.
According to onset of laser processing temperature [
3D morphologies of laser microtextured surface.
Laser microtextured AISI-O1 with lower input energy. Processing parameters:
Laser microtextured AISI-O1 with higher input energy than (a). Processing parameters:
Laser microtextured AISI-O1 steel with medium input energy Processing parameters:
Laser microtextured AISI-O1 with higher input energy than (c). Processing parameters:
Laser microtextured AISI-O1 with more higher input energy. Processing parameters:
It shows that when the input energy is lower the effect of laser processing parameters on the morphology of AISI-O1 is not distinct, as shown in Figure
Generally, increase in input energy simultaneously raised up the heat input to the surface substrate. Too high energy is likely to melt the surface of substrate which subsequently changes the surface morphology and mechanical properties of the AISI-O1 specimens resulting in the failure of laser microtexturing. Compared with the originally machined surface (Figure
SEM of laser microtextured surface topographies at various input energies.
The cross-section micrograph of laser microtextured specimen with the processing parameters same in Figure
Cross-section microstructures of laser microtextured specimen Processing parameters:
Wear was studied using a Cameron-Plint TE67 wear test rig (Made in UK) under dry conditions with a sliding speed 1.34 m/s at constant applied loading of 36.7135 N. The stroke was set to 400, 600, and 1600 mm, respectively.
Ultrasonic cleaner with 28
Wear loss under the various sliding distances.
Sample | Load | Sliding distance | Initial weight | Finished weight | Lost weight |
---|---|---|---|---|---|
(N) | (mm) | (g) | (g) | (g) | |
A | 36.7135 | 400 | 6.0694 | 6.0684 | 0.0010 |
600 | 5.7536 | 5.7523 | 0.0013 | ||
1600 | 5.5323 | 5.5304 | 0.0019 | ||
B | 36.7135 | 400 | 6.5421 | 6.5413 | 0.0008 |
600 | 6.2667 | 6.2657 | 0.0010 | ||
1600 | 6.0356 | 6.0343 | 0.0013 | ||
B* | 36.7135 | 400 | 5.9155 | 5.9142 | 0.0013 |
600 | 5.6722 | 5.6704 | 0.0018 | ||
1600 | 5.2968 | 5.2945 | 0.0023 | ||
C | 36.7135 | 400 | 5.7397 | 5.7388 | 0.0009 |
600 | 5.2394 | 5.2383 | 0.0011 | ||
1600 | 6.0682 | 6.0667 | 0.0015 | ||
D | 36.7135 | 400 | 5.5043 | 5.5033 | 0.0010 |
600 | 6.3472 | 6.3457 | 0.0015 | ||
1600 | 6.5172 | 6.5153 | 0.0019 |
Thickness of coating on the substrates.
Sample | A | B | B* | C | D |
---|---|---|---|---|---|
Precoating | Non | 0.3 mm | 0.3 mm | 0.5 mm | 1 mm |
Relationship between the wear loss and sliding distance.
Also, the antiwear quality of the coating with laser microtexturing at the thickness of 0.3 mm (line B) and 0.5 mm (line C) is better than that without coating (line A) in all three sliding cases. Furthermore, the wear loss of samples without laser microtexturing (line B*) is higher than that of without coating as initial condition and coating with microtexturing both. It demonstrates that because of the laser microtexturing on the surface the coating will be bonded with the substrate more effectively. As for the coating without laser microtexturing, in addition to ridges and grooves, there are still a lot of particles/debris distributed on the surface even though after being carefully cleaned by acetone and pure ethyl alcohol as shown in Figures
The fatigue test was also carried on the Cameron-Plint TE67 wear test rig, where the maximum heating temperature was
Fatigue results with various conditions.
Sample | Cycles (1 unit = 200 cycles) | |||||||||||||||
1 | 2 | 3 | 4 | 5 | 15 | 16 | 17 | 18 | 19 | 20 | 21 | 22 | 23 | 24 | ||
A | ||||||||||||||||
B | ||||||||||||||||
B* | ||||||||||||||||
C | ||||||||||||||||
D |
Fatigue results with various conditions.
Microsurface texturing of AISI-O1 is attained irradiated by pulsed Nd:YAG laser with various microprocessing parameters. Studied by Atomic Force Microscopy (AFM), Scanning Electron Microscopy (SEM), and Optical Microscopy (OM), it shows that the wearability and antifatigue of AISI-O1 with the thermal spray coating are significantly increased with the appropriate microtextured surface.
The work described in this paper was supported by a grant from City University of Hong Kong (no. SRG7002236).