Abstract:Several techniques can be used to improve surface properties. These can involve changes on the surface chemical composition (such as alloying and surface welding processes) or on the surface microstructure, such as hardening and melting. In the present work surface melting with a 3kW CO2 cw laser was done to alter surface features of an AISI 304 stainless steel. Microstructure characterisation was done by optical and scanning electron microscopy. Vickers and Knoop microhardness tests evaluated mechanical featu… Show more
“…A similar cooling rate is observed in the strip casting process [8]. On the other structures it must be pointed out that the columnar-cellular can be observed in the laser melting, requires a 10 5 K/s cooling rate [9]. The higher estimated cooling rate was 10 6 necessary K/s that explains the presence of ferrite.…”
“…A similar cooling rate is observed in the strip casting process [8]. On the other structures it must be pointed out that the columnar-cellular can be observed in the laser melting, requires a 10 5 K/s cooling rate [9]. The higher estimated cooling rate was 10 6 necessary K/s that explains the presence of ferrite.…”
“…These micrographs indicated that laser surface melting resulted in fine solidification structure of the alloys. This could be attributed to the faster cooling rates, developed as a consequence of the temperature gradients generated in the material 31,32 The solidification occurred epitaxially from the boundary between the treated region and the untreated matrix.…”
Laser surface melting of Ni based superalloys (alloys 600, 690 and 693) was carried out to study the effect of surface modification on the corrosion behaviour in simulated nuclear high level waste (HLW) and chloride medium. Surface characterisation was performed by optical microscopy, scanning electron microscopy and X-ray diffraction. The alloys exhibited cubic crystal system and cellular microstructure. Double loop electrochemical potentiokinetic reactivation test in 0?5M H 2 SO 4 containing 0?0001M KSCN showed a low degree of sensitisation compared to the solution annealed specimens. Laser surface melting resulted in enhancement of corrosion resistance of the alloys in simulated HLW and chloride medium when compared to as received and solution annealed specimens; nevertheless, no discernable difference was found between the laser surface melted alloys 600, 690 and 693 in simulated HLW. However, the laser surface melted alloy 690 showed superior pitting corrosion resistance. The results of the present investigation are discussed in this paper.
“…According to the optical microscope image obtained at 500× magnification, the microstructure consists of a γ-austenite matrix with δ-ferrite having a dendrite size of about 20 μm. During the solidification of austenitic stainless steel, such as AISI 304 stainless steel, the first phase to solidify as the temperature drops below the point of peritectic transformation is δ-ferrite [46]. Hence, δ-ferrite tends to transform into austenite (γ) during cooling.…”
The selective laser-melting (SLM) process can be applied to the additive building of complex metal parts using melting metal powder with laser scanning. A metal mesh is a common type of metal screen consisting of parallel rows and intersecting columns. It is widely used in the agricultural, industrial, transportation, and machine protection sectors. This study investigated the fabrication of parts containing a mesh pattern from the SLM of AISI 304 stainless steel powder. The formation of a mesh pattern has a strong potential to increase the functionality and cost-effectiveness of the SLM process. To fabricate a single-layered thin mesh pattern, laser layering has been conducted on a copper base plate. The high thermal conductivity of copper allows heat to pass through it quickly, and prevents the adhesion of a thin laser-melted layer. The effects of the process conditions such as the laser scan speed and scanning path on the size and dimensional accuracy of the fabricated mesh patterns were characterized. As the analysis results indicate, a part with a mesh pattern was successfully obtained, and the application of the proposed method was shown to be feasible with a high degree of reliability.
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