Study on the Effects of Direct and Hybrid Laser Processing in Fabrication of Surface Features on Different Fe-Cr-Ni Enriched Alloys

Abstract

A Fe-Cr-Ni enriched alloy holds the beneficial properties that have high strength, excellent corrosion resistance, and good mechanical properties. The exact composition can vary widely, allowing these alloys to be tailored for specific applications. Just like that, the most pronounced Fe-Cr-Ni enriched alloys are A4SS and SDSS-2507. Both A4SS and SDSS-2507 are widely used in harsh environments for their unique individual characteristics. However, being a dual-phase material SDSS-2507 is a combination of desirable properties of individual phases. That makes it difficult to process by any means due to its lower machinability index. However, a new era Yb:YAG fiber laser technology has the remarkable ability to spur innovation and expand the limits of what can be achieved in processing these materials. That is why fiber laser has become widely recognized as an excellent option in advanced manufacturing due to its exceptional processing capabilities. Since direct laser processing (DLP) is a temperature-dependent process, it causes surface heating with melting, exhibiting a reciprocal relationship between productivity and processing quality. Nevertheless, it causes several surface imperfections and oxidation. If it falls short of finding a viable remedy, it inevitably leads to material property depreciation. Therefore, the applied thermal cycle needs to be controlled to minimize the oxidation behavior of the materials. In order to overcome such problems hybrid laser processing (HLP) holds its dominance considerably in the field of innovation which brings new standards to the products concomitantly with higher productivity. Apart from this, while processing with a laser by any means, scan mode is a crucial processing window through which the major laser energy controllers can be directed, especially for the fabrication of simple to intricate surface features on a wide range of materials. Based on such major points, the current research objectives are framed in three different stages. At the primary stage, an experimental investigation was carried out on the existing area fill scan mode (AFSM) and unique scan mode like orbit-in-orbit laser beam positioning strategy (O-OLPS) with the other laser processing variables during the fiber laser micromachining approach (FLMMA). In order to provide insight into contemporary scan modes, the current research also scrutinized the channel’s dimensional and surface traits alongside surface morphology, elemental composition, phase quantification, micro - hardness, crystallite size, and lattice strain. The current research outcomes revealed that the O-OLPS strengthens the grain boundary in the present micro-machining process by reducing crystallite size. The comparative study revealed that the O-OLPS offers around 28% reduced taperness with a controlled deeper and less widening channel profile, which might be a possible way to enhance micro-channel effectiveness for marine applications. In the second stage, an effective scan mode i.e., O-OLPS is adopted in this study for producing micro-channels on A4SS and SDSS-2507 for marine applications. As FLMMA is one of the most demanding manufacturing processes, this research aims to enhance the FLMMA by introducing O-OLPS in DLP and HLP as an existing industrial potential by altering the laser processing variables via tailoring the scan factors of the fiber laser. The core goal of this research is to scrutinize the materials’ responsiveness like dimensionality, material ablation, and surface traits. By tweaking the laser processing variables like energy and scan factors along with the environmental factors, the O-OLPS was examined under DLP and HLP. Apart from these, both the materials’ comparative performance was studied through phase quantifications, elemental analysis, surface morphology, corrosion study, and possible identification of corrosion products by utilizing Raman spectroscopy. It has been observed that the formation of defects and oxides is higher in A4SS compared to SDSS - 2507. Moreover, SDSS-2507 provides superior surface performance with higher corrosion resistance before and after laser processing compared to A4SS. However, from the material ablation perspective, A4SS holds a higher material removal ability compared to SDSS - 2507. From the Raman and corrosion studies, it can be concluded that A4SS is more susceptible to forming iron oxyhydroxides compared to SDSS-2507. The superior corrosion resistance of SDSS-2507, particularly in chloride environments, is less likely to undergo localized corrosion processes, which led to the formation of iron oxyhydroxides. Lastly, the SDSS-2507 surface outperformed the A4SS surfaces when processed under DLP and HLP and proved its efficacy in the application of a harsh environment. At last, the purpose of conducting the second stage fulfills its intention by selecting the most suitable material for marine applications. In the final stage, the versatility of O-OLPS was scrutinized under varied environments like DLP, active and inactive gas supported laser processing (A and IA-GSLP), and chemical- supported laser processing (CSLP) during the fabrication of a multi-pattern integrated surface (MPIS) feature, an intricate profile on SDSS-2507. This research also sheds light on the comparative mechanism that how the dynamic interaction occurs during the fabrication of MPIS under DLP, GSLP, and CSLP. Artificial chemical environments namely H3PO4, NaCl, and NaNO3, and their concentration, different gases like active and inactive, and their pressure levels along with controllable laser processing windows like energy and scan factors, were used to perform GSLP and CSLP to study SDSS-2507’s material ablation and surface characteristics. As SDSS-2507 holds a dual phase with varied thermal characteristics, this research further examined each phase’s sensitivity to laser-induced chemical reactions and attacks from aggressive and non-aggressive ions during CSLP. In order to acquire insight into the DLP, GSLP, and CSLP effects on SDSS-2507, phase analysis, surface morphology, surface chemistry, crystallite size, residual stress, mechanical property, and lattice strain were also studied. After DLP, GSLP, and CSLP, the SDSS - 2507’s resistance against aggressive Cl− ions was also scrutinized through electrochemical corrosion analysis and the oxide products were analyzed by Raman study. It has been found that by taking advantage of O-OLPS, surfaces processed under NaCl-CSLP and A-GSLP exhibited superior performance in terms of material ablation rate among the other environments, whereas the IA-GSLP solely performed well in terms of a clean surface with minimal leftover residue after H3PO4 compared to all. In comparison to NaNO3-CSLP and NaCl-CSLP, a decrease in crystallite size of up to 22.49%, and 19.12% was also seen respectively in H3PO4-CSLP. Similarly, compared to DLP and A-GSLP a decrease in crystallite size of up to 6.52%, and 5.08% was seen in IA-GSLP. Moreover, in comparison to before laser processing these values are 26.23% and 24.22% lower in H3PO4-CSLP and IA-GSLP respectively. Similarly, when compared to before laser processing, the corrosion rate was found to be 20.75%, 35.84%, 23.25%, and 28.30% lower in case of NaNO3-CSLP, H3PO4-CSLP, A-GSLP, and IA-GSLP respectively. While, there was a reduction in corrosion resistance observed in case of NaCl-CSLP and DLP. The above findings suggest that the MPIS fabricated under H3PO4-CSLP performed well in all aspects and can readily be applicable in harsh environment. Based on the facts presented above, it can be concluded that the MPIS that was fabricated using H3PO4-CSLP outperformed the others in every respect, and it can possibly maintain its integrity and functionality in any harsh environment especially marine without significant degradation.