Pulsed laser ablation (PLA) in single shot on polycrystalline Al thin foil ca. 50£gm in thickness was conducted in air and water to study the heat and shock affected zone (HSAZ) under specific wave length (532 nm), pulse duration time (16 ns) and laser input energy (400, 600 and 800 mJ/pulse) with a specified spot size of 0.03 mm2. The combined optical and electron microscopic observations indicated water is more effective than air to reduce HSAZ which increases with the increase of pulse energy yet with negligible recrystallization of Al substrate. Oxidation of the Al foil and redeposition of aluminum oxide nanocondensates on the laser incident side caused thermal mismatch between the coating and the Al substrate (especially when only 30£gm in thickness), and hence intra- and intergranular cracking along thermally etched subgrain boundary and grain boundary, respectively. The minimum interspacing of successive shots for effective fabrication of aluminum oxide nanocondesates from Al substrate are 470 and 250£gm, for the present PLA in air and water, respectively.
PLA fragmentation of £\-Al2O3 powder (mainly 100 nm in size) in water was also conducted under free-run mode (1064 nm, 240 £gs pulse duration) vs Q-switch mode (532 nm, 16 ns pulse duration) having laser spot size 0.03 mm2 and focal point 5 mm beneath the water level for an accumulation time of 20 min at 10 Hz. Comparing with the case of 1064 nm, the 532 nm laser incidence suffered less water absorption and was more effective to produce nanocondensates mainly in the form of £^ and £_* derived phases ranging from 5 to 20 nm in diameter which were occasionally (111)-specifically coalesced as twinned bicrystals.
| Identifer | oai:union.ndltd.org:NSYSU/oai:NSYSU:etd-0703111-231740 |
| Date | 03 July 2011 |
| Creators | Wu, Hsin-Chung |
| Contributors | none, Pou-Yan Shen, none |
| Publisher | NSYSU |
| Source Sets | NSYSU Electronic Thesis and Dissertation Archive |
| Language | Cholon |
| Detected Language | English |
| Type | text |
| Format | application/pdf |
| Source | http://etd.lib.nsysu.edu.tw/ETD-db/ETD-search/view_etd?URN=etd-0703111-231740 |
| Rights | not_available, Copyright information available at source archive |
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